What is "r-process"

n. (context physics astronomy English) The relatively rapid nucleosynthesis process, in supernovae, in which a large neutron flux allows rapid neutron capture and synthesis of elements up to the transuranic elements.

The r-process is a nucleosynthesis process that occurs in core-collapse supernovae (see also supernova nucleosynthesis) and is responsible for the creation of approximately half of the neutron-rich atomic nuclei heavier than iron. The process entails a succession of rapid neutron captures (hence the name r-process) by heavy seed nuclei, typically Fe or other more neutron-rich heavy isotopes.

The other predominant mechanism for the production of heavy elements in the universe (and in the Solar System) is the s-process, which is nucleosynthesis by means of slow captures of neutrons, primarily occurring in AGB stars. The s-process is secondary, meaning that it requires preexisting heavy isotopes as seed nuclei to be converted into other heavy nuclei. Taken together, these two processes account for a majority of galactic chemical evolution of elements heavier than iron.

The r-process occurs to a slight extent in thermonuclear weapon explosions, and was responsible for the historical discovery of the elements einsteinium (element 99) and fermium (element 100).