Synthesis of tritium-free water for liquid-scintillation counting, 1

In order to carry out the measurement of low-level tritiated samples, such as environmental ones, liquid scintilation couting method is mainly used. In this method the back-ground water, tritium free water, plays a vital role. Generally, deep well water or deep sea water are adopted, but it is difficult to prove clearly that the waters do not contain any tritium . On this account, we developed an apparatus which synthesizes 'tritium free water' from natural gas. The gas and oxygen mixed with argon were circulated in a closed system, the gas was oxydized to water by means of paradium catalyst, and synthesized water was trapped by a column filled with molecular sieve. The examination results on the synthesized water, which was produced by using the commercial oxygen gas products, indicated an unexpected level of tritium, 6.8±1.6pCi/l, and it was clarified that the presence of tritiated methane in the oxygen caused it. By this reason, we concluded that using more purified oxygen and improving the system would bring us 'tritium free water' which was practically fit for use. (author)