Laboratory Scale Investigation of Some Factors Affecting Radon-222 Air Concentrations

A.M. Mamoon (Egyptian Atomic Energy Authority)

In a continuing investigation to develop simple laboratoy scale exposure systems to determine changes in 222Rn air concentrations in response to various relevant factors two laboratory systems are being tested for their reliability. One exposure septem is a large laboratary desiccator (14.5L) in which a radon source (crushed granite in a container) and a charcoal canister can be placed. Standard charcoal canister technique along with gamma spectroscopy was used for 222Rn assay in the ambient air. The 222Rn concentration in the desiccator's air increased almost liniarly with increase of source mass and also with increase in duration of exposure. The radon concentration was highest at the bottom of the desiccatar and decreased with vertical distance only when the desiccatar was in semi-open situation but almost unchanged when the desiccator was completely closed. This is most likely due to homogenisation of 222Rn air cancentrations. The effect of ambieent temperature was studied by using a two canister system: a bottom canister which was emptied from charcoal and has instead the crushed source and on top of it, an inverted regular charcoal canister. Both canisters were sealed with three layers of vinyl tape. Many such two canister systems were placed either in a thermostated refigerator or in a self regulating oven. Exposure temperatures varied from –10°C to 55°C. Little change in 222Rn air concentration was observed inside the two canister system until about 40°C when radon concentration started to rise. It should be noted that while increase in ambient temperature my help release trapped radon in the source it also decreases the adsorption of radon by charcoal. The mitigating effect of charcoal was obvious when 150 gram of source were covered with about 80 grams of activated charcoal resulting in about 87% reduction in 222Rn air concentratian. The collective results reported from these expeiments are in agreement with simlar studies carried out in the open environment which indicates the reliability of the exposure systems used.

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