The statistical distribution of the number of prompt gamma rays emitted in the fission of uranium-235.

摘要

When a neutron beam bombards a 235U sample and the fission reaction occurs with emission of fission fragments neutrons and gamma rays. A four-detector array is used to detect the prompt gamma rays in coincidence with nanosecond time resolution. The coincidence module developed and built in our laboratory uses 3-GHz slew rate transistors to acquire the coincidence data. Barium fluoride scintillation crystals and Hamamatsu photomultiplier tubes comprise the fast gamma-ray detectors. If we assume that the number of prompt gamma rays is a random variable then it can be considered the first term of a moment expansion of either a Poisson distribution or a sharp distribution. The higher order moments are determined by measuring the numbers of double, triple and quadruple coincidences. Further higher order moments can be obtained by using more detectors. From the analysis of the two distributions, the number of prompt gamma rays was determined. The average number of the prompt gamma rays is 7.77.