Sensitivity and linearity of optical fiber-based neutron detectors using small 6Li-based scintillators

Abstract We developed optical fiber-based neutron detectors that use small pieces of  6 Li-based scintillators, namely, Eu:LiCaAlF 6 crystals and LiF/Eu:CaF 2 eutectics. Considering that these elements have high light yields (more than 10,000 photons/neutron), they can produce pulse height spectra with clear peaks even when using optical fiber light guides. To adjust the neutron sensitivity, we controlled the amount of  6 Li in the scintillator. We fabricated three different detectors using Eu:LiCaAlF 6 and LiF/Eu:CaF 2 with various amounts of  6 Li and then evaluated the neutron sensitivity of each detector. This approach confirmed that there was a linear relationship between the neutron sensitivity and amount of  6 Li, thus implying that the  6 Li mass measured by a high-precision balance could be a good metric of neutron sensitivity. We also checked the linearity of the output of the detector at relatively high neutron fluxes by using an accelerator-based neutron source. Although the detectors showed saturation behavior at high count rate, we were able to cover a relatively wide dynamic range by combining multiple detectors using different amounts of  6 Li. After correcting for the pulse height distortion and count loss due to pile-up events, we were able to confirm the linearity of the detectors up to a count rates of 100 kcps.