Uranium Photofission Yields

The photofission yield-mass curve of natural uranium for 48-Mev x-rays was determined radiochemically. Isolation of selected peak and trough fission products at various maximum x-ray energies, 7 Mev, 10 Mev, 16 Mev, 21 Mev, 48 Mev, 100 Mev, and 300 Mev showed that the peak-to-trough ratio decreased from 300 to 4 as the maximum x-ray energy increased from 7 Mev to 300 Mev. The observed photofission yield curves may be quantitatively interpreted as the superposition of two components, a low-energy asymmetric (doublehumped) curve and a high-energy single-humped curve. The average cross section for symmetric fission for photons in the energy range 16 Mev to 300 Mev is about 7 millibarns.