Li Foil Thermal Neutron Detector

In this paper we report on the design of a multilayer thermal neutron detector based on Li reactive foil and thin-film plastic scintillators.. The design configuration provides for a double-sided readout of the lithium foil, resulting in a doubling of the efficiency relative to a classical reactive film detector and generating a pulse height distribution with a valley between neutron and gamma signals similar to 3He tubes. The tens-of-microns thickness of the plastic scintillator limits the energy deposited by gamma rays, which provides the necessary neutron/gamma discrimination. We used MCNPX to model a multilayer lithium foil detector design and compared it with the standard high-level neutron coincidence counter HLNCC-II (18 3He tubes operated at 4 atm). The preliminary results of the 6Li configuration show higher efficiency and one-third of the die-away time. These properties, combined with the very short dead time of the plastic scintillator, offer the potential of a very-high-performance detector.