W values and other transport data on low energy electrons in tissue equivalent gas

The degradation of low energy electrons in a methane based, tissue equivalent gas was studied experimentally by ionization chamber experiments and theoretically by Monte Carlo electron transport simulation in the energy range between 25 eV and 5 keV. From measured ionization yields and calculated ionization and energy dissipation profiles, the mean energy W required to produce an ion pair, the differential omega value, backscatter coefficients, different types of mass ranges, and stopping powers were determined. A comparison of our experimental results with those of the calculations shows a very satisfactory agreement in the whole energy range. In addition to these data some quantities of interest in the fields of radiation biology and microdosimetry, such as the statistical fluctuation of ionization yields, the energy transfer to and the ionization yields in thin material layers of the tissue equivalent gas, together with the distance distribution of energy transfer and the dose average of the specific energy, have been studied. A comparison of these results with those for electrons in water showed the great similarity of both stopping media for many purposes in the fields of radiation research.