[en] A nonperturbative model-space truncation procedure is utilized to include the effects of a single g boson on the parameters of the neutron-proton Interacting Boson Model in the realistic case of nondegenerate single-particle orbits. Particular emphasis is given to the single-boson energies epsilondsub(p) (p = v, π), with numerical results presented for the even isotopes of Hg. Only part of the observed renormalization is obtained. Possible sources of further renormalizations to epsilondsub(p) are discussed. Results are also presented for the renormalizations of the boson quadrupole parameters k and xsub(p). (orig.)

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[en] The ^191-200Hg nuclei are investigated by in-beam gamma methods and conversion electron spectroscopy. (orig.)

[en] The positive-parity yrast states of the transitional sup(189-198)Hg isotopes are interpreted within the Bengtsson and Frauendorf version of the cranking model. The very sharp backbendings can be explained by small interaction matrix elements between the ground and s-bands. The experimentally observed large aligned angular momenta and the low band-crossing frequencies are well reproduced in the calculations. (orig.)

[en] The Core-Quasiparticle Coupling Model (CQCM) for odd-mass nuclei, which is based on dynamical field theory and the Bardeen-Cooper-Schrieffer (BCS) method, has been applied to two problems. In the first, a study of Pauli exchange effects for the odd particle in the Interacting Boson-Fermion Model (IBFM) is made by a comparison with the CQCM. Spectra for a partly filled j-shell coupled to Interacting Boson Model cores are calculated in both models, and values of the IBFM exchange parameter Λ₀ are found which lead to spectra similar to those in the CQCM. In the second application, CQCM calculations have been performed for the i/sub 13/2/ bands in the odd-mass Hg isotopes, h/sub 9/2/ bands in the odd-mass Tl isotopes, and the h/sub 11/2/ bands in the odd-mass Au isotopes (A = 189 to 195). The even-mass Hg core descriptions were taken from previous proton-neutron Interacting Boson Model (IBM-2) calculations, and thus a comparison between the experimental and calculated level schemes for the odd-mass isotopes can be interpreted as a test of the core description. A predicted transition from positive Q(2⁺) near A = 195 to negative Q(2⁺) near A = 191 is not borne out by the odd-mass data. The radioactive decay of ²⁰³At to ²⁰³Po has been studied with mass-separated sources from the UNISOR facility. Time-sequenced spectra of γ-rays, x-rays, and conversion electrons have been obtained, together with γ-γ-t, γ-X-t, e^--γ-t and e^--X-t coincidence data. From this information, a decay scheme has been constructed, consisting of 30 excited states and 45 transitions that incorporate approximately 90% of the decay intensity assigned to ²⁰³At. All excited states below 1 MeV have been assigned unique spin-parity values, and the observed level scheme can be qualitatively understood in terms of a particle-core weak coupling description. The ground-state decay energy has been deduced

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[en] The isotope shift in the lambda = 2537 A line of the even isotopes ²⁰⁶Hg, ¹⁹⁰Hg, ¹⁸⁸Hg, ¹⁸⁶Hg, ¹⁸⁴Hg as well as of the I = 13/2 isomers of ¹⁹¹Hg, ¹⁸⁹Hg, ¹⁸⁷Hg, ¹⁸⁵Hg has been measured by use of a tunable dye laser at the on-line masseparator ISOLDE at CERN. The resulting delta< r²> values follow the line, extrapolated from the chain ²⁰⁵Hg-¹⁸⁷Hg which is known to have spherical nuclear shape at the heavy end changing smoothly to slight oblate deformation for the lighter isotopes. Previous measurements of the I = 1/2 groundstates of ¹⁸¹Hg. ¹⁸³Hg and ¹⁸⁵Hg revealed a sharp shape transition to strong deformation. Combined with the new results the following effects can be proved for the first time from the model-independent quantity delta< r²>: 1) the existence of odd even-shape staggering, 2) the coexistence of very different shapes in one and the same nucleus as manifested by the huge isomer shift in ¹⁸⁵Hg, 3) the absence of mixing of the different shapes. (author)