B Question about Iron-56 binding

[ProjectFringe]

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?

 

[Vanadium 50]

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.

 

[ProjectFringe]

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.

 

[snorkack]

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+22ν_e
This reaction is spontaneous above a certain pressure, below which Fe-56 is stable. Does anyone know the value of that pressure?

 

[ProjectFringe]

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+22ν_e
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?

 

[hutchphd]

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?

 

[ProjectFringe]

Where did it say (reference please) that the stars will revert to iron stars eventually?

https://en.wikipedia.org/wiki/Iron-56

 

[snorkack]

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.

 

[ProjectFringe]

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?

 

[snorkack]

At low pressure, it is Fe-56.

 

[ProjectFringe]

Got it! Thanks again

 

[mfb]

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.