Term used to describe the addition of a 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 Click on Term to Read More Core of an atom, where nearly the entire mass and all positive charge is concentrated. It consists of protons and neutrons. Click on Term to Read More (4He) to existing nuclei with in a giant Self-luminous object held together by its own self-gravity. Often refers to those objects which generate energy from nuclear reactions occurring at their cores, but may also be applied to stellar remnants such as neutron stars. to form heavier elements. At temperatures above 2 x 108 K, a 12C nucleus colliding with 4He nucleus can produce 16O. Although the 16O produced may fuse with other 16O nuclei at ~109 K to form 32S, it is much more probable that an 16O nucleus will capture a 4He nucleus (if one is available) to form 20Ne. Thus, as the star evolves, heavier elements tend to form through 4He-capture rather than 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 Click on Term to Read More of like nuclei.
The α process will continue up to the formation of 56Ni. However, 56Ni is unstable and decays rapidly into 56Co, then into stable 56Fe (the most stable of all nuclei). Thus, the alpha process leads inevitably to the buildup of iron in the stellar In the context of planetary formation, the core is the central region of a large differentiated asteroid, planet or moon and made up of denser materials than the surrounding mantle and crust. For example, the cores of the Earth, the terrestrial planets and differentiated asteroids are rich in metallic iron-nickel. Click on Term to Read More. Because helium-capture reactions are so much more common, elements with nuclear masses of 4 units (4He, 12C, 16O, 20Ne, 24Mg, and 28Si) have markedly higher cosmic abundances (below).
Some or all content above used with permission from J. H. Wittke.