Answers are grounded in this paper and cite their sources.
The Bureau of Mines, Helium Field Operations, in Amarillo, Texas, has developed a method for direct measurement of the helium 3 content of air by mass spectrometry. The helium is preconcentrated by passing samples of air through a charcoal trap at liquid nitrogen temperature. Sample measurements are compared with identically made measurements of gravimetrically prepared standards. The helium 3 content of near‐surface atmospheric air is determined to be 7.27±0.20 parts per trillion by volume (pptv). The accuracy of 0.20 pptv is at the 68% confidence level. The helium 4 content of near‐surface atmospheric air has recently been determined at this facility to be 5.2204±0.0041 parts per million by volume (ppmv). The helium 3/helium 4 ratio for atmospheric helium, RA, is established as 1.393×10−6 by independent measurements of the separate components.
No takes yet. Share an insight, caveat, or question.
Davidson et al. (1990) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: