Band crossings in the gamma -soft nucleus 136Nd.

Abstract

High-spin states have been populated in /sup 136/Nd using the /sup 116/Cd(/sup 24/Mg,4n..gamma..) /sup 136/Nd reaction. Several rotational bands have been observed based on two- and four-quasiparticle configurations. The ground-state band backbends sharply at a frequency h-dash-bar..omega.. = 0.34 MeV due to the alignment of a pair of h/sub 11/2/ protons. Both signatures of a negative parity side band based on a ..pi..h/sub 11/2/x..pi..g/sub 7/2/ configuration were observed to backbend at a frequency h-dash-bar..omega.. = 0.44 MeV, again due to the alignment of a pair of h/sub 11/2/ protons. All these bands are prolate because of the stabilizing influence of the h/sub 11/2/ quasiprotons on the ..gamma..-soft core. In addition to the h/sub 11/2/ proton alignment in the ground-state band, a rotational band is observed built on a second 10/sup +/ state, which involves the alignment of a pair of h/sub 11/2/ neutrons. An alignment of neutrons from the upper h/sub 11/2/ midshell drives the nucleus towards a collectively rotating oblate (..gamma.. = -60/sup 0/) shape. Both signatures of a band based on a ..nu..h/sub 11/2/x..nu..g/sub 7/2/ configuration were observed, also possibly oblate. The observation of both neutron and proton low-frequency alignments is consistent with cranked-shell model calculations and theoreticalmore » estimates of the prolate-oblate energy difference for this nucleus.« less