Fission cross section and fragment angular distribution for fast neutron-induced fission of U234

Abstract

The neutron-induced fission cross section for U234 has been measured to 4 MeV neutron energy. The angular distribution of the fission fragments has been investigated between bombarding energies of 0.4 and 3.8 MeV.The shape of the cross section curve is explained in terms of the suggestion of Wheeler, that neutron inelastic scattering competes with fission to an extent dependent in part on available levels in U234 for inelastic scattering. Levels above 790 keV are known to exist, and serve to depress the fission cross section between 850 and 1050 keV neutron energy.The shape of the angular distribution curve is analysed in terms of Bohr's theory of fission through discrete levels of a collective nature thought to exist near saddle point. This analysis points to a K-band structure in the compound nucleus U235∗ near the saddle point deformation of 12+, 32−, 12−, with the ground levels of each band separated by the order of a few hundred keV.For neutron bombarding energies of 500, 850 and 1050 keV estimates are made of the extent to which each band contributes to fission.