COMPARISON OF THE KINETIC ENERGIES OF FISSION FRAGMENTS OF U-238 PRODUCED BY 3- AND 15-MEV NEUTRONS

An attempt was made to determine whether the kinetic energy of fission fragments is dependent on the level of excitation of the fissioning nueleus. Neutrons with energies of 3 and 15 Mev were generated by the D(d,n)He/sup 3/ and T(d,n)He/sup 4/ reactions, respeetlvely. A 45o microgram/cm/sup 2/ natural U target was used, determining the energy of the fission fragments with a double ionization chamber and recording simultaneously the pulse amplitudes resulting from the fragment pairs. For each mass ratio the energy distribution and the highest probable kinetic energy of the 2 fragments were determined. It was found that for mass ratios of 1.25 to 1.65 the highest energy is obtained with 3-Mev neutrons. The relatively small differences indicate that the kinetic energy is obtained at the expense of the Coulomb repulsion forces as the distance between charge centers does not change with the excitation level. The data do not agree with the results of the calorimetric study of P. Stevenson et al. (Phys. Rev., 117: 186(1960)). (TTT)