Abstract
β-delayed γ-neutron spectroscopy has been performed on the decay of A=84 to 87 gallium isotopes at the RI-beam Factory at the RIKEN Nishina Center using a high-efficiency array of He3 neutron counters (BRIKEN). β-2n-γ events were measured in the decays of all of the four isotopes for the first time, which is direct evidence for populating the excited states of two-neutron daughter nuclei. Detailed decay schemes with the γ branching ratios were obtained for these isotopes, and the neutron emission probabilities (Pxn) were updated from the previous study. Hauser-Feshbach statistical model calculations were performed to understand the experimental branching ratios. We found that the P1n and P2n values are sensitive to the nuclear level densities of 1n daughter nuclei and showed that the statistical model reproduced the P2n/P1n ratio better when experimental levels plus shell-model level densities fit by the Gilbert-Cameron formula were used as the level-density input. We also showed the neutron and γ branching ratios are sensitive to the ground-state spin of the parent nucleus. Our statistical model analysis suggested J≤3 for the unknown ground-state spin of the odd-odd nucleus Ga86, from the Iγ(4+→2+)/Iγ(2+→0+) ratio of Ga84 and the P2n/P1n ratio. These results show the necessity of detailed understanding of the decay scheme, including data from neutron spectroscopy, in addition to γ measurements of the multineutron emitters.
| Original language | English |
|---|---|
| Article number | 064307 |
| Journal | Physical Review C |
| Volume | 108 |
| Issue number | 6 |
| DOIs | |
| State | Published - Dec 2023 |
Funding
This experiment was performed at the RI Beam Factory operated by RIKEN Nishina Center and CNS, University of Tokyo. This research was sponsored in part by the Office of Nuclear Physics, U.S. Department of Energy under Awards No. DE-FG02-96ER40983 (UTK), No. DE-AC05-00OR22725 (ORNL), and No. DE-SC0016988 (TTU) and by the National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Award No. DE-NA0002132. This work was supported by National Science Foundation under Grants No. PHY-1430152 (JINA Center for the Evolution of the Elements), No. PHY-1565546 (NSCL), and No. PHY-1714153 (Central Michigan University). This work was partially funded by the Polish National Science Center under Contracts No. UMO-2015/18/E/ST2/00217, No. 2020/39/B/ST2/02346, and No. 2017/01/X/ST2/01144. This work was also supported by JSPS KAKENHI (Grants No. 14F04808, No. 17H06090, No. 25247045, 20H05648, No. 22H04946, and No. 19340074), by the UK Science and Technology Facilities Council, by NKFIH (NN128072), by Spanish Ministerio de Economia y Competitividad grants (FPA2011-06419, FPA2011-28770-C03-03, FPA2014-52823-C2-1-P, FPA2014-52823-C2-2-P, SEV-2014-0398, IJCI-2014-19172), by Generarlitat Valenciana regional Grant No. PROMETEO/2019/007, by European Commission FP7/EURATOM Contract No. 605203, by the UK Science and Technology Facilities Council Grants No. ST/N00244X/1, No. ST//P004598/1, and No. ST/V001027/1, by the National Research Foundation (NRF) in South Korea (No. 2016K1A3A7A09005575 and No. 2015H1A2A1030275), and by the Natural Sciences and Engineering Research Council of Canada (NSERC) via the Discovery Grants No. SAPIN-2014-00028 and No. RGPAS 462257-2014. TRIUMF receives federal funding via a contribution agreement with the National Research Council of Canada. The author R.Y. acknowledges support from JSPS KAKENHI 22K14053. G.G.K. acknowledges support from the Janos Bolyai research fellowship of the Hungarian Academy of Sciences. M.W.-C. acknowledges support from the Polish NCN project Miniatura No. 2017/01/X/ST2/01144. M.P.-S. acknowledges support from Polish National Science Center Grants No. 2019/33/N/ST2/03023 and No. 2020/36/T/ST2/00547. T.K. carried out this work under the auspices of the National Nuclear Security Administration of the U.S. Department of Energy at Los Alamos National Laboratory under Contract No. 89233218CNA000001. A.A. Acknowledges partial support of the JSPS Invitational Fellowships for Research in Japan (ID: L1955).