By determining the specific activities of two mass-spectroscopically analyzed samples of barium carbonate containing ${\mathrm{C}}^{14}$, the half-life of the ${\mathrm{C}}^{14}$ was found to be 5100±200 years. In order to determine the relative abundance of ${\mathrm{C}}^{12}$, ${\mathrm{C}}^{13}$, and ${\mathrm{C}}^{14}$, the C${\mathrm{O}}_2$ was roasted from the barium carbonate and introduced into the mass spectrometer. Weighed portions of the barium carbonate were subsequently counted in a low absorption beta-counter. Details of the analysis, weighing, and counting are given.

• Received 3 November 1947

DOI:https://doi.org/10.1103/PhysRev.73.350