Variace radonu a davkoveho prikonu na tektonickych poruchach v sedimentarnich horninach Ceskeho masivu

The variations of radon concentrations and gamma dose rate (referred as Rn and D´) were studied in sedimentary rocks of the Bohemian massif along profiles oriented perpendicularly to assumed and detected faults. The measurements follow-up the research performed on metamorphic and magmatic rocks (Pacherová et al. 2016). Three areas were chosen for profile measurements (10 points each, distance of points 3 m, Rn measured in the depth 80 cm using radonmeter RM 2, D´ measured 1 m above soil surface by radiometer RP 2000). In the area Hořice the equivalent gamma dose rate H´ was measured by dosimeter PTF 2 due to collapse of radiometer RP 2000. Area near Stod (Westphalian-Stephanian claystones and sandstones) SW of Pilsen comprised 9 profiles, area Nové Město nad Metují (NE Bohemia, Turonian marlites and claystones) was covered by 14 profiles. The rest of profiles (19) was situated in the NE Bohemia between Hořice and Trutnov (Cenomanian sandstones and Autunian aleuropelites). The localization is given in Fig. 1. The results of mutual trends of Rn and D´ along measured profiles in all three areas (with respect to assumed position of fault in point 5 of each profile) are presented in Tabs 1, 2 and 3. In sedimentary rocks the position of faults is detected by the decrease both of number of maxima of Rn and D´ (H´) at point 5 - fault core (Fig. 2), the same variations can be observed for medians of both measured quantities (Fig. 3). On the contrary, the increased number of maxima and medians´ values is detected in points 3 and 8 instead of the point 5, which indicates the presence of wider fault damage zone (up to 15 m) preventing the radon release from bedrock due to clayey character of weathered fault core and damage zone. Table 4 and Fig. 4 present the summarizing response of maxima position of Rn and D´ along 79 profiles measured in metamorphic, magmatic and sedimentary rocks. The increase of Rn concentration is concentrated around the position of fault core (at point 5 of measured profiles), whereas the maxima D´ (H´) values were observed at points 3 and 8. The results of radon and gamma dose rate variations along the profiles across the faults in different lithology allow us to consider the faults as the radon prone areas. Subsequently this confirmation will be incorporated into the map server of Czech Geological Survey in applications Actualized radon risk maps and Complex radon information.

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