Question about antimatter

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Sockmonkey
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Question about antimatter

Postby Sockmonkey » Mon Jul 14, 2014 10:21 pm UTC

Is it possible to construct an atom out of both matter and antimatter?
As in using antiprotons and antineutrons in the nucleus but standard electrons for the orbital shells since particles only react with their specific antiparticle?

algorerhythms
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Re: Question about antimatter

Postby algorerhythms » Mon Jul 14, 2014 10:38 pm UTC

One difficulty of doing that would be that the negative electrons would not be bound to the negative antiproton nucleus, so you couldn't form a stable atom that way.
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speising
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Re: Question about antimatter

Postby speising » Mon Jul 14, 2014 10:48 pm UTC

so could you put a proton in the shell?

Hypnosifl
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Re: Question about antimatter

Postby Hypnosifl » Mon Jul 14, 2014 10:59 pm UTC

I think the basic answer is that if you put a proton and antiproton near each other there is a high probability they will undergo a reaction where both disappear and are replaced by two high-energy photons--matter-antimatter "annihilation"--whereas with the proton and electron, although there are reactions where they convert to other particles, they are very low-probability, or perhaps require that the particles have high kinetic energy (not sure on the details). There's some discussion of this here: http://van.physics.illinois.edu/qa/listing.php?id=18323

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Re: Question about antimatter

Postby algorerhythms » Mon Jul 14, 2014 11:17 pm UTC

And in terms of constructing an atom out of matter and antimatter, you can construct something atom-like using an electron and a positron: Positronium
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Hypnosifl
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Re: Question about antimatter

Postby Hypnosifl » Mon Jul 14, 2014 11:34 pm UTC

algorerhythms wrote:And in terms of constructing an atom out of matter and antimatter, you can construct something atom-like using an electron and a positron: Positronium

Yes, although the wiki article notes that even under optimal conditions they aren't likely to last much over 142 nanoseconds before annihilating each other.
Last edited by Hypnosifl on Mon Jul 14, 2014 11:36 pm UTC, edited 1 time in total.

speising
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Re: Question about antimatter

Postby speising » Mon Jul 14, 2014 11:36 pm UTC

algorerhythms wrote:And in terms of constructing an atom out of matter and antimatter, you can construct something atom-like using an electron and a positron: Positronium

oh, is that what Data's brain was made of? i wonder how he kept it from anihilating..

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Re: Question about antimatter

Postby Xanthir » Wed Jul 16, 2014 2:45 am UTC

Sockmonkey wrote:Is it possible to construct an atom out of both matter and antimatter?
As in using antiprotons and antineutrons in the nucleus but standard electrons for the orbital shells since particles only react with their specific antiparticle?

As others said, the charge is a problem if you have antiprotons but normal electrons, or vice versa.

Even if you just had antineutrons, though, you'd run into problems, becasue neutrons are really just a bound triplet of two down quarks and one up, so an antineutron is two anti-down and one anti-up. The protons it's mixing with are two up and one down, so there'd be plenty of quark/antiquark annihilation going on.
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Re: Question about antimatter

Postby PM 2Ring » Wed Jul 16, 2014 8:43 am UTC

Hypnosifl wrote:I think the basic answer is that if you put a proton and antiproton near each other there is a high probability they will undergo a reaction where both disappear and are replaced by two high-energy photons--matter-antimatter "annihilation"--whereas with the proton and electron, although there are reactions where they convert to other particles, they are very low-probability, or perhaps require that the particles have high kinetic energy (not sure on the details). There's some discussion of this here: http://van.physics.illinois.edu/qa/listing.php?id=18323


Actually, when a proton and antiproton react total annihilation into photons is not a very likely outcome. You generally get some mesons, and electrons & positrons as well as photons. Of course, the mesons soon decay in various ways, and the positrons soon annihilate with electrons in the vicinity, but some electrons will escape the reaction site.
From http://en.wikipedia.org/wiki/Annihilati ... nihilation
Wikipedia wrote:When a proton encounters its antiparticle (and more generally, if any species of baryon encounters any species of antibaryon), the reaction is not as simple as electron-positron annihilation. Unlike an electron, a proton is a composite particle consisting of three "valence quarks" and an indeterminate number of "sea quarks" bound by gluons. Thus, when a proton encounters an antiproton, one of its constituent valence quarks may annihilate with an antiquark, while the remaining quarks and antiquarks will undergo rearrangement into a number of mesons (mostly pions and kaons), which will fly away from the annihilation point.

The newly created mesons are unstable, and will decay in a series of reactions that ultimately produce nothing but gamma rays, electrons, positrons, and neutrinos. This type of reaction will occur between any baryon (particle consisting of three quarks) and any antibaryon (consisting of three antiquarks). Antiprotons can and do annihilate with neutrons, and likewise antineutrons can annihilate with protons, as discussed below.


Hypnosifl wrote:
algorerhythms wrote:And in terms of constructing an atom out of matter and antimatter, you can construct something atom-like using an electron and a positron: Positronium

Yes, although the wiki article notes that even under optimal conditions they aren't likely to last much over 142 nanoseconds before annihilating each other.


Sure, but notice how the half-life of ortho-positronium is over a thousand times longer than that of para-positronium. FWIW, you can delay any nuclear decay event by repeatedly observing the particle(s) involved, due to the Quantum Zeno effect, aka the Turing paradox, but that's only practical for delaying very small numbers of reactions. OTOH, there may be some way to utilise this to stabilise significant quantities of positronium.

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Re: Question about antimatter

Postby Soralin » Fri Jul 18, 2014 10:07 am UTC

There's Muonium: http://en.wikipedia.org/wiki/Muonium Which is a pairing of an anti-Muon and an electron, which apparently won't annihilate each other. Muons decay after a couple of microseconds, but other than that, it acts sort of like an atom, and you can make chemical compounds out of it and other atoms


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