High-precision helium isotope measurements in air Journal Article uri icon

DCO ID 11121/7228-1371-3819-9280-CC

is Contribution to the DCO

  • YES

year of publication

  • 2013

abstract

  • Helium has two natural isotopes which have contrasted, and variable sources and sinks in the atmosphere (3 He/4 Heair  = 1.382 ± 0.005 × 10−6 ). Variations in the atmospheric helium isotopic composition may exist below typical measurement precision thresholds (0.2 to 0.5%, 2σ ). In order to investigate this possibility, it is necessary to be able to consistently measure helium isotopes in air with high precision (below 0.2% 2σ ). We have created an air purification and measurement system that improves the helium isotope measurement precision. By purifying a large quantity of air at the start of a measurement cycle we can make rapid standard-bracketed measurements. Controlling the amount of helium in each measured aliquot minimizes pressure effects. With this method we improve the standard errors by 2× over measuring the same amount of gas in a single step. Individual measurements have standard errors of 0.2 to 0.3% (2σ ), with three repeat samples needed to reach 0.1% or better errors. The long-term reproducibility of our calibration sample is 0.033% (2σ ).

publication date

  • 2013

volume

  • 28

issue

  • 12