The R-Process (Rapid Neutron Capture process) is a Nucleosynthesis process in Core Collapse Supernovae consisting of repeated Neutron Capture under conditions where Beta Decay is suppressed, resulting in synthesis of isotopes with an increase in atomic weight more than one but remaining at the same atomic number. When conditions revert to allowing beta decay, such decays happen until the nucleus reaches a stable configuration. The r-process explains the Abundances of Germanium, Xenon, and Platinum and many elements heavier than Iron and Nickel.
The Spectral Line signatures of r-process-created nuclei can be used to identify and age old stars. Very old (high Redshift?) galaxies have been observed with r-process-produced elements but not S-Process-produced elements, suggesting that at an early time, the r-process was working but the s-process was not. Individual stars with similar characteristics are presumed to be of similar age.