Abstract:
In order to reduce the experimental uncertainty in the 235U resonance energy region and improve the detection efficiency for neutron total cross section measurements compared with the neutron total cross section spectrometer (NTOX), a dedicated lithium-containing scintillation detector has been considered to be developed on the Back-n beam line at the China Spallation Neutron Source (CSNS). The FAst Scintillator-based neutron Total cross section (FAST) spectrometer has been designed based on a Cs2LiLaBr6 (CLLB) scintillator considering the γ-ray flash and neutron environment on the Back-n beam line. Response of the CLLB scintillator to neutrons and γ-rays has been performed with different ratios of 6Li/7Li abundance using Geant4. The neutron-γ discrimination performance of the CLLB has been simulated considering different scintillation parameters, physical designs and light readout modes, respectively. A cubic 6Li-enriched (> 90%) CLLB scintillator, which has a thickness of 4-9 mm and a side length no less than 50 mm to cover the Φ50 mm neutron beam at the spectrometer position, has been proposed coupling to a side readout SiPM array for the construction of the FAST spectrometer. The developed simulation techniques in neutron-γ discrimination performance could provide technical support for other neutron-induced reactions measurement on the Back-n beam line.