Importance of (n,p) reactions for stellar beta decay rates

Recent (n,p) experiments on ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{56}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, and ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ have measured Gamow-Teller resonances which are crucial for determining stellar beta decay rates in ${}_{}{}^{54}{}_{}{}^{}\mathrm{Mn}$, ${}_{}{}^{56}{}_{}{}^{}\mathrm{Mn}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Co}$, and ${}_{}{}^{59}{}_{}{}^{}\mathrm{Fe}$, respectively. These nuclei are important players in the iron-core URCA process, which is a dynamic balancing of electron capture and beta decay rates during the final stage of nuclear burning in massive stars. We find that three of the nuclei, after calibration from (n,p) measurements, have significantly stronger decay rates than currently expected. These stronger rates will cause a more vigorous URCA process, resulting in presupernova cores which are cooler and less neutron rich than is presently used in core collapse calculations. © 1996 The American Physical Society.