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 Click on Term to Read More 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 Click on Term to Read More 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 Click on Term to Read More.
Some or all content above used with permission from J. H. Wittke.