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DETERMINATION OF ENVIRONMENTAL "'RN BY ADSORPTION IN A DIFFUSION BARRIER ACTIVATED CARBON COLLECTOR USING LIQUID SCINTILLATI ON COUNTING

By Andreas C. George, Jason Esposito and Nancy Bredhoff

Abstract

Activated carbon collectors using gamma-ra spectroscopy have been used successfully for the past 15 years for short-term measurements of indoor radon ( Rn). The collectors are usually 10 to 20 times heavier than the 20 ml vials that use alpha and beta liquid scintillation counting (LSC). Because several steps were required to prepare the samples for analysis, the LSC method did not enjoy the popularity of the more direct gamma counting method. An attractive alternative LSC method was investigated, developed, and made more direct by eliminating steps such as; the need for a desiccant, sample transfer, and the risk of sample degassification. A 20 rnl clear polyethylene terephthaiate (PET) plastic vial containing 2 g of very sensitive activated carbon is capped with a screw cap with a 6 mrn opening fitted with a 1 mm filter paper that serves as the diffusion barrier. The extraction of ^Rn from the exposed collector is carried out in the same plastic vial using a cocktail with a very high xylene content The extraction efficiency increases to 85 % after 3 hours of contact time and to 100 % in 15 hours. The PET vial was found to be impervious to ^Rn and cocktail. Analysis for ^Rn is performed with a Beckman LS 5000TD Liquid Scintillation System in a two-phase orientation. Calibration of the collector at different conditions of ^Rn concentration (1-50 pCi/L), relative humidity (30-70%), and exposure time (2-7 days) show adequate sensitivity. The Lower Limit of Detection (LLD) is 0.25 pCi/L for a 4 day exposure with analysis 3 days post exposure. The measurement errors at the 95 % confidence level for 1 pCi/L (37 ~ ~ land m 4 ~ pCi/L) (148 ~ q/m~) are 25 % and 8% respectively, when counting time is 10 minutes

Year: 2013
OAI identifier: oai:CiteSeerX.psu:10.1.1.371.6504
Provided by: CiteSeerX
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