First $\beta$-decay spectroscopy of ${}^{135}$In and new $\beta$-decay branches of ${}^{134}$In

Abstract

The $\beta$ decay of the neutron-rich ${}^{134}$In and ${}^{135}$In was investigated experimentally in order to provide new insights into the nuclear structure of the tin isotopes with magic proton number $Z=50$ above the $N=82$ shell. The $\beta$-delayed $\gamma$-ray spectroscopy measurement was performed at the ISOLDE facility at CERN, where indium isotopes were selectively laser-ionized and on-line mass separated. Three $\beta$-decay branches of ${}^{134}$In were established, two of which were observed for the first time. 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 $\beta$-delayed one- and two-neutron emission branching ratios of ${}^{134}$In were determined and compared with theoretical calculations. The $\beta$-delayed one-neutron 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. In total, six new levels were identified in ${}^{134}$Sn on the basis of the $\beta \gamma \gamma$ coincidences observed in the ${}^{134}$In and ${}^{135}$In $\beta$ decays. A transition that might be a candidate for deexciting the missing neutron single-particle $13/2^{+}$ 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. Using the fast timing technique, half-lives of the $2^{+}$, $4^{+}$ and $6^{+}$ levels in ${}^{134}$Sn were determined.

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