Porfidia, B.

n the frame of the geochemical monitoring of seismicity mainly aimed at deepening the relationships between active seismotectonics and fluid geochemistry, i.e. earthquake prediction, a 222 Rn study was accomplished. It is addressed to inter-calibrate in diverse tectonic settings different methods to measure radon in groundwater: Alpha Scintillation Method using Lucas Cells (ASM-LCC) and Gamma Spectrometry Method (GSM), adopting both the Charcoal Trap Method (CTM) by Active Charcoals Canisters (ACC) and the Beaker Marinelli (BM) sampling devices. The intercalibration occurred on the field as well as in the laboratory, to finally select the best-fitting to gather radon information in each situation. Three Italian areas were selected to verify radon behavior and background concentration in different seismotectonical, geo-structural and lithological settings: ancient metamorphosed rocks – quiescent faults (Eastern Alps), carbonate foreland – active faults (Gargano) and quiescent volcanic structure overlapping a carbonate basement – swarm seismic activity (Colli Albani). The high radon concentration variability and the factors affecting radon behavior in groundwater (i.e. carrier gases presence, convection along fault systems, lithology influence, etc.) strongly constrain the measurement method to be adopted. The results point out apparently that the ASM-LCC method may be useful for expeditious and quick response of groundwater radon concentration during geochemical surveys aimed at grossly detecting the presence of tectonic structures, the deepening of circulation or the peculiar geological features linked to the presence of U-Th minerals. This method is not reliable for accurate measurements, while the GSM methods showed low standard deviation (higher precision with respect ASM-LCC) and accurate radon measurements. Finally, a customized DINCE Standard Radiactive Source (DSRS) was set up, and first used for the efficient estimation of the ING available Lucas Cells. A calibration factor for each ING Lucas Cell was defined and the most critical aspects of the ASM-LCC method revised.

A new 222Rn monitoring prototype has been designed, assembled and tested at the Istituto Nazionale di Geofisica (ING) specifically addressed to seismic surveillance tasks, exploiting environmental monitoring, etc. It operates with an a scintillation technique (photomultiplier + Lucas Cell) coupled with a water input system, that lets continuous dehumidified gas flow, stripped from groundwater under monitoring. Several laboratory tests have been carried out to check the stability and versatility of the system; moreover statistical tests have been accomplished on several data sets obtained with an 241Am radioactive standard source, to check stability of the photomultiplier. A customised water flow system has been developed to perform both the highest efficiency and lowest influence of external noise parameters. This new prototype is very cheap and will be integrated within the new multiparametric geochemical monitoring system GMS II, that is currently being developed at ING, specifically designed for geochemical surveillance of seismic events.