Core Polarization Effects in Odd A ≈ 80 Nuclei

Abstract

The nucleus 81Sr provides one of the best examples of the effects of an unpaired nucleon in polarizing the nuclear core. Four different rotational bands can be seen in the level scheme [1–3] of 81Sr, shown in Fig. 1. Each is built upon a different single-particle configuration and each exhibits distinctive properties. The large signature splitting of the strongly decoupled g9/2 Yrast rotational band is consistent with the nearly oblate shape (β2=0.23, γ=-50°) predicted by Woods-Saxon cranking model calculations [1,4]. The measured B(E2) strengths (See Fig. 2) also imply |β2| ≈ 0.22 in this band. The nuclear shape changes substantially after the proton quasiparticle alignment at ℏω ≈ 0.5 MeV. The signature splitting nearly vanishes and ΔJ=1 transitions become strong. A similar band crossing has been seen [5] in 81Kr, and a nearly identical one has recently been reported [6] in 79Kr. Theoretically, the alignment polarizes the core towards a triaxial or more nearly prolate shape with γ ≥ -30°.