Charge-changing transitions and capture strengths of pf-shell nuclei with T _z =−2 at proton drip-line

Abstract

Charge-changing transitions, commonly referred to as Gamow-Teller (GT) transitions, and electron capture/β ⁺-decay strengths for pf-shell nuclei with T _z =−2 at proton drip-line have been calculated using the proton-neutron quasi-particle random phase approximation (pn-QRPA) model. The total GT₊ strength values and electron capture/β ⁺-decay rates are needed for the study of the late stages of the stellar evolution. The pn-QRPA theory is used for a microscopic calculation of GT strength distribution functions and associated stellar electron capture/β ⁺-decay rates of proton-rich pf-shell nuclei with T _z =−2 in the mass range 46≤A≤56 at proton drip-line. Standard quenching factor of 0.74, usually implemented in the shell model calculation, has been incorporated for the comparison with experimental data (wherever available). The calculated GT strength of the two proton-rich nuclei, ⁵²Ni and ⁵⁶Zn are compared with experimental data of corresponding mirror nuclei. It has been found that the pn-QRPA results are in good agreement with the experimental data as well as shell model result. It is noted that the total GT strength increases linearly with the increase of mass number. The electron capture/β ⁺-decay rates for proton-rich nuclei are calculated on a temperature and density scale relevant to presupernova evolution of massive stars. The β ⁺ decay half-lives are compared with measured and other theoretical calculations.