Proton-induced fission at 190 MeV of natW, 197Au, natPb and 232Th

Proton-induced fission at 190 MeV of natW, 197Au, natPb, 208Pb, and 232Th is studied by means of an innovative method based on activation analysis. The fission-product mass distribution is reconstructed from the fission-product yields, which are obtained from off-line observed γ-ray spectra. For natW, 197Au, 208Pb, and natPb the fission process results in a symmetric mass distribution. In the case of 232Th the mass yield curve is decomposed into a mixed symmetric-asymmetric contribution originating from fissioning nuclides in the neighbourhood of the target mass and a purely symmetric contribution from very neutron-deficient nuclides. The fission cross sections are extracted by integrating over the reconstructed mass distribution. The width of the mass distribution is determined as a function of target mass. The results for the fission cross sections are compared with other experimental data as well as with theoretical model calculations using the LAHET and the ALICE-91 codes. 34 refs