ELECTRON-CAPTURE AND BETA-DECAY IN PRESUPERNOVA STARS

We carry out calculations of electron capture and β-decay from several odd-even and odd-odd nuclei with A > 60, seeking the largest transitions. Of these, only the 60Co + e- → 60Fe + ve transition has been previously evaluated in a shell model calculation, by Fuller et al., in a form suitable for inclusion in stellar evolution calculations. For neutron-rich stellar cores with Ye = Z/A = 0.42 to 0.43, this single transition accounts for roughly half of the total electron capture in present evolutionary calculations, even though the abundance by mass fraction of 60Co is only on the order of 10-5. We show that nuclei with A > 60, essentially not included to date, may make significant contributions to the electron capture and β-decay rates in the last stages of stellar evolution.