Characterization of $^{10}$B Lined Proportional Counters and Moderator Design*

An SA-B1-0824-101 $^{10}$B lined neutron counter from G.E. Reuter-Stokes was characterized and moderator was designed and tested for detecting fast neutrons. The neutron counters are single-wire cylindrical proportional counters with a Boron tube lining enriched to 92\% $^{10}$B and are filled with Ar gas. Thermalized neutrons interact with the Boron layer through the $^{10}$B(n,$\alpha$)$^{7}$Li reaction, and the reaction products deposit energy in the Ar gas. The deposited energy pulse is amplified by a proportional counter bias potential of 800 V, resulting in a detectable signal. The detector consisting of four tubes was simulated in Geant4 and the dependence of the detector efficiency on the thickness of the $^{10}$B layer was determined. The detector efficiency was measured experimentally with a $^{241}$AmBe source of known neutron activity. A modular design for the high density polyethylene moderator allows the detector to be composed of four proportional counters for optimum efficiency, or be split into two separate detectors for ($\gamma$, n) polarization measurements.