Liquid scintillation counting is the preferred method.during his tenure as a professor at the University of Chicago.Libby estimated that the radioactivity of exchangeable carbon-14 would be about 14 disintegrations per minute (dpm) per gram of pure carbon, and this is still used as the activity of the modern radiocarbon standard.
One side-effect of the change in atmospheric carbon-14 is that this has enabled some options (e.g., bomb-pulse dating Carbon-14 is produced in coolant at boiling water reactors (BWRs) and pressurized water reactors (PWRs).
It is typically released to the atmosphere in the form of carbon dioxide at BWRs, and methane at PWRs., radioactive carbon dioxide.
The gas mixes rapidly and becomes evenly distributed throughout the atmosphere (the mixing timescale in the order of weeks).
The fraction of the radiation transmitted through the dead skin layer is estimated to be 0.11.
Small amounts of carbon-14 are not easily detected by typical Geiger–Müller (G-M) detectors; it is estimated that G-M detectors will not normally detect contamination of less than about 100,000 disintegrations per minute (0.05 µCi).