Modular next generation fast-neutron detector for portalmonitoring

Nuclear nonproliferation is of critical importance for global security. Dangerous fissile materials including highly enriched uranium and weapons-grade plutonium are especially important to detect. Active interrogation techniques may result in much better sensitivity but are difficult with conventional portal monitors that rely on detecting thermal neutrons. Also, most conventional portal monitoring systems rely on 3 He, which has a finite and continually decreasing supply. By designing a highly segmented array of organic scintillators, we posit that we can accurately and quickly identify fissile materials, including weapons-grade plutonium and highly enriched uranium, being smuggled. We propose a new design for a fast-neutron detector that overcomes the limitations of the current generation of portal monitors. MCNP6 simulations have been performed in conjunction with the UMPBT statistical model to determine the sensitivity limitations of the proposed detector. Results suggest that the proposed detector may be 10 times more efficient than current-generation thermal neutron detectors and may be able to positively identify a 81 mg 235 U source in as little as 192 seconds utilizing active interrogation techniques.