Enhancement of B(E2)↑ and low excitation of the second 0+ state near N=40 in Ge isotopes

The long-standing problem of dramatic structure change near N=40 in Ge isotopes is investigated by means of large-scale shell model calculation. The analysis of simulated calculations suggests a possible understanding of the problem in terms of rapid increase in the g9/2 proton and neutron occupation. The observed variation in excitation of the second 0+ state in 70,72,74Ge appears to correlate closely with the g9/2 occupations induced by strong proton–neutron interactions. The enhancement of the g9/2 occupancies is probably due to correlations in the 1g2d3s shell.