Production of Heavy Nuclides in 440-MeV Proton Fission of Uranium

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Abstract
The recoil properties of 20 nuclides of mass about 140 formed in the 440-MeV proton fission of uranium were determined. The average kinetic energy, cascade deposition energy, and angular anisotropy for each fission product were calculated from the recoil results. The kinetic energy and excitation energy of the primary fragments leading to these fission products, and the total kinetic energy and excitation energy of the primary-fragment pair, were calculated from those of the fission products. The primary-fragment results indicate a dependence of the deformation of the fissioning nucleus on its excitation energy, and explain the trends observed in the kinetic energy and cascade deposition energy of the fission products. The theory used to explain the angular distribution of fission products produced by low-energy (<50 MeV) bombarding projectiles was applied successfully in the explanation of the angular anisotropies observed at 440 MeV. The charge dispersion of the fission products of mass 139 was determined, and was fitted by a Gaussian curve with a full width at half-maximum of 3.2 charge units. The primary fragments leading to isobaric fission products differ from each other by two mass units per charge unit, and are more constant in neutron-to-proton ratio than the fission products.