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ChromaticDragon t1_jbysxii wrote

You seem to be asking multiple questions. We may have to separate these to provide meaningful answers.

Since both neutrons and antineutrons both have neutral charge, can we distinguish between them?

Yes. The Wikipedia page has details and more in the referenced links. One difference is the magnetic moment.

Can antineutrons exist in the nuclei of regular atoms?

In the most general sense, no. A neutron and an antineutron would annihilate. So you cannot replace them one-by-one.

Could you have anti atoms with antineutrons, antiprotons and positrons?

Sure. Here's a good article on antimatter with some history of such. Trouble is that you have to keep it separated from regular matter which will annihilate it in short order.

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OtHanski t1_jbyu4ig wrote

In addition to what u/ChromaticDragon already mentioned, if I recall correctly, it would in theory be possible to have an atomic nucleus comprised of protons and antineutrons. However, the protons consist of 3 quarks (uud) and the neutrons consist of 3 antiquarks (-udd).

=> The atom would not be very stable, as the quarks might interact and annihilate with the antiquarks.

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Bag-Weary t1_jbyuv63 wrote

Replying to Oheligud (#2,215,919)

A neutron is made of up, down, down quarks, and a proton is made of up, up, down. An antineutron would be antiup, antidown, antidown, and the ups and antiups and the downs and antidowns would annihilate if it was in the same atom as a proton.

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Ridley_Himself t1_jbyvn95 wrote

Replying to Oheligud (#2,215,919)

The issue here is that protons, neutrons, and their respective antiparticles are not elementary particles; they are made of quarks and antiquarks respectively bound together by gluons. A proton contains two up quarks and one down quark. An antineutron contains two down antiquarks and one up antiquark. A quark from the proton and an antiquark from the antineutron would annihilate and produce mesons from the remaining (anti)quarks, which would quickly decay.

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ChromaticDragon t1_jbz47a9 wrote

Replying to Oheligud (#2,215,919)

To give you some meat to chew on regarding the descriptions others have already provided you, check out this paper, specifically section 5.5:

>Annihilation on neutrons
>Antiproton–neutron or antineutron–proton interactions at rest offer additional opportunities to study annihilation dynamics.

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Narwhal_Assassin t1_jbzcasy wrote

Replying to LeN3rd (#2,216,676)

You’d have an up quark-antiquark annihilation, and a down quark-antiquark annihilation, leaving behind an up quark and a down antiquark. These have charges of +2/3 e and +1/3 e, respectively, so they can combine to form a meson with a +1 charge (I forget what the specific name would be, probably a pi meson?). So, the proton-antineutron annihilation is totally fine in terms of charge conservation and in terms of not leaving solo quarks.

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Equoniz t1_jbzm072 wrote

Replying to ChromaticDragon (#2,215,881)

You have answered if an atom can have some neutrons and anti-neutrons at the same time, but that wasn’t really the meat of the question was it? You haven’t answered if an atoms could have all of its neutrons be anti-neutrons. Obviously getting there one at a time isn’t an option, but could it get there in any way? And even if it couldn’t actually get there, could it be a stable solution to our equations that describe the system?

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mfb- t1_jbzmvab wrote

Replying to Oheligud (#2,215,919)

> I thought antiparticles only annihilated with their respective particles?

Reacting with the respective partner is easier (in the sense that it's always possible), but annihilation is not limited to that. Protons and antineutrons will react in almost the same way as protons and antiprotons or neutrons and antineutrons, producing a couple of pions as most likely result.

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CainIsmene t1_jc0bw4s wrote

No. Antineutrons don't exist in the proverbial vacuum, they're comprised of more fundamental particles called quarks, in this case antiquarks.

Antineutrons are made of two antidown quarks and one antiup quark.

A proton is comprised of two up quarks, and a down quark.

So, if you stick an antineutron in contact with say two regular protons they'll annihlate and, if you're lucky, create a Δ++ baryon that'll decay into a proton and a positively charged pion that'll then decay into a muon and muon neutrino, and then that muon will decay into an electron, an electron neutrino, and an antimuon neutrino that'll annihilate with the muon neutrino that was made when the pion decayed and leave you, ultimately, with a hydrogen atom.

subatomic physics is weird my man

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ApeMummy t1_jc0hsqq wrote

Replying to Narwhal_Assassin (#2,216,747)

Question: how do sets of quarks annihilate simultaneously? Why doesn’t the energy released from the first annihilation cause the other quarks to scatter? Do they occupy the same physical space meaning all the annihilations are simultaneous?

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Emu1981 t1_jc0imbi wrote

Replying to migueltrout (#2,217,452)

>It absolutely boggles my mind that we as human beings have discovered this knowledge.

What is even more mind boggling is that we could be completely wrong about it all and not even know it - the old story about the blind men describing a elephant by touch comes to mind. We cannot "see" quarks but rather we can only see how they effect the physical world (e.g. via destroying matter in a particle accelerator).
We then infer what they are and build models to describe what we see. All it would take is a discovery that changes our understanding of one little part to completely upend the model.

*edit* bleh, no idea why Reddit insists that there should be a line break in there.

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Hotdropper t1_jc0rs2a wrote

Replying to Sable-Keech (#2,218,066)

Quantum chromodynamics is the answer here, I believe.

