Systematics of even-even Tz= 1 nuclei in the A= 80 region: High-spin rotational bands in 74Kr, 78Sr, and 82Zr

Abstract

High-spin states of ${T}_{z}=1$ nuclei were studied with the reactions ${}^{58}$Ni${(}^{28}$Si,$3\ensuremath{\alpha})$${}^{74}$Kr, ${}^{58}$Ni${(}^{28}$Si,$2\ensuremath{\alpha})$${}^{78}$Sr, and ${}^{58}$Ni${(}^{28}$Si,$2p2n)$${}^{82}$Zr at 130 MeV beam energy. The Gammasphere array in conjunction with the $4\ensuremath{\pi}$ charged-particle detector array Microball was used to detect $\ensuremath{\gamma}$ rays in coincidence with evaporated light charged particles. The known $\ensuremath{\pi}=+$, $\ensuremath{\alpha}=0$ yrast bands were extended to $I=28\ensuremath{\Elzxh}$ at 20 MeV excitation energy. For all three nuclei, a number of positive- and negative-parity sidebands were established; altogether 15 new rotational bands were found. The data are discussed using the pairing-and-deformation self-consistent total Routhian surface (TRS) model: High-spin structures of ${}^{74}$Kr and ${}^{78}$Sr are governed by the shell gaps at large prolate deformation while ${}^{82}$Zr seems to exhibit shape coexistence. Nearly identical bands were established which may be explained as arising from the $\mathrm{fp}$ orbits acting as spectators at very elongated shapes. The experimental data in these ${T}_{z}=1$ nuclei are in good agreement with predictions of the TRS model using conventional $T=1$ like-nucleon pairing correlations.