Application of photofission reaction to identify high-enriched uranium by bremsstrahlung photons

Abstract

The applicability of the photofission reaction ratio (PFRR) method to identify high-enriched uranium is studied by switching the photon source from the Gaussian spectrum to a bremsstrahlung spectrum. The combination of 6 and 11 MeV Gaussian photon energy was used in previous study for applying PFRR method because the photofission cross sections between 235U and 238U at these two energies differ significantly. A parametric study was conducted with the incident electron energy 7.0 MeV and the result showed that these electrons generate similar photofission reactions as that of 6.0 MeV Gaussian photons, while 13.5 MeV electrons is found to give even better results for PFRR considering the measurement noise contributed by multiple neutron emission, (γ, 2n) reaction. Bremsstrahlung photons were injected into a 1 mm thick uranium metal target with varying uranium enrichment. The PFRR increases linearly with uranium enrichment, and is found to provide a higher sensitivity than the Gaussian photons owing to higher total photofission reactions.