Operational properties of fine powder aerosol as radiation detection medium in gaseous proportional counters

摘要

Due to its exceptional properties, He-3 proportional counters are the golden standard for neutron detection, particularly in homeland security applications where large area detectors are deployed. However, in recent years He-3 has become severely scarce, which led to a tremendous price increase and acquisition restrictions of this material. Motivated by this, the development of He-3-free solutions became a priority. In a previous work, we have established a novel concept for neutron detection: a proportional counter with boron carbide (B4C) fine powder suspended in the proportional gas, forming a neutron sensitive aerosol that relies on the B-10 neutron capture reaction. Computer simulations and prototype exposure to a cold neutron beam yielded favorable results, validating the detection concept, which may also be applied to hard x-ray and gamma ray detection by using fine particles made of a heavy element, such as Bi or Au. In this work we study the effect of the presence of B4C microparticles in the charge gain and energy resolution of a proportional counter filled with Ar-CH4 (90%-10%), by irradiation with x-rays from a Fe-55 source. For the same applied voltage, an average gain loss by a factor of 36% and energy resolution (FWHM) increase by 15% (absolute value) was observed with the inclusion of B-4 C microparticles. Intrinsic energy resolution was calculated, obtaining 15% for pure P10 operation and 32% in the presence of the microparticles. While the gain drop is recoverable by increasing anode voltage, energy resolution degradation may be a drawback in low energy applications, were energy resolution is favored over detection efficiency.