Abstract
A high-efficiency neutron counter has been built, consisting of 40 1.5-m 10BF 3 proportional counters imbedded in a graphite cylinder 1.83 m long and 1.53 m in dia. The system is surrounded by 0.6 m of water on all sides to act as a reflector and shield, and is operated with the neutron sources placed at the center. The basic design was dictated by the requirements for an energy independent, high neutron efficiency for weak neutron sources in the presence of high γ-ray activity. This ruled out moderators having a high neutron absorption cross section or low photo-neutron threshold. The configuration design was based upon diffusion studies and extensive Monte-Carlo calculations. The resulting configuration consisted of a hexagonal matrix of individual counters forming five rings parallel to the cylindrical axis. The measured total efficiency was found to be about 60% and nearly independent of energy, although the relative efficiency among rings was energy dependent.
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