Fusion vs. Fission and Nuclear Transmutation

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It is my understanding that nuclear fission (rather than fusion) is used for energy because it can release energy in a a stream of smaller packets, where fusion releases one big mass of it. However, research is still being conducted on the possibility of fusion energy. This leads me to wonder- what exactly are the restrictions in this situation? Are there just no reactors strong enough to withstand the forces produced? Would the way we use fission energy be substantially different from what we would do if we could use fusion?

 

Also, does nuclear transmutation have any practical application whatsoever? Could it( I.e. To produce extremely rare or valuable elements)?

[Strange]

It isn't about the rate at which energy is released, after all you can have both an atom bomb (fission) and a hydrogen bomb (fusion).

 

Fusion occurs in large atoms, which means they form solids. So materials like uranium and plutonium. This means they are relatively easy to work with and contain. Fusion works with light elements (typically hydrogen) which is a gas. This means that to have a fusion reaction you need some way of containing a gas a very high temperatures (like 100 million degrees). It also requires very high pressures. No material can withstand that, so it needs to be contained by magnetic fields. But trying to contain a hot, rapidly moving, high-pressure plasma in a magnetic field is not easy.

 

Transmutation might be useful for converting nuclear waste to something less hazardous. I don't know how practical it is on a large scale.

[Sensei]

It is my understanding that nuclear fission (rather than fusion) is used for energy because it can release energy in a a stream of smaller packets, where fusion releases one big mass of it.

Not exactly.

Either fusion and fission releases energy.

Energy can be in kinetic energy of produced particles, photons, or neutrinos.

Details depend on specific input particles.

 

However, research is still being conducted on the possibility of fusion energy. This leads me to wonder- what exactly are the restrictions in this situation? Are there just no reactors strong enough to withstand the forces produced? Would the way we use fission energy be substantially different from what we would do if we could use fusion?

Fusion releases very few energy. Tritium and Deuterium are producing the largest known fusion energy 17.6 MeV per reaction. But Tritium you have to make first. And Deuterium is rare isotope.

See example giant planets like Jupiter - they have the same/similar content as Sun at the beginning of its life, but they don't fuse Hydrogen nor Helium.. Why? Because concentration/quantity of these particles in their volume is too small.

Fusion reactor needs to create such high density by itself before any fusion will take place. There is need to spend substantial amount of energy before any energy is produced during fusion.

 

Decay of unstable particles happens spontaneously. Nothing is needed to cause it.

 

See thread in my signature to learn more how to calculate energy released during decay of unstable isotopes. And the same calculation can be used to calculate fusion energy.

 

Also, does nuclear transmutation have any practical application whatsoever? Could it( I.e. To produce extremely rare or valuable elements)?

It's done on daily basis. It's the only way Plutonium can be made.

 

If you want to see traces leaved by unstable isotopes that decay see videos below:

 

 

 

Edited October 2, 2014 by Sensei

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Thanks sensei+strange. Your answers are really helpful. But how can all of the byproducts of nuclear processes be contained in a magnetic field? What about things like gamma radiation?

[swansont]

To add to the previous: one huge difference is that we have not yet been able to sustain a fusion reaction for any appreciable length of time. This is in part due to the environment strange noted: it has an activation potential, so it needs to be exceedingly hot and confinement is difficult. You can't use a technology commercially that doesn't commercially exist.

[Strange]

Thanks sensei+strange. Your answers are really helpful. But how can all of the byproducts of nuclear processes be contained in a magnetic field? What about things like gamma radiation?

 

Not all the byproducts are contained, but the "fuel" (for want of a better word) must be contained. Actually, I'm not sure but I don't think fusion creates a lot of gamma radiation - that is another of its potential advantages.

[Sensei]

Actually, I'm not sure but I don't think fusion creates a lot of gamma radiation - that is another of its potential advantages.

See thread, where I am describing it with detail:

http://www.scienceforums.net/topic/85656-solar-fusion-neutrinos-and-age-of-solar-system/

Fusion produces a lot of gamma photons.

At least from typical input particles (A<4)..

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But photons can be contained by a magnetic field.

[Strange]

See thread, where I am describing it with detail:

http://www.scienceforums.net/topic/85656-solar-fusion-neutrinos-and-age-of-solar-system/

Fusion produces a lot of gamma photons.

At least from typical input particles (A<4)..

 

You are right. But I found this easier to follow:

http://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain_reaction

[studiot]

Fission and Fusion usually refer to atoms, or more precisely their nuclei.

 

Banging together other particles to create bigger or smaller ones is not normally called fission or fusion.

 

In principle you can 'bang together' or fuse nuclei that are smaller than the Iron nucleus and obtain energy.

 

If you wish to break them apart to smaller nuclei (fission) you would have to input energy.

