High-precision mass measurements of neutron deficient silver isotopes probe the robustness of the N = 50 shell closure
Abstract
High-precision mass measurements of exotic 95-97Ag isotopes close to the N = Z line have been conducted with the JYFLTRAP double Penning trap mass spectrometer, with the silver ions produced using the recently commissioned inductively-heated hot cavity catcher laser ion source at the Ion Guide Isotope Separator On-Line facility. The atomic mass of 95Ag was directly determined for the first time. In addition, the atomic masses of β-decaying 2+ and 8+ states in 96Ag have been identified and measured for the first time, and the precision of the 97Ag mass has been improved. The newly measured masses, with a precision of ≈ 1 keV/c2, have been used to investigate the N = 50 neutron shell closure confirming it to be robust. Empirical shell-gap and pairing energies determined with the new ground-state mass data are compared with the state-of-the-art ab initio calculations with various chiral effective field theory Hamiltonians. The precise determination of the excitation energy of the 96mAg isomer in particular serves as a benchmark for ab initio predictions of nuclear properties beyond the ground state, specifically for odd-odd nuclei situated in proximity to the proton dripline below 100Sn. In addition, density functional theory (DFT) calculations and configuration-interaction shell-model (CISM) calculations are compared with the experimental results. All theoretical approaches face challenges to reproduce the trend of nuclear ground-state properties in the silver isotopic chain across the N =50 neutron shell and toward the proton drip-line.