A.D. Stauffer

The Fano factor in gaseous xenon: a Monte Carlo calculation for X-rays in the 0.1 to 25 keV energy range

Abstract A calculation of the Fano factor for gaseous xenon is carried out using a detailed Monte Carlo simulation of the absorption of X-rays in the 0.1 to 25 keV energy range. This factor is found to be energy dependent with values ranging from 0.17 to 0.32 and has sharp increases near the xenon absorption edges. An interpretation of the calculated results is made in terms of the relative importance of photoelectron and Auger/Coster-Kronig cascading electron processes.

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

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 significa...

Variation of energy linearity and w value in gaseous xenon radiation detectors for X-rays in the 0.1 to 25 KeV energy range: a Monter Carlo simulation study

Abstract For X-ray photon energies in the range E = 0.1 to 25 keV, a calculation of the mean energy to produce an electron-ion pair, w, in gaseous xenon, and the average number of primary electrons produced, N , is carried out, using a detailed Monte Carlo simulation. We found that the curve N (E) is a nonlinear function, with sharp steps close to the xenon absorption edges. Moreover, w was found to be energy dependent, with values ranging from 21.7 to 24.6 eV. An interpretation of the calculated result is made in terms of the contribution of the different subshells for photoelectron and Auger/Coster-Kronig electron production.

Energy resolution of xenon proportional counters: Monte Carlo simulation and experimental results

The gas multiplication factor M and energy resolution R of xenon gas cylindrical proportional counters are investigated experimentally and calculated theoretically using a Monte Carlo technique to simulate the growth of single-electron-initiated avalanches. A good agreement is found between calculated and experimental data. The experimental and the calculated results are presented as a function of the reduced voltage K and the reduced anode radius Na, where N is the number density and a the anode radius. The Monte Carlo results for the intrinsic energy resolution R/sub int/ are discussed in terms of the parameter f which characterizes the statistical fluctuations of the avalanche gains. The present calculations have revealed that there is an intrinsic dependence of f on the critical value S/sub c/ of the reduced electric field at the onset of multiplication. This has enabled the parameterization of f and of the intrinsic energy resolution R/sub int/ in terms of the reduced voltage K only and has explained why, for a given range of operating values for M, energy resolution in a cylindrical proportional counter is improved for thinner anode wires and lower pressures.

Unidimensional Monte Carlo Simulation of the Secondary Scintillation of Xenon

An unidimensional Monte Carlo method is used to calculate the secondary scintillation (electroluminescence) intensity in xenon gas proportional scintillation counters. Other transport parameters like electron drift time, average number of collisions, efficiency for light production and induced charge pulse amplitude are also calculated. The values obtained agree well with the experimental data available.

Analytical expressions for phase shifts and cross sections for low energy electron-atom scattering in noble gases

Abstract Analytical expressions which reproduce recent reliable data on low energy (0 to ∼20 eV) electron-noble gas atom elastic scattering phase shifts are presented, allowing an accurate calculation of elastic integral and differential cross sections at any chosen energy through the use of the appropriate formulae. Fittings to the integral elastic cross sections thus obtained and to inelastic and total (elastic + inelastic) cross sections are also presented within this energy range. These expressions are of interest in Boltzmann and Monte Carlo calculations of electron drift phenomena in noble gases at low values of E p and are applicable to certain types of nuclear radiation detectors.

Monte Carlo simulation study of the characteristics of Xe-Ne gas mixtures as detection media in gas proportional ionization counters

A Monte Carlo simulation has been developed in order to assess the use of Xe-Ne gas mixtures as detection media in gas proportional ionization counters, examining in particular the parameter most relevant for the performance of a detection medium: the intrinsic energy resolution R/sub int/. This parameter, which establishes a theoretical limit to the detection capability of a detector, has been calculated as a function of the mixtures composition. The Monte Carlo simulation code developed fully reproduces the growth of single-electron-initiated avalanches in cylindrical geometry and results for R/sub int/ are discussed in terms of the parameter f, the statistical fluctuations parameter characterizing single-electron-avalanches. This parameter is calculated for each mixture as a function of the reduced anode voltage K=V/ln(c/a), where V is the voltage applied to the anode-wire and c/a is the cathode-to-anode radius ratio. Results for the gas multiplication factor M, characterizing each mixture composition at a given applied electric field, were also obtained.

Monte Carlo Simulation Study of the Characteristics of Xe-Ne Gas Mixtures as Detection Media in Gas Proportional Ionization Counters

A Monte Carlo simulation has been developed to investigate the performance of Xe-Ne filled proportional ionization counters, with a special interest on the intrinsic energy resolution Rint as a function of the Xe-Ne mixtures composition. The Monte Carlo simulation reproduces the growth of single-electron-initiated avalanches in cylindrical geometry, and the results for Rint are discussed in terms of the influence of the Penning ionization on the statistical parameter f characterizing the fluctuations of single-electron avalanches gain. The results for Rint, and f, as well as for the multiplication factor M, are calculated for each mixture as a function of the reduced anode voltage K=V/ln(c/a), where V is the voltage applied to the anode-wire and c/a is the cathode-to-anode radius ratio

The response of a gas proportional scintillation counter to conversion electrons: simulation and experimental results

Monte Carlo and xenon gas proportional scintillation counter energy spectra are presented for the absorption of X-rays and conversion electrons from the decay of a Cd/sup 109/ source and its daughter Ag/sup 109m/. Pulse duration distributions are also calculated, and compared with the results measured with a digital pulse-height analyser. A good agreement is found for the Monte Carlo and the experimental data.

The effect of electron multiplication on the electroluminescence yield of pure xenon and xenon-neon gas proportional scintillation counters: experimental and simulation results

In applications of the gas proportional scintillation counter to the detection of 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 would have originated near the detector window. However, xenon-neon mixtures produce lower electroluminescence yields than pure xenon. The highest electroluminescence yield that can be achieved without jeopardizing the energy resolution is limited by the additional fluctuations introduced by electron multiplication and, consequently these detectors are usually operated at reduced electric fields below the ionization threshold. In this work, a compromise between electroluminescence output and energy resolution is investigated for xenon-neon mixtures at a total pressure of 800 Torr (with 5%, 10%, 20%, 40%, 70%, 90% and 100%Xe), and for 5.9 keV X-rays. Using experimental and Monte Carlo studies, the effects of introducing a limited amount of charge multiplication on the electroluminescence yield and on the detector energy resolution are analysed and discussed, and the optimum operating conditions for gas proportional scintillation work are established.