Systematic approach to β and 2vββ decays of mass A=100-136 nuclei

In this work we perform a systematic study of pairs of single-beta-decaying nuclei in the mass region A = 100-136 to extract information on the effective value of the axial-vector coupling constant g(A). As the many-body framework we use the quasiparticle random-phase approximation (QRPA) and its proton-neutron variant (pnQRPA) in single-particle valence bases with Woods-Saxon-calculated single-particle energies. It is found that, to a reasonable approximation, g(A) is a linear function of the mass number A, with a slightly different parametrization below and above the mass A = 121. Using the values of gA extracted from the linear fit, as well as an average constant value of g(A), we calculate the two-neutrino double-beta (2v beta beta) decay half-lives of 11 beta(-)beta(-) decays and 10 mixed beta(+) and electron-capture (EC) decays, beta(+)beta(+)/beta+EC/ECEC, to both the ground state and the lowest three excited states.