Abundance and origin

Helium is the second most abundant element in the Universe after hydrogen both elements are concentrated in the stars. The He abundance in the Sun is 3 x lO that of Si, whereas on Earth it is only 5 x 10 that of Si. There are two naturally-occurring isotopes, He and He, which may be either primordial or radiogenic in origin. Primordial He is formed by the collision of hydrogen and deuterium atoms  

The two He isotopes have approximately the same abundance throughout the universe. Some primordial helium was trapped during the accretion of the Earth, with an estimated He/ He ratio of 10 . This is still retained in the mantle and, to a lesser extent, the core, and is now outgassing along deep faults and fissures and during volcanic eruptions. The 

Both isotopes of He can also be radiogenic in origin. Most terrestrial and atmospheric He is radiogenic and has formed since the accretion of the Earth as a product of the alpha-decay of some naturally-occurring radioactive isotopes. On ejection from its parent isotope, an alpha particle (which is a He nucleus comprising two neutrons and two protons) 

Although most terrestrial He is primordial, there is a significant radiogenic component in both the cmst and the atmosphere. The main source is the decay of tritium  

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Lambert DL(1992) The p-nuclei. Abundances and origins. Astron Astrophys Rev 3 201-256 Larimer JW (1967) Chemical fractionation in meteorites. 1 Condensation of the elements. Geochim Cosmochim Acta 31 1215 -123 8... 

Zheng, M., Wan, T.S.M., Fang, M., Wang, F., 1997. Characterization of the non-volatile organic compounds in the aerosols of Hong Kong Identification, abundance and origin. Atmos. Environ. 31, 227-237. 

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