Factors influencing reactivity of thermal H(T) atoms with solids. I. Physical effects

sum The effects of surface area and the nature of the surface were investigated for samples labeled by the microvave discharge activation (MDA) - tritium atom technique. When labeling powdered samples of different chemical structure the crude specific activity (prior to purification) was shown to increase linearly with t he specific area (m2/g) although the final specific a ctivity of the purified compound was found to be dependent on the chemical nature of reacting sample. Samples deposited on high surface area, microporous membrane filters, showed large i ncreases in specific activities compared to the l abeling of powdered samples. In this case the specific activity was found to be a function of sample thickness (mg/m2) reaching a maximum when the amount of sample was less than or equal to a monolayer on the filter surface and decreased as the reciprocal of the sample weight when a monolayer was exceeded. Finally, a survey of the labeling p roperties of 20 selected filters using L-proline as a model compound was carried out. Cellulosic (hydrophilic) filters were found in general to labeled proline of the highest specific activities whereas the hydrophobic (vinyl, fluorocarbon, etc.) yielded the lowest. It was also found that the specific activity of most (15 of 20) of the filters was linearly related to tritium yield (X tritium recovered in proline after purification) in the labeled p roline.