Isotopic analysis of hydrogen-helium mixtures

A direct sampling method utilizing capillary sampling lines is described. Mass spectrometers (MS) with low resolution (m/Δm less than 150) are useful in monitoring tritium purity. Medium resolution mass spectrometry (m/Δm = 600) provides quantitative analysis of mixtures known to be in isotopic equilibrium. An example is a Mound-built magnetic scanning cycloid MS which produces deuterium and tritium analyses with accuracy of 2% relative or better for concentrations of 15 mole % or greater. Helium is less accurate by a factor of two because of low ionization cross section. An instrument for inert gas and total tritium analysis has also been developed at Mound with accuracy for total tritium and helium of 1% relative or better above 15 mole %, and 2% or less down to 2 mole %. All accuracies have been determined using Mound deuterium/tritium/helium-3 standard mixtures traceable to NBS. An overall improvement of accuracy occurs from the systematic combination of results from multiple instruments. The need for high resolution MS (m/Δm greater than 1500) to quantify HT and D2 in non-equilibrium mixtures is presented