These are designated C12, C13 and C14 in scientific notation, the letter C being the symbol for elemental carbon and the isotopes having atomic weights 12, 13 and 14 respectively.
By 1949, when Libby and Anderson (now joined in Chicago by James Arnold) published results of a world-wide assay of radiocarbon, enrichment was no longer necessary.
The assay showed the contemporary level of radiocarbon in wood to be the same globally.
They showed that methane collected from the Baltimore sewage works had measurable radiocarbon activity, whereas methane manufactured from petroleum did not, and the implications of the findings for dating of carbonaceous materials were noted.
These first experiments required enrichment of the radiocarbon in the sample to make it easily detectable.
In 1946 he published a paper suggesting that radiocarbon might exist in living matter.