Short Pulse Active Interrogation System to find Fissile Materials

The passive gamma and neutron systems work reasonably well for unshielded fissile material, or Special Nuclear Material (SNM), that have a strong gamma or neutron signal. However, many SNM materials do not emit a strong gamma or neutron signal even if unshielded, and are particularly problematic to detect with passive systems, if the fissile material is shielded. The detection sensitivity of these traditional systems can be somewhat improved by using very long count times and large detectors, and/or large numbers of detectors. However, such options may not be as practical as desired in the field. Active interrogation methods have been used for detecting illicit, shielded SNM transport. However, the traditional active systems do not have the detection sensitivity for field operation and pose a number of other logistics problems. Many configurations use neutron generators that are too large, too powerful, too expensive, and/or create too much exposure for the personnel operating them to be practical for rapid, portable detection capability. These weaknesses can be overcome by using a neutron source that emits very short and intense neutron pulses. Short intense neutron pulses cause fissile materials to emit strong characteristics radiation for a brief period of time that is easy to detect at a distance. The short period of time the radiation pulses are present also makes our system safe to use at a minimal stand-off distance. The system (neutron source, detector, shielding, power, etc.) is portable and expected to weigh approximately 30 lbs. when completely industrialized. As an active system, it can detect both uranium and plutonium in shielded and unshielded scenarios. The system is very fast with the neutron generator being on for a fraction of a second per measurement. The analysis results are available in a minute or two. In this paper, we will present the status of this joint research and development project between Sandia National Laboratories, Los Alamos National Laboratory, and AQUILA, and some of the results obtained with test scenarios so far.