Deposition of radioiodine to surfaces

Elemental iodine is a reactive gas, and the rate of uptake on certain surfaces is controlled by the rate of diffusion through the boundary layer over the surface. At some surfaces, tracer quantities of iodine are adsorbed irreversibly, at others reversibly. In most applications the amount of iodine on the surface is much less than a monolayer, and the equilibration between the adsorbed and airborne iodine cannot be considered in terms of vapour pressure. In 1949, experiments were started at Harwell, both in the wind tunnel and in the field, to study the deposition of elemental 131I vapour to surfaces. 

The velocity of deposition of radioiodine, defined as in equations (2.3) and (2.4), is controlled by the rate of adsorption at the surface. When the adsorption or chemisorption at the surface is strong, the rate of deposition of 131I, when expressed in terms of suitable non-dimensional parameters, is similar to the rate of heat transfer to or from the surface (Chamberlain, 1953). In field experiments, artificial leaves of copper or silver foil were attached to vegetation, and it was found that the uptake of 131I to real leaves was typically 0.4 to 0.7 times the uptake to artificial leaves. Since a thin film of paraffin was found to inhibit 

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