Shape transition and oblate-prolate coexistence in N=Z fpg-shell nuclei -: art. no. 051301

Nuclear shape transition and oblate-prolate coexistence in N = Z nuclei are investigated within the configuration space (2p(3/2), 1f(5/2), 2p(1/2), and 1g(9/2)). We perform shell-model calculations for Zn-60, Ge-64, and Se-68, and constrained Hartree-Fock (CHF) calculations for Zn-60, Ge-64, Se-68, and Kr-72, employing an effective pairing plus quadrupole residual interaction with monopole interactions. The shell-model calculations reproduce well the experimental energy levels of these nuclei. From the analysis of potential-energy surface in the CHF calculations, we found shape transition from prolate to oblate deformation in these N = Z nuclei and oblate-prolate coexistence at Se-68. The ground state of Se-68 has an oblate shape, while the shape of Zn-60 and Ge-64 are prolate. It is shown that the isovector matrix elements between f(5/2) and p(1/2) orbits cause the oblate deformation for Se-68, and four-particle four-hole (4p-4h) excitations are important for the oblate configuration.