Analysis of the hydrogeological conditions in Bulgaria in connection with the radon potential

Natural radon (222Rn) is a radioactive noble gas that occurs in every rock or soil due to the content of radium (226Ra), part of the 238U family, in the lithosphere. Different types of rocks and soils possess different 226Ra content and different permeability. Radon has high mobility and is driven by diffusion and convection with the soil gas throughout connected and water-unsaturated pores and/or cracks in permeable rocks and soils. Therefore, the radon potential of the area could depend on hydrogeology and its particular settings. The study deals with the general characteristics of the groundwater depths in Bulgaria based on the published since 1960’s sources. After analysis of the collected data several distinct regions have been elaborated based on different depth of the groundwater table regarding lithological, tectonic and geomorphological conditions. In addition, zones for screening assessment of groundwater table influence of radon potential have been precised.

Radium content in Bulgarian mineral waters

This study presents the results of 226Ra content in 104 Bulgarian mineral waters as well as the investigated correlations between the physicochemical parameters, geological structure, and specific activity of 226Ra. The results show that the 226Ra activities range from <30 mBqL-1 to 4900 mBqL-1 with a mean value of 156 mBqL-1. The highest concentrations of 226Ra were measured in mineral waters originating from the carbonate strata, as the dominant geological structure. Thus it is well connected with the estimated moderate positive correlation between Ca2+, Mg2+, and Ra2+ cations in the water. The estimated annual dose shows large dispersion of values ranging from 6 ?Sv to 1000 ?Sv with a mean value of 32 ? 9 ?Sv. The results demonstrate the need for further investigation of every mineral water, but greater attention should be given to the mineral waters with low pH and high content of Ca2+ and Mg2+.

The dose from radioactivity of covering construction materials in Serbia

The indoor dose due to the radiation of ceramic and granite tiles, marble, granite and travertine plates, as well as some components of covering materials, produced in Serbia or imported from other countries, was estimated in the work. Activity concentrations of 226Ra, 232Th, and 40K were measured by the standard gamma-spectrometry system. The lowest content of the radionuclides was found in white marble (ARa = 2 Bq/kg, ATh < 2 Bq/kg, and AK < 3 Bq/kg), while the highest activities were in some granite samples (Balmoral red: ARa = 200 Bq/kg, ATh = 378 Bq/kg, and AK = 1679, and Madura Gold: ARa = 273 Bq/kg, ATh = 20 Bq/kg, and AK = 1456 Bq/kg). The indoor absorbed dose rate in air due to the gamma radiation from covering materials was determined based on the specific absorbed dose rate computed in this work. Concentration of 222Rn that emanated into the indoor space was also calculated from the known 226Ra content. The radiation hazard estimated from the usage of each sample was expressed through the evaluated effective dose. Almost all samples, except one, fulfil the dosimetric criterion for safe use.

Predicting the Rate of 222Rn Entry from Soil into the Basement of a Dwelling Due to Pressure-Driven Air Flow

A combination of analytical and numerical methods is applied to the problem of computing 222Rn transport from soil into a dwelling having a basement. Transport is assumed to occur solely by pressure-driven air flow, and the basement shell is assumed to have a single dominant leak that is uniformly distributed around the perimeter at the level of the floor. The results show that for small flow rates of air through the soil, the radon entry rate into the basement increases in proportion to ?Po, the outdoor-indoor pressure difference at the soil level. For large flow rates, the entry rate increases only in proportion to ?Po2/3, due to depletion of radon concentration in the soil. A sample calculation indicates that via this transport mode, soil having ordinary 226Ra content and moderately high permeability can be responsible for indoor radon concentrations of the order of 500 Bq.m-3, greater than recommended guidelines for new housing.