Speaker
Description
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.
| Contribution category | Experiment |
|---|---|
| Presenter status | Faculty/Staff |