A new beaded carbon molecular sieve sorbent for {sup 222}Rn monitoring
- Department of Energy, New York, NY (United States)
A new commercially available beaded carbon molecular sieve sorbent, Carboxen-564 (20/45 mesh), was tested and compared to Calgon-PCB (40/80) activated carbon for its adsorptive and desorptive characteristics under controlled conditions of temperature (25{degrees})C and relative humidity (RH). The amount of water vapor adsorbed by the beaded carbon molecular sieve material was typically a factor of 4 lower than the activated carbon, with a concomitant fourfold increase in the {sup 222}Rn adsorption coefficient, K{sub Rn}. The maximum K{sub Rn} value for a thin layer of Carboxen-564, following a 2-d exposure at 40% RH, was 7.2 Bq kg{sup {minus}1} per Bq m{sup {minus}3}. The K{sub Rn} for a 1-cm bed, following a 2-d exposure was 5.5 Bq m{sup {minus}3}, a 25% reduction. under dynamic sampling conditions, where 0.4 g of the beaded carbon molecular sieve was contained in a 6 cm x 0.4 cm diameter tube, the maximum K{sub Rn} value was 6.5 Bq m{sup {minus}3} after 2.5 h of sampling at 29% RH when the input flow rate was 4.2 x 10{sup {minus}3} m{sup 3} h{sup {minus}1}. Kinetic studies were also conducted under passive sampling conditions. The data show that the {sup 222}Rn buildup time-constant for a thin layer of the beaded carbon molecular sieve material was 1.3 h, whereas that of a 1 cm bed was 13 h. The {sup 222}Rn desorption time-constants, from gram amounts of the beaded carbon molecular sieve material was 1.3 h, whereas that of a 1 cm bed was 13 h. The {sup 222}Rn desorption time-constants, from gram amounts of the beaded carbon molecular sieve material into air and into a commercially available toluene based liquid scintillation cocktail, were 2 h and 3 h, respectively. Carboxen`s high {sup 222}Rn adsorbing capacity, rapid kinetics, hydrophobicity and physical properties makes it an attractive alternative to other commercially available activated carbon used in passive and dynamic sampling devices. 18 refs., 7 figs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 283159
- Journal Information:
- Health Physics, Vol. 70, Issue 5; Other Information: PBD: May 1996
- Country of Publication:
- United States
- Language:
- English
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