p process

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The term p-process ( p for proton ) is used in two ways in scientific literature to research the astrophysical origin of the elements ( nucleosynthesis ):

  • originally a proton accumulation process was meant, which produces certain proton-rich isotopes of the heavy elements from selenium to mercury . These nuclides are called p-nuclei .
  • Although it has been shown that the originally proposed p-process cannot generate the p-nuclei, the term was later sometimes used broadly as a generic term for any nucleosynthetic process that generates p-nuclei.

Mixing the two meanings often leads to confusion. Therefore, in the more recent scientific literature, it is suggested to use the term p-process only for the actual astrophysical nucleosynthesis process (as is also common with other processes), i.e. for proton attachment under certain conditions.

procedure

To create proton-rich nuclei, protons can be captured by the nucleus of another element with a lower number of protons (the seed nucleus ). The original idea for generating the p-nuclei was therefore that such proton accumulations take place on heavy elements already present in stars , which were previously generated in the  s and / or r process .

However, such a proton capture can hardly generate p-nuclei, because the higher the number of protons in the atomic nucleus, the higher the Coulomb wall , which every newly added proton has to overcome: the higher the Coulomb wall, the more energy a proton needs to penetrate into the atomic nucleus and there can be captured.

The mean energy of the protons is determined by the temperature of the stellar plasma . If the temperature is too high, however, protons are knocked out of the atomic nuclei by photodisintegration faster than they can be deposited.

The solution would be to have a large number of protons, so that the effective number of captures per second is large, even if the temperature is not increased too much. However, these conditions are not found in the relevant astrophysical environments (e.g. core collapse supernovae ) .

Historical

The p-process was originally proposed as a synthesis process of the p-nuclei, and it was assumed to take place in the hydrogen shell of massive stars that explode as core collapse supernovae . However, it was later shown that the required conditions could not be achieved there.

Alternatives to pure proton capture were also considered in the work at that time, e.g. B. a pure photo- disintegration process (now called γ-process ) or a combination of p-process and photo-disintegration.

See also

Individual evidence

  1. ^ A b c E. M. Burbidge , GR Burbidge , WA Fowler , Fred Hoyle : Synthesis of the Elements in Stars . In: Reviews of Modern Physics . 29, No. 4, 1957, pp. 547-650. doi : 10.1103 / RevModPhys.29.547 .
  2. ^ A b c d A. GW Cameron : Nuclear Reactions in Stars and Nucleogenesis. In: Publications of the Astronomical Society of the Pacific , Vol. 69, 1957, pp. 201-222. ( bibcode : 1957PASP ... 69..201C )
  3. ^ A b M. Arnould, S. Goriely: The p-process of stellar nucleosynthesis: astrophysics and nuclear physics status. In: Physics Reports 384, 2003, pp. 1-84.
  4. ↑ a b T. Rauscher: Origin of p-Nuclei in Explosive Nucleosynthesis. In: Proceedings of Science PoS (NIC XI) 059, 2010; arxiv : 1012.2213
  5. ↑ J. Audouze, JW Truran: P-process nucleosynthesis in supernova envelope post squatting environments. In: The Astrophysical Journal , Vol. 202, 1975, pp. 204-213. ( doi : 10.1086 / 153965 )

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