Radiochemical studies of nuclear fission

The relative yields of 19 nuclides* have been measured in the 14-MeV neutron-induced fission of natural uranium, and have been shown to fall on the familiar type of double- peaked mass-yield curve. The measurements on the two xenon isotopes ((^133)Xe and (^135)Xe) indicate the presence of fine structure in the region of the heavy peak. The mean peak-to-trough ratio is 9.1, which is of the order expected for fission at this energy, and the best fit for the mirror-points is obtained when v, the number of prompt neutrons emitted per fission, is taken to be 4. The condition that the sum of the yields of all the fission-products must be 200% enables values for the absolute yields to be determined: the value so obtained for (^99)Mo is (6.31 ± 0.23)%. A Cockcroft-Walton accelerator was used to produce the 14-MeV neutrons by the D+T reaction. At this neutron energy the cross-sections for (^235)U and (^238)U are of the same order of magnitude, so the results are essentially those for the fission of (^238)U.