Prompt-delayed ${\hat{I}}^3$-ray spectroscopy of neutron-rich ${}^{119,121}$In isotopes

Abstract

The fusion and transfer induced fission reaction ${}^9$Be(${}^{238}$U,~f) with 6.2 MeV/u beam energy, using a unique setup consisting of AGATA, VAMOS++ and EXOGAM detectors, was used to populate through the fission process and study the neutron-rich ${}^{119,121}$In isotopes. This setup enabled the prompt-delayed ${\hat{I}}^3$-ray spectroscopy of isotopes in the time range of $100\mathrm{ns}-200\hat{\mathrm{I}}¼\mathrm{s}$. In the odd-$A$ ${}^{119,121}$In isotopes, indications of a short half-life $19/2^{-}$ isomeric state, in addition to the previously known $25/2^{+}$ isomeric state, were observed from the present data. Further, new prompt transitions above the $25/2^{+}$ isomer in ${}^{121}$In were identified along with reevaluation of its half-life. The experimental data were compared with the theoretical results obtained in the framework of large-scale shell-model calculations in a restricted model space. The $\langle πg_{9/2} νh_{11/2};I \arrowvert \hat{\mathcal{H}}\arrowvert πg_{9/2} νh_{11/2};I\rangle$ two-body matrix elements of residual interaction were modified to explain the excitation energies and the $B(E2)$ transition probabilities in the neutron-rich In isotopes. The (i) decreasing trend of $E(29/2^{+})-E(25/2^{+})$ in odd-In (with dominant configuration $\ddot{I}€g_{9/2}^{-1}\hat{I}½h_{11/2}^{-2}$ and maximum aligned spin of $29/2^{+}$) and (ii) increasing trend of $E(27/2^{+})-E(23/2^{+})$ in odd-Sb (with dominant configuration $\ddot{I}€g_{7/2}^{+1}\hat{I}½h_{11/2}^{-2}$ and maximum aligned spin of $27/2^{+}$) with increasing neutron number could be understood as a consequence of hole-hole and particle-hole interactions, respectively.

Accepted for publication in Phys. Rev. C