rp-process

The end point of the rp-process (the highest-mass element it can create) is not yet well established, but recent research has indicated that in neutron stars it cannot progress beyond tellurium.

[2] The rp-process is inhibited by alpha decay, which puts an upper limit on the end point at 104Te, the lightest observed alpha-decaying nuclide,[3] and the proton drip line in light antimony isotopes.

[4] The process has to occur in very high-temperature environments (above 109 kelvins) so that the protons can overcome the large Coulomb barrier for charged-particle reactions.

The seed nuclei needed for this process to occur are thought to be formed during breakout reactions from the hot CNO cycle.

Typically proton capture in the rp-process will compete with (α,p) reactions, as most environments with a high flux of hydrogen are also rich in helium.