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  • 1
    Electronic Resource
    Electronic Resource
    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 (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 8202-8213 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Xenon gas proportional-scintillation counters (GPSC) have many applications in the detection of soft x rays where their energy resolution, R, is comparable to solid-state detectors when large window areas are required. However, R is known to deteriorate for energies Exr below 2–3 keV due to electron loss to the entrance window. Since the addition of a lighter noble gas increases the absorption depth, we have investigated the use of Xe–Ne gas mixtures at atmospheric pressure as detector fillings. The results of a Monte Carlo simulation study of the Fano factor, F, the w value, and the intrinsic energy resolution, R=2.36(Fw/Exr)1/2, are presented for Xe–Ne mixtures and pure Xe and Ne. The results show that the addition of Ne to Xe reduces the intrinsic energy resolution R but this never compensates for the reduction in scintillation yield in GPSC applications, implying that the instrumental energy resolution R will only improve with the addition of Ne when electron loss to the window in pure Xe is significant. The simulation reproduces the photoionization process of the Xe and Ne atoms, the vacancy cascade decay of the residual ions, and the elastic and inelastic scattering of electrons by the gas atoms. The contribution of energy and charge transfer mechanisms such as Penning, associative, and transfer ionization is discussed in detail. It is shown that Penning and associative ionization are the crucial indirect ionization processes which determine the behavior of F and w at low concentrations of Xe. The importance of the nonmetastable Ne states is also assessed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1371281
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  • 2
    Electronic Resource
    Electronic Resource
    Full-energy absorption of x-ray energies near the Xe L- and K-photoionization thresholds in xenon gas detectors: Simulation and experimental results (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 2742-2753 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Distributions of the number of primary electrons produced per incident mono-energetic x-rays in the 1- to 41-keV energy range, which includes the xenon L- and K-absorption edges, were simulated in xenon gas detectors with the Monte Carlo technique. These simulated full-energy absorption distributions are calculated as frequency plots of the number of primary electrons produced per incident x-ray photon. The simulation includes the absorption of x-rays and the de-excitation of the residual xenon ions, followed by the development of the primary electron cloud. The discontinuities observed in the Fano factor, w-value, energy linearity and energy resolution reflect the discontinuities of the Xe photoionization cross-section at the photoabsorption edges. The simulation results are compared with experimental values measured with a gas proportional scintillation counter, and with recent data from other authors. The discontinuities in energy linearity produce an ambiguity in determining the x-ray energy in certain narrow ranges containing the edges. However, our simulation results permit a detailed analysis of observations in these regions. At the K-edge, the discontinuities in the calculated Fano factor and energy resolution were found to depend on the extent to which the K-fluorescence produced by the xenon atoms is allowed to escape. A discussion of the asymmetry of the calculated full-energy absorption peaks is made in terms of the distinction between the different decay branches initiated by photoionization of the Xe atoms, and K-fluorescence escape is found to influence strongly the skewness of the calculated distributions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366105
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  • 3
    Electronic Resource
    Electronic Resource
    Xenon–neon gas proportional scintillation counters: Experimental and simulation results (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6303-6312 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: When gas proportional scintillation counters (GPSC) are used to detect very low energy x rays, the addition of the light noble gas neon to the usual xenon filling improves the collection of primary electrons that originate near the detector window. However, xenon–neon mixtures have lower electroluminescence yields than pure xenon. Increasing the scintillation electric field jeopardizes the energy resolution because of the additional fluctuations introduced by electron multiplication. In this work we investigate the effect of a limited amount of charge multiplication on the electroluminescence yield and the energy resolution R of a xenon–neon GPSC using both Monte Carlo simulation and experimental measurements. We consider xenon–neon mixtures with 5%, 10%, 20%, 30%, 40%, 50%, 70%, 90%, and 100% Xe at a total pressure of 800 Torr. Comparing the experimental and Monte Carlo data for 5.9 keV x rays, we conclude that optimum value of R is reached in a region of weak ionization with a charge gain of less than 2. By extrapolating the experimental results for R to infinite light yield we obtain the intrinsic energy resolution Rint for 5.9 keV x rays in all mixtures. From these results we can predict Fw values, where F is the relative variance in the number of primary electrons (the Fano factor) and w is the mean energy required to produce a primary electron. From a comparison between Monte Carlo and experimental electroluminescence yields, F and w values are estimated for 5.9 keV x rays in the various mixtures. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370131
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