Nucleosynthesis
From Exampleproblems
Nucleosynthesis is the process of creating new atomic nuclei either by nuclear fusion or nuclear fission.
There are a number of astrophysical processes which are believed to be responsible for nucleosynthesis in the universe, the forerunners being the R-process, S-process, and P-process.
The four basic types of nucleosynthesis known of are:
- Big Bang nucleosynthesis occurred within the first three minutes of the universe and is responsible for most of the helium-4 and deuterium in the universe. Because of the very short period in which Big Bang nucleosynthesis occurred, no elements heavier than lithium could be formed.
- Stellar nucleosynthesis occurs in stars and creates many of the heavier elements between lithium and iron. Particularly important is carbon. It utilizes the s-process which involves the slow absorption of neutrons.
- Supernova nucleosynthesis produces most of the elements heavier than iron. Supernovae are also the most favored candidate of r-process which are elements produced by rapid absorption of neutrons, although there are still some major unanswered questions about this.
- Cosmic ray spallation produces some lighter elements such as lithium and boron through high speed bombardment of matter by particles. This process results from the impact of cosmic rays against other materials in space, including other cosmic rays.
Theories of nucleosynthesis are tested by calculating isotope abundances and comparing with observed results. Isotope abundances are typically calculated by calculating the transition rates between isotopes in a network. Often these calculations can be simplified as a few key reactions control the rate of other reactions.
