Determination of tritium by mass spectrometric measurement of 3He

Abstract

A new technique for analysis of environmental tritium is described. The method consists of mass-spectrometer measurements of 3He allowed to accumulate for suitable times in degassed samples of water sealed in containers made of Corning type-1720 glass. Twelve samplesfrom the Pacific Ocean were measured by this method and also β-particle counting at the University of Miami. Agreement between the two methods in satisfactory, although our results seem to be systematically higher than the Miami results by ∼ 2%. Mass-spectrometric measurements were also made of the tritium concentration in the 1961 NBS tritiated water standard. These gave a concentration 1.6(±0.6)%higher than that calculated from the stated NBS activity per gram using a half-life of 12.26 years, which was also used to correct for decay to August 1975. If a half-life of 12.51 years is used, the above discrepancy is eliminated. As part of this work, the 3He/4He ratio in atmospheric helium has been redetermined, and found to be 1.384 × 10-6 (±0.4%), which is in good agreement with the value of 1.399 × 10-6 (±0.9%) measured by Mamyrin, Anufriyev, Kamenskiy and Tolstikhin. © 1976.