Counter-radiation, atmospheric

The choice of source material is a difficult problem. Hard radiation is required (to achieve high penetration through the electrolyte solution) but hard X-ray photons are difficult to detect in a proportional counter, requiring the use of high pressure and expensive xenon gas. This is acceptable with a sealed detector but it means that the construction materials must be carefully chosen to be clean, or the detector gas will soon become contaminated. Softer radiation is much easier to detect, and, for example, for Cu Ka photons reasonable detection efficiencies are obtained with Ar at atmospheric pressure. All the results reported here were obtained with a Cu Ka source, which limits the solution pathlength to a few tenths of a millimeter. This clearly makes cell design critical. For Mo Ka radiation, considerably thicker solution layers would be acceptable. 

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