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The β decay of the neutron-rich 134In and 135In 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 132Sn region is required for accurate modeling of the rapid neutron capture nucleosynthesis process (r process), due to the A≈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 β-delayed neutron (βn) emitters, new experimental data that can verify and guide theoretical models describing βn emission are of particular interest. Neutron-rich isotopes 134In and 135In – being rare instances of experimentally accessible nuclides for which the β3n decay is energetically allowed [3] – constitute representative nuclei to investigate the competition between βn and multiple-neutron emission as well as the γ-ray contribution to the decay of neutron-unbound states.
The β-delayed γ-ray spectroscopy measurement was performed at the ISOLDE Decay Station. Three β-decay branches of 134In were established, two of which were observed for the first time [4]. Population of neutron-unbound states decaying via γ rays was identified in the two daughter nuclei of 134In, 134Sn and 133Sn, at excitation energies exceeding the neutron separation energy by 1 MeV. The βn- and β2n-emission branching ratios of 134In were determined and compared with theoretical calculations. The βn decay was observed to be dominant β-decay branch of 134In even though the Gamow-Teller resonance is located substantially above the two-neutron separation energy of 134Sn. Transitions following the β decay of 135In are reported for the first time, including γ rays tentatively attributed to 135Sn [4]. A transition that might be a candidate for deexciting the missing neutron single-particle ν1i13/2 state in 133Sn was observed in both β decays and its assignment is discussed. Experimental level schemes of 134Sn and 135Sn 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).
