Photofission ofU238Induced by 17.5-MeV Monoenergetic Gamma Rays

Fission yields were determined radiochemically using low-level counting techniques for fourteen mass chains from photofission of ${\mathrm{U}}^{238}$ induced by 17.5-MeV monoenergetic gamma rays from the ${\mathrm{Li}}^7(p,\gamma )2\mathrm{}{\mathrm{He}}^4$ reaction. Fine structure in the mass-yield curve in the region $A=131\mathrm{}-135$ was observed, with the peak occurring at $A=132\mathrm{}$. A striking similarity was noted between the photofission mass-yield curve in the mass-130-136 region and the relative abundance pattern of the excess fission xenon recently observed in certain meteorites.