Gamow-Teller strength and lepton captures rates on 66-71Ni in stellar matter

Abstract

Charge-changing transitions play a significant role in stellar weak-decay processes. The fate of the massive stars is decided by these weak-decay rates including lepton (positron and electron) captures rates, which play a consequential role in the dynamics of core collapse. As per previous simulation results, weak interaction rates on nickel isotopes have significant influence on the stellar core vis-$\grave{a}$-vis controlling the lepton content of stellar matter throughout the silicon shell burning phases of high mass stars up to the presupernova stages. In this paper we perform a microscopic calculation of Gamow-Teller charge-changing transitions, in the $\beta$-decay and electron capture directions, for neutron-rich nickel isotopes ($^{66-71}$Ni). We further compute the associated weak-decay rates for these selected nickel isotopes in stellar environment. The computations are accomplished by employing the deformed proton-neutron quasiparticle random phase approximation (pn-QRPA) model. A recent study showed that the deformed pn-QRPA theory is well suited for the estimation of Gamow-Teller transitions. The astral weak-decay rates are determined over densities in the range of 10 -- 10$^{11}$g/cm$^{3}$ and temperatures in the range of 0.01$\times$10$^{9}$ -- 30$\times$10$^{9}$K. The calculated lepton capture rates are compared with the previous calculation of Pruet and Fuller. The overall comparison demonstrates that, at low stellar densities and high temperatures, our electron captures rates are bigger by as much as two orders of magnitude. Our results show that, at higher temperatures, the lepton capture rates are the dominant mode for the stellar weak rates and the corresponding lepton emission rates may be neglected.