An experimental study of the -values and Fano factors for Ar-Xe gaseous mixtures at atmospheric pressures for 5.895 keV X-rays was carried out with two experimental set-ups based on gas proportional scintillation counter techniques. For the 100% Xe, Ar-40% Xe, Ar-20% Xe and Ar-10% Xe mixtures at 800 Torr the measured -values were 21.61 eV, 21.63 eV, 21.64 eV and 21.42 eV, respectively, within an accuracy of 0.21 eV. For the same mixtures the Fano factors were 0.254, 0.258, 0.250 and 0.256, respectively, within an accuracy of about 0.004. For lower Xe concentrations of 5%, 3% and 1% the Fano factors were 0.24, 0.23 and 0.22, respectively. These experimental results are compared with those available in the literature.

A technique was developed for the absolute measurement of the W-value (the mean energy for the production of an electron-ion pair) for low-energy X-rays in a wide range of gases at atmospheric pressures, with a standard uncertainty better than 1%. This technique is based on the absolute measurement of the primary ionization charge produced by X-ray photons from a constant intensity monoenergetic X-ray source, e.g. a long lifetime radioactive source. The ionization charge is calibrated by the number of X-ray photons absorbed in the gas, counted with a photon detector. For this purpose, a hybrid detector system was tested and its use in W-value measurements was investigated. The technique was applied to pure xenon at 825 Torr with 5.9 keV X-rays and a W-value of 21.61> \ eV was obtained for a 68% con"dence level. The required corrections and the di!erent factors contributing to the accuracy of the results are discussed. The advantages and limitations of this technique are explored and future developments are discussed.

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Experimental absolute W values are presented in Ne–Xe mixtures for 5.9 keV x rays with a standard uncertainty lower than 1%. The measured W values range from 23.9 to 22.1 eV for mixtures in the 10% Xe–90% Ne to 80% Xe–20% Ne concentration range, respectively. The measurements were performed using a recent technique based on the measurement of the primary ionization charge produced by a certain number of x-ray photons absorbed in the gas. We experimentally investigated the dependence of the W value in Ne–Xe mixtures with the Ne or Xe concentration, showing the influence of Penning effects. The discrepancies between our W values and data obtained with other methods for W-value determination are discussed. Along with the experimental measurements, an analytical model for the W value in binary mixtures was implemented, taking into consideration the most important energy transfer mechanisms which influence the ionization yield formation, namely the Penning interactions. The experimental and the analytical model results are compared and discussed.