CGS18

14 Jun 2026, 12:00 → 19 Jun 2026, 17:00 US/Pacific

Monterey, California (USA)

Heather Crawford, Filip Kondev (ANL), Augusto Macchiavelli (Lawrence Berkeley National Laboratory), Mathis Wiedeking

The 2026 International Symposium on Capture Gamma-Ray Spectroscopy and Related Topics "CGS18" is the 18th installment in the CGS conference series. CGS18 will take place in Monterey (California, USA). Previous meetings in this series have been held in Grenoble (2023), Shanghai (2017), and Dresden (2014), with the first one in Studsvik (Sweden) in 1969.

The symposium is devoted to the general themes of the series with special emphasis on gamma-ray spectroscopy. Topics to be discussed in the symposium include, but are not limited to:

Nuclear Structure, Nuclear Reactions, Nuclear Astrophysics, Fundamental Interactions and Symmetries, Nuclear Data, Experimental Techniques and Facilities, Interdisciplinary Studies and Applications

The conference will feature plenary talks and parallel sessions with invited and contributed talks, and a poster session. The scientific program will run from Monday through Friday, with a Welcome Reception on Sunday.

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Abstract submission is closed.

Registration is now open:  Register Now

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Conference Dates: 14 - 19 June 2026

Venue: Hilton Garden Inn, Monterey, CA (USA)

Second Circular: Jan 2026

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Important Dates (subject to change):

Abstract Submission Opens	5 January 2026
Abstract Submission Closes	22 February 2026 23 March 2026
Notification of Abstract Acceptance	7 April 2026
Registration Opens	Now open
Early Bird Closes	1 May 2026
Registration Closes	5 June 2026
Registration Fees	Here
Welcome Function	14 June 2026 (18:00)
Symposium Program Starts	15 June 2026 (08:30)
Symposium Banquet Dinner	18 June 2026 (19:00)
Symposium Ends	19 June 2026 (16:00)

 

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Organized by:

 

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CGS18_FirstCircularAnnouncement.pdf

CGS18_SecondCircularAnnouncement.pdf

Sunday 14 June

Registration

Welcome Reception

1 Nuclear Physics at LBNL

Speakers: Heather Crawford, Mathis Wiedeking (Lawrence Berkeley National Laboratory)

Monday 15 June

Plenary

Convener: Mathis Wiedeking (Lawrence Berkley National Laboratory)

2 New physics results and experimental techniques on the structure of nuclei produced with thermal neutron-induced reactions

High-flux reactors such as the one at the Institut Laue-Langevin (ILL, Grenoble) provide intense neutron sources for many different physics purposes. In particular, thermal neutron-induced reactions can be used to probe different phenomena in an approach to study the structure of nuclei. Neutron capture reactions on (rare) stable or radioactive targets populate low-spin states below the neutron separation energy. With thermal neutron induced fission on actinides, neutron-rich nuclei are produced at moderately high spin. Those fission products are studied at ILL in the high-resolution gamma-ray spectroscopy setup FIPPS (Fission Product Prompt gamma-ray Spectrometer). This facility provides access to observables which cannot yet be measured at any other currently existing facility and are needed to validate theoretical models or investigate phenomena as nuclear shape coexistence.

After a general introduction about the nuclear physics activities at the Institut Laue-Langevin, recently published and to-be-published results will be outlined. In particular, the systematics of shape isomers in the Ni isotopic chain will be discussed, in comparison with Montecarlo shell model calculations. New experimental data on transition probabilities at medium-high spin in neutron-rich nuclei produced in the fission process will be also shown and discussed on the basis of very new and preliminary theoretical calculations.

Future perspectives, in particular for neutron-induced fission and neutron-capture reactions on radioactive targets, will be outlined.

Speaker: Caterina Michelagnoli (Institut Laue-Langevin and University of Grenoble-Alpes)

3 Untangling the nuclear physics and astrophysics of the r-process

Observables of rapid neutron capture (r-process) nucleosynthesis such as abundance patterns and light curves are shaped by both the nuclear physics and astrophysics of candidate sites. Thanks to the current generation of radioactive ion facilities, the ground state properties and even the reaction rates of the very neutron-rich, unstable species that participate in the r-process are within reach. Here we describe work to exploit these capabilities to extract characteristics of r-process astrophysical sites from abundance patterns. We further speculate on what, once the r-process site or sites have been definitively identified and characterized, we might learn about nuclear physics from r-process observables.

Speaker: Rebecca Surman (University of Notre Dame)

4 Prospects for constraining the spin distribution in exotic nuclei

The nuclear spin distribution defines the distribution of levels as a function of spin at a given excitation energy in a nuclear system. The spin distribution is virtually unmeasured in exotic neutron-rich nuclei and is a critical input for applications in nuclear technologies and astrophysics. With recent advances in analysis techniques, it is possible to determine model-independent partial level densities in some short-lived nuclei. The application of these analysis techniques following beta decay can provide a partial level density over a limited spin range. Combined with a means to produce and separate multiple beta-decaying states within the same nucleus with different spins, then a partial level density can be inferred within different spin windows. This provides a means to extract some of the first information on the spin distribution at high excitation energy in the resulting nucleus. The prospects of inferring the spin distribution following beta decay into $^{70}$Zn will be presented using data from the decay of isolated beta-decaying states in $^{70}$Cu: the 6$^{-}$ ground state and the 1$^{+}$ first excited state.

Speaker: Sean Liddick (FRIB/MSU)

5 Microscopic Study of Dipole Excitations in Hot Nuclei within Covariant DFT

Electric (E1) and magnetic (M1) dipole modes are key contributors to γ-ray strength functions, directly influencing reaction rates relevant to stellar evolution and rapid neutron-capture (r-process) nucleosynthesis. Understanding electromagnetic excitations in atomic nuclei under extreme conditions, including finite temperature, is therefore crucial for advancing nuclear structure theory and astrophysical modeling. Owing to the limited experimental accessibility of hot nuclei, robust microscopic theoretical frameworks are essential.

In this contribution, I present a unified microscopic analysis of E1 and M1 strength distributions using the finite-temperature relativistic quasiparticle random-phase approximation (FT-RQRPA), formulated within covariant energy density functional theory with point-coupling interactions. Particular emphasis is placed on thermal unblocking mechanisms and their influence on low-energy dipole excitations. I first discuss predictions for neutron-rich nickel isotopes, where increasing temperature leads to a pronounced enhancement of low-energy E1 strength, identified as hot pygmy dipole strength. This behaviour arises from thermally activated quasiparticle configurations and provides valuable theoretical guidance for current and future experimental efforts [1,2]. I then examine the temperature evolution of γ-ray strength functions, showing how both E1 and M1 components are progressively reshaped as thermal effects become significant [3]. These results underscore the strong temperature dependence of the electromagnetic response and provide essential microscopic input for r-process network calculations and nuclear data evaluations in hot astrophysical environments.

References:
[1] A. Kaur, E. Yüksel, and N. Paar, Phys. Rev. C 112, L051304 (2025).
[2] O. Wieland et al., Acta Physica Polonica B Proceedings Supplement 18, 2-A33, (2025).
[3] A. Kaur, E. Yüksel, and N. Paar, Physical Review C 112, 014307 (2025).

Speaker: Esra Yuksel (University of Surrey)

10:30 Coffee Break

Plenary

Convener: Yang Sun (Shanghai Jiao Tong University)

6 Illuminating Heavy-Element Nucleosynthesis via Indirect Neutron-Capture Methods

Neutron-capture nucleosynthesis occurs via a variety of processes depending on the astrophysical sites and conditions. Recent observations and stellar evolution models of carbon enhanced metal poor stars (CEMP) and Rapidly Accreting White Dwarf stars (RAWDs) suggest that an intermediate process, known as the $i$-process, exists between the traditional $s$- and $r$-processes, and is necessary to explain observed abundances in these environments. $i$-process nucleosynthesis is impacted by various nuclear data inputs, of which the main source of uncertainty arises from unconstrained neutron-capture reaction rates. Direct neutron-capture measurements are only feasible for long-lived nuclei, while for short-lived nuclei, indirect techniques are required. In this presentation I will discuss an indirect neutron-capture technique known as the $\beta$-Oslo method and highlight measurements over last decade that have been used to illuminate $i$-process nucleosynthesis across the nuclear chart at radioactive beam facilities such as the National Superconducting Cyclotron Laboratory, the Facility for Rare Isotope Beams, CARIBU & nuCARIBU at Argonne National Laboratory, and TRIUMF.

Speaker: Andrea Richard (Ohio University)

7 High Resolution Studies of Electric and Magnetic Dipole Strength Distributions at HIγS

Electromagnetic probes provide a uniquely clean and selective window into the internal structure of atomic nuclei. Real photon beams, in particular, couple directly to the charge and current distributions without introducing strong interaction distortions, thereby enabling model independent spectroscopic investigations of nuclear excitations. Their well defined spin selectivity, polarization control, and high sensitivity to transition strengths make them ideally suited for isolating electric and magnetic dipole modes across a broad excitation energy range. This capability is especially powerful for mapping dipole strength distributions from a few MeV up to and beyond the particle emission threshold, where the interplay between single particle motion and collective dynamics gives rise to a variety of nuclear phenomena, the precise characterization of which provides stringent constraints on nuclear structure models and has direct implications for astrophysical reaction rates and nucleosynthesis pathways. In this talk, I will present recent results from nuclear resonance fluorescence measurements performed with quasi monochromatic, highly polarized photon beams at the High Intensity gamma ray Source (HI$\gamma$S) at the Triangle Universities Nuclear Laboratory. Emphasis will be placed on high resolution determinations of dipole strength distributions, identification of fine structure and multipole character through polarization asymmetries and angular distributions, and the extraction of reduced transition probabilities and branching ratios. The experimental results will be confronted with state-of-the-art theoretical calculations and compared with complementary data from hadron induced reactions, to highlight the distinct selectivity, interpretive clarity, and quantitative rigor afforded by the photonuclear approach.

Speaker: Akaa Daniel Ayangeakaa (University of North Carolina at Chapel Hill & Triangle Universities Nuclear Laboratory (TUNL))

8 Nuclear Structure Studies of the Heaviest Elements

In recent years, measurements of atomic and nuclear properties have been extended to the heaviest elements that do not occur naturally, using laser spectroscopy and mass spectrometry. Such heavy elements can be produced artificially at heavy-ion accelerator facilities, such as the UNILAC at GSI, but only in extremely small quantities—often at the level of single atoms. This imposes stringent requirements on the sensitivity and efficiency of experimental techniques.
To meet these challenges, we have developed highly sensitive methods that combine laser spectroscopy with buffer-gas stopping cells, in which the reaction products are thermalized and efficiently extracted. Using these techniques, we have investigated the atomic and nuclear properties of several fermium and nobelium isotopes at the SHIP velocity filter at GSI in Darmstadt. These on-line measurements have been complemented by off-line studies at the RISIKO separator at Johannes Gutenberg University Mainz, where long-lived actinide isotopes can be studied by laser spectroscopy with high spectral resolution.
From these experiments, we have obtained precise information on changes in nuclear charge radii as well as nuclear moments across isotopic chains, providing valuable insights into the structure and deformation of heavy nuclei. In addition, we have recently resolved a long-standing question concerning the configuration of the long-lived K=8^- isomer in 254No. By applying laser spectroscopic techniques, we were able to determine its magnetic moment and hence its quasi-particle configuration.
In this presentation, I will introduce the key experimental techniques and present selected results from our most recent experimental campaigns and discuss their implications for our understanding of atomic structure and nuclear properties in the region of the heaviest elements.

Speaker: Michael Block

12:30 Lunch

Poster Session

9 High-Precision Nuclear Decay Data: Measurement and Database Development at NNDC

A low-background gamma counting facility has been developed by the National Nuclear Data Center (NNDC) at Brookhaven National Laboratory. The facility is housed within a purpose-built cave that has historically operated as a whole-body counter and is a shielded room constructed of 6-inch steel and lined with lead, cadmium, and copper [1] for shielding against the low-energy components of background radiation. The counting system consists of four high-purity germanium (HPGe) detectors: two equipped with beryllium windows optimized for X-ray and low-energy gamma-ray measurements, and two 200% relative-efficiency HPGe detectors designed for high-energy gamma-ray spectroscopy. Data acquisition is performed using CAEN digitizers operating in both singles and coincidence modes. Preliminary tests demonstrate a background reduction of approximately two orders of magnitude, achieving background count rates below 1 cps. This facility provides an ideal gamma spectroscopy environment for low-activity environmental samples. A general overview of the facility and achievable sensitivities, and the first results on studying the emission probabilities of low-energy gamma transitions in Pu isotopes, will be presented.
Concurrently, the NNDC is developing a new initiative called the Adopted Decay Data Library (ADDL). The ADDL focuses specifically on accelerating the evaluation process for β−, ϵ + β+, and α-decay data and presenting it in a modernized ENSDF format. It will also include new quantities such as atomic X-ray and Auger electron energies, with data visualized through an updated NuDat interface. This prioritized effort for assessing decay data is anticipated to lead to the establishment of a standalone Decay Data Library in the future. The presentation will highlight significant advancements in the implementation.
References:
[1] Brookhaven National Laboratory (1960) BNL Bulletin, 14, 7. Brookhaven National Laboratory Personnel Office. Retrieved from https://www.bnl.gov/bnlweb/pubaf/bulletin/files/1960/19601018.pdf

Speaker: Ms Sanjanee Waniganeththi (Brookhaven National Laboratory)

10 Investigation of Excited States in 124Sn Populated in β-Decay of 124In

Over the past several years, extensive studies have been devoted to the structure of neutron rich tin isotopes, which possess a closed proton shell, with ¹³²Sn being a doubly magic nucleus. For this reason, these nuclei play a particularly important role in testing the validity of the nuclear shell model and serve as a benchmark for theoretical predictions. Information obtained in this region of the nuclear chart is essential for developing reliable extrapolations toward even more neutron-rich isotopes.

In the experiments studied, the tin nuclei are produced by the β− decay of indium isotopes and via the emission of β− delayed neutrons or, in some cases, two β− delayed neutrons [1,2]. Data from this mass region are also highly relevant from an astrophysical perspective, as they contribute to a better understanding of the r-process nucleosynthesis responsible for the formation of heavy elements in the universe.

In the present study, we focus on the excited states in 124Sn populated in the β− decay of 124In investigated in an experiment performed at the ISOLDE Decay Station (IDS). In addition to the aforementioned motivations, an additional driving factor for studying the structure of this nucleus is the possible occurrence of the rare two-neutrino double beta decay (2β−) in 124Sn. Although 124Sn is a stable nucleus and the single β− decay is energetically forbidden, the 2β− decay is allowed and has been the subject of several investigations [3–5]. A better understanding of the nuclear structure of 124Sn will improve the reliability of theoretical predictions for this process and may help identify excited states that are more likely to be involved in the transition.

The current analysis of the β− decay of the two isomeric states of 124In includes β–γ, β–γ–γ and γ–γ coincidence spectra. A detailed comparison of the previously established decay scheme with the new experimental data led to the reassignment of six γ transitions to different positions in the level scheme. These changes were reinforced by finding new gammas that fit the changed scheme very well. To sum up the preliminary analysis, 21 new transitions were identified and included in the scheme, and 17 new excited levels were obtained.

References
[1] M. Piersa, A. Korgul et al., Phys. Rev. C 99, 024304 (2019).
[2] M. Piersa-Siłkowska, A. Korgul et al., Phys. Rev. C 104, 044328 (2021).
[3] A. S. Barabash, Ph. Hubert et al., Nucl. Phys. A 807, 269281 (2008)
[4] M. Horoi, A. Neacsu, Phys. Rev. C 93, 024308 (2016)
[5] D. Patel, P. C. Strivastava et al., Nucl. Phys. A 1042, 122808 (2024)

Speaker: Paweł Wakuluk (Faculty of Physics, University of Warsaw, PL 02-093 Warsaw, Poland)

11 Structure of $^{34}$Al Studied via the $\beta^-$ Decay of $^{34}$Mg

The $\beta^-$ decay of $^{34}$Mg has been exploited to probe the nuclear structure of $^{34}$Al at the boundary of the $N=20$ Island of Inversion, using high-efficiency $\gamma$ spectroscopy at the GRIFFIN spectrometer (TRIUMF–ISAC). Absolute $\beta$-feeding intensities and corresponding $\log ft$ values were extracted, and $\gamma$--$\gamma$ angular-correlation measurements were performed to constrain the spin assignments of several low-lying states. The decay pattern is characterized by a pronounced population of the isomeric $1^+$ state in $^{34}$Al, consistent with strong Gamow–Teller transitions from the $0^+$ ground state of $^{34}$Mg. The observed selective feeding of the lowest $1^+$ states, combined with reduced population of higher-lying excitations, indicates a fragmented distribution of Gamow–Teller strength. This decay selectivity suggests that the $^{34}$Mg ground state contains a substantial admixture of normal $0p0h$ configurations together with intruder components. The persistence of the observed GT-strength pattern when including two-body axial-current contributions further supports a strongly mixed configuration at the edge of the Island of Inversion. Large-scale configuration-interaction calculations with the FSU interaction, complemented by \textit{ab initio} approaches, reproduce the measured decay properties and confirm significant cross-shell mixing in this mass region.

Speaker: smain sekal (TENNESSEE TECH UNIVERSITY for GRIFFIN Collaboration)

12 Geant4 Simulations of Tape-Transport Systems For $\beta$-decay Gamma Spectroscopy

The precise investigation of $\beta$-decay properties across various regions of the nuclear chart requires highly optimized experimental setups to minimize background contamination from long-lived daughter activities. In this context, detailed Monte Carlo simulations were developed using the Geant4 toolkit to optimize the design and operation of a movable tape-transport system.

The primary simulated geometry accurately reproduced the experimental apparatus utilized at the University of Jyväskylä, incorporating two Broad-Energy Germanium (BEGe6530) detectors, one High-Purity Germanium (GC7020) detector, a plastic scintillation detector for $\beta$ tagging, and the tape station [1]. Furthermore, to evaluate the versatility of the tape system and compare its performance under different detection configurations, the simulations were extended to a geometry resembling the ISOLDE Decay Station (IDS), utilizing CLOVER-type high-purity germanium detectors [2]. The main objective of these simulations was to facilitate the conscious mechanical planning of the tape station, assessing its structural durability and determining the optimal tape speed to ensure maximum measurement efficiency regardless of the specific isotopes under investigation.

During the simulation, representative $\gamma$-rays were emitted from the beam implantation site. Because the Geant4 toolkit does not natively support dynamic, continuously moving geometries during a single event run, another computational approach was implemented by discretizing the physical movement of the tape station into static positional steps. By analyzing the simulated energy spectra across these discrete spatial intervals, the exact tape velocities required to effectively eliminate daughter-nucleus decays from the measurement window were evaluated.

These simulations provide critical input for the final mechanical design of the transport system across varying experimental setups, ensuring an optimal balance between tape speed, structural integrity, and spectral purity. The methodology of discretizing dynamic components in Geant4, along with the derived optimal operational parameters for the tape station, will be presented and discussed.

[1] Krzysztof Solak. "Investigation of Nuclear States of $^{115}$Pd Populated in Beta Decay of 115Rh." Master's thesis, Univeristy of Warsaw, 2025.

[2] https://isolde-ids.web.cern.ch/#setup. 2025

Speaker: Michał Młynarczyk (Faculty of Physics, University of Warsaw, PL-02-093 Warsaw, Poland)

13 Recent Advances in the β-Decay Spectroscopy of $^{118}$Pd

The investigation of $\beta$-decay properties of neutron-rich nuclei in the A $\approx $ 120 region provides essential input for testing modern nuclear-structure models and for constraining astrophysical r-process simulations. In this context, the $\beta^-$ decay of $^{118}$Pd (Z = 46, N = 72) populating excited states in $^{118}$Ag was studied at the Ion Guide Isotope Separator On-Line (IGISOL) facility of the University of Jyväskylä.

The $^{118}$Pd isotopes were produced in proton-induced fission of uranium and
mass- separated using the JYFLTRAP system to ensure isotopic purity. The decay spectroscopy setup consisted of three high-purity germanium detectors for $\gamma$-ray detection, a plastic scintillator for $\beta$ tagging, and a movable tape-transport system for activity collection and removal.

Analysis of $\beta$-$\gamma$ and $\gamma$–$\gamma$ coincidence data resulted in a significant revision of the known decay scheme of $^{118}$Pd [1]. Several new $\gamma$ transitions and previously unobserved excited states in $^{118}$Ag were identified. Moreover, a cascade of transitions potentially feeding a new isomeric state [2] has been proposed. The ongoing analysis includes the determination of $\beta$-feeding intensities and log ft values, which will enable more precise spin–parity assignments and improved modeling of $\beta$-decay strength in this mass region.

These results contribute to the systematic study of neutron-rich palladium and silver isotopes, relevant both for understanding nuclear structure near the N = 70 region and for providing experimental constraints to r-process nucleosynthesis calculations. A review of the most recent results will be given and discussed.

