A multiwire proportional counter technique for standardization of low-energy photon sources

Abstract

A wall-less multiwire anticoincidence proportional counter (MWPC) technique is presented which enables emission rates of photon sources below 50 keV to be intercalibrated to better than ±3.5% (2 σ statistical, plus linear addition of systematic, error) without knowledge of counting gas cross sections. The difficulties associated with the extension of this method to an absolute standardization technique are discussed. The source is placed external to the Be window of a large volume MWPC, the detection efficiency of which can be varied by changing the gas pressure. For a MWPC, a maximum occurs in the gas counting efficiency with variation of the pressure. If the counting rates of low-energy photons from different sources are maximized by changing the gas pressure from one source to another, then the detection efficiency of the center counter is the same, and its absolute value is dependent only on the ratio of the two geometrical distances defining the center- and ring counters. In this way several different sources may be standardized accurately against one or more primary X-ray standards.