Shell-model description of allowed and forbidden beta decaysONLINE ONLY

The values of vector (gV) and axial-vector (gA) coupling constants plays crucial role in the β-decay theory. Inside the nuclear matter the value of gA is affected by nuclear many-body, delta-nucleon and mesonic correlations. The quenched or enhanced value of gA plays an important role when data on astrophysical process, single and double β decays are to be reproduced by nuclear many-body calculations. In single β decay, the decay rate depends on the second power of gA, while to the forth power for ββ-decays [1]. Recently, we have evaluated the allowed β-decay properties of several nuclei in the sd region for different transitions with the nuclear shell model and extract the information of the effective gA values in this region [2]. We have also calculated [3] electron spectra as a function of gA for the second-forbidden nonunique β− decay of 24Na and 36Cl in the frame work of shell model and tested the role of vector matrix element in the electron spectral shapes. Also calculated [4] the electron spectra of the second-forbidden nonunique β− decay of 59,60Fe in the fp region. In the lead region we also study of the first forbidden β− decay of the 207Hg into 207Tl [5]. In this talk these results will be presented.

[1]  J. Suhonen and O. Civitarese, Weak-interaction and nuclear-structure aspects of nuclear double beta decay, Phys. Rep. 300, 123 (1998).

[2]  A. Kumar, P. C. Srivastava, and T. Suzuki, “Shell model results for nuclear β−-decay properties of sd-shell nuclei”, Prog. Theor. Exp. Phys. 2020, 033D01 (2020).

[3]  A. Kumar, P. C. Srivastava, J. Kostensalo and J. Suhonen “Second-forbidden nonunique β− decays of 24Na and 36Cl assessed by the nuclear shell model”, Phys. Rev. C 101, 064304 (2020).

[4]  A. Kumar, P. C. Srivastava, and J. Suhonen, “Shell-model description of the electron spectra for the second-forbidden nonunique β− decays of the fp-shell nuclei 46Sc and 59,60Fe”, under review (2021)

[5]  A. Kumar, and P. C. Srivastava, “Shell-model description of first-forbidden β−-decay of 207Hg into the one-proton-hole nucleus 207Tl”, under preparation (2021).