First radon measurements and occupational exposure assessments in underground geodynamic laboratory the Polish Academy of Sciences Space Research Centre in Książ Castle (SW Poland)

The article presents the results of the first radon activity concentration measurements conducted continuously between 17th May 2014 and 16th May 2015 in the underground geodynamic laboratory of the Polish Academy of Sciences Space Research Centre in Ksiąz. The data were registered with the use of three Polish semiconductor SRDN–3 detectors located the closest (SRDN–3 No. 6) to and the furthest (SRDN–3 No. 3) from the facility entrance, and in the fault zone (SRDN–3 No. 4). The study was conducted to characterize the radon behaviour and check it possibility to use with reference to long– and short–term variations of radon activity concentration observed in sedimentary rocks strongly fractured and intersected by systems of multiple faults, for integrated comparative assessments of changes in local orogen kinetics. The values of radon activity concentration in the underground geodynamic laboratory of the Polish Academy of Sciences (PAN) Space Research Centre in Ksiąz undergo changes of a distinctly seasonal character. The highest values of radon activity concentration are recorded from late spring (May/June) to early autumn (October), and the lowest – from November to April. Radon activity concentrations varied depending on the location of measurement points. Between late spring and autumn they ranged from 800 Bq·m−3 to 1200 Bq·m−3, and even 3200 Bq·m−3 in the fault zone. Between November and April, values of radon activity concentration are lower, ranging from 500 Bq·m−3 to 1000 Bq·m−3 and 2700 Bq·m−3 in the fault zone. The values of radon activity concentration recorded in the studied facility did not undergo short–term changes in either the whole annual measuring cycle or any of its months. Effective doses received by people staying in the underground laboratory range from 0.001 mSv/h to 0.012 mSv/h. The mean annual effective dose, depending on the measurement site, equals 1 or is slightly higher than 10 mSv/year, while the maximum dose exceeds 20 mSv/year. The estimated annual effective doses are comparable to the standard value of 20 mSv/year defined by Polish law for people employed in the conditions of radiation exposure. They are also in the range of annual effective dose value (8 mSv/year) recommended in workplaces by International Commission on Radiation Protection.