Direct-Interaction Effects in Medium-Energy Fission of Uranium

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Abstract
The fraction of the fission events which occur after direct interactions rather than after compound nucleus formation has been determined in a number of bombardments of uranium. The projectiles used were 10.5-Mev protons, 21-Mev deuterons, and 42-Mev alpha particles. The fraction of post-direct-interaction fissions was obtained from measurements of the angular correlation of coincident pairs of fission fragments which emerged at approximately 90° to the incident particle beam. The results indicate that (2±3)% of fission events in 42-Mev alpha particle bombardments and (5±5)% in 21-Mev deuteron bombardments follow some type of direct interaction.