[1] Z. Janas, J. Äystö, K. Eskola, P.P. Jauho, A. Jokinen, J. Kownacki, M. Leino, J.M. Parmonen, H. Penttilä, J. Szerypo, J. żylicz, Nuclear Physics A,
Volume 552, Issue 3,
1993, Pages 340-352,

[2] B. van den Borne, M. Stryjczyk, R. P. de Groote, A. Kankainen, D. A. Nesterenko, L. Al Ayoubi, P. Ascher, O. Beliuskina, M. L. Bissell et al., Phys. Rev. C 111, 014329 – Published 30 January, 2025

Speaker: Mr Michał Młynarczyk (Faculty of Physics, University of Warsaw, PL-02-093 Warsaw, Poland)

14 Study on neutron fission cross-section of 245Cm by measurements at ANNRI in MLF of J-PARC

Neutron fission cross-sections of minor actinides (MAs) are important to design reactors with MA-loaded fuels. Among the fission cross-sections of MAs, particularly $^{245}$Cm shows a noticeable difference between existing measured data and JENDL-5 [1] below 10 eV. A research project entitled “Improvement of accuracy of neutron-induced fission reaction data for MAs” is currently ongoing, which targets the fission cross-sections of MAs (i.e., $^{237}$Np, $^{241}$Am and $^{245}$Cm). The fission measurement of $^{245}$Cm was performed at the Accurate Neutron-Nucleus Research Measurement Instrument (ANNRI) of the Materials and Life Science Experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC). A sample employed to measure capture cross-section of $^{244}$Cm [2] was adopted, including 2.4% of $^{245}$Cm which was compared to 43.9% of $^{244}$Cm at time of fission measurement. Preliminary fission cross-section results were obtained by counting prompt fission neutrons with EJ-276D pulse-shape discriminating plastic scintillators. Owing to a small amount of $^{245}$Cm in the sample it was necessary to carefully extract the $^{245}$Cm events from the large $^{244}$Cm events. Some fission resonance peaks of $^{245}$Cm were found below 10 eV. The resonance shape analysis was made with the R-matrix analysis code AMUR [3].
In the presentation the results obtained will be given with the experimental methodology of fission cross sections at ANNRI in MLF of J-PARC.
Acknowledgment
This work was supported by MEXT Innovative Nuclear Research and Development Program Grant Number JPMXD0224020564.

[1] O. Iwamoto, N. Iwamoto, S. Kunieda et al., J. Nucl. Sci. Technol., 60(1), 1-60 (2023)
[2] A. Kimura, T. Fujii, S. Fukutani et al., J. Nucl. Sci. Technol., 49(7-8), 708-724 (2012)
[3] S. Kunieda, S. Endo, A. Kimura, EPJ Web of Conferences, 281, 00017 (2023)

Speaker: Nobuyuki Iwamoto (JAEA)

15 Algorithm approach to building a nuclear level scheme and exciting state analysis

The construction of nuclear level schemes from γ-ray spectroscopy data is a long-standing and computationally challenging problem, especially for complex nuclei with a large number of observed transitions. Despite its fundamental importance for the interpretation of nuclear structure experiments, only a limited number of dedicated algorithmic approaches have been proposed [1,2], leaving considerable scope for further methodological development. In this work, we present a new algorithmic approach for the automatic reconstruction of nuclear decay schemes based solely on γ–γ coincidence information.

The input to the algorithm consists exclusively of coincidence relations, i.e. information on which γ-ray transitions are observed in mutual coincidence, without any prior knowledge of level ordering. The output is a complete decay scheme, including all reconstructed excited states and all γ-ray transitions connecting them. A naive brute-force approach based on random assignment of transitions to levels leads to a combinatorial explosion, with computational complexity worse than factorial in the number of transitions. For example, even assuming the generation of one billion candidate schemes per nanosecond, reconstructing a correct scheme for a system with only 32 transitions would require a time comparable to the age of the Universe.

By introducing a dedicated recursive algorithm that systematically exploits coincidence constraints, we reduce the effective complexity of the problem by many orders of magnitude. As a result, decay schemes containing up to 200 γ-ray transitions can be reconstructed in less than one second on standard personal computing hardware. Due to the stochastic nature of certain algorithmic choices, repeated runs may give a different decay schemes that all satisfy the coincidence conditions. This feature allows the use of additional experimental observations, such as transition intensities, to select the most physically plausible solution. In cases where an exact solution satisfying all coincidence relations cannot be found, the algorithm returns the best approximate scheme along with a clear indication of which coincidence requirements are violated.

We hope that this approach will help to streamline and accelerate nuclear spectroscopy studies. The developed program can be further extended by taking into account additional experimental information, such as γ-ray transition intensities, to select the most physically probable scheme and to supplement the decay scheme with additional nuclear quantities, which will further improve the analysis process.

References
[1] I. Adam, A. A. Byalko et al., Measurement Techniques, Vol. 40, No. 6 (1997).
[2] K. Jansson, D DiJulio et al., Nuclear Instruments & Methods in Physics Research. Section A, Vol. 654, No. 1 (2012)

Speaker: Paweł Wakuluk (Faculty of Physics, University of Warsaw, PL 02-093 Warsaw, Poland)

16 Determination of Beta Feeding and Level Half-Lives in the Presence of Coupled Isomeric States Using a Monte Carlo–Based Genetic Algorithm

The determination of $\beta$-feeding values from $\gamma$-ray spectroscopy data is a fundamental step in constructing reliable nuclear decay schemes and extracting log ft values. In the standard approach, absolute $\gamma$-ray intensities are determined and the population of each excited level is obtained from the intensity balance between $\gamma$ transitions feeding and depopulating that level. However, this procedure becomes inadequate in the presence of isomeric states with intermediate half-lives, for which the assumption of instantaneous decay or complete time separation is not valid. In such cases, $\gamma$-ray intensities observed in $\beta$–$\gamma$ and $\gamma$–$\gamma$ coincidence spectra can be significantly distorted, leading to underestimated transition strengths and, consequently, incorrect $\beta$-feeding values.

Analytical solutions can be derived for simple cases involving a single isomer or even straightforward sequential isomeric cascades. However, when multiple coupled isomeric states are arranged in a complex level scheme with numerous branching transitions, the time-dependent population and depopulation pathways become strongly interdependent. In such situations, analytical treatments become impractical, and a more flexible computational approach is required to extract consistent $\beta$-feeding values.

To address this issue, we have developed a dedicated code based on Monte Carlo simulations combined with a genetic algorithm optimization procedure. The program takes as input a proposed $\gamma$-ray decay scheme, known $\beta$-feeding intensities and level lifetimes (where available), as well as experimental information on time-dependent $\gamma$-ray intensities. Unknown $\beta$-feeding values and, where necessary, level lifetimes are initially sampled within predefined physical ranges. Through successive generations, the genetic algorithm converges toward a solution that reproduces the experimentally observed $\gamma$-ray intensities within their uncertainties. The final output provides a self-consistent set of $\beta$-feeding intensities and lifetimes compatible with the measured data.

The method has been tested on experimental data from the $\beta$ decay of Indium-124 to Tin-124. The level scheme of the daughter nucleus includes two low-lying isomeric states, which complicates the extraction of $\beta$ feeding for four excited levels. The evolutionary approach successfully resolved the feeding pattern and produced results consistent with independently determined level lifetimes.

The presented framework provides a robust and flexible tool for the analysis of complex decay schemes involving multiple isomeric states and can be readily applied to other cases encountered in high-precision $\gamma$-ray spectroscopy studies. By combining Monte Carlo simulations with a genetic optimization algorithm in a fully time-dependent treatment, the method offers a novel strategy for the simultaneous extraction of $\beta$-feeding intensities and level half-lives in systems with coupled isomers.

Speaker: Paweł Wakuluk (Faculty of Physics, University of Warsaw, PL 02-093 Warsaw, Poland)

17 Systematic study of E2 matrix elements in the framework of the TPSM

The nuclides for which extended sets of E2 matrix elements have been measured by means of COULEX experiments have been studied in the framework of the triaxial projected shell model (TPSM).
The study encompasses: $_{~~~~~~~~~32}^{70,72,74}$Ge$_{38,40,42}$, $_{~~~~~~~~~~~~~~~34}^{76,78,80,82}$Se$_{42,44,46,48}$, $_{42}^{100}$Mo$_{58}$, $_{44}^{104}$Ru$_{60}$,
$_{~~~~~~~~~~~~~~~46}^{106,108,110}$Pd$_{60,62,64}$, $_{68}^{168}$Er$_{100}$,$_{~~~~~~~~~~~~~~~76}^{186,188,190}$Os$_{110,112,114}$ and $_{78}^{184}$Pt$_{106}$.
The experimental energies of the ground band, of the quasi $\gamma$ band and of some excited $0^+$ bands, as well as, their individual intra and inter band matrix E2 matrix elements are systematically accounted for by the microscopic TPSM calculations. The studied nuclei represent axial, rigid triaxial and soft triaxial shapes from the perspective of the collective model. The discriminating features are demonstrated by comparing the Kumar-Cline shape invariants derived from the TPSM results with the experimental ones. The TPSM uses the static triaxial deformation of the mean field as the only input adjusted to the experiment. The relation between the model’s capability to account for the different shape characteristics and the superosition of multi quasiparticle excitations will be discussed.

Speaker: Stefan Frauendorf (University Notre Dame)

Plenary

Convener: Filip Kondev (ANL)

18 Neutron induced charged particle emitting reaction measurements on radionuclides at Los Alamos Neutron Science Center (LANSCE)

To further strengthen our understanding of nuclear reactions underpinning astrophysics, next-generation reactor designs, and national missions, we expanded reaction measurements on both stable nuclei and radionuclides. At Los Alamos Neutron Science Center (LANSCE), we perform direct measurement of the (n,p) and (n,$\alpha$) reaction cross sections using the LENZ (Low Energy NZ) instrument. We have been working to improve outgoing charged particles’ angular distributions and energy spectra by validating measured cross sections with theoretical predictions. Key results from the measured differential cross sections of $^{35}$Cl, $^{39,40}$K, $^{54,56}$Fe, and $^{56,58,59,60}$Ni will be presented and compared with Hauser-Feshbach model calculations, with particular emphasis on radionuclides, $^{40}$K, $^{56}$Ni and $^{59}$Ni. I will conclude with the ongoing effort of developing the optimized solenoid spectrometer at LANSCE for improving the fidelity of directly measured reaction data on radionuclides.

This work benefits from the LANSCE accelerator facility and is supported by the U.S. Department of Energy under contract No. 89233218CNA000001, the Laboratory Directed Research and Development program of Los Alamos National Laboratory under project numbers 20130758ECR and 20180228ER, and the US Nuclear Data Program under U.S. Department of Energy Office of Science-Nuclear Physics.

Speaker: Hye Young Lee (LANL)

19 A Universal Fate for Spin-Orbit Partners in the Weak-Binding Regime

Experimental data on single-particle energies in weakly bound systems have materialized over the past decade or so. Perhaps the most discussed has been for the neutron-rich nuclei around $N = 20$ and 28. A smooth decrease in the separation of the $2p_{3/2}$-$2p_{1/2}$ spin-orbit splittings is observed in this region as they approach zero binding. This is at odds with the well-established trends of experimentally determined spin-orbit splittings across the chart of nuclides for well-bound states, as presented by Mairle [Phys. Lett. B 304, 39 (1993)]. In studying the contrast between experimental data, mean-field descriptions, and the trends discussed by Mairle for both well-bound and weakly bound systems across the nuclear chart, with a focus on neutron spin-orbit partners, a seemingly universal behavior emerges that could prove predictive. This can be tracked to unbound resonances in a systematic way. Many of the regions explored have connections to other prominent topics in nuclear physics, such as $r$-process nucleosynthesis, where the ordering of single-particle energies near threshold in weakly bound systems influences reaction rates. Throughout, I will highlight one of the principal techniques for extracting such data: the solenoidal spectrometer technique, now used at ATLAS, CERN, and FRIB.

Speaker: Ben Kay (Argonne National Laboratory)

20 Recent results on the double-gamma decay

The nuclear two-photon or double-gamma (2γ) decay is a second-order electromagnetic decay process whereby a nucleus in an excited state emits two gamma rays simultaneously. Compared to first-order decay pathways, such as single photon emission or internal electron conversion, the two-photon decay rate is very small. Ideal cases for this search are $0^+ \rightarrow 0^+$ transition where single photon emission is prohibited. However, the only cases where the 2γ decay from a first-excited 0+ state was successfully observed using γ-ray spectroscopy are $^{16}$O, $^{40}$Ca and $^{90}$Zr [1, 2], where the high energy of the transitions is favorable for the 2γ branch. More recently, also the competitive 2γ decay was observed from the long-lived $11/2^-$ isomer in $^{137}$Ba [3].

For lower decay energies the 2γ branch becomes prohibitively small to be observed in γ-ray spectroscopy (<10$^{-6}$). We have therefore combined the isochronous mode of the Experimental Storage Ring (ESR) at GSI with Schottky resonant cavities. This newly developed Schottky plus Isochronous Mass Spectrometry (S+IMS) allows to study exotic decays of short-lived nuclear states. The obtained mass resolving power enables experiments on nuclear isomers with excitation energies down to ∼100 keV and half-lives as short as a few ms. The first measurement of the partial half-life for the isolated 2γ decay of the 0$^+$ isomer in $^{72}$Ge turned out to be surprisingly short [4]. Recent results for the 2γ decay of the 0$^+$ isomers in $^{98}$Zr and $^{98}$Mo will be presented as well as first steps to measure the weak 2γ branch in $^{72}$Ge by direct γ-ray spectroscopy.

[1] J. Schirmer J. Schirmer, D. Habs, R. Kroth, N. Kwong, D. Schwalm, and M. Zirnbauer, {Double gamma decay in 40Ca and 90Zr, Phys. Rev. Lett. 53, 1897–1900 (1984).
[2] J. Kramp, D. Habs, R. Kroth, M. Music, J. Schirmer, D. Schwalm, and C. Broude, Nuclear two-photon decay in 0+ → 0+ transitions, Nuclear Physics A 474, 412–450 (1987).
[3] C. Walz, H. Scheit, N. Pietralla, T. Aumann, R. Lefol, and V. Yu. Ponomarev, Observation of the competitive double-gamma nuclear decay, Nature 526, 406-409, (2015).
[4] D. Freire-Fernández, W. Korten, Y. Litvinov et al., Measurement of the Isolated Nuclear Two-Photon Decay in 72Ge, Phys. Rev. Lett. 133, 022502 (2024) and https://arxiv.org/pdf/2312.11313.

The main results are based on the experiments E143 and G22-00018, which were performed at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt (Germany) in the context of FAIR Phase-0. This work was supported by the Slovenian Research and Innovation Agency under Grants No. I0-E005 and No. P1-0102, by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (ERC-AdG NECTAR, grant agreement No 884715; ERC-CoG ASTRUm, grant agreement No 68284), by the State of Hesse (Germany) within the Research Cluster ELEMENTS (Project ID 500/10.006), by the STFC (UK), by the NSF grant PHY-2110365, by the BMBF under grant NuSTAR.DA 05P19RDFN1, by the JSPS KAKENHI Grant Number T23KK0055. Work at ANL is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under contract No. DE-AC02-06CH11357.

Speaker: Wolfram KORTEN (CEA Saclay)

15:00 Coffee Break

Plenary

Convener: Ani Aprahamian (University of Notre Dame)

21 A study of statistical nuclear properties and the low energy enhancement in 70Zn using β-decaying ground and isomeric states of 70Cu

Statistical nuclear properties like the $\gamma$-ray strength function ($\gamma$SF) and nuclear level density (NLD) can be used to probe trends in nuclear structure and constrain astrophysical neutron capture reaction rates. Features in the $\gamma$SF such as the giant dipole resonance, pygmy dipole resonance, scissors mode, and low energy enhancement (LEE), can provide insight into properties of $\gamma$-decay. In particular, the nature of the LEE has been the subject of much debate in the nuclear physics community, with no definitive theoretical or experimental conclusion as to why it occurs. Here, we present a novel combination of experimental and analytical techniques used to probe statistical properties in the nucleus $^{70}$Zn, with a particular focus on the nature of the LEE. At the Facility for Rare Isotope Beams at Michigan State University, beams of the ground state (J$^\pi$=6$^-$) and second isomeric state (J$^\pi$=1$^+$) of $^{70}$Cu were isolated using the Low Energy Beam and Ion Trap (LEBIT) and delivered to the upgraded Summing NaI(Tl) Total Absorption Spectrometer (SuN++). The NLD and $\gamma$SF of $^{70}$Zn extracted using the Shape and $\beta$-Oslo methods from both $\beta$-decaying states in $^{70}$Cu will be presented, along with the resulting implications for the nature of the LEE from their comparison.

Speaker: Eleanor Ronning (INFN-Padova)

22 Studying Neutron-Induced Reactions at LANSCE

Neutron-induced reactions play important roles in understanding a wide variety of natural and man-made environments, from the production of the heavy elements in astrophysical environments, to reaction pathways in nuclear reactors, to influencing the performance of structural materials being considered for future fusion energy sources. Further, they provide a unique probe of the nucleus, allowing reach into regions of relatively high nuclear excitation with very low angular momentum transfer. This has informed our knowledge of nuclear features such as the optical model potential, low-spin nuclear structure, nuclear pairing, and probes of the electromagnetic interaction in the nuclear system.

Because neutrons naturally decay, traditional measurements have focused on producing neutron beams which impinge on relatively large samples of stable or near stable isotopes for study. The Los Alamos Neutron Science Center (LANSCE) provide high-intensity, energy-resolved neutron time-of-flight beams coupled to a wide range of detector arrays to study different reaction properties.

In this overview of measurements at LANSCE, I will focus on recent work with a particular emphasis on advancing the state-of-the art in direct neutron-induced measurements on radioactive isotopes. These measurements have been enable by a combination of new capabilities for rare isotope production, instrument advances allowing use of ever smaller samples, and improvements in the neutron source intensity. These measurements are informing theoretical models for nuclear
reactions with constraints as we move away from the valley of stability, improving predictions in the most challenging scenarios mentioned above.

Speaker: Aaron Couture (Los Alamos National Laboratory)

23 Decay Spectroscopy Studies with GRIFFIN at TRIUMF-ISAC

Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei (GRIFFIN) is a high-efficiency spectrometer comprised of 16 Compton-suppressed high-purity germanium (HPGe) clover detectors that has been optimized for $\gamma$-ray detection following $\beta$ decays of the low-energy (30-60 keV) beams of radioactive isotopes provided by the ISAC-I facility at TRIUMF. A key feature of the spectrometer is the incorporation of a powerful suite of auxiliary detection systems that makes GRIFFIN an extremely versatile facility for a wide range of decay spectroscopy research. Following a brief overview of the GRIFFIN spectrometer and its capabilities, this presentation will discuss a number of research highlights from the first decade of GRIFFIN operations at the ISAC facility. Future opportunities for research with GRIFFIN at TRIUMF's new Advanced Rare Isotope Laboratory (ARIEL) will also be discussed.

Speaker: Carl Svensson (University of Guelph)

24 Low-energy enhancement of the magnetic dipole radiation in heavy nuclei

A low-energy enhancement (LEE) has been observed in the $\gamma$-ray strength function ($\gamma$SF) of mid-mass nuclei and several lanthanides, and configuration-interaction (CI) shell model calculations suggest that this enhancement originates in the magnetic dipole ($M1$) $\gamma$SF [1]. However, conventional CI shell model calculations are intractable in heavy nuclei, and the standard approach to calculate $\gamma$SFs -- the quasiparticle random-phase approximation (QRPA) -- does not reproduce the LEE. Thus the theoretical identification of a LEE in heavy open-shell nuclei has been an open problem. If a LEE persists in neutron-rich heavy nuclei, it would likely have profound effects on $r$-process nucleosynthesis by significantly enhancing the radiative neutron-capture rates of nuclei near the neutron drip line [2].

The shell model Monte Carlo (SMMC) method [3] is a powerful method to calculate thermal observables in model spaces that are many orders of magnitude larger than those that can be addressed in conventional methods. We used a combination of SMMC and other many-body methods in chains of even-mass samarium [4] and neodymium [5] isotopes and identified a LEE in their $M1$ $\gamma$SF. We also identified a LEE in the odd-mass samarium and neodymium isotopes despite a Monte Carlo sign problem that originates from the projection on an odd number of particles [6].

Recently we have extended SMMC to the heaviest nuclei ever thus modeled, the actinides, which requires many-particle space dimensions as large as 10$^{32}$ [7]. We identified a LEE in the $M1$ strength function for a selected set of actinides, the first such observation either theoretically or experimentally in this mass region [8].

This work was supported in part by the U.S. DOE grant No.~DE-SC0019521.

[1] J.E. Mitdbo, A. C. Larsen, T. Renstrom, F. L. Bello Garrote, and E. Lime, Phys. Rev. C 98, 064321 (2018), and references therein.

[2] A.C. Larsen and S. Goriely, Phys. Rev. C 82, 014318 (2010).

[3] For a recent review, see Y. Alhassid, in Emergent Phenomena in Atomic Nuclei from Large-Scale Modeling: a Symmetry-Guided Perspective, edited by K. D. Launey (World Scientific, Singapore, 2017), pp. 267-298.

[4] P. Fanto and Y. Alhassid, Phys. Rev. C Letters 109, L031302 (2024).

[5] A. Mercenne, P. Fanto, W. Ryssens, and Y. Alhassid, Phys. Rev. C 110, 054313 (2024) [Editors' Suggestion].

[6] D. DeMartini and Y. Alhassid, Phys. Rev. C 111, 034315 (2025).

[7] D. DeMartini and Y. Alhassid, arXiv:2509.26571.

[8] C. Rodgers, D. DeMartini and Y. Alhassid, arXiv:2511.11565.

