Weak-interaction rates in stellar conditions

Abstract

Weak-interaction rates, including ¯-decay and electron capture, are studied in several mass regions at various densities and temperatures of astrophysical interest. The study includes even-even and odd-A nuclei in the pf-shell region involved in presupernova formations, as well as neutron-deficient and neutron-rich medium-mass isotopes involved in the rapid-proton and rapidneutron capture processes, respectively. Weak rates are relevant to understand the late stages of the stellar evolution, as well as the nucleosynthesis of heavier nuclei [1,2]. The nuclear structure involved in the weak processes is studied within a quasiparticle proton-neutron random-phase approximation with residual interactions in both particle-hole and particle-particle channels on top of a deformed Skyrme Hartree-Fock mean field with pairing correlations [3]. First, the energy distributions of the Gamow-Teller strength, as well as the ¯-decay half-lives are discussed and compared with the available experimental information, measured under terrestrial conditions from beta-decay in the case of the unstable nuclei [4,5] and from charge-exchange reactions in the case of stable nuclei [6]. Then, the sensitivity of the weak-interaction rates to both astrophysical densities and temperatures is studied [7]. Special attention is paid to the relative contribution to these rates of thermally populated excited states in the decaying nucleus and to the electron captures from the degenerate electron plasma.