Yield of Photoneutrons from U235 Fission Products in Beryllium and Deuterium

The yield of photoneutrons from a sample of U235 fission products at the center of a 9‐in. diameter Be sphere was measured. Samples of U235 were exposed to neutrons in the reactor for periods of 15 min, 6 hr, and 74 hr. The photoneutrons created by the fission product gamma rays acting upon the Be nuclei were observed from 0.3 sec to about 4 weeks after the end of the exposure. Curves showing the photoneutron yield as a function of time, relative to the delayed neutron yield, are given for these exposure and observation times. The attempt was made to account for the observed yields from Be in this experiment, and the yield from D2O observed in an earlier experiment, in terms of known fission product gamma emitters.