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Nuclei


Origin of Elements

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.

Figure 14-03 Element Abundance
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The rest of the heavy elements come from a poorly understood process, which requires the presence of a staggering numbers of neutrons. It is thought that such event may occur in the collision of neutron stars or from supernova explosions that form neutron stars. There are 92 elements 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 14-03 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.

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