NWY Model Calculations for Nucleon-Induced Multistep Direct Reactions

Abstract

Calculations of the preequilibrium process are performed with the theory of Nishioka, Weidenmüller, and Yoshida (NWY), which is a quantum mechanical approach to the preequilibrium nuclear reactions. For a one-step process, cross sections given by the NWY theory are sum of DWBA cross sections which excite various lp-lh states, and those are averaged over the residual state weighted by the final states density. A true level density which is based on a random matrix model is used for this. A comparison of the calculated NWY one-step process with the experimental data is shown. For a two-step process, the NWY theory adopts a “sudden approximation.” An example of the two-step cross section calculation is made for ²⁰⁸Pb(p, p’) reaction.

Keywords:

• Nishioka-Weidenmüller-Yoshida theory
• pre-equilibrium reaction
• multistep direct reaction
• distorted-wave Born approximation