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Title: Adsorption and desorption of noble gases on activated charcoal: II. sup 222 Rn studies in a monolayer and packed bed

Adsorption and desorption of noble gases on activated charcoal: II. sup 222 Rn studies in a monolayer and packed bed The adsorptive and desorptive characteristics of canisters containing a petroleum-based charcoal were investigated under controlled conditions of temperature, relative humidity, and Rn concentration. Charcoals exposed in a monolayer and packed bed during exposure intervals of 1-7 d demonstrate that Rn adsorption and desorption are dependent on bed depth and the amount of water adsorbed. Changes in the adsorptive and desorptive properties of the charcoal occurred near the break-point where the pores became occluded by water vapor that condenses in the entrance capillaries. Radon-222 adsorption is decreased by an order of magnitude as the amount of adsorbed water exceeds the break-point of the charcoal. The reduction in pore surface due to adsorbed water results in a marked increase in the rate of Rn loss from exposed canisters, accounting for reduced adsorption. The apparent desorption time-constant for a 2-cm bed of loose Witco 6 x 10 mesh charcoal containing 0.220-0.365 kg H{sub 2}O kg-1 is typically between 2-8 h. The apparent desorption time-constant for an equivalent packed bed containing a water vapor content of 0.026-0.060 kg H{sub 2}O kg-1, which is below the break-point of the charcoal, is about 15-30 h. Conventional charcoal canisters, if exposed in the fully-opened configuration, can achieve more » the break-point in less than 4 d at 70% humidity. The use of a diffusion barrier would allow for longer exposure times until the break-point of the charcoal is achieved. « less
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Publication Date:
OSTI Identifier:6373241
Resource Type:Journal Article
Data Type:
Resource Relation:Journal Name: Health Physics; (USA); Journal Volume: 59:4
Country of Publication:United States
Language:English
Subject: 54 ENVIRONMENTAL SCIENCES; RADIATION MONITORS; DESIGN; RADON 222; RADIATION MONITORING; ACTIVATED CARBON; ADSORPTION; CHARCOAL; DESORPTION; PACKED BED; RADIOECOLOGICAL CONCENTRATION; ADSORBENTS; ALPHA DECAY RADIOISOTOPES; CARBON; DAYS LIVING RADIOISOTOPES; ECOLOGICAL CONCENTRATION; ELEMENTS; EVEN-EVEN NUCLEI; HEAVY NUCLEI; ISOTOPES; MEASURING INSTRUMENTS; MONITORING; MONITORS; NONMETALS; NUCLEI; RADIOISOTOPES; RADON ISOTOPES; SORPTION 540130* -- Environment, Atmospheric-- Radioactive Materials Monitoring & Transport-- (1990-)