Vapor exchange tritium

The surface waters of the ocean are the largest sink for tritium. Transfer into the surface ocean occurs by water vapor exchange, precipitation and continental run-off (e.g., Weiss et al. 1979 Weiss and Roether 1980). Most of the nuclear weapons tests were performed in the northern hemisphere, leading to a strong asymmetry in the global north-south distribution of bomb tritium in the ocean surface waters. Concentrations in the northern hemisphere are relatively high compared to those in the southern hemisphere (Weiss and Roether 1980 Fig. 1). 

The deposition of tritium to the oceans occurs both by direct precipitation and by vapor exchange. Vapor exchange is a two-way process, and in general dominates over the direct precipitation. There are relatively few direct measures of tritium concentration in atmospheric water vapor, but studies indicate that it is closely related to levels in precipitation. This linkage has been exploited in order to construct tritium depositional histories for ocean basins from tritium in precipitation records. 

D2O-DT exchange can be used for transferring tritium from heavy water to deuterium. Further enrichment is achieved by cryogenic distillation. Because of the similarity between deuterium and tritium, platinum on charcoal is the catalyst for vapor phase exchange, whereas hydrophobic catalyst is used for liquid-gas exchange. 

Investigations utilizing tritiated molecules are fraught with numerous methodological problems. Most significant among these are the exchange of tritium between radiolabeled molecules and water and the subsequent loss of tritiated water vapor into the atmosphere (for example see Jacobs,... 

Several factors influence the half-time of tritium loss from the film tubes (Table 1). As size of the air space above the scintillator (and therefore the total exchange surface area of the tube) increases, the rate of loss of THO increases. This indicates that THO not only diffuses out of the tube directly from the solvent phase but from the gas phase above the scintillator as well. Solvent systems which increase the water vapor pressure in the enclosed tube by decreasing the soliiiility coefficient of water, micelle stability or micelle surface area to volume ratio would be eiqjected to decrease the half-time for THO loss. This would e q)lain the difference in half-times between the toluene and xylene derivative based scintillation solutions. 

Since 1952, most of the tritium measured in the atmosphere originates from thermonuclear explosions. Like hydrogen, deuterium and tritium also exhibit molecular isomerism. Because of the important differences between the relative atomic masses of the three isotopes, their physical properties (e.g., density, enthalpy of vaporization) differ greatly. This allows an easier isotopic separation than for any other element. Several separation processes are used for the enrichment and separation of hydrogen isotopes. Most of these processes use isotopic exchange reactions (e.g., H D-H O or NH3-HD) and to a lesser extent fractional distillation and water electrolysis (e.g., Norway, Canada). 

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