VG-5400 noble gas mass spectrometer
The VG-5400 is a dedicated mass spectrometer for noble gas isotopes. It is a double focusing instrument with extended geometry.
It has a Nier-type ion source, an electromagnetic analyser, a Faraday collector with a 100 GOhm resistor, and an ion counter (SEM: secondary electron multiplier). The sample is admitted the mass spectrometer through a cryogenic preparation and purification line. The sensitivity of the mass spectrometer is 1×10-3 A/Torr and 2×10-4 A/ Torr for argon and helium, respectively. It enables us to detect even 5000 3He atoms. The resolution of more than 600 at 3 amu allows us to resolve a 3He+ peak and H3+/HD+ double peak. The tritium concentration of environmental water samples are determined via the mass spectrometric analysis of its daughter, 3He. The pressure sensitivity and hence the systematic error of the measurement of low level helium abundances are eliminated by adding an ultrapure 4He spike to each tritiogenic 3He samples. The 10-20 % of systematic error could be reduced below 2 permil. Besides tritium analyses, noble gases dissolved in groundwater are determined by the mass spectrometer. 3H/3He apparent ages and recharge temperatures can be calculated from the noble gas concentrations and helium isotope ratios. All these values are applied in the research of recharge areas and palaeoclimate.