FULL-ENERGY ABSORPTION OF X-RAY-ENERGIES NEAR THE XE L-PHOTOIONIZATION AND K-PHOTOIONIZATION THRESHOLDS IN XENON GAS DETECTORS - SIMULATIONAND EXPERIMENTAL RESULTS

Distributions of the number of primary electrons produced per incident mono-energetic x-rays in the 1- to 41-keV energy range, which include s the xenon L- and K-absorption edges, were simulated in xenon gas det ectors with the Monte Carlo technique. These simulated full-energy abs orption distributions are calculated as frequency plots of the number of primary electrons produced per incident x-ray photon. The simulatio n includes the absorption of x-rays and the de-excitation of the resid ual xenon ions, followed by the development of the primary electron cl oud. 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 simula tion results are compared with experimental values measured with a gas proportional scintillation counter, and with recent data from other a uthors. The discontinuities in energy linearity produce an ambiguity i n 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 t he calculated Fano factor and energy resolution were found to depend o n the extent to which the K-fluorescence produced by the xenon atoms i s allowed to escape. A discussion of the asymmetry of the calculated f ull-energy absorption peaks is made in terms of the distinction betwee n the different decay branches initiated by photoionization of the Xe atoms, and K-fluorescence escape is found to influence strongly the sk ewness of the calculated distributions. (C) 1997 American Institute of Physics.