Evaluation of (n,n') scattering cross sections from 0.8 to 2.5 MeV for higher collectivebands of 232Th and 238U in ''standard'' (CN + DI) and ''unified'' (Weidenmueller S-matrix) formalisms

Angle-integrated cross sections for inelastic scattering of fast neutrons from 0.8 to 2.5 MeV on 232Th and 238U, proceeding to higher collective (quadrupole and octupole vibrational) states in the residual nuclei, have been computed in a ''standard'' and a ''unified'' approach; the resulting excitation functions have been compared with the experimental data of the Lowell group. In all calculations, a consistent set of optical potential and deformation parameters, as derived by Haouat and Lagrange of the Bruyeres group, was used. The ''standard'' formalism employed an incoherent sum of compound-nucleus (CN) and coupled-channel direct-interaction (DI) cross sections, evaluated with the programmes ''CINDY'' and ''KARJUP'' (Karlsruhe version of ''JUPITOR'') respectively. Provision was made for the effect of level-width fluctuations and for competing neutron exit channels. The results in general compared well with the measured values, but in several instances disagreed significantly with the ENDF/B-V evaluated data. Still better agreement ensued from the use of the ''unified'' formalism based upon energy-averaged second moments of transformed S-matrix elements in a statistical approach developed by Weidenmueller et al. and embodied within a new fluctuation programme 'NANCY'' with coupled channels and competing channels to generate and manipulate the grand ensemble of S-matric elements. With only the coupling strengths as adjustable parameters, this offers a promising, reliable means of analysis well suited to the interpretation of neutron scattering on deformed actinide nuclei