Measuring polarization in the x-ray range: simulation for the impact gas mixture and pressure in gaseous detectors

The development of new technology in micropattern gaseous detectors makes it possible to measure x-ray polarization for energies where the photoelectric effect is the main mechanism of interaction with matter. In a previous work, we showed that a modification of the Geant4 simulation code is a useful toolkit to simulate the photoelectric interaction of linearly polarized x-rays with micropattern gas detectors. In particular, by properly taking into account the direction of the photoelectron, we developed a new calculation of the final state. We simulated one experimental setup found in the literature and showed that the simulation results obtained are in agreement with the experimental data. In this work, we present new results on simulation of a mixture of two gases with different pressures and study the impact in the modulation factor. The simulations were done for both low and high Z mean mixture. With these gas mixtures, we observed that the modulation factor was greater for a low Z mixture than that with a high Z, but the efficiency was opposite. We also observed that the modulation factor for high Z was influenced by the absorption edge of the photoelectric cross section. Copyright © 2009 John Wiley & Sons, Ltd.