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p-Nuclei (''p'' stands for proton-rich) are certain proton-rich, naturally occurring isotopes of some elements between selenium and mercury which cannot be produced in either s- or r-process. == Definition == The classical, ground-breaking works of Burbidge, Burbidge, Fowler and Hoyle (1957) and of A. G. W. Cameron (1957)〔A. G. W. Cameron: ''Nuclear Reactions in Stars and Nucleogenesis.'' In: ''Publications of the Astronomical Society of the Pacific'', Vol. 69, 1957, p. 201-222. ((online ))〕 showed how the majority of naturally occurring nuclides beyond the element Iron can be made in two kinds of neutron capture processes, the s- and the r-process. Some proton-rich nuclides found in nature are not reached in these processes and therefore at least one additional process is required to synthesize them. These nuclei are called p-Nuclei. Since the definition of the p-nuclei depends on the current knowledge of the s- and r-process (see also nucleosynthesis), the original list of 35 p-nuclei may be modified over the years, as indicated in the Table below. For example, it is recognized today that the abundances of 152Gd and 164Er contain at least strong contributions from the s-process.〔C. Arlandini, F. Käppeler, K. Wisshak, R. Gallino, M. Lugaro, M. Busso, O. Straniero: ''Neutron Capture in Low-Mass Asymptotic Giant Branch Stars: Cross Sections and Abundance Signatures.'' In: ''The Astrophysical Journal'', Vol. 525, 1999, p. 886-900. ( )〕 This also seems to apply to those of 113In and 115Sn, which additionally could be made in the r-process in small amounts.〔Zs. Nemeth, F. Käppeler, C. Theis, T. Belgya, S. W. Yates: ''Nucleosynthesis in the Cd-In-Sn region.'' In: ''The Astrophysical Journal'', Vol. 426, 1994, p. 357-365. ( )〕 The long-lived radionuclides 92Nb, 97Tc, 98Tc and 146Sm are not among the classically defined p-nuclei as they do not naturally occur on Earth. By the above definition, however, they are also p-nuclei because they cannot be made in either s- or r-process. From the discovery of their decay products in presolar grains it can be inferred that at least 92Nb and 146Sm were present in the solar nebula. This offers the possibility to estimate the time since the last production of these p-nuclei before the formation of the solar system.〔N. Dauphas, T. Rauscher, B. Marty, L. Reisberg: ''Short-lived p-nuclides in the early Solar System and implications on the nucleosynthetic role of X-ray binaries.'' In: ''Nuclear Physics'', Vol. A719, 2003, p. C287-C295 ( , (arXiv.org:astro-ph/0211452 ))〕 p-Nuclei are very rare. Those isotopes of an element, which are p-nuclei, are less abundant typically by factors of ten to one thousand than the other isotopes of the same element. The abundances of p-nuclei can only be determined in geochemical investigations and by analysis of meteoritic material and presolar grains. They cannot be identified in stellar spectra. Therefore the knowledge of p-abundances is restricted to those of the Solar System and it is unknown whether the solar abundances of p-nuclei are typical for the Milky Way.〔M. Arnould, S. Goriely: ''The p-process of stellar nucleosynthesis: astrophysics and nuclear physics status.'' In: ''Physics Reports'' 384, 2003, p. 1-84.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「P-nuclei」の詳細全文を読む スポンサード リンク
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