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Since baryons (e.g. protons, neutrons) are composite particles it should be possible to split them apart. If so, is it then possible to extract useable energy out of the splitting of baryons in analogy to nuclear fission?

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My guess is that it'd take a lot more energy to split the proton than you'd get out, but I'll let someone else more qualified than me answer this one. – Kyle Kanos Jan 11 '14 at 18:54
The usable part of your question definitely makes the answer no with current technology. – Brandon Enright Jan 12 '14 at 4:37
up vote 4 down vote accepted

In the standard model, baryon number is conserved. The proton, being the lightest baryon, is then stable. Anything you change it into has higher mass and will absorb energy. All other baryons are unstable in isolation and will decay, releasing energy. Unfortunately, free baryons aside from protons are hard to come by. Generally they must be produced, and energy conservation demands that takes at least as much energy as you will get out.

In some models, baryon number is not conserved and you could imagine finding a way to trigger proton decay, which would release energy. It seems quite unlikely.

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So one cannot fire an electron onto a proton and by that converting it into a neutron (inverse beta decay/electron capture), waiting for the neutron to beta decay and hope that the electron that comes out has more energy than the electron that I used to begin with? But what if that happens in a radioactive nucleus or otherwise exited nucleus? Couldn't the electron that comes out have a bit more energy than the incoming one, by taking with it some energy from the nucleus? – asmaier Jan 11 '14 at 20:11
The fact that the neutron beta decays says that it has more mass than proton + electron, so you can't gain that way. In radioactive nuclei, you need to consider the binding energy of the parent and daughter nuclei. Natural decays increase the binding energy, and that is where the released energy comes from. – Ross Millikan Jan 11 '14 at 20:31
As a technical point, baryon and lepton number are not actually conserved in the standard model (electroweak theory). There is a solution to the electroweak field equations, called a sphaleron, that conserves B-L, not B and L separately. It converts 3 baryons into 3 antileptons. This is a non-perturbative solution so you cannot draw a Feynman diagram for the process. It is a high energy/temperature field configuration. At normal energies/temperatures, B and L, can be treated as being conserved. – Craig J Copi Jan 12 '14 at 5:56

To split baryons you would have to have free quarks, which as, Manishearth also says, is not possible. The quarks are only asymptotically free, which means in fact at very high energies. One would have to put a lot more energy in creating a quark gluon plasma than one could get out of it.

There also exist the weak interactions, and the neutron decays through them. But neutrons cannot be stored outside nuclei. Their decays contribute to the energies released by fission reactors, so it is baryons disintegrating that contribute to fission energies after all.

Protons are stable enough and in some models their decay is theorized.Experimentally proton decay has not been observed and the limits set it outside any useful contribution as an energy source.

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I'm not entirely sure about this answer, comments appreciated

If you want to know if breaking a baryon into three quarks will release energy, this will never happen. Charge confinement makes it incredibly hard to separate quarks, and a free quark is pretty much an impossibility — the energy you pump in will turn into extra quarks that bind to the momentarily "freed" quark leaving you with more mesons and no usable energy.

However, if you don't mind splitting it into smaller bits that aren't quarks:

Most baryons decay into mesons and leptons. Since a meson is just two quarks, one can think of it as "a part of a baryon". However, the types of quarks will be different (baryons have all quarks or all antiquarks, mesons have a quark and an antiquark), so I personally do not consider this to be "splitting of the baryon"

However, energy is released in this decay. Theoretically (in some BSM models), protons do decay, but as of now it has meagre experimental backing, and the decay has too large a half life to be useful.

Of course, on can extract energy from a baryon by introducing it to its antibaryon, and this may give a net positive extractable energy in the future though currently creating particles is very energy intensive. Viably creating them in large batches for any such process is impossible

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I wouldn't say that protons theoretically decay. In the standard model, they're stable. It's only in hypothetical BSM theories that protons can decay, but so far there is zero experimental evidence for any of that. – David Z Jan 11 '14 at 21:36
Agree with David Z. Also, did you intentionally link to the mobile version of the article? – Chris White Jan 12 '14 at 1:30
@DavidZ Oops, forgot to mention that. Thanks, fixed – Manishearth Jan 12 '14 at 5:09
@ChrisWhite Nah, was just on mobile when I wrote the answer. Fixed. – Manishearth Jan 12 '14 at 5:09

Just a point of note: You can "split" neutrons and get useful energy out of them by doing nothing at all. A free neutron has a mean lifetime of around 15 minutes, and will undergo beta decay if you wait long enough.

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