Yield of Photoneutrons from U235 Fission Products in Heavy Water

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U.S. Atomic Energy Commission, 1946 - Fission products - 20 pages
The half lives and yields of the photoneutrons created in heavy water by U(235) fission product gamma rays have been measured. Seven half lives have been found 2.5 sec, 41.2 sec, 2.38 min, 7.7 min, 27.3 min, 1.65 hr, 4.37 hr, and 53 hr. The shortest and longest one of these are least reliable. Eighty five percent of the photoneutrons appear in the two shortest half lives, the 2.5 sec component being three times as intense as the 41 sec component. The total saturated activity of the photoneutrons for an infinite amount of heavy water was calculated from measurements with a 10(exp n) radius sphere to be about 16.5% of the saturated delayed neutron activity. The data indicate that there must be of the order of two gamma rays of energy above 2.17Mev emitted per fission by fission products with half lives longer than one sec.

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