The Bremen mass spectrometric facility for the measurement of helium isotopes, neon, and tritium in water

We describe the mass spectrometric facility for measuring helium isotopes, neon, and tritium that has been operative at this institute since 1989, and also the sampling and sample preparation steps that precede the mass spectrometric analysis. For water samples in a near-equilibrium with atmospheric air, the facility achieves precision for He-3/He-4 ratios of +/- 0.4% or better, and +/- 0.8% or better for helium and neon concentrations. Tritium precision is typically +/- 3% and the detection limit 10mTU (approximate to 1.2 . 10(-3) Bq/kg of pure water). Sample throughputs can reach some thousands per year. These achievements are enabled, among other features, by automation of the measurement procedure and by elaborate calibration, assisted by continual development in detail. To date, we have measured more than 15,000 samples for tritium and 23,000 for helium isotopes and neon, mostly in the context of oceanographic and hydrologic work. Some results of such work are outlined. Even when atmospheric tritium concentrations have become rather uniform, tritium provides water ages if He-3 data are taken concurrently. The technique can resolve tritium concentrations in waters of the pre-nuclear era.