Medium-spin states in 70Ge and the role of the g9/2 orbital

Medium-spin states of 70 Ge have been studied via the 60 Ni( 12 C,2pγ) 70 Ge reaction at 45 MeV. The ground-state band and the second 0 + band have been extended to the 12+ and 8 + states, respectively. Two negative-parity bands, one of which has a coupled structure and the other has a decoupled structure, have been observed additionally. Although the latter decoupled structure was known up to the (21-) state from a previous experiment, the part of the level scheme up to the 15 ― state has been largely modified by the present experiment. Backbendings observed in the positive- and negative-parity yrast bands have been compared with those of the neighboring even Ge isotopes. The experimental level structure has been compared with the shell-model calculations in the model space (2p 3/2 , 1f 5/2 , 2p 1/2 , 1g 9/2 ) employing two kinds of effective interactions, one of which is an extended P + QQ interaction with monopole interactions and the other is developed from a renormalized G matrix. Microscopic structures of the observed bands have been discussed with the help of the shell-model calculations.