Photo-Fission of Uranium and Thorium

Fission of uranium and thorium has been observed to be produced by irradiation with γ-rays. The cross section for this photo-fission produced by the γ-ray from fluorine bombarded with protons has been measured and found to be: ${{{σ}}U,=3.5±{}1.0×{}{10}^{{-}27}{cm}²,}{{{σ}}Th,=1.7±{}0.5×{}{10}^{{-}27}{cm}².}$