ELECTROMAGNETIC AND NUCLEAR-FISSION OF U-238 IN THE REACTION OF 100-A.MEV, 500-A.MEV, AND 1000-A.MEV PB-208 WITH U-238

The folding- and azimuthal-angle and velocity distributions for the U- 238 fission fragments have been measured in reactions with 100, 500, a nd 1000 A.MeV Pb-208. These distributions were used to decompose the f ission cross section into its electromagnetic and nuclear components. The fraction of electromagnetic fission was found to be 0.16+/-0.07, 0 .48+/-0.08, and 0.60+/-0.04, respectively. The electromagnetic fission cross section as a function of the Pb-208 nucleus energy is compared with theoretical predictions. The measured fission cross section from nuclear reactions (approximate to 1.5 b) is approximately constant bet ween 100 and 1000 A.MeV.