6Li foil scintillation sandwich thermal neutron detector

Increasing needs for neutron detection and limited supply of 3He have led to the need for replacement neutron detection technology. This paper presents the design and initial results for a neutron detector (6Li foil scintillator sandwich) that uses lithium metal foil to detect thermal neutrons. The reaction products, primarily triton, deposit most of their energy in thin scintillator films and create light pulses. Gamma rays can deposit only a small amount of energy in the thin films and so produce only very small light pulses. Lithium is preferable to boron in this application because triton escapes from lithium more easily than does the alpha particle from boron, allowing the use of thicker films and hence greater efficiency. In addition, triton has a higher light output in the scintillator than the boron alpha particle. Lithium metal is preferable to a lithium compound, such as lithium fluoride, because the number of tritons that escape from the metal is greater for the same amount of lithium. Monte Carlo simulations show that good efficiency values can be achieved with reasonably sized detectors, values that are greater than that of comparable 3He systems for portal monitors. In addition, simulations of a neutron coincidence counting concept show high counting efficiency and short die-away time (16 μs), which imply better performance than that of the high-level neutron coincidence counter (HLNCC)-II. Initial experimental measurements on a prototype detector using alpha particles (having similar light output to the expected tritons) show good light collection and transport properties.