A Scintillation Detector for the Measurement of Thermal Neutrons in Subcritical Assembly

With the view toward measuring neutron flux in a subcritical assembly, a detector consisting of a γ-ray insensitive scintillator based on 6LiF, ZnS(Ag) and polyethylene combined with a long light guide has been developed. A description is given of performance obtained with this detector, in comparison with BF3 counters and glass scintillator. It has proved that the newly deviced detector with 16 mm diam. × 0.42 mm thick scintillator is almost comparable in detection efficiency to a BF3 gas filled counter (40 cmHg, 96% 10B) having the effective dimensions of 16 mmdiam.×70 mm. The fine spatial resolution obtained with the detector is demonstrated by actual measurements of neutron flux distribution in the assembly.