Preequilibrium neutron emission in the reactions 90Zr, 208Pb(p,xn) with 80 MeV projectiles.

Abstract

The reactions $^{90}\mathrm{Zr}$, $^{208}(\mathit{p}$,xn) have been measured with 80.5 MeV protons in the neutron continuum ${E}_{n}$>20 MeV and the angular range 0\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}\ensuremath{\theta}\ensuremath{\le}145\ifmmode^\circ\else\textdegree\fi{}. Whereas the angle-integrated spectrum can be explained by semiclassical preequilibrium models, this nucleon-nucleon scattering approach fails at far backward angles. In contrast, the quantum statistical multistep calculations give good agreement. They are indicative of a decrease of the effective nucleon-nucleon interaction with increasing nucleon energy.