Rapid proton capture (hence “rp”) is a process that synthesizes elements by successive proton Transfer of energy to a medium as a particle or electromagnetic radiation passes through it. Absorption of electromagnetic radiation is the combined result of Compton scattering, σ, and photoelectric absorption, τ. It may be quantified: where, t = thickness, ρ = density, and μ = mass absorption coefficient, which combines Compton and photoelectric effects (μ = σ + τ). and β+ decay; thus, it tracks somewhere between the valley of stability.
The rp-process is one of three nucleosynthesis processes that also includes the Slow neutron capture by nuclei in massive stars. In the s-process, one starts with existing iron-group nuclei. Therefore, it would only be expected to take place in second-generation stars that collapsed out of the residue of a previous supernova explosion. The flux of neutrons is small enough that rate of and the Rapid (hence "r") absorption of neutrons by atoms when the neutron flux is very high (~1022 neutrons per cm2/s) and the temperature is very high (T > 109 K). These conditions are hypothesized to occur during a supernova explosion/collapse or neutron star mergers. The time between neutron captures is much.
Some or all content above used with permission from J. H. Wittke.