Continual monitoring of radon decay products concentration in indoor and outdoor air

The goal of this work was the development of the method and construction and testing of measurement device for continual monitoring of radon daughters concentrations in the indoor and outdoor environment with regard to make possible to determine very low activities in the outdoor air (below % Bq/m3). In this method air sample is drawn through the appropriate filter material. Radon and thoron daughters both attached and unattached on aerosols particles are collected on the filter surface and then the filter activity is counted. The silicon surface barrier detector with the active area of 200 mm2 in monitor was used. The Millipore AW19-type filter was chosen and sampling rate of 30 l/min for collecting of the air samples. The determination of the individual activity concentrations in three-count method is based on the solution of the simultaneous equations describing the number of atoms of measured nuclides on the filter during and after sampling. The monitor was tested in three different environments (the average values of the activity concentrations of radon and its decay products in Bq/m3 are given): in the basement of the building: 61.4 ± 5.0 of 222Rn, 29.5 ± 2.8 of 218Po, 14.1 ± 1.8 of 214Pb and 12.1 ± 1.6 of 214Bi; in the room on the second floor of the same building:22.2 ± 7.9 of 222Rn, 7.3 ± 2.8 of 218Po, 4.6 ± 1.9 of 214Pb and 2.6 ± 1.2 of 214Bi ; in the outdoor air in front of the building: 4.1 ± 2.7 of 222Rn, 2.3 ± 0.9 of 218Po, 1.5 ± 0.8 of 214Pb and 1.4 ± 0.6 of 214Bi. The results show a good agreement with expectations of the activity concentrations in three different environments. The monitor enables to determine low activity concentrations in the outdoor with an acceptable precision during one hour counting. The monitor can be used for the research of the correlation between the atmospheric stability and activity concentrations of radon decay products