Low-Energy Photofission Yields for U238

The pattern of mass number dependence of fission yield has been determined in the photofission of natural uranium (U²³⁸) by 16-Mev electrons from the linear accelerator. The effective photon energies were principally 9-14 Mev. Yields were determined by quantitative radiochemical isolation and close approximation to absolute β counting for 19 chains. The peak-to-valley ratio is 110, the highest found yet outside of low-energy neutron studies. A spike in fission yields was found near mass number 133. Yields were also obtained for a number of chains in photofission with 10-Mev electrons.