Nuclei

Origin of Elements

Light elements (mainly hydrogen, helium and trace of deuterium, lithium) were generated in the first few minutes of the Big Bang, which was not able to produce more complex elements as the universe rapidly cooling off. Since then hydrogen and helium contribute by mass of respectively 70 and 28 per cent of all baryonic matter in the universe. Most of the remaining 2% of the elements up to iron and nickel are made in the interior of the stars. The resulting elements are thrust into space by booming stellar winds or when a star explodes as a supernova. Carbon, nitrogen and oxygen are the most abundant heavy elements. Oxygen is created by supernovae, while carbon is created in low-mass stars (red giants, planetary nebulae) and nitrogen is made by both processes mentioned above. Cosmic ray

Figure 14-03a Element Abundance [view large image]

spallation (fagmentation of larger atomic species by cosmic ray) is a significant source of the lighter nuclei, particularly Li, Be and B, that are not created by stellar nucleosynthesis.

known to occur naturally on Earth; 83 of these are stable, and the others are radioactive. More than 20 elements with atomic numbers greater than 92, have been created artificially in particle accelerators. All are extremely unstable and decay rapidly into lighter elements. The "local galactic" abundance diagram of Figure 14-03a indicates the elements from hydrogen to beryllium are generated by BB (Big Bang); heavier elements up to nickel are produced by nuclear burning inside stars; the other heavy elements come from a neutron capturing process with the neutron subsequently decays to proton. Nuclear statistical equilibrium is referred to the state in which forward and reverse nuclear reactions balance.

Figure 14-03b Generation of Elements [view large image]

Figure 14-03b lists the generation processes for all the elements in the periodic table.

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