Electron capture strength for Ni 60 , 62 and Ni 58 , 60 , 62 , 64 ( p , n ) Cu 58 , 60 , 62 , 64 reactions at 134.3 MeV

Background: The strength of electron capture for medium mass nuclei has a significant effect on the evolution of supernovae. There is insufficient knowledge of these strengths and very little data for important radioactive nuclei. Purpose: Determine whether it is feasible to obtain EC strength from studies of ${T}_{o}+1$ excitations in ($p$, $n$) reactions, and whether this might yield information for radioactive nuclei. Methods: Cross sections for the $^{58,60,62,64}\mathrm{Ni}$($p$, $n$)$^{58,60,62,64}\mathrm{Cu}$ reactions were measured over the angular range of $0.3{}^{\ensuremath{\circ}}$ to $11.6{}^{\ensuremath{\circ}}$ at 134.3 MeV using the IUCF neutron time-of-flight facility. Results: The ${T}_{o}+1$ excitations in $^{60,62}\mathrm{Ni}$ were identified by comparison with inelastic proton scattering spectra, their $B$(GT) were extracted, and the corresponding electron capture rates in supernovae were calculated. Data from the TRIUMF ($n$, $p$) experiments at 198 MeV were reanalyzed; the electron capture rates for the reanalyzed data are in moderately good agreement with the higher resolution ($p$, $n$) results, but differ in detail. The possibility of future measurements with radioactive nuclei was considered. Conclusions: It may be possible to obtain low-lying electron capture strength for radioactive nuclei by studying ($p$, $n$) reactions in inverse kinematics.