Total cross section measurements of 16O+232Th incomplete fusion followed by fission at 140 MeV.

Abstract

Total cross sections for incomplete fusion followed by fission have been measured for the reaction [sup 16]O+[sup 232]Th at 140 MeV. In-plane and out-of-plane measurements were made of cross sections for beamlike fragments in coincidence with fission fragments. The beamlike fragments were detected with a Bragg curve spectrometer which is position sensitive in the polar direction. The beamlike particles observed in coincidence with fission fragments were He, Li, Be, B, C, N, and O. One fission fragment from each reaction was detected by one of three surface barrier detectors using time of flight for particle identification. The measured cross section due to fission following incomplete fusion is 747[plus minus]112 mb, or 42% of the total fission cross section. The strongest incomplete fusion channels were the He and C channels. The average transferred angular momentum for each incomplete fusion channel was predicted using the [ital Q][sub opt] model of Wilczynski so that the [ital K] distribution could be estimated from the rotating liquid drop model. The experimental angular distributions were fitted using the saddle point transition state model, with the transferred angular momentum [ital J] and the dealignment factor [alpha][sub 0] as free parameters. The saddle-point transition state model is foundmore » to adequately describe the observed angular correlations for fission following incomplete fusion. The fitted parameter [ital J] showed systematic deviations from the [ital Q][sub opt] model predictions, suggesting that the average impact parameter is larger than expected for heavy projectile fragments.« less