Jun 13 – 17, 2022
Berkeley, CA
US/Pacific timezone

Beta-delayed neutron emission near $^{54}$Ca

Jun 16, 2022, 10:10 AM
Berkeley, CA

Berkeley, CA

Lawrence Berkeley National Laboratory
Oral Oral Presentations NS2022 Plenary


Zhengyu Xu (University of Tennessee, USA)


Beta-delayed neutron emission ($\beta$-n) plays a vital role in shaping the elemental abundance distribution in the $r$-process via modifying the decay path back to stability and by contributing significantly to the neutron flux after freeze-out [1]. Modeling the $\beta$-n process requires a good model of the beta-strength functions and of the neutron emission mechanism. Statistical neutron-emission models assume gamma and neutron decay from a compound nucleus following beta decay and have successfully predicted gross properties of $\beta$-n probabilities ($P_{1n}$, $P_{2n}$, etc) in some medium- and heavy-mass nuclei. However, recent experimental work found evidence of non-statistical neutron emission after the beta decay in the vicinity of doubly magic $^{132}$Sn [2]. Therefore, it is of great importance to study $\beta$-n spectroscopy in a broader area of the nuclear chart to provide stringent experimental constraints to the theories, which in astrophysical applications predict those properties for many more $r$-process nuclei currently out of experimental reach.

We expanded our study onto the nuclei near $^{54}$Ca, which is thought to be doubly magic. An experiment studying $\beta$-n spectroscopy of $^{52,53}$K was carried out at the ISOLDE Decay Station (IDS). These isotopes have large Q$_{\beta}$ values (energy window for $\beta$ decay) and low neutron-separation energies in their daughters ($^{52,53}$Ca respectively), making them ideal for the studies of the $\beta$-n process. In coincidence with the beta decay of $^{52,53}$K, gamma-ray and neutron-time-of-flight (TOF) spectra were measured using HPGe clover detectors and VANDLE [3]. In this contribution, I will present the latest results from the experiment, including the reconstructed excitation energies (Εx) and apparent beta feeding (I$_{\beta}$) of the neutron unbound states in $^{52,53}$Ca, together with their exclusive neutron-emission branching ratios to the states in $^{51,52}$Ca, respectively. The experimental findings were compared with the shell-model calculations and Hauser-Feshbach statistical model. These comparisons provide valuable insights into the $\beta$-n process and its
connection with the nuclear structure far from the stability line.

[1] R. Yokoyama et al, Phys. Rev. C 100, 031302(R) (2019).
[2] J. Heideman et al, being reviewed by Phys. Rev. Lett.
[3] M. Madurga et al, Phys. Rev. Lett 117, 092502 (2016).

Primary authors

Zhengyu Xu (University of Tennessee, USA) Dr Robert K. Grzywacz (University of Tennessee, USA) M. Madurga (University of Tennessee) Andrea Gottardo (INFN LNL) IDS Collaboration (ISOLDE, CERN)

Presentation materials