$\beta^-$ decay of neutron-rich $^{45}$Cl at magic number N=28

Author:

Soumik Bhattacharya, Vandana Tripathi, S. L. Tabor, A. Volya, P. C. Bender, C. Benetti, M. P. Carpenter, J. J. Carroll, A. Chester, C. J. Chiara, K. Childers, B. R. Clark, B. P. Crider, J. T. Harke, S. N. Liddick, R. S. Lubna, S. Luitel, B. Longfellow, M. J. Mogannam, T. H. Ogunbeku, J. Perello, A. L. Richard, E. Rubino, S. Saha, O. A. Shehu, R. Unz, Y. Xiao, Yiyi Zhu

Keyword:

Nuclear Experiment, Nuclear Experiment (nucl-ex)

journal:

date:

2023-05-22 16:00:00

Abstract

Results from the study of $\beta^-$-decay of $^{45}$Cl, produced in the fragmentation of a 140-MeV/u $^{48}$Ca beam, are presented. The half-life for $^{45}$Cl $\beta$-decay is measured to be 513(36) ms. The $\beta^-$ and $\beta^- 1n$ decay of $^{45}$Cl populated excited states in $^{45,44}$Ar, respectively. On the basis of $\gamma$-ray singles and $\gamma$-$\gamma$ coincidence data, decay schemes for the two daughter nuclei have been established. They are compared with shell model calculations using the FSU interaction. The low-lying negative parity states for $^{45}$Ar are well described by a single particle (neutron) occupying orbitals near the Fermi surface, whereas neutron excitations across the $N = 20$ shell gap are needed to explain the positive-parity states which are expected to be populated in allowed Gamow-Teller $\beta$-decay of $^{45}$Cl. The highest $\beta$-feeding to the 5/2$^+$ state in $^{45}$Ar from the ground state of $^{45}$Cl points towards a 3/2$^+$ spin-parity assignment of the ground state of the parent over the other possibility of 1/2$^+$. The high Q$_{\beta^-}$ value of $^{45}$Cl decay allows for the population of $1p1h$ states above the neutron separation energy in $^{45}$Ar leading to positive parity states of $^{44}$Ar being populated by removal of one neutron from the $sd$ shell. The spin-parities of the excited levels in $^{44}$Ar are tentatively assigned for the first time by comparison with the shell model calculations. The 2978~keV level of $^{44}$Ar is identified as the excited 0$^+$ level which could correspond to a different configuration from the ground state.

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