The influence of anisotropic scattering of positrons on transport coefficients

Positron Emission Tomography is widely used technique for general diagnostics of metabolic activity and for the identification of cancerous tumors. The fundamental interactions of positrons with atoms and molecules in the human body are not well understood and quantified. Modeling of damage induced by positrons traversing the living tissue (usually modeled as water) is not an easy task and almost every existing model in medicine is based on semi empirical data. In this work, positron transport is investigated in water vapour using isotropic and anisotropic scattering models, based on fundamental collisional data obtained in either beam experiments or by theoretical calculations. The latter model is particularly important since the water molecule is highly polar. Benchmark calculations are performed using a Monte Carlo simulation technique. Similar very strong effects of positronium formation are observed as in argon. Several transport coefficients has been determined for a wide range of E/N which may be used as a benchmark for testing of codes aimed at modeling of positron diagnostics and therapy.