Speaker: Prof. Y. Alhassid (Yale University)

Tuesday 16 June

Plenary

Convener: Dr Magdalena Gorska (GSI Helmholtz Centre )

25 Extreme Light Infrastructure - Nuclear Physics: achievements and perspectives

Extreme Light Infrastructure - Nuclear Physics (ELI-NP) has evolved into an international, interdisciplinary research center dedicated to the emerging field of nuclear photonics. The research activities at ELI-NP are located at the frontier between nuclear physics, particle accelerator physics, high-power laser and plasma physics, and includes the development of new technologies and methods. The field of nuclear photonics has experienced an impressive growth over the last decade with the emergence of several global initiatives to build research infrastructures based on high-power lasers. ELI-NP at the "Horia Hulubei" National Institute for Physics and Nuclear Engineering (IFIN-HH) offers a worldwide unique research infrastructure that contributes to the advancement of nuclear photonics in areas of fundamental scientific research, as well as to the development of applications with significant societal benefits in industry and medicine.

ELI-NP currently operates the world's most powerful laser system. The system consists of two ultra-short pulse lasers, each of which can deliver pulses of 10 PW peak power and reach levels of laser irradiance of 10$^{23}$ W/cm$^2$. Laser pulses at maximum power can be delivered at a repetition rate of one pulse per minute. To increase the system's flexibility, each laser arm is provided with lower power outputs and higher repetition rates, as follows: 1 PW at 1 Hz repetition rate and 100 TW at 10 Hz repetition rate.

With the successful completion of the commissioning experiments, all the experimental setups implemented at ELI-NP have progressively become operational. Since 2022, the laser system has been operated as a user facility, with beam time awarded based on scientific merit through a competitive process.
Experiments at ELI-NP have yielded key findings that contribute significantly to the development of acceleration schemes for multi-GeV electrons, hundreds of MeV/u protons and ions, and the production of GeV-scale gamma rays.

The availability of particle and photon beams generated using high-power lasers, opens new opportunities for a range of applications that can benefit from the ultra-short pulse duration and high beam brilliance. The potential of laser-based ion acceleration and X-ray beams generation in the development of medical applications for cancer treatment and diagnostics is highly promising.

The gamma beam system will provide quasi-monochromatic gamma beams with energies up to 19.5 MeV and a relative bandwidth of approximately 0.5%. The system is currently being implemented with the objective of being operational by the end of 2026. Some of the experimental setups designed for the gamma beams were used for preparatory experiments performed at the 9 MV TANDEM accelerator of IFIN-HH.

Speaker: Calin Alexandru Ur (ELI-NP / IFIN-HH)

26 Precision Physics with Highly-Charged Ions in Storage Rings: Recent Highlights and Future Perspectives

Employing storage rings for precision physics experiments with highly-charged ions (HCI) is a powerful approach for probing fundamental questions at the intersection of atomic physics, nuclear structure, and astrophysics. Storage of freshly produced secondary particles in a storage ring is a straightforward way to achieve the most efficient use of these rare species.

Major facilities include the ESR and CRYRING at GSI, CSRe at IMPCAS, R3 at RIKEN, and the newly commissioning SRing at HIAF.

Precision mass measurements and investigations of exotic decays in highly charged ions are now well-established research programs. Still, the development of new techniques such as Br-defined isochronous mass spectrometry at the CSRe or combined Schottky+isochronous spectrometry at the ESR improves the experimental capabilities in terms of sensitivity, precision and measurement speed. For example, masses of short-lived nuclei produced with vanishingly small rates of below 1 particle per day can be obtained.

Beyond mass measurements, studies of nuclear reactions were intensified significantly in the recent years. Here, beam cooling combined with windowless thin gas targets enable high angular and energy resolution. Furthermore, beam accumulation and deceleration
enable reaction measurements with radioactive projectiles across a broad range of centre-of-mass energies — from a few ten keV/u of astrophysical interest to a few hundred MeV/u.

In this contribution, the most recent highlight results will be presented. The future perspectives at the existing and planned facilities will be outlined.

Speaker: Yury Litvinov (GSI Helmholtz Center for Heavy Ion Research)

27 QRPA prediction of the de-excitation photon strength function

While maintaining the standard definition of the photon force function, many models have been developed to compensate for the lack of data for experimentally inaccessible nuclei.
In this context, the added value of microscopic approaches and the progressive reduction of phenomenological ingredients introduced in their post-processing will be presented.

As a key ingredient of microscopic strength function models, the quasi-particle random phase approximation (QRPA) approach, in particular using the effective Gogny interaction [1],
can be applied to spherical as well as deformed nuclei, to light (such as oxygen) as well as to superheavy elements.
Despite the computationally intensive effort required, large-scale calculations of the dipole strength functions have been performed with limited phenomenological ingredients [2,3,4]. The resulting photon strength functions have been shown to reproduce all experimental data with a high level of accuracy [5].

Although many other observables can be obtained within the standard QRPA,
the prediction of the half-lives of isomeric states in $N=100$ isotones [6] has been shown to require the calculation of the Coriolis coupling, i.e. transition probabilities between QRPA states.
Such intra- or inter-band transitions can be extended to electromagnetic operators to enrich the microscopic description of the dipole strength function
with a special attention to describe as well the upbend observed in the Oslo data [5].

Today, this new development allows us to systematically estimate the de-excitation photon strength function of prime relevance in the calculation of radiative capture cross sections. The de-excitation dipole strength function has been compared to the photo-absorption strength function, revealing possible deviations from the Brink hypothesis [7].
[1] S. Péru and Martini, Eur. Phys. J. A 50: 88 (2014);

[2] M. Martini S. Péru, S. Hilaire, S. Goriely, F. Lechaftois, Phys.Rev. C 94, 014304 (2016);

[3] S. Goriely, S. Hilaire, S. Péru, {\it et al.}, Phys.Rev. C 94, 044306 (2016);

[4] S. Goriely, S. Hilaire, S. Péru, and K. Sieja, Phys.Rev. C 98, 014327 (2018);

[5] S. Goriely {\it et al.}, The European Physical Journal A 55, 172 (2019);

[6] L. Gaudefroy, S. Péru {\it et al}, Phys.Rev. C 97, 064317 (2018);

[7] S. Goriely, S. Péru and S. Hilaire, Phys. Lett. B 868 (2025) 139677.

Speaker: Sophie Péru (CEA)

28 Experimental studies of the dipole response of $fp$-shell nuclei via one-neutron transfer reactions

In this invited contribution, I will present recent results from $(d,p)$ experiments performed with the Super-Enge Split-Pole Spectrograph at the John D. Fox Accelerator Laboratory of Florida State University [1] to study single-particle strengths in $fp$-shell nuclei [2-4]. After briefly highlighting the capabilities of the experimental setup [1,5], I will focus on three specific examples. First, I will provide a brief overview on our results obtained for the neutron-adding strengths in the $N=29$ isotone $^{53}$Cr [3], comparing to strengths measured earlier for $^{55}$Fe [6]. Then, I will pivot and focus on the rich dataset which we obtained for $^{50}$Ti. I will briefly point out similarities and differences between the fragmentation of neutron-adding strengths to excited states of even-$A$ $^{50}$Ti and odd-$A$ $^{51}$Ti, before I discuss $1^+$ and $1^-$ states of $^{50}$Ti populated in the $(d,p)$ reaction. By comparing to observables obtained from complementary experiments, I will make a case for how $(d,p)$ can be used to study the microscopic origin of the spin-flip $M1$ resonance [4] and of the low-energy $E1$ strength, often referred to as pygmy dipole resonance (PDR) [2,7].

The experimental program at the FSU John D. Fox Laboratory is supported by the U.S. National Science Foundation (PHY-2412808 and PHY-2405485) and by the U.S. National Nuclear Security Administration (DE-NA0004150) as part of CENTAUR. Support from Florida State University is gratefully acknowledged.

References:

1. M. Spieker and S. Almaraz-Calderon, Frontiers in Physics 12, 1511394 (2024).
2. M. Spieker, L. T. Baby, A. L. Conley, B. Kelly, M. Müscher, R. Renom, T. Schüttler, and A. Zilges, Phys. Rev. C
   108, 014311 (2023).
3. M. Spieker, L. A. Riley, M. Heinze, A. L. Conley, B. Kelly, P. D. Cottle, R. Aggarwal, S. Ajayi, L. T. Baby, S. Baker,
   I. Conroy, I. B. D’Amato, J. Esparza, S. Genty, I. Hay, K. W. Kemper, M. I. Khawaja, P. S. Kielb, A. N. Kuchera,
   E. Lopez-Saavedra, A. B. Morelock, J. Piekarewicz, A. Sandrik, V. Sitaraman, E. Temanson, C. Wibisono, and
   I. Wiedenhoever, Phys. Rev. C 112, 064331 (2025).
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   E. Litvinova, H. Pai, N. Pietralla, D. Savran, W. Tornow, N. Tsoneva, A. Volya, and V. Werner, Phys. Rev. Lett.
   136, 082502 (2026).
5. A. Conley, B. Kelly, M. Spieker, R. Aggarwal, S. Ajayi, L. Baby, S. Baker, C. Benetti, I. Conroy, P. Cottle, I. D’Amato,
   P. DeRosa, J. Esparza, S. Genty, K. Hanselman, I. Hay, M. Heinze, D. Houlihan, M. Khawaja, P. Kielb, A. Kuchera,
   G. McCann, A. Morelock, E. Lopez-Saavedra, R. Renom, L. Riley, G. Ryan, A. Sandrik, V. Sitaraman, E. Temanson,
   M. Wheeler, C. Wibisono, and I. Wiedenhöver, Nuclear Instruments and Methods in Physics Research Section A:
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6. L. A. Riley, I. C. S. Hay, L. T. Baby, A. L. Conley, P. D. Cottle, J. Esparza, K. Hanselman, B. Kelly, K. W. Kemper,
   K. T. Macon, G. W. McCann, M. W. Quirin, R. Renom, R. L. Saunders, M. Spieker, and I. Wiedenhöver, Phys.
   Rev. C 106, 064308 (2022).
7. M. Spieker, Eur. Phys. J. A 61, 197 (2025).

Speaker: Mark Spieker (Florida State University)

10:30 Coffee Break

Plenary

Convener: Ben Kay (Argonne National Laboratory)

29 Commissioning Experiments Using Gamma-ray Spectroscopy at RAON

The RAON accelerator facility in Korea has recently commenced operations with its low-energy superconducting linear accelerator (SCL3) and ISOL system, providing unique opportunities for nuclear structure studies with both stable and RI beams. The Center for Exotic Nuclear Studies (CENS) is leading several experimental programs at RAON, focusing on nuclear shell evolution, collective excitations, and the fundamental properties of exotic nuclei. To support these scientific goals, CENS has developed advanced detection systems, including the ASGARD HPGe clover array and the STARK Jr. silicon detector array designed to be integrated with the ASGARD array for coincident measurements. In this presentation, we will report on the current status of these detection systems at RAON and discuss the early results from the commissioning experiments conducted over the past year, highlighting the RAON’s potential for high-resolution gamma-ray spectroscopy.

Speaker: Kevin Insik Hahn (Center for Exotic Nuclear Studies, IBS)

30 Evidence for multiple shape coexistence in the Z=40, N=60 region

The evolution of ground-state shapes usually proceeds smoothly, however for Rb, Sr, Y, and Zr nuclei nuclei there is an abrupt shape transition that occurs at $N=60$ (see Refs. [1,2] for reviews). Some recent calculations, using the state-of-the-art Monte Carlo Shell Model (MCSM) [3,4] and the Interacting Boson Model employing the Intertwined Quantum Phase Transition (IQPT) [5], have been able to reproduce this abrupt change for the Zr isotopes and predict that shape coexistence occurs both above and below the critical $N=60$ point. The MCSM calculations also predict multiple shape coexistence in Zr. Moving away from $Z=40$, the abruptness of the transition becomes attenuated, with a smoother evolution observed in Mo, for example [2].
Over the past decade, there has been a large number of experimental investigations, using a variety of probes, that are bringing new insights into nuclei in the $N=60$ region. Deformed band structures have been revealed through detailed $\gamma$-ray spectroscopy following $\beta$-decay [6-9] and fission [10-13]. Coulomb excitation studies have provided important matrix elements and quadrupole moments [14-16] and have been complemented by lifetime measurements [17-20]. A conversion electron study has provided a measurement of the change in radii of the $^{98}$Zr and $^{100}$Zr nuclei [21].
Using $\beta$-decay and Coulomb excitation measurements, we have recently added high-precision data on excited states of $^{94}$Zr, $^{96}$Zr, and $^{98}$Zr. This has enabled us to characterize the excited states belonging to deformed structures. For $^{94}$Zr, our Coulomb excitation results provide firm evidence for an oblate-triaxial deformed structure for the $0^+_2$ state [22]. In $^{96}$Zr, we have refined the in-band $B(E2;2^+_2\rightarrow 0^+_2)=39(6)$ W.u. [23] from the previous value of 37(11) W.u. [24]. The increased level of precision of the $B(E2)$ value, combined with other properties of the $0^+_2$ band, has led us to suggest that its configuration is different from the corresponding state in $^{94}$Zr [23]. Our data also firmly identify the deformed band built on the $0^+_3$ state in $^{98}$Zr [25]. Considering these data, and through comparison with other nuclei, especially $^{96,98}$Sr, leads us to the suggestion of triple shape coexistence in the Zr isotopes.
References
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[25] K. Mashtakov et al., to be published (2026).

Speaker: Prof. Paul Garrett (University of Guelph)

31 The Nucleosynthesis of Strontium – an i-process puzzle

In recent astronomical observations, stellar abundance patterns of certain elements cannot be explained by traditional nucleosynthesis processes, namely the slow (s) and rapid (r) neutron-capture processes. Therefore, the emergence of an independent nucleosynthesis pathway, the intermediate (i-) process, is required to explain these observations. However, some open questions remain for the i process, such as potential astrophysical site where this process occurs, and the conditions required for this process to take place. For nuclei that are involved along this pathway, structural properties such as masses and $\beta$-decay half-lives are experimentally well constrained except for neutron-capture reaction rates, which are almost entirely provided by theory.
Current models that explore the i-process significantly underproduce the abundances of strontium (Sr) compared to observational data, while neighbouring elements such as yttrium (Y) and zirconium (Zr) are well described through this comparison. It is evident that this discrepancy is due to the uncertainties associated with the nuclear physics input, especially on the neutron-capture reaction rate of the $^{88}$Kr(n,$\gamma$)$^{89}$Kr reaction.
In this presentation, the first experimental constraint on the $^{88}$Kr(n,$\gamma$)$^{89}$Kr reaction rate will be discussed utilizing the $\beta$-Oslo method, obtained by exploiting its statistical properties. The indirect method of $\beta$-decay from $^{89}$Br into $^{89}$Kr was utilized at the CARIBU facility in Argonne National Laboratory. Subsequent $\gamma$-rays were detected the using the Summing NaI(Tl) detector, SuN, with the combination of the SuNTAN tape transport system and a plastic scintillator barrel, SuNSPOT.
This presentation will feature the experimentally constrained reaction rate for $^{89}$Kr, with a discussion on its impact on current i-process models and on the underproduction of Sr.

Speaker: Sivahami Uthayakumaar (Facility for Rare Isotope Beams (FRIB) / Michigan State University)

12:30 Lunch

Poster Session

Parallel: Parallel 1A

32 Development of the M1 gamma strength function with the neutron number.

Understanding the global Z-N-dependence of the γ strength functions (γsf) is important for reliably predicting reaction rates in astrophysical and technical applications. For this reason, the Notre Dame-HZDR-Kashmir collaboration has calculated the M1 and E2 γsf for extended series of the Sn, Ge, Gd and Sm isotopes using the conventional spherical shell model (SSM) and, as a new tool, the triaxial projected shell model (TPSM). The appearance of the strong enhancement of the M1 γsf (low energy magnetic radiation-LEMAR) is demonstrated for the semi magic isotope chain $_{~~~~~~~~~~50}^{106-130}$Sn. The SSM calculations for $_{~~~~~~~32}^{64-80}$Ge show the LEMAR spike for all cases, except for $_{32}^{64}$Ge, where isospin conservation suppresses it. Approaching the midshell region the bimodal structure of the LEMAR spike and a bump around 3 MeV, interpreted as the scissors resonance (SR), develops, which disappears again toward the shell closure. The calculated E2 γsf and $B(E2,2_1^+\rightarrow 0_1^+)$ values indicate that the bimodal structure appears as a consequence of quadrupole deformation, which reaffirms the results for the Fe and Sm isotopes found by the collaboration before [1,2]. The TPSM calculations for $_{~~~~~~~~~~64}^{154-164}$Gd demonstrate the transition from the monomodal LEMAR spike for the transitional N=90 isotope to the bimodal LEMAR+SR profile for the well deformed N=100 isotope. The TPSM calculations for the odd-A Sm isotopes provide analogue results.
The number of studied examples suggests that the LEMAR spike is commonly ![enter image description here][1]present, except special conditions like isospin conservation in N=Z nuclei suppress it. Deformation causes a partial shift of the M1 strength from the LEMAR to the SR. Possible interpretations of the nature of LEMAR will be discussed.
[1] R. Schwengner et al., Phys. Rev. Lett. 118, 092502 (2017)
[2] F. Naqvi et al., Phys. Rev. C 99, 054331 (2019)

Speaker: Prof. Stefan Frauendorf (University Notre Dame)

33 Nuclear structure studies using electron-gamma coincidence reactions

The all-electromagnetic $(e,e^\prime\gamma)$ reaction provides an exclusive access to nuclear properties. It had first been used for nuclear structure measurements in the 1980s [1]. Since then, very few experiments were based on this reaction. One of its challenges lies in the coincident bremsstrahlung, which - apart from the angular distribution - cannot be distinguished from the $\gamma$-radiation of nuclei decaying to their ground state after excitation by inelastic electron scattering.
Over the last years, first successful $(e,e^\prime\gamma)$ measurements with unprecedented performance were conducted at the S-DALINAC (Superconducting DArmstadt electron LINear ACcelerator) of Technische Universität Darmstadt, Germany. The resolution of electron energy, gamma energy and coincidence time were improved by two orders of magnitude as compared to previous setups [2]. The scattered electrons were registered with the QCLAM magnetic spectrometer. The $\gamma$-radiation was detected by DAGOBERT (Darmstadt Array for coincident Gamma-ray OBservation in Electron scattering ReacTions) consisting of LaBr$_3$:Ce detectors. DAGOBERT@QCLAM is a worldwide unique device for high-resolution electron-gamma coincidence experiments. Recent upgrades for the experimental setup enhanced the performance for upcoming experimental campaigns.
Measurements on $^{12}\textrm{C}$, $^{96}\textrm{Ru}$ and $^{140}\textrm{Ce}$ targets were performed and demonstrated the superior performance of the new facility over previous attempts to study $(e,e^\prime\gamma)$ reactions. The measurement on $^{96}\textrm{Ru}$ is the first electron-gamma coincidence experiment of a medium-heavy open-shell nucleus.
The performance of the set-up will be reported and scientific results on the $\gamma$-decay behaviour and angular distributions will be presented.

This work is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - Project-ID 279384907 - SFB 1245 and Project-ID 499256822 – GRK 2891 “Nuclear Photonics”. It was supported by the State of Hesse within the Research Cluster ELEMENTS (Project ID 500/10.006).

[1] C. N. Papanicolas et al., Phys. Rev. Lett. 54, 26 (1985).
[2] B. Hesbacher et al., Nucl. Instrum. Methods Phys. Res. A 1078, 170574 (2025).

Speaker: Bastian Hesbacher (Institut für Kernphysik, Technische Universität Darmstadt)

34 Experimentally constraining the $\gamma$-ray strength function of $^{147,148}$La using the $\beta$-Oslo method

For exotic nuclei, theoretical predictions of the $ \gamma $-ray strength function ($ \gamma $SF) exhibit large variations, which represent the dominant uncertainty in Hauser Feshbach calculations of neutron capture reaction rates. In particular, constraining the $ ^{146} $La(n,$ \gamma $)$ ^{147} $La and $ ^{147} $La(n,$ \gamma $)$ ^{148} $La reactions through experimentally determined nuclear level densities (NLDs) and $ \gamma $SFs will improve neutron reaction network calculations in the $ A = 147 $ mass region under neutron rich conditions. At Argonne National Laboratory using nuCARIBU at ATLAS, total absorption spectra and $ \gamma $-ray spectra for these La isotopes will be measured to constrain the NLDs and $ \gamma $SFs and, in turn, provide experimentally anchored neutron capture cross sections that are important for U.S. stockpile stewardship applications and for understanding the nucleosynthesis of heavy elements in the cosmos.

For La isotopes near stability, Oslo style measurements of $ ^{138,139,140} $La at the Oslo Cyclotron Laboratory indicate either a modest low energy enhancement (LEE) or a plateau like behavior at low $ \gamma $-ray energies. For Mo and Nd isotopes, the LEE decreases with increasing neutron number. This work will investigate whether a similar trend emerges for more neutron rich La isotopes. The high efficiency Summing NaI (SuN) detector, in combination with the SuN Tape system for Active Nuclei (SuNTAN), will be employed in an upcoming experiment that uses the $ \beta $ decay of $ ^{147,148} $Ba beams to populate excited states in $ ^{147,148} $La. The experimental plan for this campaign at nuCARIBU, along with anticipated analysis challenges, will be presented using a synthetic data set and the $ \beta $-Oslo method to assess the sensitivity to the NLD and $ \gamma $SF in this region.

