MEASUREMENT OF HELIUM ISOTOPE RATIOS BY MASS-SPECTROMETRIC COMPARISON WITH SYNTHETIC BLENDS with a possible application to the leak testing of large rigs

摘要

The relative abundance of helium isotopes in a mixture has been measured by comparison with synthetic blends of known compositions using a modified AEI Type MS3 mass spectrometer. A single collection procedure with direct read-out on a carefully calibrated desk meter gave a precision of 1.7 x 10-3 for a single comparison lasting 10 minutes. By intercalibrating a series of synthetic blends, the accuracy of the method was shown to be 2.5 x 10~3 (2d).nThe procedure has been applied to measure the relative abundance of small amounts of helium isotopes present in a large excess of carrier gas, during an evaluation of a new method of leak testing large sodium rigs based on an isotopic tracer technique. In this case, a preliminary separation of the helium from the carrier gas is required. The equipment used to do this introduced a small fractionation during sample transfer amounting to 1 ± 1%.