Shell model description of the $N=82$ isotonic chain with a new effective interaction

Abstract

In this work, we present a systematic study of low-lying states and electromagnetic properties of the semi-magic $N=82$ isotonic chain with proton number $Z=51$-77, using the full configuration interaction shell model with a newly developed high-quality effective interaction. The calculations are performed in a large model space that includes all proton orbitals between $Z=50$ and 82: $0g_{7/2}$, $1d_{5/2}$, $1d_{3/2}$, $2s_{1/2}$, and $0h_{11/2}$. The effective interaction is derived through the principal component analysis approach, starting from 160 two-body matrix elements and 5 single-particle energies and considering up to 30 degrees of freedom. Those are optimized by fitting to 204 available experimental energy levels. The resulting root-mean-square deviation is as low as 102 keV. The new interaction successfully reproduces the binding energies, low-lying spectra, electric quadrupole transition probabilities $B(E2)$, and magnetic dipole moments across both even-even and odd-mass isotones. The nuclear structure of low-lying states is analyzed in detail. Additionally, predictions are made for several more proton-rich nuclei beyond current experimental reach, including ${}^{155}\mathrm{Ta}$, ${}^{156}\mathrm{W}$, ${}^{157}\mathrm{Re}$, ${}^{158}\mathrm{Os}$, and ${}^{159}\mathrm{Ir}$.