Thermal enhancement of radon emission from geological materials. Implications for laboratory experiments on rocksunder increasing deformation

Abstract

Radon gas is the subject of a great deal of research because its concentration builds up into indoor air and the long-term radon exposure is considered the second cause of lung cancer, after smoking. In addition to that, the release of radon from soil is under investigation in active volcanic and seismic areas because radon anomalies are believed to occur before earthquakes and volcanic eruptions. Several papers report results of laboratory experiments on the effects of activity concentration of 222Rn and 220Rn precursors, humidity content and grain size of geological materials over the radon emission. However no correspondent studies have targeted the effect of the temperature on radon release. The present contribution focuses on the influence of temperature, varying from 20 to 60 °C, on 222Rn and 220Rn emission from two volcanic rocks, a tuff and a lava flow. The experimental apparatus consists of a small accumulation chamber coupled to solid-state alpha spectroscopy; it also allows to keep constant the experimental temperatures applied to the rock sample. The effect of ambient temperature on detection efficiency is also investigated. Results show a significant enhancement of radon emissions from rocks with increasing temperature. The results of these experiments suggest that thermal enhancement of radon emission can be used to investigate more precisely the correlation between physical mechanisms determining damage in stressed rocks and radon release, taking advantage of the improved radon emission. Experimental test with a better resolution are the key to interpret radon anomalies preceding earthquakes or volcanic eruption.