The Ranges of Fragments from High-Energy Fission of Uranium

The ranges in aluminum of several fragments from the fission of ${\mathrm{U}}^{238}$ induced by 18-Mev deuterons and by 335-Mev protons have been measured by a radiochemical method. The ranges found are of the same order of magnitude as those reported for slow-neutron-induced fission. The difference in the forward and backward recoil ranges in the deuteron (18-Mev) case is consistent with the momentum corresponding to compound nucleus formation. The ranges found in the proton (high-energy) case are shorter than those of the deuteron case, the differences being greater for the lighter fragments. These differences are explained by the change in mass of the complementary fragments due to evaporation of neutrons prior to fission in the proton case, which causes the observed fragment to receive a smaller fraction of the total kinetic energy.