Question about Iron-56 binding

  • #1
Is it possible for two 56Fe atoms to fuse together?

As I understand they won't. So what happens when the two atoms undergo extreme heat/pressure? Do they break down into neutrons?
 

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  • #2
Vanadium 50
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What makes you think anything will happen under "extreme heat/pressure"?
Then question is so filled with unstated assumptions that it is virtually impossible to answer.
 
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  • #3
What makes you think anything will happen under "extreme heat/pressure"?
Then question is so filled with unstated assumptions that it is virtually impossible to answer.
I read that all matter in the universe, through fission or fusion, will eventually create 'iron stars' comprised of 56Fe, which will then eventually collapse into neutron stars and black holes.
 
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Extreme heat and pressure have different effects.
Extreme heat favours high entropy - therefore smaller nuclei.
Extreme pressure, that is, high electron chemical potential, favours lower proton fraction... which leads to bigger nuclei.
First reaction for Fe-56 fusion is:
31 Fe-56+22e-=28Ni-62+22νe
This reaction is spontaneous above a certain pressure, below which Fe-56 is stable. Does anyone know the value of that pressure?
 
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  • #5
Extreme heat and pressure have different effects.
Extreme heat favours high entropy - therefore smaller nuclei.
Extreme pressure, that is, high electron chemical potential, favours lower proton fraction... which leads to bigger nuclei.
First reaction for Fe-56 fusion is:
31 Fe-56+22e-=28Ni-62+22νe
This reaction is spontaneous above a certain pressure, below which Fe-56 is stable. Does anyone know the value of that pressure?
As I understand you are saying that above a certain pressure an atom of Fe-56 does become unstable.
In theory, is going beyond this critical pressure point what causes the collapse of an iron star into a neutron star?
 
  • #6
hutchphd
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I know that if one plots binding energy/ nucleon vs nucleon number, 56Fe is at the maximum. In some sense then it is the most "stable"
I don't think the rest of what you say is pretty fanciful. Where did it say (reference please) that the stars will revert to iron stars eventually?
 
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  • #8
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As I understand you are saying that above a certain pressure an atom of Fe-56 does become unstable.
In theory, is going beyond this critical pressure point what causes the collapse of an iron star into a neutron star?
There are a number of unstable nuclei that form before electron chemical potential is enough to support free neutrons. And one more stable nucleus: Ni-64. Edit: looked up, two stable nuclei, the second is Kr-86. And while I did not find express pressure to which Fe-56 is stable, the density was given: 8 t/cm3.
 
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There are a number of unstable nuclei that form before electron chemical potential is enough to support free neutrons. And one more stable nucleus: Ni-64. Edit: looked up, two stable nuclei, the second is Kr-86. And while I did not find express pressure to which Fe-56 is stable, the density was given: 8 t/cm3.
Thanks for the info!

So my understanding was that all matter would revert to Fe-56, rather than Ni-62, even though Ni-62 has a higher binding energy. Wikipeida states this as being due to the competition between photodisintegration and alpha capturing during nucleosynthesis.

So does what you are saying mean Ni-64 and Kr-86 have higher binding energies compared to Fe-56 and Ni-62? And is the reason given for the formation of Fe-56 rather than Ni-62, true for Ni-64 and Kr-86 as well?

As I understand, all unbalanced systems reach a point where they start to move back toward a state of equilibrium. I guess my ultimate question is what is the 'highlander' (last man standing) of elements when 'equilibrium of elements' is reached, before reverting to neutrons? Is it Fe-56 or something else, like Ni-64 or Kr-86, as you mentioned?
 
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  • #10
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At low pressure, it is Fe-56.
 
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Almost certainly we'll get proton decays and a full decay of all baryons long before any obscure "multiple iron nuclei fuse to multiple nickel nuclei" reaction.
Is it possible for two 56Fe atoms to fuse together?
Yes, if you collide them with sufficient energy. The naive fusion product would be Tellurium-112 (half life 2 minutes), in practice we can expect a few neutrons to fly away, so we get some even more exotic isotopes. Decays will quickly convert it to antimony, tin, indium and then cadmium or something like that.
 
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