Multi-layer plastic scintillation detector for intermediate- and high-energy neutrons with $n$-$\gamma$ discrimination capability

A new type of neutron detector, named Stack Structure Solid organic Scintillator (S${}^4$), consisting of multi-layer plastic scintillators with capability to suppress low-energy $\gamma$ rays under high-counting rate has been constructed and tested. To achieve $n$-$\gamma$ discrimination, we exploit the difference in the ranges of the secondary charged particles produced by the interactions of neutrons and $\gamma$ rays in the scintillator material. The thickness of a plastic scintillator layer was determined based on the results of Monte Carlo simulations using the Geant4 toolkit. With layer thicknesses of 5 mm, we have achieved a good separation between neutrons and $\gamma$ rays at 5 MeV${}_{\mathrm{e}\mathrm{e}}$ threshold setting. We have also determined the detection efficiencies using monoenergetic neutrons at two energies produced by the $d$+$d\to n$+${}^3$He reaction. The results agree well with the Geant4 simulations implementing the Li$\grave{\mathrm{e}}$ge Intranuclear Cascade hadronic model (INCL++) and the high-precision model of low-energy neutron interactions (NeutronHP).