The treaty verification field is of renewed importance as
continued nuclear weapons disarmament is prioritized nationally in
partnership with other nuclear weapons states. This interest has
led to research and development on technologies that could support
future U.S. verification missions. A technology employing pulses of
high-energy photons from an electron linear accelerator is one
technique under consideration. High energy photons are advantageous
as an interrogation source because they penetrate thick shielding
and can generate neutrons inside a measurement object.
The neutrons would then multiply when presented with an object
containing fissile material and allow for detection in a time
domain immediately after the pulse. The purpose of this work was to
develop an understanding of neutron behavior following a
high-energy photon pulse and then develop a tool set to analyze
data from this region to determine if a measurement object contains
multiplying material, the mass of that material if present, and the
moderation in the measurement object. Results indicate the tool
sets developed were able to determine multiplication was present
accurately in 3 out of 4 realistic verification objects.
Additionally the state of the moderation in each object was able to
be determined, and the mass could potentially be determined by
calibrating to representative samples.