Study of the reaction238U (?, ??f) atE ?=480 MeV

The excitation function of the fission probability PEEx) for238U has been measured in the reaction238U(α, α′f) at 480 MeV bombarding energy. The reaction mechanism of this reaction is discussed for excitation energies belowBnf, the threshold for second chance fission, and aboveBnf up toEx=37 MeV. In comparing with results from fission induced by photons and by particle transfer reactions the (α, α′f) reaction gives too low values for the fission probabilityPf at excitation energies well aboveBnE. The role of the quasi-elastic knock-out process in this reaction is discussed.