We are developing a detector that uses liquid scintillator loaded with 6Li for the efficient measurement of fast neutrons and their energy. The detector would have both scientific applications such as quantification of neutron energy spectra in underground science facilities, as well as security applications such as detection of contraband fissile materials. Fast neutrons deposit energy in the scintillator by nuclear recoil scattering. If the neutron loses enough energy, it can be captured by lithium and produce scintillation photons. Since background gammas produce scintillation light by electronic recoil scattering, we must reject them with high probability. With a prototype detector, we demonstrate the feasibility of a method to identify a sequence of events corresponding to nuclear recoil scattering followed by delayed neutron capture by 6Li. Our discrimination method is based on the Matusita distances between the corresponding normalized voltage pulses produced by each event and estimated template pulses corresponding to nuclear recoil events and electronic recoil events, and information about the pulse amplitude distribution corresponding to neutron capture events. We then estimate the pulse amplitude distribution corresponding to fast neutron calibration sources. (This talk is based on joint work with D. Vecchia, J. Nico and B. Fisher).
Dr. Kevin Coakley
Statistical Engineering Division/ITL