Changes in the concentration of tritiated water under vacuum distillation at around ambient temperature

When measuring the tritium concentration in environmental water by liquid scintillation counting, distillation of the water sample is indispensable. To investigate changes the tritium concentration during distillation, tritiated water was distilled under vacuum at around ambient temperature. During vacuum distillation, the tritium concentration in the residual sample water increased and that in the condensed sample water decreased. The change in the tritium concentration during the distillation process was explained by Rayleigh distillation model. When the volume of the condensed water sample was about 80% of that of the original sample, its tritium concentration was about 97% of that in the original sample. Therefore, water sample should be distilled above 80% of sample water to keep an underestimation of tritium concentration within 3%. (author)