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

摘要

We developed optical fiber-based neutron detectors that use small pieces of ~6Li-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 photonseutron), 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 ~6Li in the scintillator. We fabricated three different detectors using Eu:LiCaAlF~6 and LiF/Eu:CaF_2 with various amounts of ~6Li 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 ~6Li, thus implying that the ~6Li 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 ~6Li. 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.