nucleosynthesis - Processes, Types of nucleosynthesis

The creation of chemical elements by nuclear reactions in stars and other cosmic explosions. Current theory suggests that the very early universe consisted only of hydrogen and helium. Hydrogen burning in stars, and nuclear explosions at the end of a star's life, have formed all other elements by transmutation. Carbon atoms in the ink on this page were made thousands of millions of years ago in an exploding star by fusing together three helium nuclei at a temperature of 10^7–8 degrees.

Nuclear processes
Radioactive decay processes Alpha decay Beta decay Cluster decay Double beta decay Double electron capture Electron capture Gamma radiation Internal conversion Isomeric transition Neutron emission Positron emission Proton emission Spontaneous fission Nucleosynthesis Neutron Capture The R-process The S-process Proton capture: The P-process The Rp-process Spallation

Nucleosynthesis is the process of creating new atomic nuclei from preexisting nucleons (protons and neutrons). The subsequent nucleosynthesis of the elements (including all carbon, all oxygen, etc.) occurs primarily in stars either by nuclear fusion or nuclear fission. Fred Hoyle's original work on nucleosynthesis of heavier elements in stars (including a detailed mechanistic analysis for the production of carbon) occurred just after World War II, but this work was in search of a way to produce heavier elements from hydrogen in stars, in the steady state model of cosmology.

Processes

There are a number of astrophysical processes which are believed to be responsible for nucleosynthesis in the universe. The successive nuclear fusion processes which occur inside stars are known as hydrogen burning, helium burning, carbon burning, neon burning, oxygen burning and silicon burning. These processes are able to create elements up to iron and nickel (62Ni is the isotope with the highest binding energy). Heavier elements can be assembled within stars by a neutron capture process known as the s process or in explosive environments, such as supernovae, by a number of processes. Some of the more important of these include the r process which involves rapid neutron captures, the rp process which involves rapid proton captures and the p process (sometimes known as the gamma process) which involves photodisintegration of existing nuclei.

Types of nucleosynthesis

The types of nucleosynthesis known of are:

Big Bang nucleosynthesis (see link for details), which occurred within the first three minutes of the universe is responsible for much of the abundance ratios of H (deuterium), helium-3 (He), in the universe . Although H continue to be produced by spallation and certain types of radioactive decay (proton emission and neutron decay), most of the mass of these isotopes in the universe, and all but the insignificant traces of the Li, are believed to have been formed when the universe was between 100 and 300 seconds old, after the primordial quark-gluon plasma froze out to form protons and neutrons. It is responsible for generation of elements between helium and iron by nuclear fusion processes. Carbon is also the main element used in the production of free neutrons within the stars, giving rise to the s process which involves the slow absorption of neutrons to produce elements heavier than iron and nickel (Ni). In explosive environments such as supernovae further nucleosynthesis processes can occur, such as the r process (in which elements heavier than iron and nickel are produced by rapid absorption of free neutrons) and the rp process (which involves the rapid absorption of free protons).