A Redetermination of the Relative Abundances of the Isotopes of Carbon, Nitrogen, Oxygen, Argon, and Potassium

TLDR

The authors produced pure ${}^{36}$A and ${}^{40}$A samples by thermal diffusion, used them to create synthetic argon isotope mixtures with accurately measured ${}^{36}$A/${}^{40}$A ratios, and employed these mixtures to evaluate mass‑discrimination effects in two mass spectrometers while determining new relative isotope abundances for carbon, nitrogen, oxygen, argon, and potassium. The study reports new relative isotope abundances for carbon, nitrogen, oxygen, argon, and potassium, a conversion factor of 1.0002783 ± 5 between physical and chemical atomic weight scales using atmospheric oxygen, and a K⁴⁰ abundance of 0.0119 ± 0.0001 %—about ten percent higher than the accepted value.

Abstract

Essentially pure samples of ${\mathrm{A}}^{36}$ and ${\mathrm{A}}^{40}$ have been produced by thermal diffusion and used for the preparation of synthetic argon isotope mixtures whose ${\mathrm{A}}^{36}$/${\mathrm{A}}^{40}$ isotope abundance ratios were very accurately determined. The mixtures were then employed for determining the mass discriminating effects in two mass spectrometers. Carbon, nitrogen, oxygen, argon, and potassium were investigated and new values given for the relative abundances of the isotopes. With atmospheric oxygen as a standard, the conversion factor between the physical and chemical atomic weight scales is 1.0002783\ifmmode\pm\else\textpm\fi{}5. The percentage abundance of ${\mathrm{K}}^{40}$ in potassium is found to be 0.0119\ifmmode\pm\else\textpm\fi{}0.0001 percent, a figure of special interest in geophysical problems, and approximately ten percent higher than the present accepted value.