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 th e long-term equilibrium factor indoors to better ascertain the dose which p opulation is exposed to. The method used in our laboratory to obtain long-t erm equilibrium factors indoors is based on simultaneous measurements of Rn -222 and Po-214 in air by using a detector with two Makrofol-ED (polycarbon ate) foils covered with aluminised mylar: one placed inside a diffusion cha mber, and the other one in direct contact with air, allowing, respectively, the measurement of Rn-222 and Po-214 activity concentrations. The equilibr ium factor is estimated from the ratio of these two concentrations. The det ector has been calibrated at the radon chamber of the National Radiological Protection Board (NRPB), Chilton, UK. Sensitivity values of epsilon(0) = ( 0.85 +/- 0.04) (tr.cm(-2))/(kBq.m(-3).h) and epsilon(4) = (3.0 +/- 0.2) (tr .cm(-2))/(kBq.m(-3).h) have been obtained from the calibration for the meas urement of Rn-222 and Po-214, 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.