Speaker
Description
The $\beta$ decay of the neutron-rich $^{134}$In and $^{135}$In was investigated experimentally with the aim of providing new insights into the nuclear structure of the tin isotopes above $N=82$. Better understanding of exotic nuclides from the $^{132}$Sn region is required for accurate modeling of the rapid neutron capture nucleosynthesis process ($r$ process), due to the $A \approx 130$ peak in the $r$-process abundance pattern being linked to the $N=82$ shell closure [1, 2]. Because a vast number of nuclei involved in the r process are $\beta$-delayed neutron ($\beta n$) emitters, new experimental data that can verify and guide theoretical models describing $\beta n$ emission are of particular interest. Neutron-rich isotopes $^{134}$In and $^{135}$In – being rare instances of experimentally accessible nuclides for which the $\beta 3n$ decay is energetically allowed [3] – constitute representative nuclei to investigate the competition between $\beta n$ and multiple-neutron emission as well as the $\gamma$-ray contribution to the decay of neutron-unbound states.
The $\beta$-delayed $\gamma$-ray spectroscopy measurement was performed at the ISOLDE Decay Station. Three $\beta$-decay branches of $^{134}$In were established, two of which were observed for the first time [4]. Population of neutron-unbound states decaying via $\gamma$ rays was identified in the two daughter nuclei of $^{134}$In, $^{134}$Sn and $^{133}$Sn, at excitation energies exceeding the neutron separation energy by 1 MeV. The $\beta n$- and $\beta 2n$-emission branching ratios of $^{134}$In were determined and compared with theoretical calculations. The $\beta n$ decay was observed to be dominant $\beta$-decay branch of $^{134}$In even though the Gamow-Teller resonance is located substantially above the two-neutron separation energy of $^{134}$Sn. Transitions following the $\beta$ decay of $^{135}$In are reported for the first time, including $\gamma$ rays tentatively attributed to $^{135}$Sn [4]. A transition that might be a candidate for deexciting the missing neutron single-particle $\nu 1i_{13/2}$ state in $^{133}$Sn was observed in both $\beta$ decays and its assignment is discussed. Experimental level schemes of $^{134}$Sn and $^{135}$Sn are compared with shell-model predictions, including calculations considering particle-hole excitations across the $N=82$ shell gap [5].
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[2] M.R. Mumpower, R. Surman, G.C. McLaughlin, and A. Aprahamian, Prog. Part. Nucl. Phys. 86, 86 (2016).
[3] M. Wang, W. J. Huang, F. G. Kondev, G. Audi, and S. Naimi, Chin. Phys. C 45, 030003 (2021).
[4] M. Piersa-Siłkowska et al. (IDS Collaboration), Phys. Rev. C 104, 044328 (2021).
[5] H. Jin, M. Hasegawa, S. Tazaki, K. Kaneko, and Y. Sun, Phys. Rev. C 84, 044324 (2011).
