A process of nucleosynthesis thought to take place when there is a relatively high flux of neutrons. Heavy elements are built up by the capture of more than one neutron by a nucleus in rapid succession, before there has been time for an unstable intermediate isotope to decay. The r stands for rapid. This is the only means be which some of the heaviest known elements and particular isotopes could be made naturally. The r-process is believed to occur in the explosion of a supernova. See also: s-process.