Speaker: Adriana Sweet (Lawrence Livermore National Laboratory)

35 Measuring 39K(3He,α)38K with GODDESS to search for energy levels in 38K important for the 37Ar(p,γ)38K reaction rate

The 37Ar(p,γ)38K reaction plays a critical role in determining the abundances of several stable isotopes at the endpoint of rp-process nucleosynthesis in novae. To inform the astrophysical reaction rate of proton capture on 37Ar and guide any future direct measurements, a better understanding of the 38K energy levels above the 37Ar+p threshold is essential. Experimentally, these excited states of 38K just above the proton threshold may be probed through alternative, experimentally-accessible reactions.

To this end, the 39K(3He,αγ)38K reaction in regular kinematics was measured. The ATLAS accelerator at Argonne National Laboratory provided a beam of 3He at 30 MeV/u, which was incident on an enriched potassium-39 target. Gamma rays and charged particles were detected using the GODDESS system, comprised of the Oak Ridge Rutgers University Barrel Array (ORRUBA) for charged particles, and the Gamma Ray Energy Tracking In-beam Nuclear Array (GRETINA) for gamma rays. The spectroscopy provides information on the excited states of 38K, including those near the proton separation energy of 5.2 MeV. Experimental constraints on the energies and spin-parities of low-spin states in this region, which are of astrophysical importance, as well as their implications for the rp-process, will be discussed.

Speaker: Ashwin Nagarajan

Parallel: Parallel 1B

Convener: Aaron Couture (Los Alamos National Laboratory)

36 Coulomb Excitation Activation Analysis of Debris from the Fukushima Daiichi Nuclear Power Plant toward Its Decommissioning

It has now been 15 years since the Fukushima Daiichi nuclear power plant accident, and we are still working toward our mission of achieving safe decommissioning, which is expected to require approximately 40 years. One of the most difficult challenges is the presence of approximately 880 tons of nuclear fuel debris in the reactors that melted during the accident. Key questions include: (1) how can the debris be safely removed, (2) how can nuclear fuel be separated from alpha-contaminated waste within the debris, and (3) how can long-term storage of the debris be managed? The answers depend strongly on the actual composition of the debris.

Japan Atomic Energy Agency (JAEA) has successfully obtained two debris samples, which were transported to the JAEA Tokai campus in November 2024 and April 2025. From isotopic and elemental analyses using ICP-MS and SEM, the majority of components, such as uranium and iron, have been identified. However, trace components (<1%), including 243Am, 243Cm, 238Pu, 239Pu, and 10B, are difficult to identify due to interfering nuclides, even though these nuclei are critical for controlling criticality and ensuring safe decommissioning.

To analyze such trace components using state-of-the-art nuclear physics and chemistry techniques, we employ (1) Coulomb excitation activation analysis coupled with a Ge detector array and (2) alpha–gamma coincidence measurement techniques. As a validation experiment for method (1), mock debris targets were prepared using electrodeposition techniques and irradiated with a 58Ni beam from the JAEA-Tokai tandem accelerator. Preliminary results will be presented.

Actual debris samples will be provided to us in 2026. We will then perform both alpha–gamma coincidence measurements and Coulomb excitation activation analysis using real debris samples.

Speaker: Taiki Tanaka (Japan Atomic Energy Agency)

37 Pygmy resonance and photon strength functions in 204-Tl from resonance neutron capture.

Level density (LD) and photon strength functions (PSFs) are fundamental quantities describing $\gamma$ decay in the statistical regime, where individual nuclear levels cannot be experimentally resolved. When neutron-capture cross sections -- crucial inputs for heavy element nucleosynthesis calculations -- are unavailable, LD and PSFs provide essential inputs for Hauser-Feshbach calculations. An open question in our understanding of the PSFs is the pygmy dipole resonance (PDR), a low-energy oscillation manifesting in neutron-rich nuclei. One leading theoretical interpretation describes the PDR as an oscillation of the neutron skin against the nuclear core; consequently, the PDR is expected to be more prominent in neutron-rich nuclei far away from stability, which are important for $r$-process calculations. Currently, no reliable systematics of PDR properties is available across nuclei.

This work presents a study of the PSFs and PDR from $^{203}$Tl(n,$\gamma$)$^{204}$Tl reaction measured with the DANCE detector. DANCE -- a highly segmented 4$\pi$ BaF$_2$ scintillator array -- provides high-efficiency coincidence $\gamma$-ray spectra validated against simulations of $\gamma$ cascades using DICEBOX. This analysis benchmarks models of LD and PSFs in $^{204}$Tl and characterizes properties of the PDR. No experimental PSF data currently exist in the PDR region for thallium isotopes in the Photon Strength Function database [1].

A strong PDR centered at 5.4 MeV was identified in the dataset, with a PSF shape similar to previous measurements in $^{206}$Pb and $^{196}$Pt. Notably, none of the recommended PSF models in the database reproduce the experimental spectra. Due to strong parity asymmetry in low-lying levels of $^{204}$Tl, $s$-wave and $p$-wave $\gamma$-ray spectra exhibit different sensitivities to E1 and M1 components of the PSF, providing clear distinctions between two groups. In addition to the measured $\gamma$-ray spectra, the implications of the observed PDR on neutron-capture cross section calculations will also be presented. Together with previous measurements in the region of nuclei near doubly magic $^{208}$Pb, these results will help to benchmark the PSF models and improve predictive power for neutron-rich nuclei away from stability.

[1] IAEA Photon Strength Function Database, version v2024.1, available from: https://nds.iaea.org/PSFdatabase

Speaker: Ingrid Knapova (Los Alamos National Laboratory)

38 On the nature of shape coexistence and quantum phase transition phenomena in odd-even systems

The shape coexistence phenomenon is related with the presence in the same energy region of eigenstates with different deformations. Shape coexistence appears almost everywhere in the mass table, but its presence is specially remarkable in the Pt-Hg-Pb or in the Sr-Zr-Mo regions [1,2].

On the other hand, the concept of quantum phase transition (QPT), which has gained a lot of attention in nuclear physics, among other fields, during the last twenty five years, appears when the Hamiltonian that describes the quantum system can be written in terms of two pieces, at least, each one with a given symmetry, and a Hamiltonian parameter, i.e., a control parameter, allows to pass from one to the other symmetry. This passing supposes a sudden change in an order parameter and a discontinuity in the ground-state energy of the system or in some of its derivatives.

The goal of this talk is to try to clarify the connection between shape coexistence and QPT, two seemingly unrelated phenomena, but that, once studied in deep, share common aspects: the rapid change in the ground state structure when going through an isotope chain or the presence in the mean-field energy surface of several minima. To illustrate the similarities and differences between both phenomena, we will focus in the Zr and Sr region (including also Mo and Ru) which is known for the rapid change of the ground state deformation and also for the presence of intruder states coming from two-particle two-hole excitations across Z=40 shell closure [4,5,6]. Then we will move into the case of odd-even systems where we will study the Nb nuclei using the recently proposed intrinsic state formalism of the Interacting Boson Model with configurations mixing for odd systems [7,8]. This formalism allows to deal with two or more different configurations, with triaxial shapes and with single- or multiple-j shells.

[1] K. Heyde and J. L. Wood, "Shape coexistence in atomic nuclei", Rev. Mod. Phys. 83, 1467 (2011).

[2] P. E. Garrett, M. Zielińska, and E. Clément, "An experimental view on shape coexistence in nuclei", Prog. Part. Nucl. Phys. 124, 103931 (2022).

[4] J.E. García-Ramos and K. Heyde, "Subtle connection between shape coexistence and quantum phase transition: The Zr case", Phys. Rev. C 102, 054333-16p (2020).

[5] E. Maya-Barbecho and J.E. García-Ramos, "Shape coexistence in Sr isotopes", Phys. Rev. C 105, 034341 (2022).

[6] E. Maya-Barbecho, S. Baid, J. M. Arias, and J.E. García-Ramos, "At the borderline of shape coexistence: Mo and Ru", Phys. Rev. C 108, 034316 (2023).

[7] E. Maya-Barbecho and J.E. García-Ramos, "An intrinsic-state formalism for the Interacting Boson-Fermion Model with configuration mixing", Phys. Lett. B 868 (2025) 139724.

[8] E. Maya-Barbecho and J.E. García-Ramos, "An study of Nb isotopes using the intrinsic-state formalism of the interacting boson-fermion model with configuration mixing", under consideration in Phys. Rev. C.

Speaker: José Enrique García Ramos (University of Huelva)

39 Constraining the 85Rb branching point in the astrophysical γ process

There are 35 proton-rich stable isotopes, known as p-nuclei. Their existence is attributed to the $\gamma$ process, primarily consisting of a network of photodisintegration reactions on s- and r-process seed nuclei. The abundances of p-nuclei can be obtained based on simulations of this network, with most of the isotopes involved being radioactive. For this reason, direct measurements of these reactions are challenging, thus reaction rates are often obtained via theoretical calculations based on the Hauser-Feshbach (HF) theory. The Nuclear Level Density (NLD), gamma-ray strength function (gSF) of the compound nucleus is given as inputs to the theory as well as the Optical Model Potential (OMP) to obtain a theoretical cross section. Constraining theoretical models is crucial to obtain experimentally constrained cross-section values for unstable elements. In the present work, we focus on reactions around $^{85}\mathrm{Rb}$, relevant to the astrophysical $\gamma$ process, where reaction flow is defined by the competition between two reactions, the (γ, n) and the (γ, p). Depending on which is the dominant channel, that affects the production of the $^{78}\mathrm{Kr}$ p nucleus. Therefore, constraining the reaction rates for both channels is crucial to obtaining more accurate abundances for $^{78}\mathrm{Kr}$. Here we use the $^{84}\mathrm{Kr}(p,\gamma)^{85}\mathrm{Rb}$ reaction to populate the $^{85}\mathrm{Rb}$ compound nucleus, and constrain the NLD, gSF.

The $^{84}\mathrm{Kr}(p,\gamma)^{85}\mathrm{Rb}$ proton capture reaction was measured with the SuN detector at NSCL at MSU. A stable $^{84}\mathrm{Kr}$ beam was impinged onto a hydrogen gas target in the energy range of 2.7 MeV/u to 3.7 MeV/u. We present a re-analysis of the proton capture data in which we provide new values for the reaction cross section, and in addition, we use the γ-ray spectra to constrain the statistical properties of $^{85}\mathrm{Rb}$, namely the NLD and the gSF. In addition, the proton optical model potential (pOMP) parameters were modified to obtain a better fit on the experimental data of $^{84}\mathrm{Kr}(p,\gamma)^{85}\mathrm{Rb}$, $^{84}\mathrm{Kr}(p,n)^{84}\mathrm{Rb}$ and $^{84}\mathrm{Kr}(p,2n)^{83}\mathrm{Rb}$ reaction channels. The constrained NLD and gSF, as well as the modified pOMP, were used to calculate the astrophysical reaction rates for the $^{85}\mathrm{Rb}(\gamma,p)^{84}\mathrm{Kr}$ and $^{85}\mathrm{Rb}(\gamma,n)^{84}\mathrm{Rb}$ channels.

Speaker: KONSTANTINOS BOSMPOTINIS (Michigan State University)

14:50 Coffee Break

Parallel: Parallel - 2B

Convener: Benjamin Crider (Mississippi State University)

40 Development and Characterization of a CeBr₃ Implantation Detector for β-Decay Spectroscopy at FRIB

$\beta$-decay spectroscopy of neutron-rich nuclei near the limits of stability provides powerful benchmarks for nuclear structure models [1]. Such measurements rely critically on the ability to correlate implanted ions with their subsequent decay products, including $\gamma$-ray transitions and $\beta$-decay electrons, making implantation detectors a central component of modern $\beta$-decay experiments. As experimental programs push toward increasingly exotic nuclei, implantation detectors must provide excellent timing performance, spatial resolution, and operational stability under high-rate conditions [2].

As part of detector development efforts at the Facility for Rare Isotope Beams (FRIB), a CeBr$_3$ scintillator was developed and characterized as a primary ion-implantation detector for the FRIB Decay Station Initiator (FDSi). The detector consists of a $48 \times 48 \times 3\,\mathrm{mm}^3$ CeBr$_3$ crystal coupled to a pixilated $16 \times 16$ Position Sensitive Photomultiplier Tube (PSPMT), which has thus far allowed for full implantation of the cocktail beam within the scintillator volume. Detailed characterization studies were performed to evaluate the detector response, timing performance, position sensitivity, and long-term stability under sustained beam conditions. Following these studies, the detector was integrated into the FDSi data acquisition system [3].

The experimental implementation of the CeBr$_3$ implantation detector as a component of the FDSi setup occurred during the FRIB E23055 experiment, which focused on neutron-rich nuclei in the region from $N=40$ toward $N=50$, with a beam setting centered around $^{68}$Ni. The detector demonstrated excellent timing and position resolution, resulting in good $\beta$-correlation efficiencies during the experiment. An update on the ongoing analysis to extract $\beta$-decay half-lives and identify isomeric states in populated nuclei will be presented.

References
1. T. Otsuka, A. Gade, O. Sorlin, T. Suzuki, and Y. Utsuno, "Evolution
of shell structure in exotic nuclei," Rev. Mod. Phys. 92, 015002 (2020).
2. R. Yokoyama et al., "Segmented YSO scintillation detectors as a new $\beta$-implant detection tool for decay spectroscopy in fragmentation facilities", Nucl. Instrum. Methods Phys. Res. A 937, 93--97 (2019).
3. "FRIB Decay Station Initiator Proposal," (2020), https://fds.ornl.gov/wp-content/uploads/2020/09/FDSi-Proposal-May2020.pdf.

Speaker: Tawfik Gaballah (Mississippi state university)

41 Intermediate-energy Coulomb Excitation of $^{70}$Fe

The region of $N=40$, below the Ni isotopes, is now well-established as a region of deformed ground-states and nuclear collectivity. While the body of spectroscopic information in the so-called N=40 Island of Inversion, centered around $^{64}$Cr, is growing, its boundaries remain undefined, particularly moving from neutron number 40 toward $N=50$. In addition, quantities which more directly provide insight into the wavefunctions in this region, such as B(E2), have only been measured up to $^{68}$Fe. Such quantities provide important benchmarks for theory, both large-scale shell model effective interactions (e.g. LNPS) and ab-initio calculations which are now reaching into this region (e.g. IM-VSRG). We will present preliminary results for an intermediate energy Coulomb excitation measurement performed on neutron-rich $^{70}$Fe ($N=44$) using GRETINA at FRIB. The first direct measurement of the reduced transition probability from the $0^+$ ground state to the first $2^+$ excited state is a useful validation for shell model calculations as we move from the $N=40$ Island of Inversion toward $N=50$.

Speaker: Emma Rice

42 Improving Neutron-Capture γ-Ray Cascade Modeling

Neutron-induced γ-ray cascades provide key signatures for nondestructive assay, active interrogation, nuclear security applications, and nuclear data validation. Modern data needs go beyond capture γ-ray spectra alone and require proper correlations between emissions to be preserved event by event. Existing tools often lack the information needed to reconstruct complete cascades, leading to important quantities such as energy conservation being preserved only on average. These limitations were recently addressed with an extended GNDS-based representation of Evaluated Nuclear Data File (ENDF) data, designed to store the necessary experimental information and model-based inputs. Coupled to the GIDI+ event-generation framework, this approach enables inline neutron-capture and inelastic-scattering γ-ray cascades with event-by-event energy conservation and access to coincidence observables. This new capability is intended for use in transport simulations. In this talk, we will focus particularly on neutron capture, and discuss the impact of missing or incomplete primary γ-ray data, the need for additional measurements and dedicated validation setups, and the role of python libraries to access data such as pyEGAF in making existing experimental primary γ-ray information easier to access and use.
Work at Brookhaven National Laboratory was sponsored by the Office of Nuclear Physics, Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-98CH10886 with Brookhaven Science Associates, LLC.

Speaker: Emanuel Chimanski (BNL)

43 Search for Shape Coexistence Signatures in 100Ru using Thermal Neutron Capture Reaction.

At the forefront of nuclear structure research is the topic of shape coexistence, which occurs when states within the same nucleus at similar energies possess distinct shapes. Studies of nuclei in the Zr (Z=40) - Sn (Z=50) region have shown evidence for shape coexistence with deformed rotational-like bands coexisting with spherical or weakly-deformed ground state configurations. In the Ru(Z=44) isotopes, strong evidence has emerged for shape coexistence within 102Ru and 104Ru from Coulomb excitation [1,2], and it was suggested to be present in 98Ru and 100Ru as well [3]. In order to explore shape coexistence in 100Ru, and also probe possible vibrational motion, key mixing ratios and the observation of low-energy, and hence often very weak intensity, transitions between non-yrast states are required. The study of 100Ru presented in this work aims to extract precise transition multipolarity mixing ratios, unobserved weak g-ray transitions, and transition probabilities to resolve its structural nature. We used the thermal neutron capture reaction, 99Ru(n,g)100Ru, carried out at the Institut Laue-Langevin in Grenoble, France. The g-ray transitions depopulating the excited states in 100Ru were detected by the FIPPS array consisting of two sets of eight clover-type hyper-pure Germanium detectors. FIPPS provides high efficiency and the ability for perform detailed gamma-gamma angular correlations due to its high granularity. Results from the current analysis will be presented with an emphasis on the structural implications of the results.

Speaker: Sangeet-Pal Pannu (University Of Guelph)

Parallel: Parallel 2A

Convener: Thibault Laplace (University of California, Berkeley)

44 The Nuclear Structure of $^{72,74}$Ge from Inelastic Neutron Scattering

The germanium nuclei have been of recent interest for several reasons. First, $^{76}$Ge is one of the leading candidates for the observation of neutrinoless double-beta decay. Thus, detailed understanding of the structure is important for improving the nuclear matrix element calculation for the process in order for the half-life to be extracted. Knowledge of the entire isotopic chain is beneficial in this respect. In addition, the structure of the Ge nuclei has many interesting features. Open questions of triaxiality and shape coexistence remain.

In order to better understand the structures of these nuclei, we have undertaken studies of $^{76,74,72}$Ge using inelastic neutron scattering (INS) at the University of Kentucky Accelerator Laboratory. INS provides non-selective, statistical population of the low-lying, low-spin states, including non-yrast states, allowing characterization of the comprehensive level scheme. Moreover, the Doppler-shift attenuation method following INS is utilized to measure level lifetimes in the femtosecond regime. Overall, the method allows the extraction of gamma-ray energies, level energies, level lifetimes, $a_2$ and $a_4$ angular distribution coefficients, branching ratios, and multipole mixing ratios. These data can then be used to calculate reduced transition probabilities which can be compared to theoretical calculations to further our understanding.

The focus of this presentation will be $^{72,74}$Ge. A number of new structural features have been identified and characterized in each nucleus, including the first observation of shape coexistence in the Ge nuclei in $^{74}$Ge. Large-scale shell-model calculations have also been performed and show remarkable agreement with experimental data.

This material is based upon work supported by the U. S. National Science Foundation under Grant No. PHY-2209178, 2514845, and 2110365.

Speaker: Erin Peters (Department of Chemistry, University of Kentucky, Lexington, KY 40506 USA)

45 A study of the 85gKr(d,pg) reaction to constrain the s-process branching point

About half of the elements heavier than iron are synthesized through the slow neutron capture process, in which the neutron-capture timescales of the nuclei involved are typically longer than their $\beta$-decay lifetimes. In the modeling of this process, significant uncertainties arise from the competition between neutron capture and $\beta$-decay in certain isotopes called “branching points”. $^{85}$Kr is one of the most important branching points of the s-process, influencing both the $^{86}$Kr/$^{82}$Kr ratio measured from presolar grains and the abundances of heavy Sr isotopes, which are also produced by the r-process.

A precise description of this branching point requires a well-constrained $^{85}$Kr(n,$\gamma$) cross section. However, a direct measurement of this cross section is extremely challenging due to the radioactivity of the sample (T$_{1/2}$ = 10.7 yr). An alternative approach is to use $^{85}$Kr as a beam to perform the (d,p$\gamma$) reaction, which has been demonstrated to be a reliable indirect probe of the (n,$\gamma$) cross section.

The $^{85}$Kr(d,p$\gamma$)$^{86}$Kr reaction was performed at 10 MeV/u in inverse kinematics at Argonne National Laboratory using the HELIOS spectrometer coupled with the Apollo array. Neutron excitations around and above S$_n$ in $^{86}$Kr were populated, achieving a Q-value resolution of about 150 keV. The coupling of Apollo with HELIOS enables the coincident detection of $\gamma$-rays and protons, allowing the determination of $\gamma$-ray emission probabilities as a function of excitation energy [P$_{p\gamma}$(E$_{ex}$)].

The $2^+ \to 0^+$ and $4^+ \to 2^+$ $\gamma$-rays were clearly observed, showing the characteristic constant behavior of P$_{p\gamma}$ below S$_n$ and a decrease above S$_n$. These results are used to extract the cross sections of the $^{85}$Kr(n,$\gamma$) reaction and demonstrate the strong potential of this approach for future indirect studies of the (n,$\gamma$) reaction.

Speaker: Sara Carollo (University and INFN Padova)

46 New isomers in the neutron-rich rare-earth region studied by DESPEC

The low excitation energies of the first excited $2^+$ states in the neutron-rich rare-earth nuclei are an indication of their degree of deformation [1]. Close to the double mid-shell, a subtle evolution seems to take place as the neutron number approaches $N = 104$ [2]. Additionally, recent progress in microscopic nuclear theory are providing alternative interpretations of the established view of these nuclei as prolate, axially symmetric rotors [3].

