Some problems on handling of tritium

When the problems of handling tritium-labelled compounds are pointed out, their difference from unlabelled compounds must be considered. The important points in this difference are that 3H compounds are very diverse, that the energy of 3H β-ray is very low, and that the isotopic effect is very large. Those utilized most frequently as 3H compounds are 3H2 and 3H2O. 3H is usually produced by 7Li(n,α)3H reaction, but the radionuclidic abundance is usually 98--99%. The origin of other H than 3H is not known yet. Recently, the total amount of supplied 3H is almost in agreement with the described amount. The radionuclidic purity is almost 100% in case of 3H2 or 3H2O. The radiochemical purity on experimental phenomena is not necessarily equal to the radiochemical purity of samples. In order to make exact experiment, radioactive impurity is diluted with not-radioactive one, and refining must be repeated until the original purity is recovered. Then the radioactivity due to the impurity is reduced remarkably. In order to conserve 3H compounds by reducing their primary self-radiolysis, they are dissolved in inactive, volatile solvents, and cooled to the temperature of liquid nitrogen. The derived working limit of 3H should be calculated on the basis of physicochemical and biological data, and the leak of 3H2 should be prevented carefully because of its high specific radioactivity. The decontamination of 3H compounds must be considered case by case. For the laboratory-scale disposal of 3H compounds, they should be converted to 3H2O and diluted with a large quantity of water. The absolute containment of 3H is impossible. (Kako, I.)