Equivalence of Pure Propane and Propane-TE Gases for Microdosimetric Measurements

In microdosimetry tissue-equivalent proportional counters (TEPCs) are commonly assumed to measure the distribution of energy imparted in micrometric volumes of tissue when irradiated by ionizing radiation. To achieve this aim at least the elemental composition of the walls and the filling gas of a TEPC should be as close as possible to that of tissue. In this respect, propane-based tissue-equivalent gas is generally accepted as a good approximation for the elemental composition of tissue, and represents at present the most frequently used filling gas. In sealed TEPCs, the drawback of using gas mixtures is that the composition of the filling gas may change with time due to a different absorption of the gas mixture components with the detector walls. From this point of view, the use of pure propane as the filling gas of a sealed TEPC offers practical advantages: the composition of the filling gas is more stable on long-time operation, and higher gas gains can be reached as compared with the C3H8-TE gas. Therefore, the aim of this study was to develop an experimental procedure which can be applied in measurements with C3H8-filled TEPCs to get a detector response very similar to that of TEPCs filled with C3H8-TE-gas.