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Fission mass yields from the compound nucleus U 236 have been measured for 19-29-MeV alpha-particleinduced fission of Th 232 and 9-18-MeV neutron-induced fission of U 235 with particular attention to the yields of symmetric fission. Decreases in the symmetric fission yield are seen at the 25-MeV onset of (a,2nf) fission and the corresponding 14-MeV onset of (n,2n'f) fission. Above these energies, the symmetric fission yields are approximately 13% greater for alpha-particle-induced fission than for neutron-induced fission at the same excitation energies. This increase is partially explained by the fission-chance ratio of higher energy fissions relative to fissions of the most de-excited nuclei being greater for alpha particles than for neutrons. Angular-momentum-dependent cross sections for these fissions were calculated, and the use of reasonable values of level densities with a rigid moment of inertia resulted in a calculated effect of about one-half this observed effect. The difference remaining is possibly explained by fissions following direct interactions. Mass yields of 9.1-18.1-MeV neutron-induced fission of Th 232 and 4.7-18.1-MeV neutron-induced fission of U 238 were also measured.

Angular distributions of fragment activities from neutron-induced fission of U 233 and Pu 239 have been measured and show in detail the energy dependence of these distributions. The theoretically expected difference in low-energy anisotropy for these nuclides, which have similar fission thresholds but significantly different target spins, was not observed. A statistical model of fission anisotropy is applied to the data from the low-spin target Pu 239 to determine the energy dependence of KQ, the standard deviation of the distribution in the angular-momentum projection on the nuclear symmetry axis. The anisotropics indicate an increase of KQ with energy in excess of the fission barrier, with K$ values for even-even fissioning nuclei at excitation energies approximately 1 Mev higher than those for odd-^4 nuclei. The effective moment of inertia about the symmetry axis, similarly obtained from application of a statistical model to the data, is found to be ^0.

The ionization vs energy relation has been measured for fission fragments stopped in nitrogen, neon, argon, and argon plus CO2 (3%). The fission fragments were obtained from thermal-neutron-induced fission of U 235 . Results of these measurements are consistent with the nuclear recoil effect and show that the ionization produced is not simply proportional to the fragment energy.

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