Rpprocess

Rpprocess, more commonly known as the rp-process (rapid proton capture process), is a nucleosynthesis pathway in high-temperature, high-density astrophysical environments. In this process, atomic nuclei grow by rapid successive captures of protons (p, gamma) followed by beta-plus decays, moving toward increasingly proton-rich isotopes near the proton drip line. The flow of matter through the rp-process is governed by the relative speeds of proton captures and beta decays, as well as by competing reactions such as photodisintegration at higher temperatures.

The rp-process is most notably associated with explosive hydrogen burning on the surfaces of accreting neutron stars in close binary systems, where X-ray bursts create the extreme conditions required for rapid proton captures. During these bursts, sequences of proton captures and beta-plus decays occur on timescales much shorter than typical stellar burning processes, allowing the synthesis of heavier, proton-rich nuclei. The path of the process is punctuated by waiting points—nuclei with relatively long beta-decay half-lives or unfavorable proton-capture rates—which slow the flow and shape the resulting abundance pattern and energy release.

Outcomes of the rp-process contribute to the energy output of X-ray bursts and influence nucleosynthesis in proton-rich environments. The endpoint of the process remains uncertain, depending on nuclear masses, reaction rates, and astrophysical conditions; it is generally expected to reach nuclei beyond iron but is limited by nuclear physics and runaway reaction rates.

Overall, the rp-process is distinct from the r-process (rapid neutron capture) and is a key concept in the study of explosive hydrogen burning and advanced nucleosynthesis in accreting neutron star systems.