γ-Spectrometric method for determining the natural radionuclides in atmospheric air and air inside rooms

Abstract

Most city residents live and work under conditions where the concentration of radon and its decay products does not exceed 20-200 Bq/m 3, while the world average is 5-150 Bq/m 3, including in Russia where the concentration is 4.8-160 Bq/m 3 [1, 2]. A small fraction of the population (-0.1%) encounters radiation hazardous conditions (concentration of radon and its decay products equal to 200-300 Bq/m 3 and higher), since the operating stapdards limit the emanation content to 100 Bq/m 3 for new buildings and 200 Bq/m 3 for old buildings [3].The main sources of radon inside buildings are soil and building materials with a high uranium or radium concentration, boilers, central thermal and electric power plants and thermal and electric plants burning coal and especially natural gas. The atmosphere in industrially developed cities can be contaminated with radon up to a level of 1.5 kBq/m 3 [4]. In the latter cases, the following radionuclides (in 101~ Bq) enter the atmosphere together with the products of incomplete fuel combustion: up to 6.8 238U, 4.2 232Th, 9.1 4~ and up to 1.1.1014 Bq 222Rn, including up to 1-104 and 0.1-3-1014 Bq/yr as a result of the combustion of gas and coal, respectively [1].Our objective in the present work was to develop the technical and methodological means for obtaining samples and for bulk determination of radionuclide composition of atmospheric air and air inside buildings, including radon and its decay products, with the aid of semiconductor "r-spectrometry under conditions of low-background measurements as well as radon in air in rooms with the aid of very simple radiometric means available to any ordinary radiation-monitoring laboratory.Determination of Radionuclides in Atmospheric Air. Atmospheric air was investigated in the southeastern part of Rostov-on-the-Don. To obtain aerosol samples, using a typical ventilation unit with a capacity of 54 m3/h, a stationary filteringventilation system was assembled. The system was placed in open air so that its intake opening was located 1.5 m above the ground. Dust was removed from the intake airflow by means of cotton fabric and impinged on a board with aerosol filters of the type AFA-RMA-20 with a total area of 740 cm 2. The velocity of the airflow at the exit was determined with a ASO-3 anemometer.Aerosol samples were obtained to determine the short-lived radon decay products within a time of 1-3 h and long-lived radionuclides (decay products of thoron and other nuclides) within a time of 10-24 h. The "y-ray spectrum of the filters was measured on a ROUS-II-15 setup after sampling was completed; the setup was certified by the Scientific and Industrial Association "All-Russia Scientific--Research Institute of Ph3/sicotechnical and Radioelectronic Measurements" of the State Standards Office of the Russian Federation as a second class sample system. The setup was assembled on the basis of a typical DGDK-80 Ge(Li) detector and a low-background chamber with multitayer shielding, which decreased the instrumental background by a factor of 80-100 [...