The photodisintegration of ${\mathrm{U}}^{235}$ has been studied, using nearly monochromatic photons obtained from the annihilation in flight of fast positrons. The partial cross sections $\sigma (\gamma ,F)$, $\sigma (\gamma ,n)$, and $\sigma (\gamma ,2n)$ were determined. Integrated cross sections for these reactions were found to be 1.07, 1.00, and 1.49 MeV·b, respectively. Structure in the giant resonance of the compound-nucleus-formation cross section was observed and from this a quadrupole moment of 12.8±1.3 b was found. An energy dependence in the quantity $\frac{{\Gamma }_n}{{\Gamma }_f}$ was observed.

• Received 27 September 1963

DOI:https://doi.org/10.1103/PhysRev.133.B676