Structure of upper-g9/2-shell nuclei and shape effect in the Ag94 isomeric states

Using a shell model which is capable of describing the spectra of upper g_9/2-shell nuclei close to the N=Z line, we study the structure of two isomeric states 7⁺ and 21⁺ in the odd-odd N=Z nucleus Ag94. It is found that both isomeric states exhibit a large collectivity. The 7⁺ state is oblately deformed, and is suggested to be a shape isomer in nature. The 21⁺ state becomes isomeric because of level inversion of the 19⁺ and 21⁺ states due to core excitations across the N=Z=50 shell gap. Calculation of spectroscopic quadrupole moment indicates clearly an enhancement in these states due to the core excitations. However, the present shell model calculation that produces the 19⁺-21⁺ level inversion cannot accept the large-deformation picture of Mukha [Nature (London) 439, 298 (2006)].