A flat response 4π-neutron detector has been constructed by arranging BF3 counters in multiple concentric rings in a cylindrical paraffin moderator. The sensitivity is flat within ±5% for neutrons between 50 keV and 700 KeV. The absolute efficiency is 2.24% for 50 to 700 keV neutrons and 1.76 % for RaD–Be neutrons in the standard counter arrangement. This efficiency can be increased by mounting more BF3 counters but the relation is not linear because of the mutual interference effect in BF3 counters. The dependence of the counting efficiency on the angular distribution of neutron source was investigated by measurements of thermal neutron distributions in the moderator, and it has proved to be quite small (<1.5%) even for the T3(p, n) He3 reaction in its threshold region.
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Teranishi et al. (1964) studied this question.
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