By means of deuteron beams from the cyclotron, the variation of fission yield with deuteron energy is determined for uranium and thorium. In both cases, a rapid rise is found in the region from 8 to 9.5 Mev. For an energy of 9 Mev, the cross section in uranium is estimated to be 5×${10}^{-27\mathrm{}}$ ${\mathrm{cm}}^2$, and for this energy the ratio between the cross sections for uranium and thorium is found to be 0.7, supporting the theoretical expectation that we have in these fission processes to do with successive transformations.

• Received 12 August 1940

DOI:https://doi.org/10.1103/PhysRev.58.867