|WikiProject Astronomy||(Rated C-class, Mid-importance)|
Direct Si burning
According to my reference, "Cauldrons in the cosmos" by Rolfs and Rodney, page 432, direct silicon burning (fusion of Si to Si) does not occur in stars. Before the temperature required to provide sufficient penetration of the Coulomb barrier for Si to fuse to Si is reached, photodisintegration of Si begins. Thus, iron and the iron peak elements are formed by the disintegration of Si by high energy photons. This process provides the needed alpha paticles, protons and neutrons which can fuse with Si (and other nuclei) to make the stable iron peak elements.
- That sounds like a minority opinion, actually. At least "Discovering the Universe", Kaufmann, ISBN-0-7167-2054-X, and "The Cambrige Atlas of Astronomy", ISBN-0-521-36360-8, speaks about Si-burning as real. Rursus 22:54, 17 April 2007 (UTC)
email to Hyperphysics
- To: RodNave:gsu.edu
- Subject: at odds with "The Most Tightly Bound Nuclei"
- Why do the masses (2003) for Fe-56 and Ni-62 show that m/A is lower for Fe-56, which is different from B/A?
- -lysdexia 14:57, 11 April 2007 (UTC)
- I've revised two paragraphs accordingly. Although iron–58 and nickel–62 have the two lowest binding energies (lower even than nickel–56), the next step in the alpha process is zinc-60, which has slightly greater binding energy (is a slight dip in the graph). Since this dip is energetically unfavorable, this can't occur and nickel–56 so the last element to be synthesized. For nucleosynthesis to end up with the two elements with the very lowest binding energies, it would have to add nucleons in twos (which doesn’t happen in the alpha process). Greg L (my talk) 00:23, 18 April 2007 (UTC)
- --- Rod Nave <rodnave:gsu.edu> wrote:
- > Hello, Autymn,
- > I think the case for Ni-62 being the most tightly
- > bound is well
- > established.
- > Does "isotopic masses(2003)" refer to a specific
- > table?
- Atomic Mass Evaluation: http://www.nndc.bnl.gov/amdc. You can also find the tables at http://wikipedia.org/wiki/Isotopes_of_nickel.
- > The only thing I can suggest is that at the required
- > level of accuracy,
- > m/A is not exactly the same thing as binding energy
- > per nucleon because
- > of the difference between neutron and proton mass.
- > Ni-62 with 28 n, 32
- > p is a slightly higher percentage neutrons than
- > Fe-56 with 26 n, 30 p
- > . Since showing their difference in binding energy
- > requires four
- > significant figures, this difference in percentage
- > neutrons may tip the
- > balance in mass per particle the other way.
- That's a good point; neutròns suffer more from the nuclear bonds.
- mn-mp = .001388
- Ni-62: 61.9283451u, .99884428u/A
- Ni-60: 59.9307864u, .99884644u/A
- Ni-64: 63.9279660u, .99887447u/A
- Fe-56: 55.9349375u, .99883817u/A
- Fe-58: 57.9332756u, .99884958u/A
- mp = 1.00727646688u; mn = 1.00866491578u
- However, that brings up a new problem, that Ni-64 seems to win out:
- Ni-62: 28mp + 34mn = 62.4983482u -> 61.9283451u => .5700031u
- Ni-60: => .5502320u
- Ni-64: => .5877120u
- Fe-56: 26mp + 30mn = 56.4491356u -> 55.9349375u => .5141981u
- Fe-58: => .5331898u
- -lysdexia 21:17, 23 April 2007 (UTC)
- > However, that brings up a new problem, that Ni-64
- > seems to win out:
- > Ni-62: 28mp + 34mn = 62.4983482u -> 61.9283451u =>
- > .5700031u
- > Ni-60: => .5502320u
- > Ni-64: => .5877120u
- > Fe-56: 26mp + 30mn = 56.4491356u -> 55.9349375u =>
- > .5141981u
- > Fe-58: => .5331898u
- Never mind! I didn't divide by A: .0091936, .0091705, .0091830, .0091821, .0091829. Then the strongest nuclei are Ni-62, Ni-64, Fe-58, Fe-56, Ni-60.
- -lysdexia 23:19, 23 April 2007 (UTC)
It might be nice if this article were formatted similarly to the other stellar nucleosynthesis entries such as neon burning process? Specifically, equation formats… --Belg4mit 05:55, 17 July 2007 (UTC)
- I started to do modify the format of the equasions, but noticed that this page also contains a lot of the information available on the pages related to Carbon, Oxygen and Neon burning. I think that information should be removed (optionally replaced with a mention of these processes and links). A more drastic rewrite would seem in order, styled like the afformentioned burning articles. I personally lack the knowledge to make sure that I would write an accurate representation of the facts. I may give it a shot at some point if no one else does. SkyLined (talk) 23:29, 2 March 2008 (UTC)
- What I need is the exact formulae for the reactions; I assumed that the molecular numbers increased through the alpha process, but noticed that when Silicon and Sulfur are created by burning lighter elements through the alpha process, this would mean that Silicon is burned to create Sulfur. Unfortunately, Silicon burning is mentioned below that reaction, so I'm obviously missing somthing.SkyLined (talk) 00:06, 5 March 2008 (UTC)
Presence of Helium
The article doesn't explain that the "helium" in the equations is actually formed from photodisintegration of the heavier nuclei (see Neon burning). Obviously, if there was a lot of helium around already, the star would fuse that and would not ultimately run out of fuel. So there must be just a small number of alpha particles(helium) that have detached in order to keep these processes going. —Preceding unsigned comment added by 126.96.36.199 (talk) 19:33, 25 August 2010 (UTC)
- Additionally, the statement that the nickel to zinc reaction consumes energy is confusing. I believe it does not. 55.942132 u + 4.002602 u = 59.944734 > 59.941827 u. The reaction is exothermic. I should be using the ionized masses maybe and the difference is not exactly that, but it's still exothermic. What's endothermic is the combined reaction of photodisintegration and alpha process, e.g.
- This is critical to understand why the process stops at |56
28Ni. But I can't really add this information as I guess it's OR. The issue of photodisintegration should also be discussed at Alpha_process, or this page, that, and Neon burning should perhaps be merged.Morngnstar (talk) 22:49, 12 February 2013 (UTC)