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What actually happens when an anti-matter projectile collides with matter?

If a large amount of antimatter is suddenly released or launched in the open and expands, annihilating a large area of matter, including air particles, land, etc, what would be the result? Would there be a void of low (no) pressure that would pull everything nearby into it? Would it cause an outward explosion? Would new molecules/atoms be created?

As a follow-up: Out of plain curiosity, would this concept, in theory, have the potential to be used as a weapon in the future (should technology advance that far)?

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user17636
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  • Seems to duplicate http://physics.stackexchange.com/q/7063/520 and http://physics.stackexchange.com/q/30900/520 and is related to http://physics.stackexchange.com/q/35085/520 – dmckee --- ex-moderator kitten Jan 08 '13 at 18:20
  • @dmckee the proposed duplicates do not deal with the "weapon" part of the question, which is the one I concentrated on, and if you merge the answers to this with the others mine here would not make much sense. – anna v Jan 08 '13 at 18:34
  • @annav Do you prefer the link I called "related" or suggest that I re-open the question? – dmckee --- ex-moderator kitten Jan 08 '13 at 18:40
  • @dmckee: I don't think any of the previous answers explain how messy the annihilation is. I'm sure I remember a really good description of this from Anna, but I've searched and can't find it. However if you want to leave this closed I'm not fussed. – John Rennie Jan 08 '13 at 18:48
  • @dmckee if you merge yes, the answer would be close to the "related". I do not have a strong view on reopening, except that it is a new user – anna v Jan 08 '13 at 18:49
  • user17636, could you read the answers to the questions I linked, and if they don't answer your question let me know how: I (or another moderator) can re-open this if there are issues outstanding. The closing the question as a duplicate is not meant as a punishment of any kind but to keep answers to like questions together. – dmckee --- ex-moderator kitten Jan 08 '13 at 19:22

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Particle-antiparticle annihilation is generally a messy business because the energy released by the annihilation is enough to create other particles. Even when the kinetic energy of the protons is low you get several particles out. See for example the picture in this article.

So reaction of a large chunk of antimatter with ordinary matter would produce huge numbers of energetic particles, and these would in turn collide with and heat the matter around them. The end result would be very similar to a thermonuclear explosion i.e. a colossal bang!

Yes, antimatter would be an excellent weapon if we could make it, contain it safely then deliver it to the target. At the moment we can do none of these things and there is no evidence to suggest we'll be able to do so in the near future, which is probably a good thing for world peace :-)

John Rennie
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  • antimatter would also be an excellent starship fuel if we could make it and contain it safely, and the fact that there is no evidence to suggest that we'll be able to do so in the near future is probably a very bad thing for human exploration and colonization of space – lurscher Jan 08 '13 at 18:09
  • As a comment to the last paragraph, we can currently produce and trap amounts of antimatter atoms, mostly antihydrogen isotopes, roughly in the low millions of atoms per "batch". The total number of antimatter atoms produced for all research purposes is in the hundreds of millions, 10^8. That is less than one quadrillionth of one mole (6.02*10^23 atoms) of antihydrogen. – KeithS Jan 08 '13 at 18:10
  • @lurscher The US air force has simulated anti-matter rockets of various designs with exactly that in mind. Their results were disappointing because it was very hard to generatea large asymmetry of effect (i.e. to get much thrust). Now, that may just be a technological issue but don't underestimate the amount of R&D stat stands between getting macroscopic samples of antimatter and having a starship fuel. – dmckee --- ex-moderator kitten Jan 08 '13 at 18:39
  • I doubt that the US air force has managed to store enough anti-hydrogen for benchmarking this kind of combustion. If you refer to the positron trap thing, that was bound to be disappointing because the density of storage is many orders of magnitude bigger than the energy density, so that won't scale. I'm referring to diamagnetically levitated anti-hydrogen frost, which does require not only a huge revolution in production and storage, but also some decent way to reflect 200 MeV gamma rays (and a magnetic nozzle for the pions) – lurscher Jan 08 '13 at 18:53
  • @lurscher Simulation. As in particle physics Monte Carlo. No one had any anti-matter in hand when they first studied this stuff. The basic problem is that most of the energy comes out in gammas and pions, and while you can try to turn the pions with a magnetic horn (taking into account that they decay to muons at inconvenient times) the gamma flux remains spherically symmetric. So you end up proposing to use matter-antimatter as a heat source for a simple thermal rocket and get a relatively low ISP. Again, there may be a way to finess that, but I've never heard of it. – dmckee --- ex-moderator kitten Jan 08 '13 at 19:54
  • we are starting to find ways to do gamma ray optics. But the main issue is storage, even more so than generation. If efficient storage can be achieved (and efficient meaning for rocket applications, meaning fuel weight to storage weight ratios above 0.1) then the other problems can always be approached by brute-force – lurscher Jan 08 '13 at 20:18
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The hydrogen bomb, which utilizes the energy released when two hydrogen atoms fuse into a deuteron in conjunction with the energy released by uranium fission, releases the difference in binding energy

enter image description here

which at maximum is of order of a few MeV per nucleon.

Antiproton proton annihilation would release twice the mass of the proton in energy, i.e. about 2*10^3 Mev. For equal masses of the bomb, the destructive power would have about two thousand times the destructive power of an H bomb.

The impacts on land and water would react to such a factor, but otherwise there is no difference in whether the energy would come from annihilation, fusion, of fission. If one released 2000 H bombs the effect would be the same.

Fortunately there is no way to concentrate anti protons , let alone higher mass anti nucleons, in a small volume except by magnetic fields which need unwieldy equipment. A vacuum also is necessary because there should be no matter for the antiprotons to meet when in storage. In no way can the density of trapped antiprotons come near to hydrogen densities , i.e.10^23 protons per mole, so no such destructive weapon can be built in the foreseeable future, and hopefully civilization will have advanced enough not to need such weapons in the far future.

anna v
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