Finite-temperature electron-capture rates for neutron-rich nuclei around N=50 and effects on core-collapse supernovae simulations

Abstract

The temperature dependence of stellar electron-capture (EC) rates is investigated, with a focus on nuclei around N = 50, just above Z = 28, which play an important role during the collapse phase of core-collapse supernovae (CCSN). Two new microscopic calculations of stellar EC rates are obtained from a relativistic and a non-relativistic finite-temperature quasiparticle random-phase approximation approaches, for a conventional grid of temperatures and densities. In both approaches, EC rates due to Gamow-Teller transitions are included. In the relativistic calculation contributions from first-forbidden transitions are also included, and add strongly to the EC rates. The new EC rates are compared with large-scale shell model calculations for the specific case of 86 Kr, providing insight into the finite-temperature effects on the EC rates. At relevant thermodynamic conditions for core-collapse, the discrepancies between the different calculations of this work are within about one order of magnitude. Numerical simulations of CCSN are performed with the spherically-symmetric GR1D simulation code to quantify the impact of such differences on the dynamics of the collapse. These simulations also include EC rates based on two parametrized approximations. A comparison of the neutrino luminosities and enclosed mass at core bounce shows that differences between simulations with different sets of EC rates are relatively small (≈ 5%), suggesting that the EC rates used as inputs for these simulations have become well constrained.

Nuclear Weak Rates and Nuclear Weak Processes in Stars

“…Correlations beyond thermal QRPA are shown to be important for further shift of the GT + strength to lower energy and enhancement of the e-capture rates in nuclei around 78 Ni [115]. Electron-capture rates for neutron-rich nuclei around N =50 obtained by finite-temperature QRPA calculations are also found to be enhanced compared with those of large-scale shell-model calculations [116].…”

“…The β-decay half-lives of neutron-rich nuclides, 100 Kr, 103−105 Sr, 106−108 Y, 108−110 Zr, 111,112 Nb, 112−115 Mo, and 116,117 Tc, which lie close to the astrophysical r-process path, have been measured at RIBF (Radioactive-Isotope Beam Factory), RIKEN [165]. The results idicate an overestimation of the half-lives predicted by FRDM+QRPA model by a factor of 2 or more in the A=110 region.…”