Radiative capture, particle emission and fission in heavy nuclei

Abstract

Cross sections were determined radiochemically following bombardments of 234U, 235U, 236U, 238U and 239Pu with 5–25 MeV deuterons and 237Np with 20–50 MeV helium ions. Although fission accounts for most of the reaction cross section for all target isotopes, products from radiative capture and various spallation reactions were observed. Products corresponding to the (d, γ) reaction were observed from 238U and other uranium isotopes, with a cross section of about 1 mb. Both compound-nucleus and direct-interaction characteristics are apparent in the spallation excitation functions. The uranium (d, 2n), (d, 3n) and (d, 4n) excitation functions show a “mass” effect; that is, the heavier target isotopes have generally higher spallation-product yields. This corresponds to a neutron partial-level width ratio Γ n/( Γ n+ Γ t) increasing with N. Results from 239Pu+d and 237Np+ α, both of which form the compound system 241Am*, are consistent with the compound nucleus theory, in that (d, 2n) and (d, 3n) excitation functions correlate with ( α, 2n) and ( α, 3n) excitation functions. Direct interaction features include (d, n) stripping and a prominent ( α, αn) reaction in 237Np. Yield curves and fission cross sections have been obtained to characterize the fission reaction.