EXPERIMENTAL EVALUATION OF WIRE MESH SCREEN COUNTING PARAMETERS FOR MEASUREMENTS OF THE UNATTACHED FRACTION OF RADON PROGENY

Direct measurements (specifically the front-to-back ratio) of alpha ra dioactivity from radon progeny deposited on the front and back of a 40 0-wire mesh screen were performed under realistic aerosol conditions o utdoors with two scintillation alpha detectors facing both sides of th e screen simultaneously. Two flow regimes were tested: one which kept the flow Reynolds number (Re(f)) for the wire below one (200 L min-1) and a second with the now Reynolds number for wire > 1 (400 L min-1). To estimate the radioactivity loss in the screen, parallel measurement s of open and backup filters were also performed. The average front-to -back ratio expressed as a ratio of the potential alpha energy concent ration as measured on the screen side facing the airflow to the other side of the screen for 200 L min-1 and 400 L min-1 was 3.42 +/- 0.32 ( standard error) and 2.30 +/- 0.14 (standard error), respectively. The loss of radioactivity in the screen expressed as a ratio between the p otential alpha energy concentration measured on an open filter minus b ackup filter to the sum of the potential alpha energy concentration me asured on the front and back of the screen was 1.29 +/- 0.13 and 1.27 +/- 0.22 for 200 and 400 L min-1, respectively.