Design of an ultrathin cold neutron detector

We describe the design and performance of an ultrathin (< 2 mm) cold neutron detector consisting of (LiF)-Li-6:ZnS(Ag) scintillator in which wavelength shifting fibers have been embedded to conduct scintillation photons out of the medium to a silicon photomultiplier photosensor. The counter has a neutron sensitive volume of 12 mm wide x 30 mm high x 1.4 mm deep. Twenty-four 0.5 mm diameter wavelength shifting fibers conduct the scintillation light out of the plane of the detector and are concentrated onto a 3 mm x 3 mm silicon photomultiplier. The detector is demonstrated to possess a neutron detection efficiency of 93% for 3.27 meV neutrons with a gamma ray rejection ratio on the order of 10(-7).