Stability of oblate shapes in the vicinity of N = Z=34 68Se:: Bands in 69Se and 67As -: art. no. 064311

The gamma -ray decay schemes of Se-69 and As-67 have been considerably extended using the Ca-40(S-32,2pn)Se-69 and Ca-40(S-32,alphap)As-67 reactions at 100 MeV and Ca-40(Ar-36, alpha 2pn)Se-69 and Ca-40(Ar-36,2 alphap)As-67 reactions at 145 MeV, with the aim of studying oblate bands arising from the strong coupling of a valence g(9/2) particle (or hole) to the oblate deformed ground state band of Se-68. A new T-1/2 = 12 +/- 2 ns J(pi) = 9/2(+) isomeric bandhead was identified in As-67. A transitional quadrupole moment of Q(0) = - 2.7(6) eb was deduced for the band built on the 9/2(+) isomer in Se-69, corresponding to a rigid oblate deformation of beta (2) = - 0.4(1), consistent with theoretical predictions. However, it appears that the relevant oblate configuration in Se-69 and As-67 are not nearly so favored as they are in Se-68, and are rapidly crossed by prolate configurations that form the high spin yrast lines.