Absolute W value measurements for 5.9 keV x rays in Ne-Xe mixtures at atmospheric pressures

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 ran ge 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 exper imentally 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 measureme nts, an analytical model for the W value in binary mixtures was implemented , taking into consideration the most important energy transfer mechanisms w hich influence the ionization yield formation, namely the Penning interacti ons. The experimental and the analytical model results are compared and dis cussed. (C) 2000 American Institute of Physics. [S0021-8979(00)02420-8].