Boron-lined proportional counters with improved neutron sensitivity

Boron-lined proportional counters with higher neutron sensitivity have been developed by introducing baffle structures within the sensitive volume. the results are compared to devices developed with multiple cathode assemblies in a single enclosure. in either case, the increase in the boron-coated surface area results in higher neutron sensitivity. one of these counters has 51 annular baffles coated with natural boron with 10 mm hole for the anode wire to pass through. filled with p-10 gas at 20 cm hg, it has an overall diameter of 30 and 300 mm length. multiple dip coating method was employed for better uniformity in boron thickness. the neutron sensitivity of this counter is 1.6 cps/nv, which is 2.5 times that of a counter with standard electrode geometry. another counter was developed with three cathode assemblies (30 mm ID×300 mm) coated with 92% 10B while the third has seven assemblies coated with natural boron (16 mm ID×750 mm length). the neutron sensitivity is 10 and 5.5 cps/nv, respectively. the change in neutron sensitivity in 8 R/h gamma background was 12%, 18% and 22% in the case of the counter with baffles, 3 and 7 cathode assemblies.