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/sci/ - Science & Math

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2672900 No.2672900 [Reply] [Original]

Fusion reactions in stars:

Why Iron? Seems like kind of a weird place to stop being able to fuse, right in the middle of a valence shell there. wassupwithat?

>> No.2672914

>>2672900
In this case, it probably has more to do with the nucleus than the valence electrons.

>> No.2672918

>>2672914
I realized this right after I posted. Plasma state.

>> No.2672963
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2672963

>> No.2673002

>>2672900
damn that's one fuckable piece of iron

>> No.2673018
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2673018

That picture slightly reminds me of this.

>> No.2673022

>>2673018

Forever a stone.

>> No.2673024

>>2673018
There is clearly a vagina at the center, I don't care what you say.

>> No.2673028

It takes more energy to fuse iron atoms than you get from the fusion itself. It's not energetically favorable, so it doesn't happen.

>> No.2673031

>>2673024
Ah, /sci/'s virgin takes on female anatomy.

>bags of sand, amirite?

>> No.2673035

>>2673028
Why?

>> No.2673033

Fusion of elements lighter than iron releases energy. Fusion of elements heavier than iron consumes energy.

>> No.2673044
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2673044

>>2673035
Nuclear binding energies. If you want to go one "why" deeper than that, you need to get to graduate-level physics.

>> No.2673046

>>2673044
>>2673035
http://en.wikipedia.org/wiki/Nuclear_binding_energy

>> No.2673047

Can't remember exactly right now, but it has something to do with mass defect. When you fuse two atoms with atomic number below that of Iron, you get energy out because the mass of the created nucleus is less than that of the two original nuclei by a little bit. Above Iron, the mass is greater, so it takes energy to fuse them. This is why stars die so fast - once it starts fusing iron, all the energy that kept it from collapsing gets sucked up by fusing the iron. This is also the basis for all nuclear technology, reactors, bombs, and whatnot.

>> No.2673071

>>2673044
If it's not too hard for you to write up one why deeper, would you humor me?

I'm out of the loop here but I do know how to read to understand. I'm at graduate level biochemistry.

>> No.2673084

Because the ratio of binding energy within the atom and the number of nucleons (protons and neutrons) is in its most stable state in Iron. Any element before Iron is unstable and wants to gain nucleons to stabilize (Fission in stars); and elements after Iron are unstable and want to lose nucleons through radioactive decay ( the lose of an electron turning a neutron into a proton for one example) changing the element and thus bringing the atom closer to Iron.

>> No.2673118

>>2673071
Well, the next "why" is "why are those the nuclear binding energies". This is mainly determined by the strong force. Nucleons (protons and neutrons) bind together by the strong force, which is mediated by passing gluons back and forth. To make calculations, you have to get into quantum field theory.

Maybe I can just talk in more detail about nuclear binding energies instead. The Liquid Drop model explains the nuclear binding energy trend, but it isn't "true". It's just a fair approximation.

Nuclei that are too large aren't very tightly bound. This also means that two medium-sized nuclei have less total energy than forcing them to become one huge nucleus, and so it takes energy to make it happen. That's why only supernova make elements heavier than iron - the fusion process needs really high energy densities to make the process happen even once in a while, because the process costs energy.
http://en.wikipedia.org/wiki/Liquid-drop_model

>> No.2673171
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2673171

>>2673118
More than enough to start wrapping my brain around, thanks

>> No.2673218
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2673218

iron is the most stable element. every element wants to either take electrons or give electrons to become as stable as iron. the density of most stars is insufficient to cause nuclear fusion between iron atoms. thus the star implodes upon itself before exploding into space. pretty rad.

>> No.2673235

>>2672900
>valence shell
Do you think fusion gives a fwizzle about electrons? No. It only cares about the nucleus. Iron takes the most energy to fissure.