We performed the first ever projectile-fragmentation of $^{170}$Er with an energy of 1 GeV/u at the GSI Helmholtzzentrum für Schwerionenforschung GmbH in Darmstadt, Germany to expand the sparse nuclear structure information of the exotic neutron-rich rare-earth isotopes. The subsequent reaction products were cleanly separated and identified on an ion-by-ion basis using the GSI Fragment Separator before being implanted in the decay spectroscopy setup of the DESPEC collaboration [4]. Using the HPGe array DEGAS and LaBr$_3$ array FATIMA in combination allows for simultaneous high resolution spectroscopy and fast-timing measurements.

Our setup gives access to non-yrast isomeric states, providing new transitions, levels and lifetimes based on the $\gamma$ rays emitted after implantation of neutron-rich nuclei with $N\leq 102$ and $Z\leq67$. The unique production mechanism and exceptionally high yields allowed the discovery of new isomers as well as greatly expanding level schemes with levels not accessible with previous methods.

The isomeric decay of the $N = 102$ nucleus $^{168}$Dy was previously observed at RIKEN [5]. The significantly increased level of statistics in this work has allowed the observation of many new transitions, and required a reassessment of the previously deduced level scheme. The reinterpreted isomer with $K=6$ exhibits decays into several newly-observed structures indicating a complex wave function that overlaps with many different configurations.

This contribution focuses on the novel structures observed for $^{168}$Dy and other selected nuclei and how our results push the experimentally available nuclear structure information away from stability. We also theoretically describe our results using modern nuclear theory.

[1] A. Bohr and B. Mottelson, Nuclear structure volume 2: Nuclear deformations (World Scientific Publishing, New York,
1975).
[2] Z. Patel et al., PRL 113, 262502 (2014).
[3] T. Otsuka et al., EPJ A 61, 126 (2025).
[4] A. Mistry et al., NIM A 1033, 166662 (2022).
[5] G. Zhang et al., PLB 799, 135036 (2019).

Speaker: Johan Emil Linnestad Larsson (Technische Universität Darmstadt, 64289 Darmstadt, Germany)

47 Magnetic moments of isomeric states populated in projectile-fragmentation reactions: the region around $^{68}$Ni

Magnetic moments of excited nuclear states provide sensitive probes to the contributions of single-particle configurations to the nuclear wave functions. This is especially true close to shell closures where the wave functions are expected to be quite pure, and the magnetic moments should be close to the Schmidt values of the single-particle approximation. However, similarly to the effective charges for protons and neutrons, effective spin $g$ factors are often used in calculations to improve agreement between experiment and theory.

The nickel isotopic chain, with three doubly-magic isotopes, makes for a fruitful testing ground for various theoretical models. A peculiar case is that of $^{68}$Ni which lies at the $N=40$ sub-shell closure between the fp shell and the $g_{9/2}$ orbital. It notably exhibits some properties associated with doubly-magic nuclei, such as a $0^+$ first excited state [1] and a low $B(E2)$ value of its $2^+_1$ state [2,3]. However, no sign of magicity at $N=40$ was observed in the $S_{2n}$ from mass measurements [4]. Further insight into the nuclear structure of $^{68}$Ni could be obtained through the magnetic moments (or $g$ factors) of excited states. Targeting directly the excited states in $^{68}$Ni experimentally is still quite challenging, so instead, as a first step, the $g$ factors of $g_{9/2}$ isomeric states in neighboring isotopes were used to shed light on the nuclear structure in the region, with measurements on the $9/2^+$ isomers in $^{65}$Ni [5] and $^{67}$Ni [6].

A follow-up experiment aiming to measure the magnetic moments of $g_{9/2}$ isomeric states in the vicinity of $^{68}$Ni was performed at the NSCL facility at MSU, USA. The main goals of the experiment were to determine the $g$ factors of the $8^+$ isomer in $^{70}$Ni ($T_{1/2}=232(1)$ ns) and the $(19/2^-)$ isomer in $^{69}$Ni ($T_{1/2}=439(3)$ ns), together with a re-measurement of the $g$ factor of the $9/2^+$ isomer in $^{67}$Ni ($T_{1/2}=13.3(2)~\mu$s). The nuclei of interest were produced following a projectile-fragmentation reaction of a $^{76}$Ge primary beam (130 MeV/A) on a Be target. The fragments passed through the A1900 separator and were implanted at the center of a dedicated detector setup.

The half-lives of these isomers, as well as those of isomers in $^{71,72}$Cu present in the data, were measured, leading to improved precision in some cases. The Time-Dependent Perturbed Angular Distribution (TDPAD) method was employed to extract the $g$ factors of the isomeric states of interest by observing the Larmor precession of the oriented nuclear spins in an external magnetic field. The results obtained in this experiment [7] will be presented and compared to state-of-the-art shell-model calculations with the LNPS interaction, showing evidence that calculations in large valence spaces can mostly negate the need for effective spin $g$ factors. Ideas for future measurements of magnetic moments following projectile-fragmentation reactions for both long- and short-lived isomeric states will also be discussed.

References:
[1] M. Bernas et al. Phys. Lett. B, 113(4):279-282, 1982.
[2] O. Sorlin et al. Phys. Rev. Lett., 88:092501, Feb 2002.
[3] N. Bree et al. Phys. Rev. C, 78:047301, Oct 2008.
[4] C. Guenaut et al. Phys. Rev. C, 75:044303, Apr 2007.
[5] G. Georgiev et al. Journal of Physics G, 31(10):1439, 2005.
[6] G. Georgiev et al. Journal of Physics G, 28(12):2993, 2002.
[7] K. Stoychev, G. Georgiev et al., submitted to Phys. Rev. C, 2025.

Speaker: Konstantin Stoychev (University of Guelph)

48 Probing shape coexistence in $^{110}$Cd using Coulomb excitation

Mid-shell Cd nuclei were traditionally considered to be the best examples of vibrational nuclei. Recent studies that combined detailed $\gamma$-ray spectroscopy with sophisticated beyond-mean-field calculations had suggested [1,2] that the low-lying 0$^+$ states in $^{110,112}$Cd possessed prolate, triaxial, and oblate shapes with rotational-like bands built upon them. If confirmed, this would have major implications on structural interpretations of nuclei in the Z = 50 region, and perhaps beyond. Soon afterwards a similar picture was suggested for $^{106}$Cd [3,4].

The low-energy Coulomb-excitation technique represents an ideal tool to study nuclear deformation. It enables a direct determination of electromagnetic transition matrix elements between low-lying excited states including spectroscopic quadrupole moments and signs. Those can be further analysed in terms of quadrupole invariants [5] yielding model-independent information on shape parameters of individual states. This requires, however, extensive sets of high-precision experimental data.

A multi-faceted experimental program to ascertain the deformation of low-energy states in $^{110}$Cd has been initiated. We seek to firmly establish the shape of the first three lowest-lying 0$^+$ states through the use of the rotation-invariant sum rules for $E$2 transitions. Coulomb-excitation measurements were performed using various reaction partners: $^{14}$N and $^{32}$S beams with EAGLE at HIL UW (Warsaw, Poland) [6,7], $^{60}$Ni beam with AGATA at LNL (Legnaro, Italy) [8] and $^{110}$Cd beam on a $^{208}$Pb target with GRETINA at ANL (Argonne , USA). These measurements have been complemented by an experiment performed at TRIUMF-ISAC with the GRIFFIN spectrometer examining the decays of $^{110}$Ag/$^{110}$In that will provide high-precision data on $\gamma$-ray branching ratios and transition mixing ratios. First results on quadrupole deformation parameters for the 0$^+_1$ and 0$^+_2$ states, demonstrating non-axial character of the ground state in $^{110}$Cd, will be presented. These experimental findings will be discussed in the context of: (i) Symmetry-Conserving Configuration-Mixing approach [1,2] and, (ii) new calculations with the general quadrupole collective Bohr Hamiltonian model involving two variants of interactions: SLy4 and UNEDF0.

Future perspectives will be outlined, including a brief overview of Coulomb-excitation studies addressing shape coexistence in the Z ∼ 50 region within the experimental campaigns at HIL Warsaw and at LNL Legnaro.

References
[1] P. Garrett et al., Phys. Rev. Lett. 123 (2019) 142502.
[2] P. Garrett et al., Phys. Rev. C 101 (2020) 044302.
[3] M. Siciliano et al., Phys. Rev. C 104 (2021) 034320.
[4] D. Kalaydjieva , PhD thesis, Universite Paris-Saclay, 2023.
[5] K. Kumar et al., Phys. Rev. Lett. 28 (1972) 249.
[6] K. Wrzosek-Lipska et al., Acta Phys. Pol. B 51 (2020) 789.
[7] K. Wrzosek-Lipska et al., accepted to be published in Phys. Lett. B,
https://doi.org/10.1016/j.physletb.2026.140315
[8] I.Z. Piętka et al. , Acta Phys. Pol. B Proc. Suppl. 18 (2025) 2-A26.

Speaker: Katarzyna Wrzosek-Lipska (Heavy Ion Laboratory, University of Warsaw Poland)

Wednesday 17 June

Plenary

Convener: Carl Svensson (University of Guelph)

49 Machine Learning for global predictions of nuclear excited states

The comprehensive characterization of nuclear excited states is fundamental to our understanding of nuclear structure and is a cornerstone for modern applications. In this work, we introduce a robust machine learning (ML) framework designed for the global prediction of nuclear energy levels with high precision. Utilizing the Evaluated Nuclear Structure Data File (ENSDF) as a foundational dataset, we employ a data-driven approach to map spectral properties across the nuclear landscape. Despite using a sparse training set of only 20%, the model reproduces the remaining 80% of known levels with a mean deviation within 100 keV. The model demonstrates a capacity for extrapolation into presently unreachable regions of the nuclear chart, providing a predictive roadmap for future rare-isotope beam facilities.

Speaker: Dr Matthew Mumpower (Los Alamos National Laboratory)

50 Microscopic origin of the spin cutoff problem in nuclear level density

Despite long-term research, the origin of spin cutoff parameter of angular-momentum distribution in nuclear level density (NLD) remains incompletely elucidated. The lack of spin information in the NLD severely impacts many applications, including nuclear astrophysics, fragment study in nuclear fission, and nuclear data evaluation. To classify the NLD based on total angular momentum J, it was hypothesized that a complex nucleus is analogous to a rigid rotor with effective moment of inertia, possessing 2 J + 1 K quantum numbers to define the orientation of J. Following this line of thought, exploring the relationship between spin cutoff and moment of inertia has been a major research direction; however, the research has achieved limited success.

We find that the existence of the spin cutoff problem can be traced back to Bethe’s initial assumption that nucleons are independent random variables. By constructing a statistical ensemble that enforces rotational invariance through angular-momentum coupling [1], we obtain an analytical expression for the spin cutoff parameter, which includes a previously undiscovered finite population correction (FPC). The FPC term fully incorporates the shell effect, and its correction to the spin distribution varies with the temperature-dependent occupancy of single particles. At the high temperature limit, the degeneracy is much greater than the occupation number, the FPC term can be ignored [2].

Our finding does not change the general Gaussian form provided by Ericson’s formula, but rather explores the physical origin and inevitability of the spin distribution. It shows that even in the absence of interaction, nuclear many-body states exhibit correlations arising from fermionic antisymmetry and angular-momentum coupling. From this perspective, we propose that spin cutoff may be interpreted as a quantitative measure of the geometric correlation imposed by symmetry in nuclear level statistics, to distinguish the dynamic correlation caused by the usual residual interactions [3].

[1] J.-C. Guo and Y. Sun, New angular momentum coupling method based on Wigner rotation theory, Phys. Rev. C 112, 064307 (2025).

[2] J.-C. Guo, A novel method for studying nuclear level density based on fundamental principles of quantum mechanics, Doctoral dissertation, Shanghai Jiaotong University, (2025).

[3] J.-C. Guo and Y. Sun, Symmetry-imposed correlation in nuclear level statistics: The spin distribution, to be published.

Speaker: Prof. Yang Sun (Shanghai Jiao Tong University)

51 The Gamma-Ray Energy Tracking Array (GRETA)

The Gamma-Ray Energy Tracking Array (GRETA) is 4$\pi$ detector designed to study a broad science program in nuclear structure over a wide range of beam energies and velocities from Coulomb barrier to 100’s MeV/A. It combines highly segmented HPGe crystals with advanced digital electronics and signal processing to identify individual gamma-ray interaction points within the crystals to simultaneously achieve high energy resolution, high efficiency, and good background rejection (peak-to-total).

The GRETA Project started in 2017, following nearly a decade of successful science with the predecessor GRETINA array, and completed construction and initial commissioning of all technical systems (mechanical, electronics and computing) with a subset of Quad Detector modules at LBNL in the summer of 2025. It is currently being installed at the Facility for Rare Isotope Beams (FRIB) with first science measurements expected early 2027. I will review the GRETA project, both science and technical as well performance, and the progression toward anticipated first science at FRIB.

Speaker: Paul Fallon

52 Quadrupole collectivity and new type of shape coexistence in $^{60}$Ca

Recently, a spectroscopic study in $^{62}$Ti has provided important information on nuclear structure approaching $^{60}$Ca [1]. A large-scale shell model calculation shows that the ground state of $^{60}$Ca has strong quadrupole collectivity, which suggests that $^{60}$Ca belongs to the so-called "island of inversion" at $N=40$ [2].
To study the quadrupole collectivity around $^{60}$Ca, we employ the so-called five-dimensional quadrupole collective Hamiltonian method based on density functional theory (DFT). In this method, the potential energy surface in the $\beta$-$\gamma$ plane is calculated using the constrained Skyrme Hartree-Fock-Bogoliubov (CHFB) method. The inertial functions in the kinetic energy terms are calculated using local quasiparticle random phase approximation (LQRPA) [3]. This method overcomes drawbacks of the so-called cranking formula that has been used in inertial functions in the former DFT-based collective Hamiltonian methods.
In this talk, we will present our results for the low-lying structure of neutron-rich $N = 40$ isotones, including $^{60}$Ca. Then, we will discuss an emergence of a new type of shape coexistence that we discovered in $^{60}$Ca. In particular, we will explain how the LQRPA inertial functions affect the first excited $0^+$ state and contribute to the emergence of shape coexistence.
[1] M. L. Cortes et al., Phys. Lett. B 800, 135071 (2020).
[2] S. M. Lenzi, F. Nowacki, A. Poves, K. Sieja, Phys. Rev. C 82, 054301 (2010).
[3] K. Washiyama, N. Hinohara, T. Nakatsukasa, Phys. Rev. C 109, L051301 (2024).

Speaker: Kouhei Washiyama (The University of Osaka)

10:30 Coffee Break

Plenary

Convener: Stefan Frauendorf (University Notre Dame)

53 TBD

Speaker: Kostas Kravvaris

54 Correlated Neutron and Gamma Ray Measurements from (n,x) Reactions using GENESIS

The Germanium Neutron Energy Spectrometer for Inelastic Scattering (GENESIS), developed at the Lawrence Berkeley National Laboratory’s 88-Inch Cyclotron, enables the concurrent detection of neutrons and gamma rays from (n,x) reactions. The experimental setup utilizes broad-spectrum, energy-tunable neutron beams generated via thick-target deuteron breakup. To achieve simultaneous observation of reaction products, the GENESIS array couples high-purity germanium detectors with organic liquid scintillators. In concert, we are developing analysis methodologies that tightly integrate theoretical reaction modeling with experimental results. This involves a forward-model approach using a modular simulation of the array to precisely calculate its response, which is then coupled to TALYS to optimize reaction model parameters against experimental observations. This talk will detail the current state of the GENESIS array, present recent experimental results, and discuss expected near-term outcomes.

Speaker: Dr Josh Brown (University of California Berkeley)

55 Particle emissions following muon captures and photo-nuclear reactions

Recent advances in beam technologies have enabled the application of weakly and electromagnetically interacting probes [1]. As these applications expand, an accurate understanding of nuclear reactions induced by muon capture and photo-nuclear processes becomes increasingly important, particularly in relation to radiation protection and the production of secondary radioactive isotopes. In particular, particle emissions following such reactions are highly relevant for both fundamental nuclear physics and practical applications.

To construct a reliable database for weak and electromagnetic nuclear reactions, both new experimental data and advanced theoretical models are required. Our recent work has demonstrated that couplings to higher-order configurations, such as two-particle–two-hole (2p–2h) states, are crucial for describing particle emission spectra from muon capture on 28Si. These studies were carried out using fully microscopic approaches based on Skyrme–Hartree–Fock combined with the second random-phase approximation and the second Tamm–Dancoff approximation [2–5].

We have also shown that contributions from pre-equilibrium processes and meson-exchange currents, described within the exciton-model framework [6], are essential for reproducing experimental observables. This theoretical framework was successfully extended to describe muon capture on 40Ca as well. Encouraged by these results, we are now systematically investigating muon- and neutrino-induced reactions across the nuclear chart.

In this work, we present our latest physical insights into these reactions and discuss progress toward the construction of a consistent nuclear data set for weak and electromagnetic probes.

[1] M. Niikura, S. Abe, S. Kawase, T. Matsuzaki, F. Minato, et al., arXiv:2403.19965 (2024).
[2] F. Minato, arXiv:2512.19961 (2025).
[3] F. Minato, T. Naito, O. Iwamoto, Phys. Rev. C107, 054314 (2023).
[4] R. Mizuno et al., Phys. Rev. C 112, 024307; Phys. Rev. C 112, 054305 (2025)
[5] S. Kawase et al., arXiv:2601.09106 (2026).
[6] O. Iwamoto, N. Iwamoto, S. Kunieda, F. Minato, K. Shibata, Nucl. Data Sheets 131, 259 (2016).

Speaker: Futoshi Minato (Kyushu University)

12:30 Lunch

Poster Session

Discussions

Thursday 18 June

Plenary

Convener: Michael Jentschel (ILL)

56 Applications and neutron capture gamma-rays

Understanding neutron capture cross sections and the resulting γ-ray emissions is critical to a wide range of scientific and industrial applications. Capture γ-rays are typically high energy (~1–8 MeV) and provide a useful, isotope-specific diagnostic. These signatures are widely used in bulk material analysis, security screening, and oil and gas well logging. Neutron capture and the resulting γ-ray emission are central to neutron detection and play a key role in neutrino detection via neutron tagging, particularly in systems employing gadolinium-doped scintillators and water Cherenkov detectors. In addition, the radioactive products formed following neutron capture emit characteristic delayed γ-rays, which are used in trace element analysis, neutron flux monitoring and dosimetry, and nuclear forensics. This presentation will provide an overview of neutron capture processes and highlight their role across these diverse applications.

Speaker: Jennifer Jo Ressler

57 Current and Future Gamma experimental stations at the Turkish Accelerator and Radiation Laboratory

H. Ðapo1, A. B. Bereketoğlu1, A. Şahin1,A. Öztürk1, A. Hacisalihoğlu2, B. Yildirimdemir1, B. Gezer1, C. Taner1, C. Doğan1, E. N. Cansiz1, F. K. Işik1, H. Vural1, H. İ. Nalçak1, H. Yildiz1, İ. Tan1, İ. E. Çolak1, K. K. Şahbaz1, M. Tamkaş1,3, M. B. Gür1, M. Özdemir1, M. Z. Şentürk1, M. Yüksel1, M. Mutlu1,
N. Ergin1, O. F. Demirtaş1, Ö. Karsli1, R. Tunç1, R. Kuyrukcu1, S. Aydinli1, S. Çakmakoğlu1, T. Olgun1, Y. Küçük1,4, Y. E. Yanar1, Z. R. Öztürk1

1 Turkish Accelerator and Radiation Laboratory, Ankara, TÜRKİYE
2Recep Tayyip Erdoğan University, Physics Department, Rize, TÜRKİYE
3Marmara University, Science Faculty, Physics Department, İstanbul, TÜRKİYE
4Akdeniz University, Department of Physics, Antalya, TÜRKİYE

The Turkish Accelerator and Radiation Laboratory (TARLA) is a user facility based on a superconducting linear accelerator designed to reach 40 MeV and 1.6 mA. TARLA will be equipped with two beamlines: one for bremsstrahlung, and the other for a free-electron laser. Currently, the first accelerating section, providing 20 MeV acceleration, is completed, while the second, for 40 MeV, is under construction. Out of the two beamlines, the bremsstrahlung beamline is expected to be available first and start to serve Nuclear resonance fluorescence experiments as soon as available. Complementing the standard high-flux bremsstrahlung option, we plan to develop and implement a polarized bremsstrahlung capability at TARLA. Such capability would expand our experimental potential. The conceptual design and technical considerations for generating and controlling photon polarization within the existing beamline infrastructure will be outlined. The current status of the accelerator, project plans, and beam application schedule will be presented. This presentation will detail the accelerator's current status, project plans, and beam application schedule. Furthermore, we will discuss the planned utilization of the operational 20 MeV section for activation and other radiation physics experiments during a pause in the 40 MeV section's construction. By employing a fast sample transfer system measurements of bremsstrahlung and decay properties of nuclei can be made by activation. Thus, a set for activation measurements using 20 MeV bremsstrahlung is planned. These measurements aim at accelerator characterization by establishing the relationship to the generated bremsstrahlung, as well as for measurements of half-lifes of a few short-lived nuclei as a demonstrator of the sample transfer system capabilities. Following the transfer, the irradiated samples will be counted using two pairs of CLOVER and single-crystal HPGe detectors with BGO active Compton suppression. The aim of this research was to measure the energy transitions and half-lives of these isotopes as a test of the detector and transfer system capabilities. We will present the status of the system as well as the measurements.

