Gas Gain Measurements of a Spherical TEPC to use as Area-Monitor

Tissue-equivalent proportional counters (TEPCs) can be used to assess the radiation quality for radiation protection purposes. Area-monitor TEPCs have usually dimensions of the order of centimetres to guarantee a sufficient pulse rate in low intensity radiation fields, and generally they simulate site-sizes of 0.2 mg/cm2 (2 µm at density of 1 g/cm3). Such detectors can be used to properly assess the radiation quality in high-energy mixed radiation fields, when all the incident particles traverse the TEPC, without stopping inside. On the contrary, when the range of the interacting particles is shorter than the site size, the measured lineal energy, y, underestimates the local energy density caused by the radiation field. Such underestimations could be reduced if TEPCs could be built, able to measure at simulated diameters significantly smaller than 2 µm. To optimize the counter design, the constructive and the operating characteristics of TEPCs simulating small site sizes, knowledge of the gas gain is of fundamental importance. A spherical TEPC detector has been designed and constructed at LNL-INFN to be used as an area monitor in unknown radiation fields such as those found in environmental space. Gas gain measurements performed in pure propane with a spherical TEPC are presented.