Can iron form via processes like the r- or s-process?

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Discussion Overview

The discussion revolves around the formation of iron in stars, specifically exploring various nucleosynthesis processes such as the r-process and s-process, as well as other potential methods. Participants examine the contributions of different isotopes and the conditions under which iron can form, including silicon burning and beta decay.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about the methods of iron formation in stars, mentioning silicon burning and beta decay of neutron-rich isotopes as potential processes.
  • Another participant asserts that while iron can form in various processes, silicon burning is the dominant source, contributing significantly more iron than other methods.
  • A participant discusses the stability of isotopes such as Mn-56 and its implications for the s-process, suggesting that it cannot lead to the formation of Fe-57 and Fe-58 due to its short half-life.
  • There is a mention of the stability of chromium isotopes and their potential pathways to iron formation through beta decay processes.
  • One participant questions whether starting with Fe-56 still qualifies as part of the s-process, noting that the reaction Fe-56+n -> Fe-57 releases energy.
  • Another participant raises the question of how Fe-54 is formed, suggesting that the alpha process and photodisintegration of Nickel-58 could be involved, while also mentioning the role of pair instability supernovae.
  • There is uncertainty expressed regarding the outcomes of starting the alpha process from different oxygen isotopes.

Areas of Agreement / Disagreement

Participants exhibit a mix of agreement and disagreement regarding the processes that contribute to iron formation. While some acknowledge the significance of silicon burning, others propose alternative pathways and raise questions about specific isotopes and their roles, indicating that the discussion remains unresolved.

Contextual Notes

Participants reference various isotopes and their half-lives, which may influence the understanding of nucleosynthesis processes. The discussion includes assumptions about the stability of isotopes and the conditions under which certain reactions occur, but these aspects remain unresolved.

Teichii492
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TL;DR
Can iron form via processes other than during silicon burning? e.g. the r- or s-process
Hi,

I was wondering by what other methods iron can form in stars? Iron can form during silicon burning and i assume it can also form via the beta- decay of neutron rich isotopes around the iron peak? Are these athe only two processes that relate to the cosmogenesis of iron?
 
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I'm certain there will be the occasional iron atom formed in these processes - but silicon burning produces so much more that it doesn't matter.
It might contribute to Fe-58 (0.3% of natural iron) and Fe-57 (2.1%).

Edit: Mn-56 has a half life of only 2.5 hours, so the s-process won't lead to Fe-57 and Fe-58.
 
mfb said:
...Edit: Mn-56 has a half life of only 2.5 hours, so the s-process won't lead to Fe-57 and Fe-58.
Chrome 52 is stable. adding neutrons to cr 53, and then cr54 are still stable. One more gets Cr55 which then beta decays to Mn55 which is stable. One more neutron is Mn 56 which beta decays to Fe56. Then add neutrons to get Fe 57 and Fe 58.

Vanadium 51 is stable. add neutron for V52 which beta decays to Cr52. All isotopes of Ti are stable 46 to 50. and Ti51 decays to V51. Sc46 beta decays to Ti46. Ca 45 decays to Sc 45. You can keep working backwards all the way.
 
Is it still the s-process if you start with Fe-56 that has so much more important origins? Eh, whatever.
Surprisingly, Fe56+n -> Fe-57 releases energy.
 
Whereas s-process skips Fe-54. How is Fe-54 formed?
Since Fe-59 has half-life 45 days, r-process forms Fe-60... which, however, has half-life 2,6 million years.
 
snorkack said:
Whereas s-process skips Fe-54. How is Fe-54 formed?
Since Fe-59 has half-life 45 days, r-process forms Fe-60... which, however, has half-life 2,6 million years.

Alpha process maybe. Ti-46 becomes Cr-50 becomes Fe-54. Photodisintegration of Nickel 58 might get the job done too. Pair instability supernova would have hydrogen present while temperatures are high enough to shove protons in there. So decay of Co-54.

I do not know what happens if you start the alpha process from Oxygen-18 instead of Oxygen-16.
 

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