On the equivalence of propane-based tissue-equivalent gas and liquid water with respect to the ionisation-yield formation by electrons and α-particles

One encouraging way, at present, to put the investigation of ionisation-yield formation in sub-cellular structures or, at least, in nanometric volumes of liquid water on an experimental basis is the use of highly sophisticated counters filled with gases at low operating pressure to simulate target volumes a few nm in diameter at unit density. To check the validity of such measurements, the ionisation-yield formation by electrons and α particles in liquid water was simulated using the Monte Carlo method and compared with that produced in propane-based tissue-equivalent gas (composition by volume: 55% C3H8, 39.6% CO2, 5.4% N2). After a short summary of the most important physical aspects of ionisation cluster formation, new results are presented and discussed from the point of view of radiation physics and radiation biology. (author)