Ground-state Gamow-Teller strength in Ni64(n,p)64Co cross sections at 90–240 MeV

Cross sections have been measured for the reaction Ni-64(n,p)Co-64 laboratory angles between 0-degrees and 10-degrees for incident neutron energies from 90 to 240 MeV. The ground-state cross sections together with the beta- decay ft value for the transition Co-64Co(g.s.)-->Ni-64(g.s.) are used to normalize the q = 0 differential cross section in units of mb/sr per unit Gamow-Teller (GT) strength. This is the first absolute measurement of the A(n,p) unit cross section for a nucleus in the (fp) shell, and it may be used to calibrate the GT strength measured in other (n,p) reactions of similar mass nuclei. Since the (e-,nu-e) channel involves the same nuclear matrix element as the (n,p) channel, knowledge of GT strength in these nuclei is important for supernova modeling codes which depend on knowledge of e- capture rates of (fp)-shell nuclei to determine parameters of stellar core collapse.