A neutron imaging detector from bundled lithium silicate glass fibers

Scientific applications of neutrons ranging from protein crystallography to non-destructive inspections require sensitive neutron detectors having a high spatial resolution that are able to discriminate against unwanted gamma ray events. To address this problem, 2 and 5 mm thick prototype detectors were fabricated as a bundled array of 120 ¿m diameter cerium activated lithium silicate glass fibers cast in a low-index epoxy resin that helps improve light transmission. Performance of this detector was determined from measured pulse height spectra of isotopic gamma-ray sources and a moderated 10 Ci Am/Li neutron source. Imaging experiments were also performed in a polychromatic neutron beam using an electron-multiplying CCD. 1.5 MeV of electron equivalent light output was determined from pulse height spectra of the bulk glass which is comparable to commercial glasses. Light output for neutron events in the 2 mm thick bundled array was about 50% lower than the bulk sample but gamma rays were similarly affected. The 5 mm thick sample exhibited poorer light output with some asymmetry in the neutron capture peak that is associated with light losses in the fiber bundle. The neutron detection efficiency of the 2 and 5 mm thick detectors was 68 and 98%, respectively. Both detectors successfully imaged patterns fashioned from cadmium neutron absorbers and indicate a spatial resolution of approximately 250 ¿m. These data demonstrate the feasibility of this approach and further studies are underway to improve overall light output and spatial resolution.