Delayed gamma-ray spectroscopy for nuclear material analysis, 2; Design of a practical system with DD neutron generator

Rossi, F. ; Rodriguez, D. ; Takahashi, Tone; Seya, Michio; Koizumi, Mitsuo 

To safeguard nuclear material at facilities like reprocessing plants, new active-interrogation nondestructive assay techniques are needed. We are developing a new delayed gamma-ray spectroscopy (DGS) system to be used together with current verification methods, like hybrid k edge/X ray densitometry, to quantify the fissile composition in high-radioactivity nuclear material samples. DGs quantifies the composition by comparing the ratios of gamma-ray peaks with energy above 3 MeV from short-lived fission products produced during irradiation of the sample by a high-rate external neutron source. Utilizing thermal neutrons allows more fission events to be produced by fissile nuclides (U-235, Pu-239 and Pu-241) to overcome the shielding required to reduce the low energy passive background from the long-lived fission products. While the dominant external sources proposed for this application are DT neutron generators, we are designing a compact system with the use of a DD neutron generator that produces neutrons with starting energies that are easier to moderate and retain. The main differences between the two systems will be presented here along with the description of the current design of our system. This technological research and development was supported by the Japanese government (MEXT). This work was performed under the MEXT subsidy to strengthen nuclear security related activities.