R-process

The rapid neutron-capture process forms heavy atomic nuclei when neutron captures outpace radioactive decay. It produces many elements beyond iron, including gold, platinum, and uranium.

Neutron capture: A nuclear reaction in which an atomic nucleus absorbs a neutron. Successive captures are the defining steps that drive the r-process toward heavier nuclei.
Neutron star merger: A collision and coalescence of two neutron stars in a binary system. Merger ejecta provide neutron-rich matter where rapid captures can occur.
Nucleosynthesis: The production of atomic nuclei through nuclear reactions in cosmic environments. The r-process is one pathway within the broader history of cosmic element formation.
Solar r-process residuals: Estimated solar-system abundances of elements attributed to rapid neutron capture after subtracting slow-process contributions. These residuals provide a benchmark for testing r-process models.
S-process: The slow neutron-capture process, in which neutron captures generally occur more slowly than beta decays. Its capture-decay ordering contrasts directly with the r-process and produces different isotope patterns.
Beta decay: A radioactive transformation in which a neutron changes into a proton, or vice versa, while emitting other particles. After captures pause, beta decay raises atomic numbers along the r-process path.
Kilonova: A transient astronomical flare powered by radioactive decay in neutron-rich ejecta from a compact-object merger. Its changing light reveals freshly synthesized r-process material.
Neutron flux: The number of neutrons passing through a unit area per unit time. A sufficiently intense flux makes neutron capture faster than beta decay.
Europium: A rare-earth chemical element with atomic number 63, commonly used as a tracer of r-process enrichment. Its abundance in stars helps identify material enriched by rapid neutron capture.
P-process: A set of processes that produce rare, proton-rich isotopes not readily made by neutron capture. It creates proton-rich nuclei rather than the neutron-rich path characteristic of the r-process.

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