I Collision of anti-hydrogen with matter

[Sasho Andonov]

TL;DR Summary

What will happen if anti-hydrogen colide with oxygen?

Fir the time being, the only anti-matter atom which was produced by humans is anti-hydrogen atom. I am wonbdering what will happen if this anti-hydrogen collide with normal atom of (for example) oxygen: What will be anihilated and what will survive?

 

[anuttarasammyak]

One of protons in oxygen core will be lost by pair annihilation and the core will become nitrogen.

 

[Bandersnatch]

There's enough energy released from the annihilation to unbind the remaining nucleus many times over.

 

[Vanadium 50]

And there is enough energy to produce pions. Many times over.

 

[topsquark]

I found a reference (three of them, actually) that anti-He was produced at Brookhaven National Lab (using the Relativistic Heavy Ion Collider) in 2011. Unfortunately, I do not have Journal access so I can't give a proper reference, but one report was from Phys.org, so it's probably legit.

But, obviously, take it with a grain of anti-NaCl!

-Dan

 

[Sasho Andonov]

One of protons in oxygen core will be lost by pair annihilation and the core will become nitrogen.

But, anihilation of the positron with electron from oxygen will produce energy which cuold affect the process of panti-proton anihilation with proton fro oxygen core. Or maybe it will not... (????)

 

[Vanadium 50]

You certainly produce anti-tritons and anti-helium-3 in collisions. Don't know what the status of anti-alphas is. The rule of thumb is that each additional nucleon reduces the production by ~1000. So you have much more anti-He-3 than anti-He-4.

These are nuclei, not atoms.

 

[mfb]

Anti-He-4 nuclei have been detected by STAR and by ALICE. There is no stable nucleus with 5 nucleons so the next heavier nucleus would be lithium-6, which is suppressed by a factor ~10⁶. We are still looking at individual events of anti-He-4, so we won't see lithium any time soon.

Antiprotons will readily react both with protons and neutrons, typically producing a couple of pions. Some of these can interact with the remaining nucleus, kicking out protons, neutrons, larger fragments, or even splitting the nucleus into multiple parts. Here are results for carbon, which isn't too different from oxygen. See page 28 for a distribution of products (neutrons are not measured in this case).

 

[snorkack]

How are the antiatoms produced? At what speed do they arrive in matter?
The halflife of ground state orthopositronium against annihilation is 10^-10 s. In multielectron atoms, molecules and solids, I suspect that the parapositronium nucleus has appreciable overlap with opposite spin electrons too, so its lifetime in ground state is in the same order of magnitude.
Lower excited states of hydrogen atom have halflife of 10^-8 s unless forbidden. Positronium has lower reduced mass, but I suspect the halflives are still not longer than 10^-7 s... but no shorter than 10^-8 when having l, and 10^-10 for s states.

What will a slow antiproton do inside matter? Eventually, it will be caught in a high l orbit of a specific nucleus, followed by a cascade of x-rays and auger electrons. But before it has picked the nucleus... when antiproton meets a film, what are its chances of annihilating with either hydrogen, carbon, nitrogen, oxygen, sulphur (of cysteine), silver or halogen (which one - chlorine, bromine, iodine?)?

 

[mfb]

Trap antiprotons, then trap positrons in the same spot (with a clever double-trap potential), some will react. Many of the produced atoms escape but some of them are trapped. There is no matter around so lifetimes of matter/antimatter systems are irrelevant for that process.

What will a slow antiproton do inside matter?

It will be captured by a nucleus and annihilate as discussed in the previous comments.

 

[snorkack]

It will be captured by a nucleus and annihilate as discussed in the previous comments.

I found an article telling that antiproton in He is extraordinarily stable (microseconds), in contrast to other substances (picoseconds).
The reasoning seems to be as follows: an antiproton at high l orbit could deexcite by photon emission or Auger electron emission. In He, photon emission at high l is slow and Auger emission of the one electron somehow forbidden, so antiproton is long lived; in other atoms there are presumably more allowed Auger lines leading to rapid cascade. (And in protonium, there are no Auger lines, but protonium being neutral and having no electrons readily combines with other atoms).
If the cascade is allegedly in picoseconds, it is rather faster than the cascade of the positron? And therefore not affected by the annihilation of positron?

 

[snorkack]

Antiprotons will readily react both with protons and neutrons, typically producing a couple of pions.

See page 3 of your link. For annihilation with proton, the average count of pions is 4,98 - I don´t understand how they get so big +-, the components do not add up! 5 is also the mode at 35%, the second is actually 6 at 23%. "Couple" is actually possible despite antiproton and proton having 6 quarks and antiquarks, at 0,38%. (One is impossible for momentum conservation. Rest mass allows a maximum of 13 regardless of charge).

Some of these can interact with the remaining nucleus, kicking out protons, neutrons, larger fragments, or even splitting the nucleus into multiple parts.

See page 4 of same link. The graph is conspicuously absurd, and links to a source which is paywalled. But it suggests that even for heavy nuclei, most pions (and presumably their energy) fly away and only a small fraction is absorbed in the nuclei - and nuclei like C or O catch much less of the pions than even the small fraction heavy nuclei do.
If it is true, is absorption of pion energy stochastic or incremental process? That is, do the residual nuclei catch at least a few MeV of the annihilation energy, or are the averages averages of a small fraction of events where the nucleus is disrupted and substantial fraction where the pions just fly away leaving the residual nucleus in ground state?

Here are results for carbon, which isn't too different from oxygen. See page 28 for a distribution of products (neutrons are not measured in this case).

 

[mfb]

The strong interaction can easily produce quark/antiquark pairs.

I said "a couple of pions", not "a pair". 3-7 pions are a couple of pions.

But is suggests that even for heavy nuclei, most pions (and presumably their energy) fly away and only a small fraction is absorbed in the nuclei - and nuclei like C or O catch much less of the pions than even the small fraction heavy nuclei do.

Right.

Nucleons gaining a few MeV will typically fly away. That's possible, as discussed before. It's also possible that all the produced pions fly away and the nucleus stays as it is. It's random, unsurprisingly.

 

[nightvidcole]

If neutral antihydrogen collides with matter, the positron from the antihydrogen will annihilate with an electron, most probably producing two 511 keV gamma rays. The antiproton will get captured into an atomic orbital and eventually lose energy and annihilate with a proton (or neutron). About half of the pions created in this reaction will probably escape the nucleus, the other half will be absorbed and most likely cause the nucleus to blow itself apart. With heavier nuclei, part of the nucleus may remain bound:

https://inis.iaea.org/search/search.aspx?orig_q=RN:14763524

Neutral pions usually decay to two gamma rays, charged pions decay (eventually) to electrons and neutrinos.

So the end result will be a few gammas, a few neutrinos, fast electrons, and some nuclear fragments. The gammas and charged particles will then lose energy by ionizing atoms in the surrounding matter, while the neutrinos will simply leave the scene without interacting further. The ionized atoms will eventually recombine and release the energy as heat and light.

After all the dust settles, you will have some slightly warmer matter with a few radioactive atoms left (and the escaped neutrinos, of course)...