States built on the 9/2⁺ isomers in ^{91, 93}Y

Abstract

The isotopes ^{91, 93}Y are located close to ⁹⁰Zr , a nucleus that has a neutron shell closure (N = 50 and a proton subshell closure (Z = 40 , and close to the stability line. However, relatively little is known about excitations above their 9/2⁺ isomers. In the present work the isotopes ^{91, 93}Y have been studied in the fission of compound systems formed in two heavy-ion-induced reactions using the Gammasphere array for $\gamma$ -ray spectroscopy. States with excitation energies up to 6.9 and 7.1MeV above the previously known 9/2⁺ isomers of ^{91, 93}Y were established, respectively. The coupling of a proton-hole occupying the $\ensuremath g_{9/2}$ orbital to the yrast states in the core nuclei of ⁹⁰Sr and ⁹²Zr can account for the first excited states of ⁹¹Y . A comparison with the first excited states in the neighboring N = 52 , 54 isotopes is also considered. The experimental results are compared to predictions from previously reported shell-model calculations. The present results enhance previous knowledge on ^{91, 93}Y from fusion-evaporation reactions and multinucleon transfer reactions, and highlight the roles of these complementary reactions in probing moderate spin excitations in this mass region.