Two-channel high-pressure helium-3 scintillation neutron detector

We have developed a two-channel, high-pressure ³He gas scintillation detector that operates in coincidence mode. The detector consists of two 16-mm diameter avalanche photodiodes viewing a 7-mm gap between them and mounted inside a stainless steel shell with 1.5-mm thick input windows. The gap is filled with a ³He+0.5%Xe gas mixture pressurized at 35 bar. The detector rejects signals generated by radiation interacting directly with the photodiodes and works as a "wall-less" detector, sensitive to interactions occurring only in the gas. The detector shows axial and radial position sensitivity to thermal neutrons within the gap between photodiodes. The position sensitivity is observed in good agreement with computer simulations. Applications are discussed.