A number of naturally occurring, proton-rich nuclides (the p-nuclei) cannot be made in the s- and r-process. It has been found that massive stars can produce p-nuclei through photodisintegration of pre-existing intermediate and heavy nuclei. This so-called gamma-process requires sufficiently high temperatures and occurs in pre-explosive or explosive O/Ne burning, depending on the mass of the star. Although the gamma-process has been successful in producing a large range of p-nuclei, two mass regions remain problematic, A<110 and 150<A<165, where a number of p-nuclei are severely underproduced. The origin of the problems is yet to be identified. A large number of unstable nuclei with only theoretically predicted reaction rates are included in the reaction network and thus the nuclear input may involve uncertainties. Deficiencies in charged-particle optical potentials at gamma-process temperatures have been found for nuclei at stability. On the other hand, the gamma-process conditions (temperature profiles, entropy of the O shell, seed composition) also sensitively depend on details of the stellar structure and evolution, as well as on the initial metallicity. Nevertheless, especially the deficient low-mass p-nuclei may call for an additional production process or site, such as production in (subChandrasekhar) type Ia supernovae. Also the (im)possibility of a synthesis in the rp- and nu-p-processes is discussed. Were this the case, the production of p-nuclei would be realized as a superposition of several different processes, not necessarily in the same site.
- Pub Date:
- December 2010
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - High Energy Astrophysical Phenomena;
- Nuclear Experiment;
- Physics - Space Physics
- 10 pages, 3 figures. Invited review talk at Nuclei in the Cosmos XI (Heidelberg, 2010), to appear in Proceedings of Science, PoS(NIC XI)059