Determination of the long-term equilibrium factor indoors by means of Makrofol track-etched detectors

From the point of view of radioprotection, it is worthwhile to determine the long-term equilibrium factor indoors to better ascertain the dose which population is exposed to. The method used in our laboratory to obtain long-term equilibrium factors indoors is based on simultaneous measurements of 222Rn and 214Po in air by using a detector with two Makrofol-ED (polycarbonate) foils covered with aluminised mylar: one placed inside a diffusion chamber, and the other one in direct contact with air, allowing, respectively, the measurement of 222Rn and 214Po activity concentrations. The equilibrium factor is estimated from the ratio of these two concentrations. The detector has been calibrated at the radon chamber of the National Radiological Protection Board (NRPB), Chilton, UK. Sensitivity values of ε0 = (0.85 ± 0.04) (tr-cm-2)/(kBq-m-3·h) and ε4 = (3.0 ± 0.2) (tr-cm-2)/(kBq-m-3-h) have been obtained from the calibration for the measurement of 222Rn and 214Po, respectively. A radon activity concentration of 44 Bq·m-3 and a mean equilibrium factor of 0.42 have been obtained in a pilot application indoors.