We describe an advanced methodology for low-level tritium measurement in regard to calibration, electrolytic tritium enrichment, liquid scintillation counting (LSC) measurement, and prevention of sample contamination. Details are given on enrichment parameters and electrode processes for optimisation of enrichment reproducibility and on optimisation of LSC stability. Intercomparison results demonstrate high accuracy of the tritium measurement system. The use of accurate tritium data for groundwater dating in the southern hemisphere is demonstrated with data from several groundwater systems of New Zealand.

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THO deposition in the Southern Hemisphere is discuseed in the light of currently available tritium measurements of Southern Hemisphere precipitation. Many new results from the New Zealend laboratory are presented. Topics discussed include the seasonal and latitudinal variations of THO fallout, the fallout history of tropospheric and stratospheric thermonuclear THO, and the effects of the continental environment upon many of the reported measurements.

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