Energy non-linearity effects in argon gaseous detectors in the region of the Ar K-absorption edge: experimental results

The response of an argon proportional counter to X-rays with energy in the range of 1.5–8 keV was investigated. The response to full-energy absorption events was found to follow different trends for X-ray energies below and above the argon K-absorption edge presenting a discontinuity at this energy. An abrupt decrease of (2.2±0.3)% in the detector amplitude at the K-edge (3.203 keV) was measured, corresponding to a region within±(70±10) eV around the edge where the X-ray energy cannot be obtained unambiguously. This discontinuity corresponds to an abrupt increase of about 0.5 eV in the argon w-value and results in a sudden increase in the energy resolution from about 17% to about 19%. The detector response to escape peak events follows a linear trend over the entire energy range, very close to the response for full-energy absorption of X-rays with energies above the K-edge.