Stellar weak interaction rates for intermediate-mass nuclei. II - A = 21 to A = 60

Abstract

Astrophysical electron and positron emission, continuum electron and positron capture rates, as well as the associated neutrino energy loss rates are calculated for free nucleons and 226 nuclei with masses between A = 21 and 60. Measured nuclear level information and matrix elements are used where available. Unmeasured matrix elements for allowed transitions are assigned as in Paper I. Simple shell model arguments are used to estimate Gamow-Teller sum rules and collective state resonance excitation energies. The discrete state contribution to the rates, dominated by experimental information and the Fermi transitions, determines the nuclear rates in the regime of temperatures and densities characteristic of the hydrostatic phases of presupernova stellar evolution. At the higher temperatures and densities characteristic of the supernova collapse phase, the nuclear rates are dominated by the Fermi and the Gamow-Teller collective resonance contributions. Also included is the important effect of neutron shell closure blocking of electron capture on neutron-rich nuclei. Uncertainties in the rate calculation are discussed. Reference is made to other treatments of the problem. Results of the calculations on a detailed temperature-density grid are available in computer readable form on magnetic tape upon request to M. J. N.