Identification of Lithium Isotopes Using Time-Tagged Neutron Scattering

Lithium deuteride and hydride salts enriched in the 6Li isotopes are integral components of thermonuclear weapons. Since 1963, the United States has not had an operational facility for enriching lithium. It is therefore important to ensure that existing stocks of this material are properly identified and stored for future contingencies. This work shows that time-tagged neutron scattering can be used to measure the hydrogen isotope and the lithium enrichment of the materials in storage containers nonintrusively. Performing verification measurements in this manner is likely to be cheaper and less hazardous than opening the containers for a destructive assay. Using a deuterium-tritium (D-T) generator to produce time-tagged and electronically collimated 14 MeV neutrons, the time of flight to travel to an object and then scatter into a detector is a particularly useful signature for determining the light isotope composition in an object. Another useful signature produced by time-tagged neutron scattering is the characteristic gamma rays produced by inelastic scattering reactions. Using Monte Carlo simulations, this conceptual study will show that the time of flight is an excellent method for measuring both the hydrogen isotopic abundances, and that both signatures can be used to measure the lithium enrichment.