Measurements and Optical-Model Analyses of Quasielastic (p,n) Reactions

Differential cross sections for quasielastic ($p,n$) scattering from 17-20-MeV bombarding energies have been measured for Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Se, Zr, and Nb in either 7.5 or 15° steps between 3 and 157.5°. A complex isospin-dependent potential, whose strengths and form factors are deduced from the Becchetti and Greenless global neutron and proton optical potentials, gave a good over-all description of the average behavior for the 17-20-MeV quasielastic ($p,n$) data. In particular, volume real and surface imaginary isospin form factors with strengths of 96 and 48 MeV, respectively, yielded a reasonable fit to both the shape and magnitude of the Fe and Nb quasielastic ($p,n$) data. On the other hand, using a purely real isospin potential requires a surface interaction of strength 126 MeV for Fe and a volume interaction of strength 107 MeV for Nb. The calculations have been extended to 30- and 50-MeV bombarding energy and have been compared with the measurements of Batty et al. At 30 MeV there is good agreement as regards both shape and magnitude; at 50 MeV the shapes are reasonably well described, but the calculated magnitudes are uniformly higher for most of the targets investigated. It is suggested that the 50-MeV data are consistent with a 30% decrease in the isospin strength in going from 30 to 50 MeV.