Relation of electron scattering cross-sections to drift measurement in noble gases

Abstract

We investigate the classic "inverse problem" of extracting collision and scattering cross sections from measurements of electron swarm behavior. A Monte Carlo technique for simulating electron motion through a gas of isotropic scatterers is presented, providing a simplified version of Biagi's MAGBOLTZ algorithm. Using this Monte Carlo software, we examine the thermalization of electron swarms, focusing on their drift velocity and informational entropy, providing justification for a set of analytic expressions for drift measurements which are valid in the hydrodynamic regime. These expressions are then used to estimate the ⁴He scattering cross section, first by a simple grid interpolation and then through a genetic algorithm (GA). This technique demonstrates that the 4He momentum-transfer cross section in the 0-7 eV range is approximately 6.5 [Angstrom]², with a peak near 2 eV, in agreement with literature values. Empirical cross sections are also presented for Xe and He:CH₄(90:10).