Department of Geomagnetism

Exposure to radon gas in the home accounts for about half of all non-medical exposure to ionizing radiation. Indoor radon activity concentration (RAC) depends on many factors, for example building material, local geology, design of a house, ventilation, and contact of a room with the subsoil.

According to the Regulation from the Ministry of Health SR No. 528/ 2007, an action level 400 Bq/m³ is recommended for an annual average RAC for existing residential buildings and 200 Bq/m³ for new and reconstructed residential buildings. A reference level recommended by the Council Directive 2013/59/EURATOM is 300 Bq/m³ in average per year.

Integration measurement of indoor RAC in houses was performed from March 2012 to February 2013 in the framework of the project “Harmonization of determining the radiation dose of the population originating from radon in V4 countries”. The objective of the project was to elaborate a common measurement protocol of the Visegrad countries for the measurement of indoor radon (²²²Rn) and thoron (²²⁰Rn) concentration (the placement of detectors, type of detectors, questionnaire).

In Slovakia, the radon survey was performed in three localities: Záhorská Bystrica, Ružomberok and Mochovce are (Nevidzany and Čifáre). Fours sets of passive alpha track detectors Raduet (Radosys, Hungary) were used, sets were replaced after three months of exposure to compare the changes in RAC activities during the year. Two detectors were placed in a house, preferably in rooms on the ground floor in which the inhabitants spent the most of their time.

Indoor RAC in selected houses ranged (40-740) Bq/m³ in average per year. In 66 % of monitored rooms the average RAC per year was less than 200 Bq/m³. However, in 10 % RAC exceeded 400 Bq/m³. Increased radon levels in houses without a cellar were confirmed. The seasonal variation of RAC with the minimum in summer and maximum in winter months was observed, probably due to the intensive ventilation of a room in the summer season.