Abstract
Level schemes of and are proposed from the analysis of coincidence data from a spontaneous fission source with Gammasphere. These schemes have the highest excitation energies and spins yet established in these nuclei, as well as weakly populated bands not reported in earlier fission- work. From these data, information on shapes is inferred. By analogy with lighter odd-even isotopes, tentative spins and parities are assigned to members of several rotational bands. In this region triaxial nuclear shapes are known to occur, and we carried out calculations for and with the triaxial-rotor-plus-particle model. The bands of both nuclei, as well as lighter isotopes studied by others, show similar signature splitting. Our model calculations give a reasonable fit to the signature splitting, collective sidebands, and transition probabilities at near-maximum triaxiality with . For the band, experiment and model calculations do not fit well, which is accounted for by greater prolate deformation of the band, a case of shape coexistence. Our data on show no backbending and thus support the idea of the band crossing in the ground band of the odd-A neighbors being due to alignment of an neutron pair. In above the band crossing (spins ) the ground band appears to split, with two similar branches. We consider the possibility that chiral doubling may be involved, but there are not enough levels to determine that.
8 More- Received 24 August 2003
DOI:https://doi.org/10.1103/PhysRevC.69.024315
©2004 American Physical Society