Isobaric analog state transitions in (p,n) reactions on 48Ca, 90Zr, 120Sn, and 208Pb at 25, 35, and 45 MeV

Differential cross sections have been measured for (p,n) reactions to the isobaric analogs of the targets 48Ca, 90Zr, 120Sn, and 208Pb at proton bombarding energies of 25, 35, and 45 MeV. The angular distributions include 00 and generally extend from 100 to 1600 in 50 steps. Neutron spectra at these scattering angles have been obtained with the time-of-flight technique. The isospin-flip strength of a phenomenological nucleon-nucleon force has been determined with microscopic DWBA calculations including the ''knockon'' exchange amplitude. The strength required to fit the data decreases with increasing bombarding energy. At the higher proton energies a realistic G-matrix effective interaction also provides a reasonable account of the observed angular distributions. (auth)