Studying Gamow-Teller transitions and the assignment of isomeric and ground states at $N=50$

Abstract

Direct mass measurements of neutron-deficient nuclides around the $N=50$ shell closure below ${}^{100}$Sn were performed at the FRS Ion Catcher (FRS-IC) at GSI, Germany. The nuclei were produced by projectile fragmentation of ${}^{124}$Xe, separated in the fragment separator FRS and delivered to the FRS-IC. The masses of 14 ground states and two isomers were measured with relative mass uncertainties down to $1\times 10^{-7}$ using the multiple-reflection time-of-flight mass spectrometer of the FRS-IC, including the first direct mass measurements of ${}^{98}$Cd and ${}^{97}$Rh. A new $Q_{\mathrm{EC}}=5437\pm 67$ keV was obtained for ${}^{98}$Cd, resulting in a summed Gamow-Teller (GT) strength for the five observed transitions ($0^{+}⟶1^{+}$) as $B(\text{GT})=2.94_{-0.28}^{+0.32}$. Investigation of this result in state-of-the-art shell model approaches sheds light into a better understanding of the GT transitions in even-even isotones at $N=50$. The excitation energy of the long-lived isomeric state in ${}^{94}$Rh was determined for the first time to be $293\pm 21$ keV. This, together with the shell model calculations, allows the level ordering in ${}^{94}$Rh to be understood.