Gamow-Teller and first-forbidden transition strengths in astrophysical processes

Gamow-Teller (GT) and first-forbidden (FF) transitions in nuclei and their possible consequences on astrophysical processes in stars are discussed. GT transition strengths in fp-shell nuclei are studied by shell model calculations with the use of new shell model Hamiltonians, GXPF1. Neutrino-nucleus reaction cross sections are re-evaluated and compared with previous investigations. Proton emission cross sections on ⁵⁶Ni are pointed out to be enhanced and lead to the enhancement of the production yields of ⁵⁵Mn and ⁵⁹Co in population III supernovae. Next, electron capture reactions on Ni and Fe isotopes in steller environments are studied. The capture rates depend sensitively on the distributions of the GT strengths. Capture rates on ⁵⁸Ni and ⁶⁰Ni obtained by GXPF1 are found to reproduce rather well those obtained from experimental GT strengths. Finally, beta decays of the N=126 isotones are studied by shell model calculations taking into account both the GT and FF transitions. The FF transitions are found to be important to reduce the half-lives by twice to several times of those by the GT contributions only. Possible implications on the short half-lives of the waiting point nuclei on the r-process nucleosynthesis are discussed for certain astrophysical conditions.