High-spin states in ¹⁸³Hg and shape coexistence in the odd-mass mercury isotopes

Abstract

High-spin states in 183Hg have been identified using the reaction 155Gd(32S,4n). Three prolate-deformed rotational bands associated with the 1 2-[521], 7 2-[514] and mixed i 13 2 neutron orbitals are observed, while the existence of an oblate 13 2+ bandhead is inferred, implying co-existing prolate and oblate nuclear shapes. A two-band mixing model used to fit the state energies of the i 13 2 neutron bands in 183,185,187Hg gives parameter values which are consistent with the existence of two bands with different deformations. The B(E2) ratios of the intra- and inter-band transitions in these coexisting bands are also investigated. Many of the features can be reproduced but difficulties remain, for example the results are not consistent with the assumption of coexistence between simple prolate and oblate shapes, a problem noted previously for the even-mass isotopes. Systematics of the prolate-oblate energy differences show that the energy of the prolate well relative to the oblate well is ∼ 350 keV lower in the odd-mass isotopes than in the even-mass isotopes. Possible reasons for this are described. The nature of the first alignment in the prolate bands in the mercury isotopes is discussed within the cranked shell model.