Within the distorted-wave impulse approximation and an extended random phase approximation theory which includes 1p 1h as well as 2p 2h excitations, we study (p,n) and (n,p) cross sections in ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$ at 200 MeV. The inclusion of 2p2h excitations allows us to calculate spreading width effects microscopically without introduction of parameters. Given a fully microscopic description reasonable agreement between theory and experiment is found in the (p,n) channel. In the (n,p) channel at forward angles we find that the compact spin-dipole resonance predicted by 1p1h random-phase approximation calculations is not strongly effected by 2p2h mixing.

• Received 1 June 1987

DOI:https://doi.org/10.1103/PhysRevC.37.1322