M. Waroquier

The decay of isomeric states in 201mTl, 202mTl and 204mTl is investigated with a Ge(Li) detector. The isomeric states are produced with LINAC bremsstrahlung (24–32 MeV). Life-times and precise energies have been determined. In the 201mTl case, shape isomerism is proposed, based on calculations of the total potential energy surfaces and calculations of the lifetime in a Nilsson model.

The aim of this work is to draw attention to the precise formulation of theelectromagnetic-multipole transition operators and moments, especially the electric ones. Their precise structure fixes their transformations under some operations, as time reversal and hermitian conjugation, and in this way they play an important role as far as properties of their matrix elements are concerned.

Another point of discussion is the consistent use of a well-defined phase convention for the angular-momentum eigenfunctions and their role in the development of the BCS formalism. A numerical example proves the importance of the use of well-defined phase-consistent eigenfunctions, operators, occupation probabilities, etc.

It has been shown that in the evaluation of the M2 transition from the Jπ=11/2-(1) to the Jπ=7/2+(1) state in the odd-proton N=82 isotones, the three-quasiparticle admixtures in the transition moment, are not negligible.
NUCLEAR STRUCTURE 141Pr; B(M2;1h11/2→1g7/2), B(E3;1h11/2→1d5/2) and the gyromagnetic ratio g1h11/2 Quasi-Tamm-Dancoff Approximation. Comparison theory experiment.

The particle-vibration coupling model is treated in a perturbation approach in order to

1. (i) obtain simple expressions for the reduced E2 transition probabilities and thus derive approximate selection rules and
2. (ii) study the convergence properties of the perturbation series (up to sixth-order) by comparing with the exact diagonalization procedure. The results are in both cases compared with diagonalization results and the experimental data available on 121Sb and 123Sb.

The perturbation expansion, treated to higher order, can be performed easily in terms of a diagrammatic method based on Goldstone and Jutsis-Bandzaitis-Vizbaraite formalisms.

It is shown that the perturbation method gives reliable results if “physical” single-particle energies are used instead of “bare” single-particle energies with the neglect of all self-energy corrections and a renormalized particle-vibration coupling strength.

This higher order perturbation expansion is applied to the case of 119Sb and 123Sb.