Fission of Pb in the He-4-induced reactions at 0.65-12.7 GeV

The fission processes from the interactions of 0.65, 1.74, 5.1, 8.8 and 12. 7 GeV He-4 with Pb have been analyzed using the polycarbonate track detecto r Makrofol in the form of a sandwich. The decay channels ending with one, t wo, or more (three, four) fragments were detected. We analyzed events in wh ich only two heavy fragments (Z > 20) are detected, irrespective of the exi stence of coincident intermediate mass fragments (8 less than or equal to Z less than or equal to 20). Using the correlation between the common observ ables which characterize fission events, we identified events originated fr om thermal (soft) fission and more violent processes. Cross sections, angul ar distributions and excitation energy have been determined for two fission mechanisms, and their variation as a function of the incident energy has b een investigated. (C) 2001 Elsevier Science Ltd. All rights reserved.