Fano factor and the mean energy per ion pair in counting gases, at low x-ray energies

Abstract

A new technique for studying the Fano factor and the mean energy per ion pair in counting gases The mean energy per ion-pair (W i ) and the Fano factor (F) are provided with high accuracy ͑2% x-ray energy range of 0.11-1.5 keV. These parameters were extracted from precise measurements of the number and temporal distribution of x-ray induced electrons, accompanied by extended simulations of the detection process. A decrease in these parameters with increasing x-ray energy was observed, accompanied by sharp increases at x-ray energies just above some atomic shells. The effect is discussed in relation to Auger electron emission. A Penning process in Ar/C 2 H 6 ͑20:80͒ and Ar/i-C 4 H 10 ͑20:80͒ is observed on the basis of comparative measurements of W i and F in these mixtures and in the pure hydrocarbons. Ways are proposed for further improving the accuracy provided by the electron counting technique to better than 1%.

A Monte Carlo study of the fluctuations in Xe electroluminescence yield: pure Xe vs Xe doped with CH4or CF4and planar vs cylindrical geometries

“…In conclusion, CF 4 may be ruled out as an additive to Xe for uniform fields in the EL range 3 , because the intrinsic energy resolution in Xe-CF 4 becomes too large and very sensitive to η CF4 . We note that the Fano factor in pure molecular gases will be higher than in xenon (for CH 4 a value ~0.28 was measured in [50]) but for the low molecular concentrations added to xenon in this work, the Fano factor in the mixtures is not expected to be significantly higher than in pure xenon. 4 and Xe-CF 4 mixtures with the indicated η CH4 and η CF4 molecular concentrations at p = 7600 Torr, T=293 K. The discontinuous lines represent the linear fittings found in [15] and in [21] to Monte Carlo and to experimental data, respectively.…”

Signal variance in gamma-ray detectors—A review

“…W decreases with increasing incident energy from about 4.3 eV at 0.05 keV to about 3.7 eV at 1 keV and exhibits sawtooth variations at the K-and L-absorption edges as observed by Santos et al [19] in Xe (discussed in Section 2 above). The variation of W with energy in Si was found to follow the photoionization cross-section [39] as was the case in Xe [18]. W was found to be highly sensitive to the number of electron-hole pairs resulting from plasmon decay, confirming the dominant role of plasmon excitation in the energy loss process.…”

“…The F values in Table 1 for He and Ne are from a calculation, while the others are from experiment. In molecular gases, experimental results show that W/I is higher than 2.1 and F is in the range 0.2-0.4 (within measurement error of 4%) [18]. From Eq.…”

“…Monte Carlo simulations [19,20] and experiments [18,20] have been undertaken to calculate W and F in gases. This is partly due to interest in Xe detectors for X-ray [21] and gamma-ray spectrometry [22].…”

A technique for the absolute measurement of the W-value for X-rays in counting gases

“…Recently, Pansky et al [12,13] developed a method based on the technique of individually counting the primary electrons N produced by a single X-ray photon in a low-pressure gas, combining experimental work with Monte Carlo simulation of the detection process. This method allowed a variable accuracy up to $3% and it is restricted to very low X-ray energies (110}1486 eV) and gases at rather low pressures (about 10 Torr).…”