Search

• pn-QRPA model used in the calculations satisfied well the theoretical Ikeda sum rule. • Half-lives calculated for Ni isotopes are in good agreement with measured data. • Calculated neutrino cooling rates for wide range of stellar temperature and density. • Our calculated rates are compared with previous calculations from other models. • For neutron rich isotopes, our rates at high temperature are enhanced. As per simulation studies, the weak reaction rates on nickel isotopes play a substantial role in affecting the ratio of electron-to-baryon content of stellar interior during the late stages of core evolution. (Anti)neutrinos are produced in weak-decay processes, and escape from the stellar content having densities less than 1011 g cm − 3. They take away energy and reduce the stellar core entropy. In this paper we report on the microscopic calculation of neutrino and antineutrino cooling rates due to weak rates on nickel isotopes in mass range 56 ≤ A ≤ 71. The calculations are accomplished by employing the deformed pn-QRPA model. Recent studies on GT strength properties of nickel isotopes show that the deformed pn-QRPA model well explained the experimental charge-changing transitions. Our calculated beta decay half-lives for selected nickel isotopes are in excellent comparison with experimental data. The (anti)neutrino cooling rates are determined over temperatures in the range of 0.01 × 109 – 30 × 109 K and densities in the range of 10 – 1011 g cm − 3 domain. The computed rates are compared with previous theoretical calculations. For neutron rich nuclide, at high temperatures, our computed cooling rates are enhanced as compared to previous calculations. [ABSTRACT FROM AUTHOR]

• Isotopes of vanadium are considered to have great astrophysical significance regarding their weak-decay rates. • pn-QRPA model was used in the calculations of lepton emission rates of 43 − 64 + V isotopes. • Lepton emission rates were calculated for wide range of stellar temperature and density. • Our calculated rates are compared with previous calculations done by using IPM and LSSM models. • IPM rates are generally bigger than QRPA rates, while LSSM rates are in good comparison with the reported rates. In astrophysical conditions prevalent during the late times of stellar evolution, lepton (e − and e +) emission processes compete with the corresponding lepton capture processes. Prior to the collapse, lepton emissions significantly affect the cooling of the core and reduce its entropy. Therefore the lepton emission rates for Fe-group nuclei serve as an important input for core-collapse simulations of high-mass stars. From earlier simulation studies, isotopes of vanadium (V) have great astrophysical significance in regard to their weak-decay rates which substantially affect Y e (fraction of lepton to baryon number) during the final developmental stages of massive stars. The current study involves the computation of the weak lepton emission (LE) rates for V-isotopes by employing the improved deformed proton-neutron Quasi-particle Random Phase Approximation (pn-QRPA) model. The mass numbers of the selected isotopes range from 43 to 64. The LE rates on these isotopes have been estimated for a broad spectrum of density and temperature under astrophysical conditions. The ranges considered for density and temperature are 10 1 to 10 11 (g/cm 3) and 10 7 to 3 × 10 11 (K), respectively. The lepton emission rates from the present study were also compared to the rates previously estimated by using the independent-particle model (IPM) and large-scale shell model (LSSM). IPM rates are generally bigger than QRPA rates, while LSSM rates are overall in good comparison with the reported rates. We attribute these differences to correct placement of GT centroid in LSSM and QRPA models. [ABSTRACT FROM AUTHOR]