L. Holewa, W.S. Charlton, “Angular Anisotropy of Correlated Neutrons and Application to Detection and Verification”, 52nd Annual Meeting of the Institute for Nuclear Materials Management (INMM), Palm Desert, CA, July 17-21, 2011.
It has been shown that neutrons emitted from the same Cf-252 fission event are preferentially emitted within small angles of each other and at angles around 180 degrees. In order to reach this conclusion, a Cf-252 source was placed in the center of an array of liquid scintillators and data was taken in list-mode. Previous work has focused on neutron angular distribution relative to the fission fragments. By considering the angular distribution between neutrons from the same fission event, information about preferential emission of neutrons from the same or opposite fission fragments is captured. After finding through simulation the extent to which neutron double scattering should occur in the system for a Cf-252 source, the effects of neutron double scattering for various angles were accounted for. After analysis of the data, it appears that neutrons are more likely to be emitted from the same fragment. Because different fissioning radioisotopes have different distributions of fission fragments, there should be differences in the distributions of angles between neutrons from the same fission event for different isotopes. It is this uniqueness that makes knowledge of the distribution of angles between neutrons from the same fission event useful for detection and verification of radioistopes. The specifications of a practical system that identifies radioisotopes in cargo containers were determined.