Key words: superconducting linac, bremsstrahlung, activation, gamma-ray spectroscopy

Speaker: Haris Dapo (Turkish Accelerator and Radiation Laboratory)

58 Competition Between Virtual Gamma-Gamma Decay and Single Gamma Decay

Virtual gamma-gamma decay was first predicted by M. Goeppert-Mayer in 1929 and is the decay mode for atomic transitions from the 2S to 1S states in hydrogen. In nuclear physics it has been observed in both 0+ to 0+ decays of 16O, 40Ca, 72Ge, and 90Zr and the M4 decay from the 662 keV level in 137mBa. The single particle behavior of level widths and for virtual gamma-gamma decays are well documented. When comparing these two decays for low spin transitions, such as M1 decays, there are regions where the virtual gamma-gamma decay competes with single particle decay widths. An estimate of this competition for dipole transitions will be offered and some possible implications will be discussed.

Speaker: Bertis Rasco (Oak Ridge National Laboratory)

59 Recent results from the AGATA campaign in Legnaro

AGATA (the Advanced GAmma-ray Tracking Array) is Europe’s most advanced high-resolution gamma-ray spectrometer, providing unprecedented Doppler-correction capabilities thanks to a combination of fine detector segmentation, efficient pulse-shape analysis algorithms, and implementation of an innovative γ-ray tracking concept. Since 2022, it is installed at Legnaro National Laboratories, Italy, for an extensive physics campaign structured into two major phases. The first phase, spanning from 2022 to mid-2026, has seen AGATA coupled with the large-acceptance PRISMA magnetic spectrometer. Among the main subjects of this campaign were the quadrupole and octupole shapes and correlations, explored through lifetime measurements and Coulomb excitation, as well as development of collectivity in the vicinity of shell closures, investigated via measurements of level energies and lifetimes. A significant portion of the allocated beam time was dedicated to reaction-mechanism studies at near and sub-barrier energies, also in the context of nuclear astrophysics.
During the second half of 2026, the array will undergo a major reconfiguration in order to enable it to be coupled with larger complementary detection systems, such as the high-efficiency scintillator array PARIS for high-energy γ rays, as well as the NEDA neutron detector array, which will facilitate studies of neutron-deficient nuclei.
I will discuss the broad lines of the campaign and present selected preliminary results, with a particular focus on nuclear shapes and shape coexistence.

Speaker: Magda Zielinska (CEA)

10:30 Coffee Break

Plenary

Convener: Kevin Insik Hahn (Center for Exotic Nuclear Studies, IBS)

60 Nuclear structure studies near shell closures with neutron-capture reactions at ILL

I will present a review of recent experimental results obtained at the Institut Laue-Langevin (ILL) using neutron-capture reactions on rare and radioactive targets and HPGe detector arrays. Various nuclear structure phenomena, including shape coexistence and particle–vibration coupling, will be examined across different regions of the nuclide chart near shell closures, with a focus on Ca and Se isotopes. Gamma-ray spectroscopy measurements and angular correlation analyses will be discussed and the results presented within the framework of shell-model calculations and energy density functional theories.

Speaker: Simone Bottoni (Università degli Studi di Milano and INFN)

61 Probing Nuclear Structure at the Limits of Stability with β-Decay Spectroscopy at FRIB

Understanding how nuclear structure evolves at the limits of stability is a central goal of modern radioactive ion beam facilities. In regions of extreme neutron excess, traditional shell closures weaken and intruder configurations and deformation can emerge. β-decay spectroscopy provides a powerful probe of these systems, particularly when production rates are extremely low and other spectroscopic approaches are impractical. This work highlights recent results from two experiments performed at the Facility for Rare Isotope Beams (FRIB) using the FRIB Decay Station initiator (FDSi), a modular decay spectroscopy system designed to correlate implanted ions with their subsequent β decays, delayed γ rays, and β-delayed neutrons.

The first study reports the first measurements of the β-decay half-lives of the neutron-rich nuclei 31F and 37Na, which lie near the neutron drip line and the N=20 island-of-inversion region. Using event-by-event implant–decay correlations, half-lives of approximately 1–2 ms were determined, among the shortest observed in this region of the nuclear chart. Comparisons with theoretical calculations show that while global models reproduce the general scale of the half-lives, they do not capture the systematics of neighboring isotopes, highlighting the importance of new experimental benchmarks. A second experiment focuses on delayed γ-ray spectroscopy of neutron-rich cobalt isotopes approaching N=50. In this study, a 202(20) µs isomer in 73Co was identified through a 1178 keV transition associated with a deformed proton intruder configuration across the Z=28 shell gap. Comparisons with theory indicate that the spherical 7/2- configuration remains the ground state, suggesting that a proton-driven shape inversion does not occur in cobalt isotopes as N=50 is approached.

This presentation will describe the design and capabilities of FDSi and the experimental techniques used to correlate implanted ions with subsequent decay signatures. Results from these two early FRIB experiments will be summarized, including the first half-life measurements of 31F and 37Na and new observation of a microsecond isomer in 73Co. These studies illustrate the range of decay measurements accessible with FDSi, from millisecond β-decay half-lives to microsecond isomeric transitions, and represent some of the new results from ongoing programs that will continue to expand decay spectroscopy studies of nuclei at the limits of stability.

Speaker: Benjamin Crider (Mississippi State University)

62 Neutron-rich beams from the nuCARIBU facility at ATLAS

The availability of heavy neutron-rich beams is critical to explore this region of weak nuclear binding and to our understanding of the astrophysical r-process responsible for the formation of most of the heavy elements. The CARIBU facility at ATLAS has been providing such neutron-rich beams for over a decade through harnessing the fission products from the spontaneous fission of 252Cf in a large RF gas catcher, mass separating them and delivering them to experiments either at low-energy or reaccelerated to Coulomb barrier energy. This facility has now been upgraded to nuCARIBU which achieves higher yields by replacing the 252Cf fission source of CARIBU by a neutron-generator that produces neutron-induced fission in a thin actinide foil located inside the gas catcher. This maintains the universality of CARIBU in that fission fragments from all species can be extracted effectively while removing the difficulties associated with the 252Cf source and its production. nuCARIBU also now offers extended experimental areas and higher efficiency post-acceleration to enable a broader range of physics.
The nuCARIBU facility and its performance will be presented. In addition, a related new facility currently under commissioning at ATLAS, the N=126 factory, which uses a similar approach to access nuclei produced by multi-nucleon transfer reaction instead of fission to reach even heavier neutron-rich isotopes, will also be presented
This work is supported in part by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357; by the National Science Foundation under Grant No. PHY-2310059; by the University of Notre Dame; and with resources of ANL’s ATLAS facility, an Office of Science National User Facility.

Speaker: Guy Savard (Argonne National Laboratory)

12:30 Lunch

Parallel: Parallel 3A

Convener: Bertis Rasco (Oak Ridge National Laboratory)

63 Rigid triaxiality in finite nuclei

Unraveling the nature (soft vs. rigid) and origin of triaxiality at low spin in nuclei, is a long standing challenge. Recent experimental and theoretical developments have spurred renewed interest in this topic. A detailed analysis of E2 matrix elements extracted from Coulomb excitation experiments provided evidence for rigid triaxiality in $^{76}$Ge [1,2,3], and data collected in ultra-relativistic heavy-ion collisions was shown to exhibit evidence for prominent triaxiality in $^{129}$Xe [4,5]. On the theoretical side, large-scale Monte Carlo shell model calculations of $^{166}$Er have questioned its traditional interpretation as axially-deformed, replacing it with triaxial rigidity [6], and leading to claims for prevailing triaxial shapes in nuclei [7]. These observations serve as the motivation for the study reported in the present contribution.

Nuclear triaxiality is traditionally described using two simple models within the framework of the Bohr Hamiltonian. The rigid triaxial model of Davydov and Filippov (DF) [8,9] has a well-defined potential minimum at a nonzero value of $\gamma$ , whereas the $\gamma$-soft model of Wilets and Jean (WJ) [10] incorporates a $\gamma$-independent potential. Nuclei are mesoscopic systems, with a finite number of constituents, hence it is important to understand how these two paradigms of triaxiality emerge in such environment. We address this issue in the framework of the interacting boson model (IBM) which describes quadrupole collective states in even-even nuclei in terms of N monopole ($s$) and quadrupole ($d$) bosons, representing valence nucleon pairs. An IBM Hamiltonian appropriate for the dynamics of a rigid triaxial shape is constructed, whose spectrum resembles that of a rigid-triaxial rotovibrator with families of $L=0,2^2,3,4^3,5^2,6^4,\ldots$ states arranged in ground and excited bands, and its classical energy surface accommodates a global deformed minimum at $(\beta>0,\gamma=30^{\circ})$. The rotational states of the ground band are obtained by angular momentum projection from a triaxial intrinsic state and closed expressions for their wave-functions are derived. The Hamiltonian has a partial SO(6) symmetry which ensures a good SO(6) quantum number for these selected states, but with broken SO(5) symmetry. The finiteness of $N$ and a conserved discrete $d$-parity govern the SO(5) admixtures in the states. For a fixed Hamiltonian, as N is varied, the system undergoes a transition from the $\gamma$-unstable limit (the algebraic analog of the WJ model) with a high SO(5) purity for small N, to the rigid-triaxial limit (the algebraic analog of the DF model with $\gamma=30^{\circ}$) exhibiting substantial SO(5) mixing for large N. Such structural changes are reflected in the evolution with N of energy and B(E2) ratios and of the odd-even staggering of the $L=2^{+}_2,3^{+}_1,4^{+}_2,5^{+}_1,6^{+}_2,\ldots$ states, that can distinguish between $\gamma$-soft and $\gamma$-rigid types of triaxiality. Attention is paid to properties of interband E2 transitions between states in the ground band and single-phonon excited beta and gamma vibrational bands.

-
[1] Y. Toh et al., Phys. Rev. C 87, 041304(R) (2013).
[2] A. D. Ayangeakaa et al., Phys. Rev. Lett. 123, 102501 (2019).
[3] A. D. Ayangeakaa et al., Phys. Rev. C 107, 044314 (2023).
[4] B. Bally, M. Bender, G. Giacalone, V. Soma, Phys. Rev. Lett. 128, 082301 (2022).
[5] S. Zhao et al., Phys. Rev. Lett. 133, 192301 (2024).
[6] Y. Tsunoda and T. Otsuka, Phys. Rev. C 103, L021303 (2021).
[7] T. Otsuka et al., Eur. Phys. J. A 61, 126 (2025).
[8] A. S. Davydov and G. F. Filippov, Nucl. Phys. 8, 237 (1958).
[9] A. S. Davydov and V. S. Rostovsky, Nucl. Phys. 12, 58 (1959).
[10] L. Wilets and M. Jean, Phys Rev. 102, 788 (1956).

Speaker: Amiram Leviatan (The Hebrew University)

64 Near-threshold resonance search in 22Ne+a

The two reactions $^{22}$Ne($\alpha,[n/\gamma])^{[25,26]}$Mg are of high importance for our understanding of stellar nucleosynthesis processes. Knowledge of their low energy cross sections in the region of the alpha and neutron thresholds is crucial for the description of the s processes, branch point populations and more. Indirect probes of near threshold states have delivered a swatch of data, but many open questions remain on the exact strengths of the two reactions channels. Direct measurements have reached their limit in surface laboratories with the determination of the strength of a strong E${_\alpha} \approx 830$ keV resonance.

Over the last years, a concerted effort to directly measure these two reactions in the threshold energy region has been undertaken at the deep underground Gran Sasso National laboratory of the INFN, funded by the ERC, the Italian Ministry of Research and within the framework of the LUNA collaboration. The first part, the measurement of the neutron channel, has been concluded in December 25 and preparations for the $(\alpha, \gamma)$ measurement have reached their final phase, with first underground beam expected late spring of 26. We will report on the preliminary neutron results and give an overview of the second part of the campaign.

Speaker: Andreas Best (University of Naples Federico II and INFN Naples)

65 In-beam $\gamma$-ray spectroscopy of $^{249, 251}$Md

In-beam $\gamma$-ray spectroscopy experiments on the heavy odd-$Z$ nuclei $^{249}$Md and $^{251}$Md were performed at the ATLAS accelerator facility of Argonne National Laboratory using the $^{203}$Tl($^{48}$Ca, 2$n$) and $^{205}$Tl($^{48}$Ca, 2$n$) fusion evaporation reactions, respectively. In both experiments the Argonne Gas-Filled Analyzer (AGFA) was used to separate recoils of interest, while Gammasphere detected prompt $\gamma$-rays emitted from excited states and the X-array provided sensitivity to isomeric states and decays.
Recoil- and recoil-decay tagging techniques were utilised to identify new rotational bands in $^{249}$Md based on one-proton quasiparticle states. One observed set of states forms a pair of strongly coupled bands with relatively strong E2 transitions, and another sequence of $\gamma$-ray transitions is indicative of a decoupled band of E2 transitions. These bands are respectively assigned as based on the Nilsson level configurations 7/2$^{-}$[514] and 1/2$^{-}$[521], corresponding to the ground and first excited state of $^{249}$Md. The presence of at least one high-$K$ multi-quasiparticle isomer was also confirmed in $^{249}$Md. This talk presents the results of the $^{249}$Md experiment, and a discussion of preliminary findings from the experiment on $^{251}$Md.

This work was supported, in part, by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-05CH11231 (LBNL), Contract No. DE-AC02-98CH10886 (BNL). This work is funded by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357 (ANL). This research used resources of Argonne National Laboratory’s ATLAS facility, which is a DOE Office of Science User Facility.

Speaker: Corrigan Appleton (LBNL)

66 Study of shape coexistence and collective properties in 94Zr isotopes via Coulomb excitation measurements

The study of shapes and collective properties of atomic nuclei is a vast area of research, and low-energy Coulomb-excitation is one of the most powerful experimental techniques for such studies. It provides information not only about the reduced transition probabilities, describing the collectivity of the transitions, but also about the spectroscopic quadrupole moments of excited states, as well as the relative signs of the extracted transitional and diagonal matrix elements.
Typically, following low-energy Coulomb-excitation experiments, a set of matrix elements is determined leading to the use of the Kumar–Cline’s sum rules [1] that allows the determination of the deformation parameters together with their widths.
Coulomb excitation measurements have been performed to study structural changes and the presence of coexisting shapes in the zirconium isotopes, which are particularly interesting as, in recent years, evidence has come to light that they are excellent cases for exhibiting type II shape evolution. In most cases, however, the nuclear matrix elements required to perform precision tests of state-of-the-art nuclear theory in this region are lacking. These isotopes span a wide range of masses from a mid-open-shell region (80Zr40)[2], which is thought to be deformed, through a closed neutron shell at 90Zr50, to a closed neutron subshell (96Zr56), and then to a sudden reappearance of deformation (100Zr60)[3], which has been shown to persist to another mid-open-shell region as far as 110Zr70[4] . This variety of behaviour is unprecedented elsewhere on the nuclear mass surface. It is, therefore, not surprising that the zirconium region has been the subject of intensive experimental and theoretical work in order to gather insight into a variety of different nuclear structure phenomena. Of particular interest is how collectivity evolves in these isotopes and the coexistence observed between various configurations. For this reason we decided to perform Coulomb excitation measurement allowing for an in-depth comparison with theoretical predictions, shedding light on the structure of low-lying excitations in these nuclei.
In this talk, our experimental results will be presented focussing on the Coulomb-excitation measurements performed on the 94Zr isotopes.

[1] K. Kumar, Intrinsic quadrupole moments and shapes of nuclear ground states and excited states, Phys. Rev. Lett. 28 (1972) 249.
[2] A. Hamaker, et al., Nature Physics 17, 1408 (2021).
[3] H. Thayer et al., Journal of Physics G: Nuclear and Particle Physics 29, 2247 (2003).

[4] N. Paul et al., Physical Review Letters 118, 032501 (2017).

Speaker: Naomi Marchini (INFN Florence section)

Parallel: Parallel 3B

Convener: Erin Peters (University of Kentucky)

67 Neutron capture cross section measurements of $^{243}$Am

The long term management of high-level nuclear waste will necessarily involve nuclear transmutations of highly radioactive materials by accelerator driving systems converting long lived radioactive waste products to short lived or stable nuclei. $^{243}$Am is the most abundant, long lived radioactive product in high-level nuclear waste while the neutron capture cross section is known with some high level uncertainty ($>$10 %) where uncertainties of approximately 2% are needed for transmutations.

The challenges of studying the neutron capture cross sections includes the traditional difficulties of working with actinide materials. We have made significant progress in the production and handling of actinide targets generally, and $^{243}$Am specifically. We implement solution combustion synthesis methods to make robust targets on a variety of backing materials. An initial measurement at the LANSCE facility using the DANCE array of detectors showed that the purity of the target can yield precise cross-sections. We intend to present our preliminary results.

This work is funded by the National Nuclear Security Administration under Grant # NA0004256.

Speaker: A. Aprahamian (University of Notre Dame)

68 Measurement of Elastic and Inelastic Neutron Scattering Cross Sections for 51V at the University of Kentucky Accelerator Laboratory

Accurate neutron scattering cross sections are essential for both fundamental nuclear
structure studies and applications in advanced reactor technologies. Vanadium,
particularly 51V, is of significant interest due to its structural and neutronic relevance
in fast-spectrum reactor systems. In this work, we report measurements of elastic and
inelastic neutron scattering cross sections for 51V at incident neutron energies of 3.0,
3.5, and 4.0 MeV.
The experiment was performed at the University of Kentucky Accelerator Laboratory
(UKAL) using the 7 MV Van de Graaff accelerator to produce a pulsed neutron
beam with a pulse rate of approximately 533 ns. Scattered neutrons from natural vanadium
targets were analyzed using the time-of-flight technique. Angular distributions
were measured over a range of 30◦ to 154◦ using a rotatable goniometer system.
To validate the experimental methodology and normalization procedure, measurements.
This work was performed under the auspices of the U.S. Department of Energy by
Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

were benchmarked against the well-established elastic scattering cross section
of 12C using a natural carbon reference target. Data acquisition was carried out with
CAEN, and subsequent analysis was performed using the ROOT data analysis toolkit.
Preliminary differential cross section results are presented for all three incident
neutron energies. These measurements contribute new data relevant for nuclear data
evaluations and improved modeling of neutron interactions in structural materials.

Speaker: Mr Daniel Araya (Mississippi State University)

69 Determination of the 12C Hoyle state E2 Radiative branching ratio using GODDESS

The Hoyle state, the triple-$\alpha$ resonance in $^{12}$C, plays a central role in stellar helium burning and is responsible for the production of nearly all carbon. The formation of $^{12}$C requires the Hoyle state to decay to the ground state through radiative channels, including a cascade of two gamma rays (both E2 transitions) via the first excited 2$^+$ state and internal pair emission (known as the E0 branch). The probability of this relaxation to the ground state through gamma emission is known as the branching ratio. Two recent direct measurements of the E2 radiative branching ratio performed before this work differ by approximately a factor of 1.5. This introduces an uncertainty of as much as 25% in stellar nucleosynthesis calculations that determine the relative production of $^{12}$C and $^{16}$O and influencing subsequent r-, p-, and i-process reaction networks. Resolving this discrepancy is therefore important for improving astrophysical reaction rate calculations.

The coincident detection of scattered charged particles with high-resolution $\gamma$ spectroscopy enables clean identification of reactions populating the Hoyle state and allows the direct observation of the two $\gamma$ rays cascade populating the ground state. GODDESS combines the ORRUBA silicon detector array for quasi-$4\pi$ charged-particle detection with the GRETINA gamma-ray tracking array, providing high energy resolution and approximately 33% of $4\pi$ solid-angle coverage. This capability provides a powerful approach for determining the E2 radiative branching ratio while suppressing competing backgrounds.

We report on a new measurement of the Hoyle-state E2 radiative branching ratio using GODDESS. The experiment was performed at the ATLAS facility at Argonne National Laboratory using a 10.5 MeV proton beam impinged on a 99% enriched $^{12}$C target, delivered under multiple beam current conditions over 120 hours of beam time. The Hoyle state was populated via 12C(p,p’), and the ratio of the observed number of two gamma-cascade to the number of particles detected gives us our branching ratio.

Experimental results and analysis of the E2 radiative decay branch of the Hoyle state will be presented.

Work supported by US Department of Energy and National Science Foundation. Some of this work was also supported through the US Department of Energy Office of Science Graduate Student Research (SCGSR) Program.

Speaker: James Christie (Oak Ridge National Laboratory)

70 Constraining the Photon Strength Function of $^{90}$Zr from Radiative Capture in $^{89}$Y(p,$\gamma$) measured with GRETINA

The electromagnetic dipole response of atomic nuclei is fundamental for understanding nuclear structure and reaction dynamics. Measurements of photon strength functions (PSFs) have revealed phenomena such as Low-Energy Enhancement, significantly affecting astrophysical reaction rates relevant to nucleosynthesis.

To investigate the shape of the PSF and the observed excitation modes below S$_{n}$, the sub-barrier $^{89}$Y(p,$\gamma$)$^{90}$Zr radiative capture reaction was performed at four (4) incident proton beam energies. The resulting $\gamma$ decays were measured using Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) [1]. By applying the Shape Method [2], the shape of the PSF will be extracted for $\gamma$-ray energies below S$_{n}$. This analysis aims to provide new constraints on the shape of PSF in $^{90}$Zr and to shed light on the LEE's underlying physical mechanisms at the lowest accessible energies.

