Introduction

Uranium U-238 is present in all rock types in different concentrations. By its radioactive decay, radon Rn-222 is generated and released from rocks and soils. Some of the rocks like granites or black shales, contain increased concentration of uranium. Therefore the risk of radon release and penetration into houses built on these rock types is higher. Radon in the indoor environment decays to daughter products, which are metallic isotopes of polonium and bismut.

The daughter products are bound to aerosol particles and are accumulated in the lungs. In higher concentrations they can increase the probability of lung cancer. The rocks and soils are the main source of radon. Therefore the attention is given to detecting rock types with higher radon potential. Based on the geological knowledge and soil gas radon measurements, the radon risk maps of different scales are constructed and used by the state and municipal authorities dealing with Radon programme of the Czech Republic.

Sources of Rn-222 (radon) in bedrock

Uranium U-238 is present in all rock types in different concentrations. By its radioactive decay, radon Rn-222 is generated and released from rocks and soils. Some of the rocks like granites or black shales, contain increased concentration of uranium. Therefore the risk of radon release and penetration into houses built on these rock types is higher. Radon in the indoor environment decays to daughter products, which are metallic isotopes of polonium and bismuth. The daughter products are bound to aerosol particles and are accumulated in the lungs. In higher concentrations they can increase the probability of lung cancer. The rocks and soils are the main source of radon compared to building materials and water in the Czech Republic. Therefore the attention is given to detecting rock types with higher radon potential.

The bedrock of the Czech Republic is formed mostly by crystalline and granitic rocks with primarily enhanced concentration of uranium. Uranium is bound both in the form of anomalous accumulations – uranium deposits (of local impact) and in the form of rock forming minerals (e.g. zircon) which substantially contribute to radon release from bedrock in aerial scale. Zirconium minerals are also concentrated in neovolcanites – mainly phonolitic and trachytic rocks. The radiometric pattern of the state territory is given in the gamma dose rate map of the Czech Republic (M. Manová, M. Matolín 1990, Czech Geological Survey).

Radon based on the geological knowledge and soil gas radon measurements, the radon risk maps of different scales are constructed and used by the state and municipal authorities dealing with Radon Programme of the Czech Republic.