Formation of heavy elements by the capture of Helium (He) Second lightest and second most abundant element (after Hydrogen) in the universe. The most abundant isotope is 4He (99.9998%), 3He is very rare. Helium comprises ~8% of the atoms (25% of the mass) of all directly observed matter in the universe. Helium is produced by hydrogen burning inside nuclei. For example, at ~6 x 108 K, Element commonly found in meteorites, it occurs in several structural forms (polymorphs). All polymorphs are shown to the left with * indicating that it been found in meteorites and impact structures: a. diamond*; b. graphite*; c. lonsdalite*; d. buckminsterfullerene* (C60); e. C540; f. C70; g. amorphous carbon; h. carbon nanotube*. can form heavier elements by Process in which two lighter atomic nuclei combine to form a heavier atomic nucleus. Very high temperatures are normally required in order for atomic nuclei to collide with sufficient energy to overcome the Coulomb barrier (their mutual electrostatic repulsions). Fusion that occurs under high-temperature conditions is called thermonuclear fusion. Fusion with other carbon nuclei:
However, fusion is more likely to occur by helium capture, which requires less energy and lower temperatures (~2 x 108 K):
Similarly, 16O may fuse with other 16O nuclei at ~109 K to form 32S, but it is much more probable that 16O will capture a 4He Core of an atom, where nearly the entire mass and all positive charge is concentrated. It consists of protons and neutrons. (if one is available) to form 20Ne. Again, 4He capture is more likely because it requires a lower temperature. Elements with nuclear masses of 4, 12, 16, 20, 24, and 28 have much higher abundances than other isotopes.
Some or all content above used with permission from J. H. Wittke.