Effects of surface area and volume on the rate of isotopic exchange between water and water vapor
- Univ. of Nevada System, Las Vegas, NV (United States)
- Univ. of California, Davis, CA (United States)
The effects of surface area and volume on the rate of isotopic exchange between water and water vapor were quantified by allowing beakers containing waters with differing D, {sup 18}O, and tritium contents to equilibrate under controlled conditions in a closed system. Over a 2-month period the waters shifted by as much as 80{per_thousand} in {delta}D, 13{per_thousand} in {delta}{sup 18}O, and 57,000 tritium unit (TU), sometimes in opposite directions (either toward being more enriched or more depleted) depending upon initial compositions of the juxtaposed waters. Over time the concentrations of the stable and radioactive isotopes approach a common value, which in an ideal closed system represents the mean composition on a volumetric basis. The exchange rate is represented by dR{sub X}/dt={minus}(R{sub X}{minus}R{sub M})ks{sub x}/v{sub x} where R{sub X} represents the actual isotopic ratio of the water at time t, R{sub M} is equal to {alpha}{sub eg}*R{sub v} and represents the isotopic ratio of the water that would at any instant be in equilibrium with ambient vapor with an isotopic ratio of R{sub v}, and s{sub X}, and v{sub X} refer to the surface area and volume of the water, respectively. In these 20{degrees}C experiments the constant k ranged from 0.12 to 0.18 cm/d and was identical for D/H, T/H, and {sup 18}O/{sup 16}O exchange for a given set of conditions. In the case of identical surface areas and volumes the composition of the waters may change, but the vapor to which the waters respond remains the same during the exchange process. In the case of differing surface areas, or differing volumes, the composition of the vapor and R{sub M} will both change. In any case, after complete exchange, all waters will attain the same equilibrium isotopic ratio. 16 refs., 9 figs., 2 tabs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 160391
- Journal Information:
- Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: D11 Vol. 98; ISSN JGREA2; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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