Measurement of the Po-214 concentration in air using Makrofol-DE detectors

The measurement of the Po-214 concentration in air with Makrofol-DE detecto rs is useful to estimate the long-term averaged equilibrium factor indoors. To differentiate alpha-particles emitted by Po-214 from those emitted by P o-218 and Rn-222, the detector must register only alpha-particles with ener gies between 6.2 and 7.5 MeV. The required energy response is obtained only if a removed layer of about 43 mu m is achieved in a chemical etching of t he detector. The methodology used to determine the etching conditions is de scribed in this paper. The optimum conditions found are: a) chemical etchin g for 6 h at a temperature of 40 degrees C, using 7.5 M KOH mixed with 50 % ethanol as an etchant, and b) electrochemical etching for 1 h at a frequen cy of 3 kHz and an electric field strength of similar to 34 kV cm(-1). Seve ral dosimeters have exposed during 2 months in dwellings located in the Bar celona area, Spain. A Po-214 averaged concentration of (13.6 +/- 8.6) Bq m( -3) was obtained.