Helium Capture

Formation of heavy elements by the capture of heliumHelium (He) Second lightest and second most abundant element (after Hydrogen) in the universe. The most abundant isotope is He (99.9998%), He 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, carbonElement 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 fusionProcess 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 nucleusCore 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.