Active interrogation of shielded fissionable material using a pulsed bremsstrahlung source

Passive detection of shielded special nuclear material (SNM) is a difficult problem, particularly at standoff distances. The SuperMISTI coded imaging and detection system was used with pulsed bremsstrahlung at the Hermes-III facility at Sandia National Laboratories to study active interrogation techniques as an alternative method of detecting shielded SNM. A combination of high- and low-Z shielding of varying thicknesses was used. Delayed gamma and neutron signatures were measured using NaI and ³He detectors, and signal-to-background ratios were calculated. Experimental setup details and results will be presented.