Evaluation of prompt fission gamma rays for use in simulating nuclear safeguard measurements

Nondestructive assay methods that rely on measurement of correlated gamma rays from ®ssion have been proposed as a means to determine the mass of ®ssile materials. Sensitivity studies for such measurements will require knowledge of the multiplicity of prompt gamma rays from ®ssion; however, a very limited number of multiplicity distributions have been measured. A method is proposed to estimate the average number of gamma rays from any ®ssion process by using the correlation of neutron and gamma emission in ®ssion. Using this method, models for the total prompt gamma ray energy from ®ssion adequately reproduce the measured value for thermal neutron induced ®ssion of 233U. Likewise, the average energy of prompt gamma rays from ®ssion has been adequately estimated using a simple linear model. Additionally, a method to estimate the multiplicity distribution of prompt gamma rays from ®ssion is proposed based on a measured distribution for 252Cf. These methods are only approximate at best and should only be used for sensitivity studies. Measurements of the multiplicity distribution of prompt gamma rays from ®ssion should be performed to deter- mine the adequacy of the models proposed in this article. Published by Elsevier Science Ltd.