Digital Characterisation of Particle Tracks for Microdosimetry

Work is in progress to develop a digital approach to microdosimetry and to construct a prototype instrument to obtain digital information about charged-particle tracks. The objective of such a device is to measure the numbers of electrons produced in various subvolumes of a chamber gas along a particle's path. This paper describes results of Monte Carlo calculations of charged-particle tracks in a cubical time-projection ionization chamber containing methane. Results are presented to show the effects of electron diffusion during charge collection. The calculations indicate that the optimum ratio of field strength and pressure is about 0.6 volts cm/sup -1/ torr/sup -1/. Examples of proton, carbon-ion, and electron tracks are shown. 2 refs., 6 figs.