Low-lying states of ${}^{98}\mathrm{Cd}$ have been populated by the two-nucleon removal reaction (${}^{100}\mathrm{In},{}^{98}\mathrm{Cd}+\gamma$) and studied using in-beam $\gamma$-ray spectroscopy at the Radioactive Isotope Beam Factory at RIKEN. Two new $\gamma$ transitions were identified and assigned as decays from a previously unknown state. This state is suggested to be based on a $\pi 1g_{9/2}^{-1}2p_{1/2}^{-1}$ configuration with $J^{\pi }=5^{-}$. The present observation extends the systematics of the excitation energies of the first $5^{-}$ state in $N=50$ isotones toward ${}^{100}\mathrm{Sn}$. The determined energy of the $5^{-}$ state in ${}^{98}\mathrm{Cd}$ continues a smooth trend along the $N=50$ isotones. The systematics are compared with shell-model calculations in different model spaces. Good agreement is achieved when considering a model space consisting of the $\pi (1f_{5/2}, 2p_{3/2}, 2p_{1/2}, 1g_{9/2}$) orbitals. The calculations with a smaller model space omitting the orbitals below the $Z=38$ subshell could not reproduce the experimental energy difference between the ground and first $5^{-}$ states in $N=50$ isotones, because proton excitations across $Z=38$ subshell yield a large amount of correlation energy that lowers the ground states.

• Received 30 April 2021
• Accepted 22 July 2021

DOI:https://doi.org/10.1103/PhysRevC.104.024302