HIGH-SPIN STATES IN HG-183 AND SHAPE COEXISTENCE IN THE ODD-MASS MERCURY ISOTOPES

High-spin states in Hg-183 have been identified using the reaction Gd- 155(S-32,4n). 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 inferre d, 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 ban ds in Hg-183,Hg-185,Hg-187 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 bu t difficulties remain, for example the results are not consistent with the assumption of coexistence between simple prolate and oblate shape s, a problem noted previously for the even-mass isotopes. Systematics of the prolate-oblate energy differences show that the energy of the p rolate well relative to the oblate well is similar to 350 keV lower in the odd-mass isotopes than in the even-mass isotopes. Possible reason s for this are described. The nature of the first alignment in the pro late bands in the mercury isotopes is discussed within the cranked she ll model.