We evaluate the β-decay rates within the gross theory of beta decay (GTBD) and compare the results for different values of the axial-vector coupling constant, g A = 0.76, g A = 0.88, g A = 1, g A = 1.13, and g A = 1.26, and also different energy distribution functions like Gaussian, exponential, Lorentzian, and modified Lorentzian ones. We use new sets of parameters as well as updated experimental mass defects and also an improved approximation for the Fermi function. We compare our calculated results for a set of 94 nuclei of interest in pre-supernova phase, with experimental data in terrestrial conditions and also with other theoretical models like the QRPA, the shell model (SM), and different versions of the GTBD. We show that best results are obtained with g A = 1 using Gaussian and Lorentzian distributions, being the rates for the 74 and 80% of our sample, respectively, of the same order of magnitude that of experimental data. Finally, we show that the present results within the GTBD are better than those within the QRPA model and also older versions of the GTBD for the isotopes of cobalt and iron families, and comparable with SM for some elements.
Alpha-decay half-life of even-even emitters has been calculated in terms of tunnelling through a quantum mechanical potential barrier. A multipolar expansion of Coulomb potential has been developed taking into account the nuclear quadrupole, hexadecapole, and hexacontatetrapole deformations. We show that using a free-parameter model the calculated half-lives do not vary significantly with higher order multipolarities of the daughter nucleus deformation.
The influence of low-lying discrete nuclear states on isotopic abundances in presupernova cores, is discussed. Assuming the hypothesis of nuclear statistical equilibrium (NSE), the Saha equation has been solved for a set of 65 nuclear species (including free protons and neutrons). Experimental data have been used in the calculation of the first terms of the nuclear partition function. The obtained abundances are compared with those evaluated using an energy level density in the computation of the nuclear partition function. We conclude that in future calculations involving isotopic abundances in presupernova cores, the low-lying nuclear states need to be treated as discrete ones when experimental data are available.
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