Smooth band termination in odd mass La nuclei:127,129,131La

Abstract

High spin states in 127,129,131La have been investigated using the 100Mo(32S,p4n), E=160 MeV, 100Mo(34S,p4n), E=155 MeV, and 100Mo(36S,p4n), E=160 MeV reactions, respectively. γ rays were detected using the EUROBALL IV (127,131La) and EUROGAM II (129La) arrays. The results have enabled the negative parity yrast band, built on the πh11/2 orbital at low spin, and the lowest lying (π,α)=(+,±12) bands to be extended to higher spins. The positive parity, α=−12, bands in 127,129La and the positive parity, α=12, band in 127La can be interpreted, with the aid of cranked Nilsson-Strutinsky calculations, as examples of smoothly terminating bands in valence space based on both signatures of the π[(g7/2d5/2)5(h11/2)2]⊗ν[(g7/2d5/2)x(h11/2)6(d3/2s1/2)2] configuration, where x=12,14 for 127,129La, respectively. The favored α=−12 bands of these configurations are predicted to terminate at 952+ and 832+, respectively, and experimentally the bands are observed to within two transitions of these terminating states. The data for the positive parity, α=12, band in 129La do not allow any firm conclusions to be made regarding the high spin structure of this band. The positive parity bands in 131La have a different structure at high spin compared with the lighter nuclei. In this case the bands may be interpreted in terms of a π[(g7/2d5/2)5(h11/2)2]⊗ν[(g7/2d5/2)12(h11/2)8(d3/2s1/2)4] configuration relative to a 100Sn core.Received 14 April 2000DOI:https://doi.org/10.1103/PhysRevC.62.034315©2000 American Physical Society