In this talk, results on the shape of $^{90}$Zr PSF obtained from radiative proton capture using the Shape Method will be discussed.

[1] S. Paschalis, et al., Nucl. Instrum. Methods A 709, 44 (2013).
[2] M. Wiedeking et al., Phys. Rev. C 104, 014311 (2021).

Research is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Contracts No. DE-AC02-05CH11231 and by the US Nuclear Data Program.

Speaker: Kgashane Malatji (University of California Berkeley, USA)

14:50 Coffee Break

Parallel: Parallel 4A

Convener: John Kelley (Duke University)

71 Neutron and gamma-ray characterization of the ATHENA NIF energy tuning assembly

A THermal Energy Neutron Assembly (ATHENA) is an experimental platform based at the National Ignition Facility (NIF) for performing neutron irradiation experiments. It consists of a cone-shaped assembly deployed as close as 6 cm from the NIF implosion, moderating the neutron flux from a pure 14 MeV DT spectrum to an analogue of a mixed fusion/fission spectrum for materials testing and integral benchmarks for nuclear data. This neutron spectrum has been modeled with neutronics codes like MCNP, but lacks comprehensive experimental verification. The photon spectrum created by neutron interactions in ATHENA is similarly ill-characterized and initial measurements with low-resolution monitors at the NIF have suggested a much higher induced photon flux than models predict.

To more accurately characterize both the moderated neutron and induced photon spectrum of ATHENA in response to DT fusion neutrons, measurements were conducted with a DT generator as the source. A number of detectors measured multiple aspects of the field in several locations, including deuterated organic scintillators, a high-purity germanium detector, a LaBr₃ detector, and a suite of activation foils. Preliminary observations from each of these detectors will be presented.

Speaker: Darren Bleuel (LLNL)

72 Two-phonon gamma-vibrational band structures in rare-earth nuclei

Experimental observation of 2-phonon gamma vibration in atomic nucleus has been challenging due to their location at excitation energies close to the pairing gap. The observation of such states provides stringent constraints on nuclear models. Although such excitations were proposed earlier in a number of transitional and deformed nuclei, it was later pointed out that many of those suggested cases may not be entirely, or even predominantly two-phonon in their characters, rather these could have fragmented vibrational strength through mixing with other close-lying, noncollective two-quasiparticle states which could well be described in terms of hexadecapole phonon vibrations, or g-boson structures [1].

Collective gamma-gamma vibration have been established in several candidate nuclei in A~160 and A~100 mass region with the most recent ones in $^{164}$Dy [2] and $^{104}$Nb [3]. It is worth noting that in the rare-earth region and elsewhere in the nuclide chart, $^{164}$Dy, $^{166}$Er, and $^{168}$Er were predicted by different theoretical models to be the most favourable ones to exhibit such collective vibration. Following an earlier measurement in $^{164}$Dy, a level at 2173.1 keV was reported to exhibit a collective enhancement in its decay to the single-$\gamma$ vibration, suggesting a possibility of the K$^\pi$ = 4$^+$ double-$\gamma$ excitation [4]. However, due to the large uncertainty in the measured B(E2) value, it remained inconclusive whether the 2173.1-keV level is predominantly two-phonon in character or if it merely has a minor two-phonon component in its wave function. Following this, an experiment was performed recently to explore the possibility of observing multiple $\gamma\gamma$ states employing the $^{163}$Dy(n$_{th}$,$\gamma$)$^{164}$Dy reaction and DURGA (Dhruva Utilization in Research using Gamma Array) facility at the Dhruva reactor, BARC, India. This new data has revealed the first identification of the lowest K$^\pi$ = 4$^+$ state in the $^{164}$Dy nucleus at 1978.5 keV. The 1978.5-keV level, together with the 2113.2-keV level, and the two other newly observed levels at 2261.4 and 2463.5 keV depopulate exclusively to the states in the $\gamma$ band with deexciting properties in reasonable agreement with Alaga rules. These four states, established in the present work, have been interpreted as the members of the rotational band built on a fragment of the K$^\pi$ =4$^+$ $\gamma\gamma$ vibration in this nucleus.
Novel calculations in the framework of Triaxial Projected Shell Model (TPSM) have been carried out for the two-$\gamma$-phonon bandhead state and the band structure built above it [2]. The TPSM results were found to be sensitive to the strength of the pair correlations. The TPSM energies with full-pairing and reduced-pairing calculations have been found to be on an average 100 keV away from the now-established $4^+_3$ level at 1978.5 keV. The state $4^+_3$ (1978.5 keV) state was found to be the collective $\gamma\gamma$ vibration, and the $4^+_4$ (2173.1 keV) to have predominantly two-quasineutron nature [2]. The calculations pointed to a fragmentation of the E2 strength between the $4^+_3$ (1978.5 keV) and $4^+_4$ (2173.1 keV) states. The predicted B(E2, $4^+_3$ → $\gamma$) TPSM value has been found to be consistent with sum of the experimental B(E2, $4^+_4$ → $\gamma$) value and the estimated B(E2, $4^+_3$ → $\gamma$) value.
In $^{168}$Er, the two-phonon character of the K$^\pi$ = 4$^+$ state (E$_x$=2.055 MeV), along with the 5$^+$ member (E$_x$=2.169 MeV) of the K$^\pi$ = 4$^+$ band, were affirmed earlier [5]. Although the 2307 keV state was proposed to be the 6+ member of this band, subsequent Coulex study [6] did not report any direct observation of this. To identify the elusive K$^\pi$ = 0$^+$ 2-phonon-gamma state in $^{168}$Er, a new experiment has been performed using the DURGA facility employing $^{167}$Er(n$_{th}$,$\gamma$)$^{168}$Er reaction. Preliminary analysis of the data does not corroborate the 2307 keV state to be the 6$^+$ member of the $\gamma\gamma$ band [7]. Nevertheless, the band has now been extended up to 7$^+$ spin with the addition of two new levels. The implication of alternate decay pathway for the 4$^+$ $\gamma\gamma$ bandhead state (and also other members of this band) to the 4$^-$ isomeric band (with T$_{1/2}$ = 157 ns) will be discussed.
[1] D. G. Burke, Phys. Rev. Lett. 73, 1899 (1994)
[2] S. Mukhopadhyay $et~al.$, Phys. Rev. C 112,064325(2025)
[3] E. H. Wang $et~al.$, Phys. Rev. Lett. 136, 072501 (2026)
[4] F. Corminboeuf $et~al.$, Phys. Rev. C 56, R1201 (1997)
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[7] W. D. Davidson $et~al.$, J. Phys. G: Nucl. Part. Phys. 17, 1683(1991)

Speaker: Mr Pramod Kumar Nayak (Bhabha Atomic Research Centre, Mumbai 400085 India, and Homi Bhabha National Institute, Mumbai 400094 India)

73 Investigation of bound-state β−-decay half-life of fully ionized $^{205}$Tl atom

Bound-state β−-decay is a rare radioactive process where the created electron is trapped in an atomic orbital instead of being emitted. It can be observed in highly ionized atoms in particular when normal beta-decay is energetically forbidden, but bound-state decay is still possible. An extremely challenging measurement of the bound-state $\beta^-$ decay of the fully ionized $^{205}$Tl was conducted at GSI using storage ring measurement$^1$. The decay rate is observed as $2.76(25)_{\rm stat}(13)_{\rm syst} \times 10^{-8} {\rm s^{-1}}$, which corresponds to a half-life of 291(+33-27) days and a log$ft$ = 5.91(5). The relevant transitions involve first-forbidden $\beta^-$ decays, including both unique and non-unique transitions. These transitions are significantly more challenging to describe theoretically than allowed decays because their decay rates depend sensitively on nuclear matrix elements and on the detailed structure of the shape factors. Reliable predictions therefore, require a microscopic treatment of nuclear structure combined with a consistent description of the lepton phase space and bound-electron wave functions.
We investigate the $\beta_b$ decay rate of $^{205}$Tl using a theoretical framework analogous to that employed for electron capture, treating the process as the time-reversed analogue of electron capture. The nuclear matrix element is evaluated employing the nuclear shell model configuration interaction approach with a refined effective interaction. We obtain a good agreement between the measured and calculated half-life for $^{205}$Tl. The developed framework can be extended to additional isotopes and higher-order forbidden transitions, contributing to more precise modeling of weak-interaction processes under extreme conditions.
1. G. Leckenby et al., Nature 635, 321 (2024)

Speaker: Dr Priyanka Choudhary (Tongji University, Shanghai, China)

74 Investigating the origin of the anomalous low-energy enhancement of the ⁵⁶Fe photon strength function

The photon strength function (PSF) of some near-shell-closure medium and heavy-mass nuclei exhibits anomalous low-energy enhancement (LEE). Angular correlation measurements demonstrate that this LEE is clearly dipole (ΔI = 1) in nature; however, its magnitude and onset at around 3–4 MeV cannot be explained by extrapolations of known mechanisms, such as the giant dipole resonance, to this energy region. This has led to speculation regarding new mechanisms that emphasize distinctly E1 or M1 dominated LEE. The asymmetry in the linear polarization of LEE γ rays is sensitive to the multipolarity of the electromagnetic transitions from which they originate. A previous measurement, leveraging GRETINA as a Compton polarimeter, measured the linear polarization of γ rays following excitation of 56Fe nuclei in (p,p′) reactions to LEE energies; however, the multipolarity of the LEE could not be conclusively determined due to large statistical uncertainties. Here we report preliminary results from a precision follow-up experiment with improved statistics and detection efficiency, aimed at conclusively determining the E1, M1, or mixed nature of LEE in a model-independent manner and thereby distinguishing between competing theoretical interpretations of its origin.

Speaker: Michael Armstrong (LBNL)

75 Constraining capture cross sections using proton inelastic scattering as a surrogate reaction

The surrogate reaction method is an alternative to direct measurements of compound nuclear reaction cross sections [1,2]. We introduce new theory tools for extracting capture cross sections from experiments that use proton inelastic scattering as a surrogate reaction mechanism. These extensions including two-step processes in populating the target nucleus in the proton inelastic scattering surrogate mechanism, Markov Chain Monte Carlo parameter inference for constraining the level density and gamma-ray strength function parameters, and accounting for the impact of partial-width fluctuations on the γ-emission probability due to the low-density of states available in competing particle emission channels. We apply these developments to 90Zr(p,p’γ) experimental data [3] to constrain the neutron capture cross section for 89Zr isotope which has a half-life of about 78 hours. We simultaneously determine the known proton capture cross section for 89Y as a benchmark for our approach.

References
[1] J. Escher et al. (2018). Phys. Rev. Lett. 121, 052501
[2] A. Ratkiewicz et al. (2019) Phys. Rev. Lett. 122, 052502.
[3] A. Thapa et al. (2025) arXiv:2511.03071
[4] S. Ota et al. (2015) Phys. Rev. C 92, 054603

Acknowledgements
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, with partial support from LDRD projects 20-ERD-030 and 19-ERD-017.

Speaker: Aaina Thapa (Lawrence Livermore national Laboratory)

Parallel: Parallel 4B

Convener: Paul Fallon

76 First Identification of Excited States in $^{78}$Zr and Implications for Isospin Non-Conserving Forces in Nuclei

One of the defining features of the strong nuclear interaction is its near charge independence: the nuclear components of the proton-proton, neutron-proton, and neutron-neutron interactions are remarkably similar. This symmetry under proton-neutron exchange gives rise to the concept of isospin, in which the proton and neutron are treated as different projections of a single nucleon. Consequently, nuclei with the same mass number $A$ but different isospin projections, members of an isobaric multiplet are expected to exhibit closely related excitation spectra. Deviations from this symmetry arise from isospin non-conserving (INC) interactions and can be quantified through the triplet energy difference (TED), defined as the double difference in excitation energies across an isobaric triplet. In addition, the proton $E2$ matrix element is expected to linearly with isospin projection across a triplet, while in deformed even--even nuclei the excitation energy of the first $2^{+}$ state is inversely correlated with the $B(E2)$ transition strength [1-5].

A fusion-evaporation experiment at the Accelerator Laboratory of the University of Jyväskylä led to the first observation of the 2⁺ and tentatively the 4⁺ states in the N = Z − 2 nucleus ⁷⁸Zr and extended the T = 1 band in ⁷⁸Y [1]. These results were achieved using the JUROGAM 3 γ-ray spectrometer coupled to the MARA vacuum-mode mass separator, employing recoil–β correlation techniques.

In this presentation, we discuss the new experimental results for the $A = 78$ triplet, which represents the heaviest isobaric triplet for which complete excitation-energy information is available. The extracted TED values are inconsistent with contemporary shell-model and density functional theory calculations [6,7]. Furthermore, we highlight how the recent extrapolation of $B(E2)$ strengths across the triplet, under the assumption of isospin symmetry, implies a significantly smaller deformation in $^{78}$Zr. This apparent contradiction reveals a tension between the expected $B(E2)$ behaviour and the deformation systematics inferred from excitation energies.

References:
[1] G. L. Zimba, P. Ruotsalainen, D.G. Jenkins, W. Satula et al., Phys. Rev. Lett. 134 022502 (2025).
[2] K. Wimmer, P. Ruotsalainen, et al., Phys. Lett. B. 847 138249 (2023).
[3] G. L. Zimba, P. Ruotsalainen, G. De Gregorio et al., Phys. Rev. C. 110 024314 (2024).
[4] J. Henderson, D. G. Jenkins, J. Heery, C. Müller-Gatermann, P. Ruotsalainen, and G. L. Zimba, Phys. Rev. C 112, 014330(2025)
[5] K. Kaneko, Y. Sun, T. Mizusaki, Y. Sun, S. Tazaki, and G. de Angelis, Phys. Rev. Lett. 109, 092504 (2012). And reference therein.
[6] K. Kaneko, Y. Sun, T. Mizusaki, and S. Tazaki, Phys. Rev. C 89, 031302(R) (2014).
[7] W. Satuła, P. Bączyk, J. Dobaczewski, and M. Konieczka, Phys. Rev. C 94, 024306 (2016).

Speaker: George Zimba (LSU)

77 Beyond Sphericity in a Semi-Magic Nucleus: Multiple Shape Coexistence in $^{116}$Sn

The evolution of nuclear shapes and the phenomenon of shape coexistence lie at the heart of our understanding of nuclear structure and the effective nuclear interaction. While dramatic examples of shape coexistence have long been established near closed shells, semi-magic nuclei have traditionally been regarded as structurally simple systems, dominated by pairing correlations and spherical mean fields. In this context, the tin isotopic chain, anchored by the robust $Z=50$ shell closure, has served for decades as the textbook paradigm of sphericity and seniority-driven structure.

This contribution will present compelling experimental evidence that fundamentally challenges this long-standing picture. Using a high-precision Coulomb-excitation experiment on $^{116}$Sn, located at the midpoint of the neutron mid-shell, an extensive and internally consistent set of electromagnetic matrix elements has been extracted. These data enable, for the first time in this nucleus, a fully model-independent determination of intrinsic quadrupole deformations for the ground and excited $0^+$ states, as well as spectroscopic quadrupole moments for multiple low-lying $2^+$ states.

The results reveal a remarkably rich and unexpected structural landscape. Rather than a spherical ground state weakly perturbed by a single intruder configuration, $^{116}$Sn exhibits multiple coexisting shapes at low excitation energy. The ground state itself is shown to possess a small but finite oblate deformation, incompatible with spherical symmetry and characterized by limited shape fluctuations. In addition, two excited $0^+$ states display distinct intrinsic deformations, providing unambiguous evidence for multiple-shape coexistence —a phenomenon observed in only a handful of nuclei across the entire nuclear chart.

These findings are discussed in the context of the experiment-driven Three-Band Mixing (3BM) model developed specifically for this work, as well as the Projected Generator Coordinate Method (PGCM) framework. Together, these approaches reveal strongly fragmented wave functions for the $0^+$ states, in stark contrast to the largely unperturbed nature of the $2^+$ states, and provide a coherent explanation of longstanding anomalies observed in nucleon-transfer reactions.

These results demonstrate that even semi-magic nuclei can host complex collective dynamics and multiple competing shapes. The case of $^{116}$Sn thus emerges not as an exception, but as a key benchmark for testing modern nuclear structure theories beyond the traditional limits of shell closures.

$$ $$ $$ $$

This research was partially supported by the European Union’s Seventh Framework Programme for Research and Technological Development (grant no. 262010), and by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under contract number DE-AC02-06CH11357.

Speaker: Marco Siciliano (Argonne National Laboratory)

78 Exploring nuclear structure near $^{100}$Sn with neutron knockout reactions

The region of the nuclear chart near the doubly-magic $^{100}$Sn is of crucial importance for understanding the atomic nucleus and an excellent testing ground for state-of-the-art nuclear models. $^{100}$Sn is the heaviest doubly-magic $N = Z$ nucleus, and additionally represents the end of the astrophysical rp-process. Experimental constraints of the single-particle orbits outside $^{100}$Sn are crucial to understand the region. In recent years there has been much discussion regarding the lowest-lying excited state of Sn, which lies at 172 keV. The spin and parity ordering of the two lowest-lying states $(J^{\pi} = 5/2^{+}, 7/2^+)$ is still unknown, and this ordering directly relates to the $\nu d_{5/2}, g_{7/2}$ single particle orbitals which inform the structure of the whole region [1, 2].

Thus, an experimental determination of the spin and parity of these low-lying states is imperative. The lightest Sn isotope for which the ordering has been experimentally measured is $^{107}$Sn [3]. Results from single neutron knockout reactions on beams of $^{104,102}$Cd and $^{104}$Sn will be presented. Neutron knockout is an excellent probe of single-particle structure, effectively utilizing weak beams, and providing a measure of the angular momentum transfer and wavefunction purity. The experiment was conducted at the Facility for Rare Isotope Beams, using the GRETINA array and the S800 spectrograph. The high-statistics $^{104,102}$Cd data provides insight into the neutron knockout reaction mechanism, with direct population of high-spin states showing down-shifted momentum distributions.

[1] D. Seweryniak et al., Phys. Rev. Lett. 99, 022504 (2007)
[2] I. Darby et al., Phys. Rev. Lett. 105 162502 (2010)
[3] G. Cerizza et al. Phys. Rev. C 93, 0221601 (R) (2016)

Speaker: Timothy Gray (University of Tennessee, Knoxville/Oak Ridge National Laboratory)

79 Quadrupole and octupole collectivity in 106Cd explored via "unsafe" Coulomb excitation

The well-accepted view of stable cadmium isotopes as excellent examples of spherical vibrational behaviour was put to question following detailed $\beta$-decay and ($n$,$n'\gamma$) spectroscopy [1-3]. A novel interpretation involving multiple shape coexistence was proposed for $^{110,112}$Cd and recently extended to $^{106}$Cd [4]. Supporting evidence for significant ground-state deformation was reported following a "safe" Coulomb-excitation study [5] in line with beyond-mean field (BMF) calculations [4].

This intriguing structural puzzle is addressed in more detail using "unsafe" Coulomb excitation of a $^{106}$Cd beam on a $^{92}$Mo target at beam energies exceeding by 8 to 40% the safe Coulomb excitation energy [6]. The state-of-the-art HPGe $\gamma$-ray tracking array AGATA [7] coupled to the VAMOS++ spectrometer [8] is used to study the balance between the Coulomb and nuclear interactions in the population of twenty excited states in $^{106}$Cd. The effects of Coulomb-nuclear interference on the experimental excitation cross sections are explored using the coupled-channel codes FRESCO [9] and GOSIA [10].

It will be demonstrated that unsafe Coulomb-excitation data can be used to extract valuable spectroscopic information, such as quadrupole and octupole transition strengths, in a model-independent way. Selected results will be presented, including the first measurement of B(E3) values obtained for several negative-parity states, and discussed in terms of a possible quadrupole-octupole coupling scenario. The extracted B(E2) values will be compared to new BMF calculations using the symmetry-conserving configuration mixing method with cranking [11].

[1] P.E. Garrett et al., Phys. Rev. C 75, 054310 (2007).
[2] P.E. Garrett et al., Phys. Rev. Lett. 123, 142502 (2019).
[3] P.E. Garrett et al., Phys. Rev. C 101, 044302 (2020).
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[10] T. Czosnyka et al., Bull. Am. Phys. Soc. 28, (1983) 745.
[11] D. Kalaydjieva et al., submitted to EPJ A (EPJA-108684), 2026.

Speaker: Desislava Kalaydjieva (University of Guelph)

Banquet Reception

Banquet Dinner

80 Fighting Cancer with the Nuclear Option: Targeted Alpha Therapy

²²⁵Ac and ²¹²Pb are at the core of over 3 dozen current pre-clinical and clinical studies as of January 2024 that have the potential of addressing upwards of 1.3 million cancer patients in the US alone. Radiochemically-pure ²²⁵Ac can be extracted from ²²⁹Th (7880 y), which is itself a decay product of ²³³U (159,000 y) while ²¹²Pb can be obtained from ²²⁸Th (1.91 y) produced via double neutron capture on 226 Ra using the High-Flux Reactor at Oak Ridge National Laboratory [1] or via ton-scale separation of ²²⁸Ra (5.75 y) from natural ²³²Th [2]. However, these decay-based production routes can produce only a small fraction of the anticipated demand due to the long-lives of the decay precursors and the availability of suitable high-flux reactors, limiting the scalability needed to facilitate large-scale radiopharmaceutical production. ²²⁵Ac accelerator production methods also have significant challenges. High-energy proton bombardment of ²³²Th targets produces significant ²²⁷Ac contamination and the use of energetic proton or photon beams on ²²⁶Ra targets result in limited production rates and dangerous levels of target heating from electromagnetic interactions in the radium target. A production pathway for these essential radionuclides is needed that doesn’t result in heating of the radium target.

