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

Abstract

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.

Monte Carlo simulation study of the Fano factor, w value, and energy resolution for the absorption of soft x rays in xenon–neon gas mixtures

“…Moreover, this explanation is consistent with the fact that recent absolute w measurements for 5.9 keV x rays in mixtures above 10% Xe, based on the collection of the primary electrons ͑not on electroluminescence͒, exhibit an almost flat behavior, roughly parallel to our w MC results in the same region. 11 We note that the rapid variation of w in the region of very low Xe concentrations observed in w MC is also supported by the results for ␣ particles in Refs. 27 and 29, where w values of ϳ25 eV at concentrations ϳ0.1% Xe are reported.…”

“…10 The w values were obtained from the ratios between the GPSC measurements and the Monte Carlo results, and the F values were deduced by combining these w values with the GPSC measurements for the intrinsic energy resolution R. More recently, the w values for 5.9 keV x-rays in Xe-Ne were measured directly in our group using an ionization chamber technique. 11 Studies of F and w for x rays can be found for several noble gases and their mixtures in the literature, but not for the case of Xe-Ne, ͑see the recent compilation in Ref. 12͒.…”

Precision laser-based measurements of the single electron response of spherical proportional counters for the NEWS-G light dark matter search experiment

“…The similarity between the W-value we measure in Ne + CH 4 (2%) with that of the value for pure methane is evidence of a strong contribution of Penning effects on the ionization yield, processes by which for example, Ne * atoms with an excitation energy higher than the ionization potential of CH 4 can ionize the latter [19]. Although the magnitude of the impact on the W-value may seem surprising given the low concentration of methane, such an effect has already been reported in Ne-Xe gas mixtures [20].…”

Fuelling the search for light dark matter-electron scattering with spherical proportional counters

“…7 we show results for a single-species gas, in reality, the noble gases would always be mixed with a small component of methane or isobutane to act as quench gases. For gas mixtures, the W -value for the mixture is much closer to the lowest W -value of the gases in the mixture [122,125]. For example, W ≈ 28 eV for a Ne + CH 4 (2%) mixture [63].…”