# What if a positron and neutron collided?

Discussion in 'Physics & Math' started by DrZygote214, Sep 3, 2014.

1. ### DrZygote214Registered Member

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Okay here's something I can't answer for myself.

We all know what happens when matter and antimatter collide, right? They annihilate each other, leaving behind no mass, only gamma ray energy.

Question is, what happens if a neutron collides with an anti-electron (positron)? The positron has much, much SMALLER mass than the neutron. So does the neutron get a little piece of it blown away into energy, then we just have this neutron with a crater in it moving around? But then the neutron wouldn't be a fundamental particle, would it?

Hmmm...

[EDIT]

i realize now that electrons and anti-electrons are NOT made up of 3 quarks like old theories thought. They are fundamental. So let me rephrase the question.

What happens when 2 fundamental particles of different mass, and one is normal matter and the other is antimatter, collide? For the sake of concreteness i nominate a muon colliding with an anti-electron.

Last edited: Sep 4, 2014
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5. ### DrZygote214Registered Member

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Thanks but i hesitate to bump that thread from 2007, and i didn't see a real answer other than suggesting some kind of beta decay.

My intuition says that the positron, made of 3 anti down quarks, collides with the neutron, made of 2 down quarks and 1 up quark. So the 2 anti down quarks annihilate the 2 normal down quarks. The neutron becomes 1 up quark and the positron becomes one anti-down quark.

They don't have the same mass... An upquark is more massive than a downquark, iirc. So what happens when this final part collides? Kinda gets me right back where i started.

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7. ### exchemistValued Senior Member

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I don't pretend to know a lot of particle physics, but what is wrong with James R's reply in that thread, saying that you can get a proton?

8. ### Farsight

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Did you mean to say that, or were you thinking of the antiproton? As far as I know, antiprotons and neutrons will annihilate. See Wikipedia where you can read this: Antiprotons can and do annihilate with neutrons, and likewise antineutrons can annihilate with protons, as discussed below. Note that electrons don't annihilate with protons, and positrons don't annihilate with protons or antiprotons. Also note that a free neutron will decay into a proton, and electron, and an antineutrino. A positron would annihilate with the electron, but not with the neutron per se. NB: you could argue that an electron or a positron is somewhat like a quark, but it isn't actually a quark.

9. ### danshawenValued Senior Member

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This question has already been asked and an answer attempted here:

http://www.sciforums.com/showthread.php?73620-If-a-positron-hits-a-neutron

Free neutrons evidently have a predisposition to recombine with protons to form a deuteron nucleus, and although the information about neutron collisions with electrons are numerous, information about whatever happens after a collision of a neutron with a positron is sketchy.

Trying to find the answer turned up an interesting link you may have seen (interactive chart of nuclides):

http://www.nndc.bnl.gov/nudat2/

And in addition, this:

http://iopscience.iop.org/1742-6596/265/1/012009

would seem to indicate that this is still an active area of research to determine the reasons for iron alloy reactor vessel embrittlement.

Finally, these guys:

http://www.tnw.tudelft.nl/over-facu...ps/neutron-and-positron-methods-in-materials/

use both positrons and neutrons to investigate materials, no doubt including the ones in which they most recently advanced in the field of quantum supercomputing.

10. ### DrZygote214Registered Member

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No, i chose "neutron with positron" because i didnt want to be confusing with "proton and positron", which both start with "p". A positron is an anti-electron.

My general question is just what happens when one antiparticle collides with a normal particle of greater mass. If they're both fundamental particles, then how can the antimatter annihilate with some of the normal matter? That would leave a fundamental particle with a hole in it, or crater, which seems impossible.

I chose a concrete scenario, neutron with anti-electron, just for the sake of concreteness.

Come to think of it, how can a proton collide with an anti-electron anyway? The both have charge = +1, so they would repel each other. I guess that's why you need huge supercolliding superconductors to accelerate these things really high and smash them into each other.

Oh and btw, i see now that an electron is NOT made of 3 down quarks like i thought. I must have gotten that from an older book in my youth, since a down quark has charge of -1/3, therefore you'd think an electron has 3 down quarks. So scratch everything i said in my previous post about which quarks annihilate with which antiquarks.

Kinda sucks that everything in nuclear physics has to be a special case.

11. ### mathmanValued Senior Member

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You seem to have finally got something right. There are no quarks in electrons or positrons. They are both elementary particles.

12. ### Farsight

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The question you should really be asking, is why doesn't the proton annihilate with the electron?

