Proportional counters as low energy photon detectors

We have investigated the response of an argon-methane proportional counter to monochromatic X-rays in the range 99-277 eV. The apparent nonlinearities in mean pulse height as a function of photon energy and the detailed shape of the pulse height distribution for each energy can be predicted quite precisely using the extensive atomic data available for argon. Based on this understanding, we propose a semiempirical system for using a limited amount of calibration data to predict the full response of counters employing less well characterized gasses. Such accurate models of proportional counter response are required to maximize the spectral information that can be derived from observed pulse height distributions. (orig.)