Unblocking of stellar electron capture for neutron-rich <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>N</mml:mi><mml:mo>=</mml:mo><mml:mn>50</mml:mn></mml:mrow></mml:math> nuclei at finite temperature
Alan A. Dzhioev, K. Langanke, G. Martı́nez-Pinedo, A.I. Vdovin, Ch. Stoyanov
Abstract
We have calculated electron-capture rates for neutron-rich $N=50$ nuclei ($^{78}\mathrm{Ni}, ^{82}\mathrm{Ge}, ^{86}\mathrm{Kr}, ^{88}\mathrm{Sr}$) within the thermal quasiparticle random-phase approximation approach at temperatures $T=0$, corresponding to capture on the ground state, and at $T=10\phantom{\rule{4pt}{0ex}}\mathrm{GK}$ (0.86 MeV), which is a typical temperature at which the $N=50$ nuclei are abundant during a supernova collapse. In agreement with recent experiments, we find no Gamow-Teller (${\mathrm{GT}}_{+}$) strength at low excitation energies, $E<7\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$, caused by Pauli blocking induced by the $N=50$ shell gap. At the astrophysically relevant temperatures, this Pauli blocking of the ${\mathrm{GT}}_{+}$ strength is overcome by thermal excitations across the $Z=40$ proton and $N=50$ neutron shell gaps, leading to a sizable GT contribution to the electron capture. At the high densities, at which the $N=50$ nuclei are important for stellar electron capture, forbidden transitions contribute noticeably to the capture rate. Our results indicate that the neutron-rich $N=50$ nuclei do not serve as an obstacle of electron capture during supernova collapse.