Microscopic description of charge-exchange nuclear resonances excited in ( p,n) reactions

The charge-exchange excitations for the 48Ca→48Sc, 90Zr→90Nb, and 208Pb→208Bi isobar pairs are calculated using the methods of the theory of finite Fermi systems with the single-particle continuum taken into account exactly. Transition densities for the isobar-analog states, Gamow-Teller resonances, dipole (L = 1, S = 0) resonances, and spin-dipole (L = 1, S = 1) resonances are calculated. Differential cross sections for the ( p,n) reactions which excite these resonances are calculated in the distorted-wave impulse approximation for proton energies E/sub p/ in the 100--200 MeV range. A detailed comparison with experimental data is performed in order to determine the nucleon-nucleon effective interaction in the charge-exchange channel as well as the local quasiparticle charge e/sub q/[sigmatau] that characterizes the quenching of low-energy spin-flip transitions. It is shown, in particular, that the theory gives a good description of experiment for the value g' = 1.1 (G/sup prime/0 = 330 MeVxfm3) of the Landau-Migdal strength parameter and for e/sub q/[sigmatau]roughly-equal0.8