Electron Recombination in Ionized Liquid Argon: A Computational Approach Based on Realistic Models of Electron Transport and Reactions

Abstract

In this work, we propose a new theoretical approach to modeling the electron-ion recombination processes in ionization tracks in liquid argon at 87 K. We developed a computer simulation method using realistic models of charge transport and electron-ion reactions. By introducing the concept of one-dimensional periodicity in the track, we are able to model very large cylindrical structures of charged particles. We apply our simulation method to calculate the electron escape probability as a function of the initial ionization density in the track. The results are in quantitative agreement with experiment for radiation tracks of relatively high ionization density. At low ionization densities, the simulation results slightly overestimate the experimental data. We discuss possible reasons for this disagreement and conclude that it can be explained by the role of δ tracks (short tracks of secondary electrons) in electron-ion recombination processes. We introduce an approximate model that takes into account the presence of δ tracks and allows the experimental data obtained from a liquid-argon ionization detector to be reproduced over a wide range of ionization density.

Gaseous and dual-phase time projection chambers for imaging rare processes

“…Given the high medium density, the solution in liquid may be approximated by neglecting diffusion. The solution in gas, on the other hand, can be obtained by assuming that recombination is small and N e(i) can be approximated in the hydrodynamic equation through numerical evaluation [107]. Most of the available information is experimental, though, given the difficulty of including additional effects like the recombination produced in the inmediate vicinity of the parent ions [108] or δ-rays [109].…”

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“…By recording these events and repeating the simulation for many independently generated tracks, the recombination (or escape) probability can be obtained. The present application of our simulation model differs from its previous applications [25,26] m are the cation mobility and mass, respectively, and e is the elementary charge. The collision probability at each time step is determined using an expression analogous to eq.…”