Essentially, the proton and neutron in a hydrogen atom (or any atom) aren’t static.

They are constantly swapping roles back and forth, the proton losing some energy and turning into a neutron, and the neutron then picking up that shed energy and turning into a proton.

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ghedipunk t1_jc11cgc wrote

Replying to ApeMummy (#2,218,472)

The models presented so far don't describe individual quarks.

Rather, nuclear particles (the protons, antiprotons, neutrons, and antineutrons) are a soup of quarks and gluons that, on average, add up to a specific number of quarks.

So, yeah... for a basic understanding, watch this: https://www.youtube.com/watch?v=WZfmG_h5Oyg

To answer your question: We're firmly outside of the ideas we're familiar with when we think of particles. There is no concept of simultaneity at this scale; you need to rely on probabilities only.

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kyrsjo t1_jc1b75z wrote

Replying to CainIsmene (#2,218,247)

Seems unlikely that the muon neutrinos will interact, but yeah.

And then the "antimuon neutrino" isn't actually a real eigenstate, so over time it will oscillate to other anti-neutrinos...

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bildramer t1_jc1q83k wrote

Replying to sejanus21 (#2,219,754)

You can build an actual machine to detect muons from space (more precisely: from the upper atmosphere), for example. The particles are all very short-lived, but they do exist.

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Sharlinator t1_jc1ujz3 wrote

Replying to sejanus21 (#2,219,754)

Well, theory predicts these reactions and experiments eg. with particle colliders have shown that the predictions match exactly what actually happens, to a high precision.

Indeed the theory (the so-called standard model of particle physics) is so successful that phycisists are frustrated because despite its success, it’s also incomplete, but not even the LHC has found even a hint of any new physics beyond the standard model.

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ElReptil t1_jc1vqqh wrote

Replying to auraseer (#2,217,700)

>and causes a massive explosion that destroys half the continent

That kind of depends on how many antineutrons are actually in a liter jar, which I guess could be anywhere from a handful in a magnetic trap to a chunk with the density of nuclear matter.

Fun fact: the energy released by the annihilation of one liter of antimatter at that density (roughly a hundred billion tons) is weirdly close to the gravitational binding energy of Earth.

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mesouschrist t1_jc20scn wrote

Replying to sejanus21 (#2,219,754)

I work on an experiment that traps antiprotons and we detect their presence by having them hit the wall of the trap (made of, obviously, normal matter) and we detect the charged pions. While these aren't antineutrons, it's the same exact concept. So yes this process is definitely observable.

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mesouschrist t1_jc21af1 wrote

Replying to CainIsmene (#2,218,247)

One small caveat - neutrino/antineutrino "annihilations" have never been detected, and probably almost never happen in nature. There is a whole branch of experimental physics with 10s of large scale experiments looking for this process (neutrinoless double beta decay experiments). And there are scores of theoretical physicists developing theories in which neutrinos don't have antiparticles (Majorana neutrinos). People doubt neutrinos are majorana particles only because that would be odd - since all the other fermions are not majorana in the known universe.

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mesouschrist t1_jc232om wrote

CainIsmene gave a great answer. I'll just add one more general concept. Particles don't *just* annihlate on their respective antiparticle. First I have to define the conserved quantum numbers:

-charge

-baryon number (number of "matter" baryons - protons, neutrons, and other exotic ones minus number of antiprotons and antinuetrons)

-and lepton number (number of electrons+nuetrinos minus antielectrons and antineutrinos asterix we don't know if antineutrinos exist)

These three things, as far as we know, are perfectly conserved in nature. Now a useful definition of "annihilate": quickly turn into lower mass particles like electrons, muons, pions, or photons with a lot of kinetic energy. Annihilation occurs if you ever bring two particles into contact, and there exists any collection of lower mass particles with the same conserved quantum numbers. There is an important caveat, however, that in some cases two particles don't directly interact, which will stop them from annihilating (like a muon cant annihilate with an anti-electron until the muon decays into an electron, which takes about a microsecond, because there's no direct interaction between the two).
-So an antiproton and a neutron can annihilate because the baryon number of the system is zero and the charge of the system is -1. three pions, two negative charge and one positive charge have the same conserved quantum numbers. And there are plenty of particle interactions that allow that conversion. So they annihilate and make those pions.

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Doc_Lewis t1_jc2ju74 wrote

Replying to sejanus21 (#2,219,754)

For a real world application, see PET scans. Positron emission tomography, a common imaging technique in healthcare, relies upon certain radioactive isotopes that undergo beta decay. That is to say, an up quark in a proton flips to down, and turns the proton into a neutron, and ejects a positron (antimatter electron). When the positron meets an electron, they annihilate and release gamma rays, which are detected.

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Quantum_Patricide t1_jc4rwsb wrote

Replying to Sable-Keech (#2,218,066)

If you look at the quantum energy levels, the proton and the antineutron, being distinct fermions, can occupy the same energy level (in this case the 1s orbital) and so would be literally in the same place as opposed to far away.

Secondly, the nuclear interaction inside nuclei essentially consists of nucleons swapping quarks with eachother (and creating virtual antiquarks so overall a meson is the exchange particle). So if the proton and the antineutron were bound then an up quark would move from the proton to the antineutron but interact with the antiup quark there and annihilate.

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