13. ### DrZygote214Registered Member

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Because they're not opposite matter, so why would they annihilate? A proton and electron are both normal matter. Did you mean anti-electron?

That would be a perfectly okay question too. However, since the proton is made of 3 quarks and the anti-electron is fundamental, maybe my question should involve 2 fundamental particles of differing mass, say a muon with an anti-electron.

I edited to OP to reflect this.

14. ### Farsight

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Because positronium is like light hydrogen. See this article: "The Positronium (Ps) atom consists of an electron and a positron orbiting their mutual center of mass. To a first approximation it can be regarded as a sort of light hydrogen atom. "

I didn't mean antielectron. People say the electron is matter and the proton is matter too. But think about it. The electron and the positron attract one another, and they're matter and antimatter. The proton and antiproton attract one another, and we say they're matter and antimatter. But why? Why don't we say they're antimatter and matter? Merely by convention. When you look at particle properties, the proton is more like the positron than it's like the electron. There baryon asymmetry and there's lepton asymmetry, but all this talk of the missing antimatter seems to me like a game of mixed doubles in tennis, with people saying the women won.

15. ### DrZygote214Registered Member

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You totally lost me. You asked why doesn't a proton and electron annihilate each other. You said u meant electron and not anti-electron. So now I hafta ask, did you mean positron instead of proton?

If so then i understand when you bring up "positronium" (1 electron and 1 positron). If not then I have no idea how you answer that question with positronium, which is NOT a proton and electron as per your question.

16. ### Farsight

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No!

Positronium is like light hydrogen. And it's neither matter nor antimatter, it's both. The inference is this: so is hydrogen. But the electron and the proton don't annihilate.

17. ### Dr_ToadIt's green!Valued Senior Member

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Total bullshit. Positronium is antihydrogen, and it is antimatter.

Where did you get that nonsense about it being both? From an Einstein quote you took out of context, or did you just pull it out of your "fundament"?

Don't offer any more physics answers, for God's sakes. You fail horribly every time you try it.

18. ### wellwisherBannedBanned

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An interesting anomaly is beta decay where matter generates an anti-matter positron.

What this implies is matter can release anti-matter (positron) if the potential is too high. The terms matter and anti-matter is not exactly a sharp dividing line. That leads me to be believe that matter, as a whole is more stable than anti-matter, which is why matter rules the universe. In the case of beta decay, less anti-matter in the nucleus adds to the stability of the daughter nucleus. Since protons will still remain in the daughter nucleus, which have the potential to decay to positrons, matter and anti-matter can coexist, since both are parts of matter.

If we go back to the original question and assume a reverse of beta decay, if we add an electron neutrino to the positron and neutron we will get a proton which is matter. The convention is misleading and should be stated as certain pairs of matter and anti-matter will annihilate, while other combinations form matter.

19. ### Farsight

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Now we're getting somewhere. Note though that there's an ambiguity in the terminology? The words matter and antimatter are used for both the particles, and the combinations of particles. See a blog I wrote on the subject.

All: please put Dr Toad on filter, he's an obnoxious antiscience troll who doesn't know any physics. As regards positronium, see New Scientist: "HALF matter, half antimatter, positronium atoms teeter on the brink of annihilation. Now there's a way to make these unstable atoms survive much longer, a key step towards making a powerful gamma-ray laser..."

Positronium is like light hydrogen, so the inference is that hydrogen is half matter and half antimatter. And so is antihydrogen! Or maybe it's better to say it's half antimatter and half matter.

Last edited: Sep 4, 2014
20. ### Dr_ToadIt's green!Valued Senior Member

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I stand corrected on the positronium part. I was under the impression that it was an antiproton and a positron, which is antihydrogen.

For the likes of you to call me an antiscience troll is just hilarious. The garbage that you posted about hydrogen being half antimatter is just that: garbage.

21. ### Captain KremmenAll aboard, me Hearties!Valued Senior Member

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Have you ever been on an anger management course?

22. ### Dr_ToadIt's green!Valued Senior Member

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I'd consider it if I were angry. Farsight irks me, but he doesn't make me mad, just his woo...

23. ### exchemistValued Senior Member

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I think there may be a misunderstanding at the root of this question. As I understand this, it is not "matter" and "antimatter" that annihilate. It is a particle and its corresponding antiparticle. For example an electron and a positron or a proton and an antiproton.

A positron and a neutron may well interact but there is no reason why "annihilation" has to feature, just because one is a constituent of "matter" and the other is a constituent of "antimatter", so far as I am aware.