|WikiProject Physics||(Rated Start-class, Mid-importance)|
|WikiProject Astronomy||(Rated Start-class, High-importance)|
Source citations needed?
This article seems OK to me. A few inter-wiki-links needed, what more?? Rursus 12:30, 23 January 2007 (UTC)
Large scale editing and re-write
In a project to update, expand, and contextualize the wikis relevant to stellar nucleosynthesis, I have made dramatic changes and added lots of information to the wiki. Below I have retained a copy of the former version, so that you may feel free to compare the two. The two major factual corrections I made: A=270 nuclei in the r-process are not the same as 'stable' A=270 elements on earth; they are far from stability, and it is hard to know without a citation what the Z value of these nuclei are. Also, r-process abundance peaks are decidedly ~10 amu below s-process peaks, not above. You can see this clearly on an N vs. Z diagram by finding the closed neutron shells near the neutron drip line and following them back on a constant A line to stability. I have omitted to include the categories and other wiki tags for this paste for convenience. DAID 07:51, 21 July 2007 (UTC)
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The R-process (R for rapid) is a neutron capture process for radioactive elements which occurs in high neutron density, high temperature conditions. Contrast with P- and S-processes. In the R-process nuclei are bombarded with a large neutron flux to form highly unstable neutron rich nuclei which very rapidly decay to form stable neutron rich nuclei. This is also known as supernova nucleosynthesis.
The site of the R-process is believed to be iron-core collapse supernovae, which provide the necessary physical conditions for the R-process. However, the abundance of R-process elements requires that either only a small fraction of supernova return R-process elements to the outside or that each supernova only contributes a very small amount of R-process elements.
Due to the much higher neutron flux in this process (on the order of 1022 neutrons per cm2 per second), the rate of isotopic formation is much faster than the beta decays which follow, meaning that this process "runs up" along the neutron drip line, with the only two hold-ups being closed neutron shells extending the time it takes to create new isotopes, and the degree of nuclear stability in the heavy-isotope region, which terminates the R-process when such nuclei become readily unstable to spontaneous fission (currently believed to be in the region of A = 270 - or roughly in the Rutherfordium - Darmstadtium area of the periodic table).
Elemental abundance peaks show some support for the idea of rapid neutron capture and delayed beta emission, as the R-process peaks are at about 10 Atomic mass units above those of the S-process peaks (which occur exactly at closed neutron shells), indicating that the "run up" along the neutron drip line reaches closed neutron shells but with sufficient proton deficiency to make the peaks resolvable.