Search

A tissue-equivalent proportional counter (TEPC) simulates micrometric volumes of tissue, if the energy deposited in the counter cavity is the same as that in the tissue volume. Nevertheless, a TEPC measures only the ionizations created in the gas, which are later converted into imparted energy. Therefore, the equivalence of the simulated diameter in two gases should be based on the equality of the mean number of ions pairs in the gas rather than on the imparted energy. Propane-based tissue equivalent gas is the most commonly used gas mixture at present but it has the drawback that its composition may change with time. From this point of view, the use of pure propane offers practical advantages: higher gas gain and longer stability. In this work, microdosimetric measurements performed with pure propane, at site sizes between 0.05 mg/cm2 and 0.3 mg/cm2, demonstrate that the response of a propane-filled detector in gamma and in neutron fields is almost the same if an appropriate gas density is used.

Tissue-equivalent proportional counters (TEPCs) measure distributions of ionizations, produced in the gas cavity by the radiation field which are afterwards converted into distributions of energy imparted by applying a calibration factor. To calibrate the pulse height spectra, firstly, a marker point must be identified in the measured spectrum. Then, an accurate value of lineal energy must be assigned to this marker. A common marker that is often used for calibration is the so-called proton-edge (p-edge). It is a distinctive feature of a proton or neutron spectrum which corresponds to the maximum amount of energy that a proton can deposit in the active volume of the detector. A precise method to identify the marker point was applied to identify the p-edge with an uncertainty below 2%. To evaluate the final uncertainty of the calibration, the uncertainty of the energy value assigned to the p-edge must also be considered. This value can be evaluated using different energy-range tables. This study investigates how the choice of different input databases for calibration purposes influences the calibration. The effect of three different frequently used sets of input data was analysed for pure propane gas and for propane-TE gas mixture.