Main cosmogenic nuclei
Carbon-14 and tritium are the main radioactive elements generated by cosmic rays. The inventory represents the total activity in the atmosphere estimated at the scale of the Earth (1 PBQ equals 1 million giga-bequerel). Some of the carbon-14 is absorbed by plants and for tritium in water. The order of magnitude of activities are of millibecquerels per cubic meter of air.
IN2P3 (Source Cours K.Gerber)