Next generation neutron multiplicity counters

When evaluating an unknown configuration of special nuclear material (SNM), it is essential to determine criticality safety risks and characterize the material. A neutron multiplicity counter records not only neutron detections but also their timing, which helps infer SNM size and configuration by analyzing spontaneous fission and neutron multiplication (MM, equivalent to keffkeff​). Current state-of-the-art detectors, such as the MC-15, rely on He-3 tubes in high-density polyethylene (HDPE) and are only sensitive to thermal neutrons. In contrast, the MC-Li, a Li-loaded plastic multiplicity counter, introduces key advantages: it is lightweight (under 25 lbs.), uses low-power silicon photomultipliers (SiPMs) instead of photomultiplier tubes (PMTs), and detects thermal and fast neutrons as well as gamma rays. Moreover, it can time-correlate these particles with specific fission events, such as neutron capture, neutron scattering, and direct gamma-ray emissions, improving SNM assessment capabilities.