Spectra and angular distributions of neutrons in the 181Ta(p,n)181W and 181Ta(n,n')181Ta reactions

Experimental and theoretical investigations have been conducted to study the mechanisms of the (n,n') and (p,n) nuclear reactions. Spectra and angular distributions of neutrons in the 181Ta(n,n')181Ta and 181Ta(p,n)181W were measured using the time-of-flight technique at Esub(n)=9.1+-0.2 MeV and Esub(p)=10.2+-0.2 MeV. The (n,n') neutron spectra have been observed to be harder than the (p,n) ones. The angular distribution of the inelastically scattered neutrons has proved to possess an asymmetric component, especially in the high energy part of the spectrum. The results have been analyzed in terms of the preeouilibrium decay of compound nuclei. The equilibrium processes are, in practice, fully responsible for the (n,n') neutron spectra, whereas the preequilibrium decay accounts for about 17% of the (p,n) spectra. The angular distribution asymmetry in the (n,n') spectra is concluded to be due to the contribution of direct processes