Changes in νg9/2 shape polarisation across the odd neutron-rich Cr isotopes

Excited states in Cr-57 have been populated to high spin in the C-14(Ca-48, alpha n) reaction at a beam energy of 130 MeV. A regular sequence of stretched quadrupole transitions has been established above the yrast 9/2(+) level. This sequence is interpreted as a rotational band associated with prolate deformation induced by the excitation of the odd neutron into the 1/2(+)[440] orbital. Total Routhian surface calculations, which follow this configuration to high spin, reproduce the observed features of the band. They are also able to account for a similar, but less well developed structure in Cr-55. In contrast, the isomeric yrast 9/2(+) state in Cr-59 appears to be a band-head state dominated by the 9/2(+) [404] configuration, which is favoured at oblate deformations. Such a marked difference presents a significant challenge for theoretical descriptions, but is consistent with features exhibited by the low-lying negative-parity states in C-59. (c) 2005 Elsevier B.V. All rights reserved.