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GEANT4 Monte Carlo simulation tool was used to model a prototype 14 MeV neutron fiber detector under development at the Sandia National Laboratories (SNL). Detail geometric design features of the prototype fiber detector were implemented in the modeling to assess directionality and performance of the detector. BCF-12, plastic fiber material, produced by Saint-Gobain, was used in the prototype development. The fiber consists of a core scintillating material of polystyrene with 0.48 mm × 0.48 mm dimension and an acrylic outer cladding of 0.02 mm thickness. A total of 64 square fibers, each with a cross-sectional area of 0.25 mm 2 and length of 100 mm positioned parallel with a fiber pitch of 2.3 mm, were used in the tracking of 14-MeV neutron induced recoil proton (n-p) events. Neutron induced recoil proton events, resulting energy deposition in two collinear fibers, were considered in reconstructing a two dimensional (2D) direction of incident neutrons. Energy resolution of the fiber detector was also considered to account uncertainty in direction reconstruction. Reconstructed direction has a limiting angular resolution of 3d ue to fiber dimension. Energy resolution of the fiber, which was estimated to be 10% at 14 MeV proton energy, resulted in further broadening of the reconstructed direction and the simulated angular resolution was 20˚. These values were determined when incident neutron beam makes an angle of 45 degree relative to the front surface of the detector. Comparable values were obtained at other angles of incidence. Results from the present simulation have demonstrated promising directionality of the scintillating fiber detector under development.

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