Constraining the trend of the $N = 50$ shell gap towards $^{100}$Sn with the masses of $^{96-98}$Cd

TL;DR

This study measures the masses of neutron-deficient cadmium isotopes to constrain the $N=50$ shell gap near $^{100}$Sn, providing new insights into nuclear structure and informing theoretical models.

Contribution

First precise mass measurements of $^{96-98}$Cd isotopes and the excitation energy of $^{97}$Cd's isomer, constraining the $N=50$ shell gap near $^{100}$Sn.

Findings

Enhanced $N=50$ shell gap towards $^{100}$Sn

Precise mass data constrains nuclear shell evolution

Comparison with advanced theoretical models

Abstract

We present the first determination of the $N = 50$ empirical shell gap at $Z = 48$ by precise mass measurements of the neutron-deficient cadmium isotopes $^{96-98}$Cd with the ISOLTRAP mass spectrometer at ISOLDE-CERN, including the first precise determination of the excitation energy of the $25/2^+$ isomer in $^{97}$Cd. Through the systematics of Coulomb Displacement Energies, we further deduce the empirical shell gap in the higher-$Z$ isotopic chains, tightly constraining the $^{100}$Sn mass-surface region. The new experimental data suggest an enhancement of the gap towards $^{100}$Sn, which is discussed in comparison to state-of-the-art calculations using energy-density functional and new ab initio approaches.