Sources of Radiogenic 4He Dissolved in Groundwater

The radioactive decay of uranium and thorium results in the formation of a series of isotopes that are radiogenic by themselves and keep disintegrating into stable lead isotopes. These radioactive disintegrations are accompanied by the emissions of 4He atoms. Three such radioactive series exist  

The production rate of the radiogenic helium in each of these decay series is determined by the respective half-lives, and the overall helium production per unit rock is determined by the concentration of uranium and thorium in the rock (common rocks containing uranium and thorium in parts per million (ppm) concentrations). 

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