Gamow-Teller strength in deformed nuclei within self-consistent pnQRPA with the Gogny force

Abstract

In recent years fully consistent quasiparticle random-phase approximation (QRPA) calculations using finite range Gogny force have been performed to study elec- tromagnetic excitations of several axially-symmetric deformed nuclei up to the 238 U. Here we present the extension of this approach to the charge-exchange nuclear excitations (pn- QRPA). In particular we focus on the Gamow-Teller (GT) excitations. A comparison of the predicted GT strength distribution with existing experimental data is presented. The role of nuclear deformation is shown. Special attention is paid toβ-decay half-lives calculations for which experimental data exist. Spin-isospin nuclear excitations, in particular the Gamow-Teller (GT) resonances, play nowadays a crucial role in several fields of physics. First, in nuclear physics since they can provide informations on the nuclear interaction, on the equation of state of asymmetric nuclear matter and on the nuclear skin thickness. Second, in astrophysics, since they influence stellar evolution and nucleosynthesis by governing the electroweak processes. Finally, in particle physics in connection with the neutrino physics beyond the standard model and the evaluation of the Vud element of the Cabibbo-Kobayashi- Maskawa quark-mixing matrix. Experimentally the spin-isospin nuclear excitations are studied via charge-exchange reactions, such as (p, n), (n, p), (d, 2 He), ( 3 He, t) or (t, 3 He) andβ-decay measurements. In spite of the great efforts and interest, the whole nuclear chart cannot be experimentally studied. To study the nuclei ex- perimentally inacessible one can rely on theoretical models. In this context one of the most employed models is the so called proton-neutron quasiparticle random-phase approximation (pnQRPA). To treat consistently isotopic chains from drip line to drip line two main features of the theoretical model are in order: the possibility to deal with deformed nuclei and the use of an unique effective nuclear force. The term unique has here two meanings. First of all, it means that the interaction is the same for all the nuclei; second, that the nuclear interaction used to describe the ground state and the excited states is the same (this is the so-called self-consistency of the calculation). In spite of the relatively large number of pnQRPA calculations, only a very few of those include both features. Furthermore, even in such self-consistent calculations, it remains at least one coupling constant, typically in the particle-particle channel, which should be considered as a free parameter usually fitted to half-lives or to the experimental position of the GT excitation energy. Here we present the fully consistent axially-symmetric-deformed pnQRPA calculation based on the finite range Gogny force. The originality of the present work consists in the use of the Gogny