Independent fission yields for ' OYm 'lYm g1Ym+6, and 92Y and cumulative yields for "Sr, 92Sr, and 93Y in the fission of 235U and 2 3 8~' b y pr6tons of energy from 20-85 MeV have been determined. Excitation functions and charge dispersion curves have been obtained. The most probable charge, Z,, moves closer to stability, ZA, with increasing energy. The values of Z, -Z,, for the two fissioning systems are identical, unlike the situation in the heavy-mass region. The values of ZA -Z, for the light-and heavy-mass regions differ considerably, showing that the equal charge displacement hypothesis does not hold even at these moderate energies.Canadian Journal of Chemistry, 48,1924 (1970) Introduction Very few data regarding the dispersion of nuclear charge in the fission of heavy nuclei as a function of energy have been published. A series of papers from this laboratory (1-9) have dealt mainly with the dispersion in heavy-mass products (A = 129-141). The broadening of the charge dispersion curves as the bombarding energy was increased, as well as the shift of Z,, the most probable charge, towards Z,, the charge associated with stability for mass A, were clearly evident from these studies. In addition, the studies pointed out the importance of the neutronto-proton ratio of the target in determining the fission product distribution (8, 9).While the amount of information regarding charge dispersion in the heavy-mass region is beginning to mount up, very little information regarding the complementary mass region exists. Hageber et al. (10) investigated light-mass products found in the fission of 238U by 170-MeV protons. They found that the charge dispersion curves were narrower than those found in the heavy-mass region by the previous investigations and were similar to those found in the thermal neutron fission of 2 3 5~ (1 1).