Development of a modular mixed-radiation directional rotating scatter mask detection system

The ability to simultaneously identify the direction of both fast neutrons, above 1 MeV, and gamma rays using a light-weight system consisting of a single 1" EJ-309 organic liquid scintillator and a plastic Spartan rotating scatter mask (RSM) is demonstrated computationally through Monte Carlo simulations and validated with experimental measurements. Two sets of directional measurements were performed with an americium–beryllium source, emitting both neutrons and gamma rays. The RSM identified the direction of the source within one 10° rotational increment in the azimuthal and polar directions based on both the neutron and gamma-ray induced signals discriminated by charge integration pulse-shape discrimination. These results indicate the RSM system is a compact, light-weight, and modular directional detection system useful for rapid identification of the type and direction of radioactive sources, a desirable feature for many nuclear security and safety applications.