Ionization chamber of new conception for environmental gas radon measurements

Long exposure to high radon levels leads to an increase of developing lung cancer risk, due to irradiation of lung tissue by the particles emitted by radon and its decay products. Another very interesting aspect related to the radon concentration is its potential use as a seismic events precursor, according to some geophysical models that suggest the release of radon from the underground as a result of tectonic deformation responsible for the earthquake (Khan et al., 1990, Richon P. et al, 1994). This paper shows the study of a gas detector operating in free air at atmospheric pressure, characterized by a metal cylindrical cathode and a wireanode placed along the axis of the cylinder Charpack et al.,2008; Charpack G. et al., 2010; Charpack G. et al., 2011). First the gas chamber behavior was studied with a solid 241Am source in order to identify the voltage values of the ionization chamber operating mode at the energy range of interest. Next the detector characterization was performed directly with radon gas source67 by using a pumping system in order to allow the gas to be distributed along the entire active volume. The resulting tests will be presented by focusing on the absolute efficiency evaluation, the Minimum Detectable Activity (MDA) and the time response to radioactivity. The obtained results made it possible to quantify system performances useful for radon measurements employment. Moreover, on the basis of these results, an updated version of the detector was built and characterized: the cathode was replaced by a cylindrical steel plate having a mesh structure. The detecting performances are similar to the previous prototype with a direct operation into the atmosphere and a reducedweight, size and energy consumption. The main advantages in using this detector are: quick response, strength, compactness, cheapness, longenough autonomy of operation, easy to install and use. Hence, this detector could be potentially used in a widespread network on the territory for the radon gas concentration measurement in living environments and/or aimed at testing of predicting earthquakes theoretical models