For research purposes, I am looking for a way to calculate how far the electrons "spread" perpendicularly to the electric field in a chamber of gas.
For example, if a beam of alpha particles ionize the gas in a chamber and leave a track of electron-postive ion pairs, is there a way to calculate how far the electrons move away from the point of ionization (perpendicular to the electric field). Note: also present in the gas chamber is an electric field, so the electrons and positive ions would move in opposite direction. I am reading W. R. Leo's Techniques for Nuclear and Particles Physics Experiments for hints on how to calculate this, but I haven't found any mention of this yet. The closest thing I found was about electron diffusion with the absent of an electric field. Please point me to articles, book chapters, equations, or links regarding information of this topic. Thanks in advance.