Ra-226 in building materials as a source of indoor radon in high-rise residential buildings in Russian cities.

The problem of indoor radon in high-rise buildings is mostly associated with exhalation from building materials. Characterization of the radon entry from building materials by diffusion is required to provide a proper control of the population indoor radon exposure. To analyze the relationship between the content of Ra-226 in building materials and the indoor radon concentration the results of the following surveys in high-rise buildings in Russian cities were used: 1) indoor radon (>1000 apartments), 2) natural radionuclides in the building materials in existing buildings by means of non-destructive field gamma spectrometry (100 apartments). The surveys were carried out in nine large cities in different climatic zones. The radon entry rate due to diffusion from building materials, D, normalized to Ra-226 activity concentration, Ra, is in the range of 0.2-0.6 (Bq/m/h)/(Bq/kg), depending on the type of building materials and building construction. In new multi-story buildings, the typical D/Ra ratio can be assumed to be 0.4 (Bq/m/h)/(Bq/kg). In new energy-efficient buildings, the ratio of the radon concentration to Ra-226 activity concentration is on average 2.1 times higher than in multi-story buildings of lower energy efficiency built before 2000. The average radon exhalation rate from the building materials, normalized to Ra-226 activity concentration, is estimated to be 0.25 Bq/m/h.