Penning effects in Ar-Xe mixtures at atmospheric pressures: absolute W-value measurements for 5.9 keV X-rays

Absolute measurements of W-values for 5.9 keV X-rays in Ar-Xe mixtures were obtained using an experimental method recently developed, based on the collection of the primary ionization charge and the counting of the number of photons absorbed. The absolute W-values obtained for the following Ar-Xe mixtures at 825 Torr, 10%, 20% and 40% Xe, are 21.42, 21.64, 21.63 eV, respectively, showing the influence of Penning effects in the ionization yields of the mixtures. The accuracy achieved in these measurements is ±1%. The benefits and drawbacks of these mixtures as filling gases for gas proportional scintillation counters are discussed