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The p process was believed to be a proton capture process which
occurrs during supernovae explosions. Then it was realized that the proton densities are to small and the observed isotopic
abundances could not be explained by this kind of reaction.
Today its believed that photodisintegration reactions are responsible for the production of the proton rich p-isotopes with
masses A>100. The relevant reactions are (gamma,n)- and (gamma,alpha)-reactions. The temperature during a supernova explosion
reaches upto 2-3*10^9 K. The black body radiation produces a photon bath that can disintegrate the seed nuclei from the s-process and r-process. This is the
reason why the p-process is sometimes called gamma-process.
The p-process contribution to isotopic abundances of elements that can also be produces in the s-process or r-process is usually very small. However there
are p-only isotopes that cannot be produced in the s- or r-process (e.g. 190^Pt or 168^Yb). These isotopes have very small
abundances compared to neighbour nuclei.
Sometimes the term p-process includes also the rp-process (rapid proton capture process). The astrophysical scenario for this process is still not firmly
established but it is believed that a neutron star in a binary system which is accrediting mass from a main sequence star could
be one possible scenario. During X-ray bursts the temperature and the proton density is high enough to start proton capture reactions and
proton rich elements upto mass A=100 can be produced.
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