Interpretation of groundwater ages Most groundwaters are mixtures of water with different ages because of the nature of flow in porous media.The age distribution depends on the hydrogeologic attributes of the aquifer concerned, as well as characteristics of the sampling point such as bore depth and screen length.In our tritium measurement, water samples of 0.5-3.0litres (or even less) are generally used for the He that has been generated from a certain amount of water and is ﬁnally determined using a helium mass spectrometer.This method is the most sensitive one that can be used to detect low-level tritium concentrations of environmental waters.Water in rain, oceans, lakes, streams and glacial ice pick up these tracers through contact with the atmosphere.
Tritium is also produced in nuclear reactions, hence there was a large peak in atmospheric tritium concentration in the 1960s and early 1970s is due to nuclear weapons testing.
In contrast to other noble gas mass spectrometric laboratories, we have developed and applied a novel helium isotope dilution technique, which has signiﬁcantly improved the accuracy of our tritium measurements.
The method consists of four major steps: (1) a water sample is ﬁrst distilled; (2) then the distilled water sample is loaded into a metal container (0.1–7.0litres) and the dissolved gases including helium are removed from the water by vacuum pumping; (3) the sample is stored for a few weeks or months so that He atoms are produced from tritium decay; and (4) the helium fraction that comes from the decay of the tritium is admitted into the noble gas mass spectrometer and then the abundance of the helium isotopes is measured simultaneously.
The tritium concentration of a sample can be calculated from the measured ), tse and tem are the times elapsed from sampling to extraction and from extraction to measurement, respectively, m and Δm are the masses of the sample and the vaporised water during the degassing step, and α=1.15 is the ratio of the tritium concentration in the liquid phase and the water vapour.
Please contact us to discuss your needs before sending your samples to our lab.