E.F. Moore

Core polarization by an intruder orbital in81Sr

Abstract A strongly deformed rotational band in 81 Sr has been studied up to a spin of312ℏ using the reaction 55 Mn( 29 Si, p2p) 81 Sr at95.2MeV. Lifetime measurements using the Doppler shift attenuation method imply an average quadruple moment of±3.5 (6) eb, corresponding to an axial deformation ofs 2 ≅0.4. These results have been interpreted as core polarization by the[431]12 + Nilsson orbital.

High-spin states and rotational coexistence in 25Mg

New high spin states in 25Mg have been located above the neutron threshold using the 12C(14N, pγ)25Mg reaction at E=23.5 MeV. The members of the ground state rotational band (Kπ=52+ have been tentatively identified up to 152+. The yrast 152+ (not a member of the ground state band) and 172+ states have also been tentatively assigned. These results support the interpretation of the new 172+ state and the previously known yrast 132+ state as fully aligned prolate configurations, i.e., prolate particle-hole states with K=I and γ=-120°.

Core Polarization Effects in Odd A ≈ 80 Nuclei

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°.