Detector sensitivity and calibration for yield measurements in fusion neutron sources

摘要

In this study, numerical simulations have been carried out to evaluate the effect of moderator parameters (material/dimensions) for standard radio-isotopic/fission (Pu-Be and Cf-252) and fusion sources (D-D). These sources are used for calibrating thermal neutron detectors, which are often employed for determining absolute neutron yield in fusion-based sources. Simulations have been carried out using the Monte Carlo based "FLUKA" code for typical moderator materials and He-3/BF3 proportional counter based thermal neutron detectors. Results have been validated against experimentally measured values for an available radio-isotopic source. A notable difference in the detector efficiency was observed due to the source energy term. The detection efficiency ratio for Pu-Be:D-D:Cf-252 sources with the same moderator thickness (optimized for Cf-252) was found to be 1 : 1.16 +/- 0.02: 1.40 +/- 0.03. For these three types of sources, optimum acrylic (Perspex) and polypropylene moderator thicknesses have been observed to be 100,100,80 mm and 80,80,60 mm respectively with the corresponding efficiency ratio of 1 : 1.15 +/- 0.02: 1.34 +/- 0.008.