Mixed - symmetry states and the structure of 200 Hg

Mixed-symmetry assignments are made to the 1.570 (l;), 1.573 (2:) and 1.659 (3:) MeV levels in 2wHg. The characteristics of the 2: level are shared with nearby 2+ levels at 1.254 and 1.593 MeV. An interacting boson approximation (IBA-2) analysis examines the sensitivity of the mixed-symmetry states to the E , parameters of the Majorana term and finds that both the magnitude and sign of the d(E2iM1) mixing ratio of 2'-2: transitions are well reproduced at the values of the tt parameters used to obtain a level energy fit. The IBA-2 calculations also give a satisfactory fit to the energy levels and in general provide X(EOiE2) values close to the experimental data. These calculations agree with the known oblate deformation of the ground state which we find to be predicted by Kumar's dynamic deformation model. Experimental data from n, yy(0) experiments together with internal conversion coefficient (ICC) results allow 1+ levels to be unambiguously established at 1.570, 1.631, 1.718, 2.061, 2.370, 2.640 and 2.979 MeV. The measurements also provide precise 6 values of many transitions while event-by-event coincidence information permits the decay scheme to the developed with previous unlocated transitions now firmly assigned. NUCLEAR REACTIONS '99Hg(n; y)ZWHg; thermal neutrons, measured I,, y-ray coincidences, yy (8 ) ; deduced 6(E2/Ml), X(EOIE2), mixed-symmetry states, level scheme; enriched target, Ge(Li) detectors.