Preequilibrium (<i>p</i>,<i>n</i>) reaction as a probe for the effective nucleon-nucleon interaction in multistep direct processes

Abstract

The spectral continua ${\mathit{E}}_{\mathit{n}}$\ensuremath{\ge}30 MeV of neutrons from the reactions $^{27}\mathrm{Al}$, $^{90}\mathrm{Zr}$, $^{208}\mathrm{Pb}$(p,xn) have been measured for ${\mathit{E}}_{\mathit{p}}$=120 and 160 MeV and angles 0\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}\ensuremath{\theta}\ensuremath{\le}145\ifmmode^\circ\else\textdegree\fi{}. Angular distributions can be explained quantitatively in absolute values and shapes over five orders of magnitude as statistical multistep direct emission in which up to six steps are involved with significant contributions. The strength ${\mathit{V}}_{0}$ of the effective nucleon-nucleon interaction applied shows a systematic dependence on the projectile energy ${\mathit{E}}_{\mathit{p}}$\ensuremath{\le}160 MeV that is consistent with that of spectroscopic factors for single step distorted-wave Born approximation results for transitions to low-lying states. The data also agree well with predictions of a recent phenomenological parametrization.