The answer involves the use of fast neutrons. Energetic neutrons can produce both the ²²⁵Ra and ²²⁴Ra precursors for ²²⁵Ac and ²¹²Pb via the (n,2n) and (n,3n) reaction respectively. Since neutrons carry no charge, they do not meaningfully heat the radium target, and their long range allows for easy production scalability using larger radium targets. In this talk I’ll review all the ²²⁵Ac and ²¹²Pb production mechanisms and show the result of two experiments at the LBNL 88-Inch cyclotron that clearly demonstrated simultaneous production of both radioisotopes using fast neutrons from thick target deuteron breakup [3].

[1] "An Experimental Generator for Production of High-Purity  ²¹²Pb for Use in Radiopharmaceuticals", Ruth Gong Li, Vilde Yuli Stenberg and Roy Hartvig Larsen. Journal of Nuclear Medicine January 2023, 64 (1) 173-176; DOI: https://doi.org/10.2967/jnumed.122.264009
[2] https://www.thormedical.com/
[3] "Secondary Neutron Production from Thick Target Deuteron Breakup. JT Morrell, AS Voyles, JC Batchelder, JA Brown and LA Bernstein. Phys. Rev. C 108, 024616 (2023). DOI: https://doi.org/10.1103/PhysRevC.108.024616

Speaker: Prof. Lee Bernstein (University of California - Berkeley/LBNL)

Friday 19 June

Plenary

Convener: Sean N. Liddick (Facility for Rare Isotope Beams (FRIB) / Michigan State University)

81 Shell evolution of superdeformed band and time evolution of deformed states

I will present two subjects on deformed shapes. The first subject is recent findings about the superdeformed band in ⁶²Ni and its evolution in more neutron-rich exotic isotopes.
While this band has been known for higher spins [1], its band members down to 0 have been recently clarified theoretically and experimentally with advanced methodologies on both sides [2]. It is a triaxial band as demonstrated by Monte Carlo Shell Model calculation [3], and the J=0+ state is identified though fragmentated, as experimentally confirmed in Bucharest and Grenoble. This band follows type-1 and -2 shell evolution scenarios [4,5] to come down in energy up to ⁷⁰Ni [3,6-8].

The second subject is about the time evolution of an intrinsic state contained in an eigenstate in the laboratory frame, which is isotropically superposed for J=0. It will be shown how this intrinsic state remains or changes as time goes by, with remarkable features with "standing time" concept [9]. This may open new scopes to reactions such as fusion and fission (all in favor), as well as the shape measurement by Relativistic Heavy-Ion Collision, providing a feasibility argument.

[1] M. Albers et al., Phys. Rev. C 94, 034301 (2016).
[2] C. Costache, Y. Tsunoda, S. Leoni, B. Fornal, N. Marginean, R. V. F. Janssens, T. Otsuka et al., in preparation.
[3] Y. Tsunoda et al., Phys. Rev. C 89, 031301(R) (2014).
[4] T. Otsuka and Y. Tsunoda, J. Phys. G, 43, 024009 (2019).
[5] Y. Tsunoda and T. Otsuka, "Configuration Interaction Approach to Atomic
Nuclei: The Shell Model", in "Handbook of Nuclear Physics" (Springer, Singapore, 2022).
[6] N. Marginean et al., Phys. Rev. Lett. 125, 102502 (2020).
[7] S. Leoni et al., Phys. Rev. Lett. 118, 162502 (2017).
[8] A. I. Morales et al., Phys. Lett. B 765, 328 (2017).
[9] T. Otsuka and Y. Tsunoda, in preparation.

Speaker: Prof. Takaharu Otsuka (University of Tokyo)

82 Development of the Charge-Exchange Oslo Method and Application Towards Constraining Reaction Rates for Nucleosynthesis of Cosmochronometer $^{92}$Nb

Charge-exchange (CE) reactions are a powerful tool for probing the spin-isospin response of nuclei. Because they are not restricted to a narrow Q-value window, they provide complementary access to weak-interaction processes such as $\beta$-decay and electron-capture. In particular, the proportionality between Gamow-Teller strength, B(GT), and the CE differential cross section makes it possible to extract B(GT) distributions up to high excitation energies, providing key input for electron-capture and neutrino-nucleus reaction rates in hot and dense astrophysical environments. By combining CE measurements with coincident $\gamma$-ray spectroscopy, we have extended the Oslo method to CE reactions, establishing the Charge-Exchange Oslo (CE-Oslo) method for extracting nuclear level densities (NLDs) and $\gamma$-ray strength functions ($\gamma$SFs). These two statistical quantities are essential for indirectly constraining astrophysical neutron-capture reaction rates. The CE-Oslo method was first tested using $^{93}$Nb$(t,{}^{3}$He$+\gamma)$ data taken with the S800 spectrometer in coincidence with the GRETINA $\gamma$-ray detector at NSCL/FRIB. Although the primary goal of that experiment was to extract the B(GT) distribution from $^{93}$Nb to $^{93}$Zr, the particle-$\gamma$ coincidence data also enabled the extraction of the NLD and $\gamma$SF of $^{93}$Zr. These were propagated through Hauser-Feshbach calculations with TALYS to estimate the $^{92}$Zr$(n,\gamma)^{93}$Zr cross section. The resulting cross section is in good agreement with direct measurements, thereby validating the CE-Oslo method. This development serves as the foundation for the planned $^{92}$Zr$({}^{3}$He,$t+\gamma)^{92}$Nb experiment at RCNP. The goal of this experiment is to constrain the $^{91}$Nb$(n,\gamma)^{92}$Nb and $^{92}$Zr$(\nu_e,e^{-})^{92}$Nb reaction rates using the CE-Oslo method and Multipole Decomposition Analysis. These two reactions, neither of which has yet been experimentally constrained, are key regulators of $^{92}$Nb production in the $\gamma$-process and neutrino-process in core-collapse and Type Ia supernovae environments. $^{92}$Nb is one of the few confirmed proton-rich short-lived radionuclides, and the meteoritic $^{92}$Nb/$^{92}$Mo ratio provides a sensitive probe of proton-rich nucleosynthesis and early Solar System formation. However, its interpretation has long been limited by both astrophysical and nuclear-physics uncertainties. Using data from two separate experiments, $^{90}$Zr$(\alpha,d+\gamma)^{92}$Nb at OCL and $^{92}$Zr$({}^{3}$He,$t)^{92}$Nb at RCNP, these two reaction rates have now been experimentally constrained and their impact on $^{92}$Nb production in supernovae environments will also be presented.

This research is supported by the U.S. National Science Foundation (NSF), the Norwegian Nuclear Research Center (NNRC), and the International Research Network for Nuclear Astrophysics (IReNA).

References:
1. R.G.T. Zegers, Handbook of Nuclear Physics (2023), pp. 739–773.
2. B. Gao et al., Phys. Rev. C 101, 014308 (2020).
2. N.D. Pathirana et al., Phys. Rev. C 113 (2026) 015801.
3. M. Lugaro et al., Proc. Natl. Acad. Sci. U.S.A. 113 (2016) 907–912.
4. C. Travaglio et al., Astrophys. J. 795 (2014) 141.
5. T. Hayakawa et al., Astrophys. J. Lett. 779 (2013) L9.
6. A.C. Larsen et al., Phys. Rev. C 83 (2011) 034315.
7. R.H. Cyburt et al., Astrophys. J. Suppl. Ser. 189 (2010) 240–252.
8. C. Ritter et al., Mon. Not. R. Astron. Soc. 480 (2018) 538–571.
9. F. Herwig et al., PoS NIC X 053 (2009) 023.

Speaker: Neshad Deva Pathirana (Facility for Rare Isotope Beams and Michigan State University)

83 Structure of unstable nuclei through electromagnetic transition rate measurements using TIP/TIGRESS at ISAC-II

Electromagnetic transition rates are recognized as observables critical for evaluation of nuclear structure effects and verification of nuclear models. Doppler-shift lifetime measurements in inverse kinematics provide an opportunity to directly access information about electromagnetic transition rates in a way which is fully independent on the reaction mechanism. As such, Recoil Distance and related Doppler Shift Attenuation Methods (RDM and DSAM), when implemented at stable and/or radioactive beam facilities, hold the promise of reaching far from stability and providing lifetime information for intermediate-spin excited states in a wide range of nuclei. In response to opportunities opened by availability of re-accelerated beams at ISAC-II (TRIUMF), a plunger-type recoil distance method device, the TIGRESS Integrated Plunger (TIP), has been constructed at Simon Fraser University to be used with the TIGRESS segmented Germanium array. The plunger is designed to achieve control of sub-micrometer shifts between target and degrader and can be run in a self-standing mode or in tandem with auxiliary charged particle detectors for reaction channel selection. A compact CsI array with digital readout has been developed as a part of the TIP program and used in spectroscopy, DSAM, and RDM experiments employing fusion-evaporation reactions. TIP is also designed to be coupled with TIGRESS and the electromagnetic spectrometer EMMA. A summary of the experimental program and examples of RDM and DSAM measurements following fusion-evaporation, neutron transfer, and Coulomb excitation reactions will be presented and discussed.

Speaker: Krzysztof Starosta (Simon Fraser University)

84 Is β-delayed neutron emission statistical?

Beta-delayed neutron (βn) emission is a dominant decay channel for neutron-rich nuclei far from stability. The current theoretical paradigm treats βn emission in two steps independently: first, β decay, and then neutron emission. Due to its complicated nature, the neutron-emission part is modeled using Bohr’s hypothesis of the compound nucleus [1]. It assumes neutron emission only depends on the spins, parities, and excitation energies of the initial and final states, and is independent of the formation process [2]. Recent experimental work suggested evidence of non-statistical βn emission near doubly magic 132Sn [3].

To address the problem in a broader range of nuclei, we have studied βn decay of many neutron-rich isotopes in various mass regions. In this talk, I will present our recent experimental efforts validating the statistical nature of βn decay around 54Ca. It includes two experiments performed at the ISOLDE Decay Station and the FRIB Decay Station initiator, respectively. In those experiments, we performed coincidence measurements on βs, neutrons, and γs, allowing us to extract the exclusive neutron-emission branching ratios from the unbound states of β-decay daughters to the low-lying states in the neutron-emission residues. The comparisons between the experimental data and the Hauser-Feshbach statistical model show surprising results, constituting a strong challenge to the existing theories of the decay process.

References
[1] N. Bohr, Nature 137, 344 (1936).
[2] T. Kawano et al., Phys. Rev. C 78, 054601 (2008).
[3] J. Heideman et al., Phys. Rev. C 108, 024311 (2023).

Speaker: Zhengyu Xu

10:30 Coffee Break

Plenary

85 Evolution of the Pygmy Dipole Resonance in the Sn mass region studied with the Oslo method

The pygmy dipole resonance (PDR) is commonly associated with an excess E1 strength on top of the low-energy tail of the giant dipole resonance (GDR) close to the neutron-separation energy in stable and unstable heavy nuclei. While its detailed structure, properties, and origin remain a matter of ongoing debates and research, the neutron-skin oscillation picture of this feature still prevails and suggests some dependence of the PDR strength on neutron excess. This might have further consequences for neutron-capture rates relevant for heavy element nucleosynthesis [1], making a systematic investigation of the PDR and the low-lying E1 strength in general in different isotopic chains particularly interesting from the nuclear structure and astrophysical perspectives.

This work presents the most recent update on a consistent systematic study of the low-lying electric dipole strength and the potential PDR in stable and unstable Pd, Cd, In, Sn, and Sb isotopes with the Oslo method [2]. The analysis focuses on dipole γ-ray strength functions (GSF) below the neutron threshold extracted from particle-γ coincidence data from light-ion induced reactions studied at the Oslo Cyclotron Laboratory (OCL). The most recent (p, p′γ) and (α, pγ) experiments have been performed with a new array of 30 LaBr$_3$(Ce) scintillator detectors (OSCAR) with an improved energy resolution and timing properties for the selection of particle-γ events as compared to the earlier experiments done with the NaI(Tl) detector array CACTUS. All previously published GSFs of $^{105,107,111,112}$Cd [3] and $^{105−108}$Pd [4] isotopes have been reanalyzed to provide a more consistent analysis of the strengths in the Sn mass region.

With a wide span of isotopes (from unstable, neutron-deficient $^{109}$In to unstable, neutron-rich $^{127}$Sb), these dipole strengths provide an excellent case for investigation of the PDR evolution with increasing proton-neutron asymmetry, comparing it with different theoretical approaches, and revealing a possible impact of this feature on the astrophysical radiative neutron-capture processes. Combining these data with available (γ, n) cross sections and the E1 and M1 strengths from relativistic Coulomb excitation experiments allows us to extract the low-lying E1 component from the total dipole strength in each case. It was found to exhaust ≈ 1 − 3% of the classical Thomas-Reiche-Kuhn (TRK) sum rule, being nearly constant throughout the whole chain of Sn isotopes and weakly increasing with neutron number in Cd and Pd isotopes. This finding is in contradiction with the majority of theoretical approaches, such as, e.g., relativistic quasi-particle random-phase and time-blocking approximations, predicting a strong, steady increase in the low-lying E1 strength with neutron number. Moreover, a presumably isovector component of the PDR was extracted for $^{118−122,124}$Sn. The most neutron-deficient case $^{109}$In studied recently at the OCL, on the contrary, exhibits little to no excess E1 strength below the neutron threshold, thus standing out among the neighboring Cd and Sn isotopes.

References
[1] S. Goriely et al., Phys. Lett. B 436 (1998) 10-18.
[2] A. C. Larsen et al., Phys. Rev. C 83 (2011) 034315.
[3] A. C. Larsen et al., Phys. Rev. C 87 (2013) 014319.
[4] T. K. Eriksen et al., Phys. Rev. C 90 (2014) 044311.

Speaker: Maria Markova (University of Oslo)

86 Improving the accuracy of thermal neutron capture gamma-rays on Ni isotopes with FAIRRAY at UMass Lowell Research Reactor

Thermal neutron capture ((n,g)) gamma-ray spectroscopy is an effective approach to accurately constrain nuclear level structures. Cross sections for the production of gamma-rays following thermal (n,g) reactions have thus been measured for numerous transitions on stable nuclei across the nuclear chart. Data libraries for the cross sections, such as EGAF [1] and ENSDF [2], have been used for various nuclear applications and nuclear physics research.

The accuracy of the thermal (n,g) capture data required for modern nuclear science goes beyond that in the traditional data libraries [3]. While accurate and systematic gamma-ray data for thermal (n,g) reactions have been taken for granted for decades, our knowledge of the data on stable nuclei is still surprisingly far from the level required by state-of-the-art nuclear applications. Our recent study revealed that particularly primary gamma-rays (first gamma transitions from the capture state) for medium (A>60) to heavy stable nuclei are almost completely absent from the traditional nuclear data libraries [1]. Developing a high-quality (n,g) gamma-ray library for these nuclei is therefore essential to facilitate advancing research in applied science, as well as in nuclear structure research. In particular, improving information on gamma-ray transitions associated with quasi-continuum states (near the neutron separation energy (Sn)) is significant to improve the existing gamma-decay data for nuclear applications and modeling of gamma-decays in compound nuclear reactions [4] that are essential for nuclear astrophysics and reactor research.

We, therefore, performed experiments at the 1 MW research reactor at University of Massachusetts Lowell (UMLRR), aiming to extract accurate information on the thermal (n,g) gamma-rays from various stable nuclei by using a new array of Compton-suppressed HPGe detectors, FAIRRAY [5]. In this contribution, we focus on results from the irradiation of Ni (A=58-64) targets. A nickel target (1”x1”x1 mm) was irradiated with a thermal neutron beam at an intensity of 10^6 neutrons/s. Prompt gamma-rays were identified and measured from about 50 keV up to the Sn and analyzed, facilitated by gamma-gamma coincidence measurements. While the obtained absolute intensities of strong primary gamma-ray transitions agree with those reported in ENSDF and EGAF libraries within experimental uncertainties, we observed some transitions that exhibit large discrepancies from the data in these libraries. The gamma-spectra are compared with simulated gamma-ray spectra using a Monte Carlo code, DICEBOX [6]. Experimental results will be presented, and future plans to implement the improved data in major nuclear data libraries through collaborations with ENSDF data evaluators will be discussed.

The work at Brookhaven National Laboratory was supported by the Office of Nuclear Physics, Office of Science of the U.S. Department of Energy, under contract No.DE-AC02-98CH10886 with Brookhaven Science Associates, LLC. This work was in part supported by the U. S. Department of Energy Office of Science, Office of Nuclear Data under Awards No. DE-SC0024373 (FAIR). A. C. was supported by the U.S. Department of Energy, Office of Science, and Office of Workforce Development for Teachers and Scientists (WDTS) under the Science Undergraduate Laboratory Internships (SULI) Program.

Speaker: Shuya Ota (Brookhaven National Laboratory)

87 Regularities and inheritance in the energies of high-spin states in 196-202Au towards N = 126

The interplay between single-particle and collective degrees of freedom in atomic nuclei constitutes a fundamental aspect in quantum many-body physics. High-spin excited states of odd-even or odd-odd nuclei typically arise from the interplay between the odd nucleons in high-j orbitals and the collective behaviour of the underlying core. In this context, Au (Z = 79) isotopes provide an excellent opportunity to explore how collective nuclear modes evolve along with high-j single-particle excitations over a long isotopic chain serving as a good playground to probe such an interplay. However, high-spin states in neutron-rich Au isotopes approaching N = 126 remain largely unexplored due to limited methods for their production. The detailed spectroscopic knowledge in this region is also relevant for astrophysical r-process calculations, particularly for constraining first-forbidden β-decay rates.
Producing and achieving unambiguous particle identification of neutron-rich nuclei in this region pose significant experimental challenges. Multi-Nucleon Transfer reactions between a 136Xe beam (7 MeV/u) with a 198Pt target were employed at GANIL, combined with a suite of complementary spectrometers. Projectile-like fragments (PLFs) were fully identified using the VAMOS++ spectrometer, and the corresponding target-like fragments (TLFs) near N ≈ 126 were selected based on isotopically identified PLFs and reconstructed excitation energies. Prompt γ rays were detected with AGATA, a state-of-the-art HPGe tracking array, enabling high-spin spectroscopy of the TLFs. Additionally, CATLIFE—a time-of-flight spectrometer coupled with the EXOGAM HPGe array—was employed to measure delayed γ rays and determine TLF mass numbers prior to neutron evaporation, providing crucial independent fragment characterization. A novel kinetic-energy calibration method based on supervised machine-learning techniques was implemented for the VAMOS++ data, improving ion charge-state identification at energies near the Bragg peak.
Among the large number of isotopic chains identified, this contribution focuses on new results on the high-spin structure of 195-202Au isotopes [1,2]. New level schemes have been constructed and known structures extended well above the long-lived high-spin isomers. New (25/2⁺) isomers in 199Au and 201Au have been identified. The measurements reveal the disappearance of the odd-J mirror bands in the level schemes of odd-odd Au isotopes for N ≥ 117. The minima in the excitation energies of the bands as a function of N built on the 11/2− and 12− isomers occur at N = 119, show a dip against an otherwise smooth evolution.
The measured excitation energies in the Au exhibit remarkable regularity as a function of neutron number and are seen to be inherited from those of the yrast-band members in the corresponding Hg (Z = 80) isotope. Large-scale shell-model calculations reproduce the observed regularity and show that these states arise from the unique-parity orbitals π0h11/2 and ν0i13/2 coupled to the Hg core. This regularity is attributed to the dominant proton configurations of the Hg and Au isotopes, where the level energies are almost independent of different neutron-orbital occupancies. The calculated Au wave functions show significant higher-spin components of the corresponding Hg core, unlike what is expected in the conventional interpretation of inheritance in terms of the weak-coupling/decoupling limits of the particle-core coupling model.

[1]. Y. Cho et al. (Submitted to Phys. Letts. B)
[2]. Y. Cho et al. (Submitted to Phys. Rev . C) )

Speaker: Youngju Cho (Argonne National Laboratory)

12:30 Lunch

Plenary: Coffee Break

Convener: Heather Crawford

88 Indirect Constraints of Neutron-Induced Reactions on Unstable Nuclei

Neutron-induced reactions on unstable nuclei are important for a variety of pure and applied studies. However, because both the neutron and the target are radioactive, direct measurements are often impossible. Several indirect approaches have been developed to constrain these important reactions. I will discuss indirect constraints, their limitations, applications, and prospects. I will share recent results of indirect measurements and suggest some targets for upcoming campaigns.

Speaker: Andrew Ratkiewicz (Lawrence Livermore National Lab)

89 Photon Strength Function Measurements

Photon strength functions for $^{58}$Fe using Oslo and Shape methods as well as the Forward Method have been extracted using particle-gamma coincidence data measured with the Detector Array for Photons, Protons and Exotic Residues (DAPPER). Using the Oslo and Shape methods, the impact on the resulting level density and photon strength function of different treatments of gamma-ray energies are explored. While the results using Oslo and Shape methods did not allow definitive evidence for a low-energy enhancement (LEE), results from the Forward Method indicated a LEE consistent with previous measurements. These results will be presented along with a description of subsequent experiments using DAPPER that are still in analysis as well as plans for the near future.

Speaker: Kris Hagel (Cyclotron Institute, Texas A & M University)

90 TBD

Speaker: Wenlong Zhan