High-j proton and neutron alignments in gamma-soft Ru-101

Abstract

The near-yrast structure of the weakly deformed, "transitional," nucleus Ru-101 has been investigated using the fusion-evaporation reaction Zr-96(Be-9,4n)Ru-101 at a beam energy of approximately 44 MeV. The experimental data are compared with theoretical calculations using the cranked Woods-Saxon-Strutinsky method. The yrast positive-parity structures are observed to undergo a backbend, consistent with the crossing of an aligned (nuh(11/2))(2) configuration. The h(11/2)([550]1/2(-)) intruder band configuration is extended to a tentative spin/parity of (47/2(-)) and excitation energy of more than 9 MeV. This structure exhibits properties which can be explained by the rotational alignment of a pair of midshell g(9/2) protons, in contrast to the behavior observed in the heavier N=57, odd-A isotones where the predicted proton crossing is delayed in favor of neutron alignments. The effect of static gamma deformation on the theoretically predicted alignment properties is investigated by means of the cranked shell model. The observed band crossings are found to be consistent with a significant triaxial rigidity, persistent into the medium-spin regime.