Measurement and analysis of neutron spectra from a thick Ta target bombarded by7.2AMeV16Oions

Abstract

Energy distributions of emitted neutrons were measured for $7.2A\mathrm{MeV}$ ${}^{16}\mathrm{O}$ ions incident on a thick ${}^{181}\mathrm{Ta}$ target. Measurements were done at $0\ifmmode^\circ\else\textdegree\fi{},$ $30\ifmmode^\circ\else\textdegree\fi{},$ and $60\ifmmode^\circ\else\textdegree\fi{}$ with respect to the projectile direction using the proton recoil scintillation technique. Comparison with calculated results from equilibrium and preequilibrium (PEQ) nuclear reaction models suggests the emission of PEQ neutrons at this projectile energy. This model also implies that PEQ emissions take place only before any scattering between target and projectile nucleons start. The paper discusses the method for selecting the initial exciton configuration with the help of measured data, and the stage at which the PEQ process is completed.