On the coexistence of oblate and prolate deformed bands in83Zr

Abstract

Deformation parameters of the positive parity yrast band and negative parity bands in S3Zr are deduced from lifetimes and E2/M1 mixing ratios. Lifetimes of high spin states have been determined from recoil distance Doppler shift and Doppler shift attenuation measurements using the S4Fe(32S, 2pn7) S3Zr reaction. Ten lifetimes and five lifetimes limits were determined. The positive parity band, built on the g9/2 K = 5/2 orbital has an average deformation [/~2[ =0.28(2), and shows a reduction of E2 transition strengths in the observed backbend region at I~g21/2 +. In contrast, the E2 strengths in the negative parity states show a steady increase up to U= 15/2-. These states are more strongly deformed than the positive parity states ([/~21=0.33(3)). The E2/M1 mixing ratios show that the negative parity band has K = 3/2 and is prolate, and favour oblate deformation for the positive parity yrast band. In the K= 1/2-band the E2 strength of the 7/2---*3/2-transition yields a deformation I/~zl = 0.26(5). The band structure is compared with calculations within the Hartree-Fock Bogoliubov cranking model.

Rotational and single-particle structures in83Zr

“…Data on lifetimes and E2/M1 mixing ratios [7,14], if interpreted with a simple axially symmetric rotor-plus-particle model, ~ive an oblate deformation offl2 = -0.28 for the [422]5/2 yrast band and a protate deformation of B2 = +0.33 for the negative parity yrast band which, however, is more consistent with a [30113/2 Nilsson assignment. The [30111/2-band was found to have a deformation of ]flail =0.26, but no sign of/72 could be established [7].…”

“…The lack of similar transitions at higher spins may reflect the different influences of the aligned protons on the nuclear shape, and hence, the wavefunctions. In addition to the results of [7], a few B(MI,I-*I-1) and B(E2,I--*I-1) rates can be determined from the measured lifetimes and mixing ratios [7,14,15]. There are two different mixing ratios reported [14,15] for the 286 keV transition, decaying from the 7/2-state, and the transition rates corresponding to both are given.…”

“…The [30111/2-band was found to have a deformation of ]flail =0.26, but no sign of/72 could be established [7]. As will be shown, the large amount of K mixing in the negative parity bands calls into question the validity of the previous Nilsson assignments in this nucleus.…”

“…New decay branches from states with previously measured [7] lifetimes make the recalculation of transition rates for some levels necessary and are presented in Table 2. The previously published transition rates did not change appreciably due to the additional 5-6% decay branches of the 339 keV 7/2-and 1014 keV 11/2-states in the 5/2-band.…”

“…2) Collectivity -the measured deformation [7] of the rotational bands limits the y-ray multipolarities to M 1, E2 and parity changing El.…”