Radon Hazard Mapping of Pyatigorsk City Considering Geological Data

Abstract

To map the potential radon hazard of territories based on the results of sample measurements of radon equivalent equilibrium concentration (EEC) in the premises of public buildings in connection with the analysis of geological information reflected in the state geological maps at the scale of 1:200 000, supported by the results of reconnaissance measurements of the content of natural radionuclides in soil samples, using Pyatigorsk as an example. Material and methods: The results of measurements of radon EEC in the premises of Pyatigorsk were used, which were carried out mainly in kindergartens, schools and higher educational institutions of the city separately in summer and winter periods with the help of the track method using the equipment set TREC-REI_1M (LR-115-2 detectors placed in REI-4 exposimeters). A total of 2851 measurements of radon EEC in 97 buildings were analysed. Measurements of the specific activity of natural radionuclides in 20 soil samples were carried out using the gamma spectrometer NaI(Tl) with ‘Progress-2000’ software. Results: The territory of Pyatigorsk was mapped according to the degree of potential radon hazard. It was found that potentially radonhazardous areas are those composed of cover loams and clays with specific activity of 226Ra 30–64 Bq/kg. The arithmetic mean value of radon EEC in buildings in these areas is 125 and 109 Bq/m3 , and the proportion of EEC values exceeding the permissible level of 200 Bq/m3 is 18 and 13 %, respectively. Areas consisting of relatively low radioactive alluvial sediments and marls are characterised by a relatively low radium content in the soil (11–32 Bq/kg) and low radon EEC values in buildings (on average 50–70 Bq/m3 ); the proportion of radon EEC values exceeding the permitted level of 200 Bq/m3 in these areas does not exceed 5 %. Maps of both preQuaternary bedrocks and Quaternary sediments were used to correctly delineate areas characterised by different soil types. In some cases, the resolution and detail of the 1:200,000 scale proved to be insufficient, requiring additional geological investigations to clarify the position of geological boundaries on the ground. In the future it is planned to carry out more detailed studies of the specific activity of radionuclides in soils and to supplement the available data with the results of surface radon flux density measurements. The experience gained in zoning can be used in the development of theoretical bases for the mapping of potentially radon-hazardous areas.