 

Conversely if you have nuclei that are larger than Iron you can obtain energy by breaking them apart, and have to input energy to bang them together to make a larger nucleus.

 

You cannot obtain energy from iron by either fusion or fission.

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Is it hader to perform fission/fission on an atom as its size is closer to that of iron then?

[studiot]

You can't 'perform' fusion on a single atom. You need two.

 

Think about it.

[Strange]

But, otherwise, yes: iron is at the minimum energy level.

[swansont]

But photons can be contained by a magnetic field.

 

Citation needed. Unless this was supposed to be a question, in which case the answer is no.

[studiot]

But photons can be contained by a magnetic field.

 

 

I missed this

 

See Rutherfords Experiment

 

http://chem-guide.blogspot.co.uk/2010/04/radioactive-rays-alpha-ray-beta-ray.html

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On the above: yes, studiot, that's what I meant. Two particles. I probably should have been more clear.

But a proton has a positive charge, no? Why does the fact that it is a gamma proton change that?

Also: what do we do with the gamma rays/particles then?

[Sensei]

On the above: yes, studiot, that's what I meant. Two particles. I probably should have been more clear.

But a proton has a positive charge, no? Why does the fact that it is a gamma proton change that?

Also: what do we do with the gamma rays/particles then?

 

Don't mix proton with photon..

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Oh. Whoops.

A testament to my amount of scientific experience.

[John Cuthber]

It isn't about the rate at which energy is released, after all you can have both an atom bomb (fission) and a hydrogen bomb (fusion).

 

Fusion occurs in large atoms, which means they form solids. So materials like uranium and plutonium. This means they are relatively easy to work with and contain. Fusion works with light elements (typically hydrogen) which is a gas. This means that to have a fusion reaction you need some way of containing a gas a very high temperatures (like 100 million degrees). It also requires very high pressures. No material can withstand that, so it needs to be contained by magnetic fields. But trying to contain a hot, rapidly moving, high-pressure plasma in a magnetic field is not easy.

 

Transmutation might be useful for converting nuclear waste to something less hazardous. I don't know how practical it is on a large scale.

At 100 million degrees there are no solids. Plutonium and uranium have both boiled several orders of magnitude cooler than that.

All the materials that might sensibly undergo fusion are plasmas.

And it's perfectly possible to do sustained fusion at fairly low pressures (much less than ordinary atmospheric pressure).

[MigL]

I'm getting more confused by the minute.

Why is fusion being discussed along with Plutonium and Uranium ?

I realise fusion and fission are easy to interchange but...

 

Fusion occurrs in light element plasmas at extremely high temps and/or pressures, and becomes less and less likely as you rise towards atomic no. 26 ( iron ). An example is the Sun's core. All thermonuclear ( fusion ) bombs use an atomic ( fission ) 'bomb' in a specific arrangement to generate the required radiation pressure and temperature to initiate the fusion reaction

 

Fission occurrs in heavy radioactive elements with no restrictions on temp./press.,and becomes less and less likely as elements become more stable coming down towards atomic no. 26. Examples are the atomic bombs dropped on Hiroshima/Nagasaki ( one Uranium, one Plutonium ).

 

I'm going to needa reference for 'sustained fusion at fairly low pressures' John.

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Do they simply need to be plasmas so that they have enough energy to fuse?

[Strange]

At 100 million degrees there are no solids. Plutonium and uranium have both boiled several orders of magnitude cooler than that.

 

Sorry - typo! - I was trying to contrast fusion and fission - I'll fix my post.

 

Dang. Cant edit it any more. What it should have said was:

 

Fission occurs in large atoms, which means they form solids. So materials like uranium and plutonium. This means they are relatively easy to work with and contain. On the other hand, fusion works with light elements (typically hydrogen) which is a gas. ...

Edited October 4, 2014 by Strange

[John Cuthber]

Fusion works with all the elements up to about iron.

That's how they are made.

They are made in stars, and the whole lot are gases under those circumstances.

 

It is, in principle, possible to make a fission reactor with uranium hexafluoride vapour.

There are plenty of plans for using molten salts for fission reactions of thorium.

 

The physical state is not fundamental to the fission/ fusion process; it's a coincidence.

[studiot]

 

That's how they are made.

 

Whilst I agree with John's clear and valuable extensions of my points,

 

I think that trans ferrous elements were also made that way, using the spare energy available in large enough stars.

 

It should not be taken to imply that fusion to create heavier elements, or fission to break lighter ones, cannot occur. Just that for this to happen would require a source of energy external to that particular fusion or fission process.

[swansont]

I think that trans ferrous elements were also made that way, using the spare energy available in large enough stars.

 

It should not be taken to imply that fusion to create heavier elements, or fission to break lighter ones, cannot occur. Just that for this to happen would require a source of energy external to that particular fusion or fission process.

 

For the heavier elements it's the energy available when a supernova occurs.