Neutron spectra in reactions with cascade evaporation of particles and the nuclear level density

We present the results from calculations of the neutron spectra in the reactions 181Ta(α, xn), 181Ta(p, xn), and 238U(n, xn) at incident energies E/sub α/ = 45 MeV for α particles, E/sub p/ = 22 MeV for protons, and E/sub n/ = 14 MeV for neutrons, respectively. The calculations are carried out in the particle cascade evaporation model taking into account the angular momentum and the competition between protons, α particles, and photons at each stage of the evaporation cascade. The accuracy of the simple approximations used to describe the particle spectra in these processes is analyzed. It is noted that decay via the radiation channel becomes dominant in the final stages of the evaporation cascade. It is shown that the use of simplified approaches can lead to erroneous values of the level density parameters, depending on the region where they are determined and on the contribution of the angular momenta participating in the reaction. The results are compared to the experimental data