Photofission and Photoneutron Emission in Thorium and Uranium

Yield-energy relations have been determined radiochemically for the photofission and photoneutron reactions in Th²³² and U²³⁸. Excitation functions for the various reactions have been obtained by photon difference analyses of the corresponding yield functions. The photofission branching ratio for excitation energies of 8 to 11 Mev has been calculated to be approximately 0.08 for thorium and 0.2 for uranium. The relative photofissionability of thorium to uranium has been found to be about 2.3 times greater at betatron energies of 7 to 8 Mev than at 20 Mev. Also, evidence for bumps in the photofission excitation functions at about 6 Mev has been observed. Tentative explanations are presented for the relative photofissionability change and the bumps in the excitation functions. Characteristics of crude (γ, 2n) excitation functions are given for the two nuclides.