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The negative parity state of [sup 172[minus]180]Os are studied in the framework of the interacting boson approximation model. The negative parity states are formed by including one [ital f] boson or allowing one boson to break into two fermions which are placed in orbits with opposite parity. The calculated level energies and [ital B]([ital E]2)'s are in reasonable agreements with experiments. From the comparison of intrinsic structure it suggests that the relative energy of the quasiparticles may be the most important factor in the calculations.

The energies of [Formula: see text] states in even-even nuclei from Dy to W are shown to be linear in the P-factor and can be described using the same slope prescription for all these nuclei. Deviations are found for Os and Pt isotopes with Np. The results for N>104 give evidence for a more complex structural evolution beyond midneutron shell.

Level lifetimes were measured for the first time for the neutron-rich isotope $^{78}\mathrm{Ge}$ by the fast electronic scintillation timing technique and B(E2) values were extracted. The energies of the low-lying states and the B(E2) values between the ${0}^{+}$ and ${2}^{+}$ states disclose a rapidly changing structure near N=40, followed by a stabilization, with $^{74\mathrm{\ensuremath{-}}78}\mathrm{Ge}$ best understood as asymmetric rotors.

A comprehensive analysis is made of the experimental information on Gamow-Teller beta decay for the light (A\ensuremath{\le}18) nuclei. Experimental data on half-lives, Q values, and branching ratios are tabulated. Experimental logft values and beta-decay matrix elements are deduced from these data. The one-body-transition densities necessary to predict the beta-decay matrix elements are then calculated using a recently constructed shell-model Hamiltonian operating in the first four major shells. Using these parameters, effective Gamow-Teller operators are deduced for the 0p shell from a least-squares fit to 16 experimental matrix elements. The effective operators are used to calculate 83 decay matrix elements. Some specific decays are discussed.

The evolution of nuclear structure along the Xe and Ba isotopes with N{lt}82 is studied in comparison with that in the Pt-Os isotopes and with interacting boson approximation calculations. As is well known, the Pt isotopes from {sup 188{minus}196}Pt exhibit a stable structure very close to O(6), the lighter Pt isotopes and the Os nuclei evolve towards a rotor, and the heaviest Pt nuclei, {sup 198,200}Pt, show a tendency towards vibrational character. In contrast, we show that the Ba nuclei are best described by a trajectory from U(5) towards SU(3) that passes through an intermediate structure that resembles O(6) for N{approximately}72{endash}76. The Xe appears to evolve from U(5) to O(6)-like. {copyright} {ital 1998} {ital The American Physical Society}

Odd-odd nuclei have been calculated before in the framework of the IBA model. However, in order to keep the calculations tractable, they were done by using supersymmetries or were limited only to unique-parity orbits. We used computer codes for the interacting-bosonfermion-fermion approximation (IBFFA) model, which adopted a very efficient model-space trunction scheme, so no restriction needed to be made and complete calculations of the excitation energy spectra were obtained. We calculated a series of odd-odd isotopes, 176–184Re. The calculations started from even-even Os cores, where a simplified hamiltonian for the SU(3) limit in the IBA-1 model was used. Both negative-and positive-parity calculations for nearby odd-mass Re and Os isotopes have also been carried out. The detailed results of excitation energy spectra of all three types of calculations are presented, also some selected quadrupole and magnetic moments, and B(E2) and B(M1) values. All calculations are compared with experimental data. One of the successes of the IBFFA model is the prediction of the doubly-decoupled bands, which have been verified from experiments.

We present the detailed results of calculations of excitation-energy spectra, quadrupole and magnetic moments, and B(E2) and B(M1) values for the odd-odd 180,182,184Re isotopes in the framework of the interacting-boson-fermion-fermion approximation model. Also, calculations are presented for both positive- and negative-parity excitations in the nearby odd-mass Re and Os nuclides and for collective states in the even-even Os core nuclides. The calculated results are compared with experimental data.