BRIDGING THE WAITING POINTS - THE ROLE OF 2-PROTON CAPTURE REACTIONS IN THE RP-PROCESS

The influence of two-proton capture reactions on long-lived waiting point isotopes near the proton drip line is discussed for the rp-process reaction flow. These reactions are characterized by two successive proton captures, where the first reaction product is unstable against proton emission, but the second reaction results in a particle stable nucleus. The reactions which have this character and involve long-lived waiting points in the rp process are O15(2p,γ)17Ne, Ne18(2p,γ)20Mg, and Ca38(2p,γ)40Ti. Their rates are presented and compared with the rates of alpha-induced reactions for stellar conditions at high temperatures and densities. We find that the two-proton captures on O15 and Ne18 can only compete for unrealistically high densities, but that Ca38(2p,γ)40Ti can act as an efficient reaction link at conditions typical for x-ray bursts on neutron stars. © 1995 The American Physical Society.