Preequilibrium neutron emission from O + Al at 7.5 MeV/nucleon and 8.8 MeV/nucleon

The thick target neutron yield from a ${}^{16}{\mathrm{O}}^{6+}$ beam on a thick $^{27}\mathrm{Al}$ target at 120- and 142-MeV (7.5- and 8.8-MeV/nucleon, respectively) incident energies is presented and compared with theoretical calculations. The theoretical estimates for the yield of a high-energy neutron was obtained using a preequilibrium (PEQ) heavy-ion reaction model (hion), whereas that for the low-energy part was obtained using the standard evaporation models pace4 and empire 3.2. In the present data a significant PEQ contribution, $\ensuremath{\sim}2%$ to 3% of the evaporation contribution, is observed even at projectile energies below 10 MeV/nucleon. The measured energy spectrum of neutrons for $Eg20\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ (the predominant PEQ region) is in good agreement with the PEQ model code hion.