Antimatter Trapped for the First Time

[Deep Sea Isopod]

http://bigthink.com/ideas/25097




OK, let talk about this.

I know what antimatter is, and there was a great program on about Atoms last month, but how have they actually trapped it?



It lasted for half a second.
The article says they first produced antimatter in 1995. But they didn't trap it? How do they know they produced it?

[klr]

I could try and explain, but I'd just be spoofing (and taking it straight from Wiki).

Is there a physicist in the house?

[PsychoSerenity]

The advantage of using anti-matter is that it is potentially 100 times more powerful than an ordinary H-bomb. Nuclear bombs are only 1% efficient in converting mass to energy (via Einstein's famous equation). But anti-matter, when in contact with matter, yields a 100% efficient conversion of mass to energy.

Why are they comparing it in terms of bomb power?

[Deep Sea Isopod]

The advantage of using anti-matter is that it is potentially 100 times more powerful than an ordinary H-bomb. Nuclear bombs are only 1% efficient in converting mass to energy (via Einstein's famous equation). But anti-matter, when in contact with matter, yields a 100% efficient conversion of mass to energy.

Why are they comparing it in terms of bomb power?

Because there'd be too many horses to count.

[GreyICE]

Magnetic fields. Anti protons have a negative charge, anti electrons have a positive charge. Thus, a magnetic field can contain them.

Problem is that anti hydrogen would have no net charge. Easiest way to contain it would probably be an awesomely powerful superconductor, using their weird properties (they always have the opposite field of anything that impinges upon their matter). Downside is, this would work only at amazingly short distances (Van der Waals, essentially). So the antimatter would need to be very, very, very cold.

It's quite an issue.

P.S. You use bomb power because it's the easiest way to comprehend it - antimatter's reaction with normal matter is far, far more more energetic and destructive than a hydrogen bomb, but a hydrogen bomb is the closest we can come to visualizing it. It's also weirder - it produces a lot of neutrinos, as I recall.

[Ian]

Do you think it'll ever be possible to conduct large-scale production and storage of antimatter? And if so, will we be able to harness it for energy uses?

[Xamonas Chegwé]

Do you think it'll ever be possible to conduct large-scale production and storage of antimatter? And if so, will we be able to harness it for energy uses?

Creating anti-matter requires huge amounts of energy - at least as much as that released by it - so, except as a really really expensive battery, I would say no.

[Deep Sea Isopod]

What would you guys say to someone who thinks the money which has been spent on this should go an something more frivolous like cancer research?

I'm thinking of Marie Curie. You know, discovering radioactivity and that stuff, is linked in a way to discovering antimatter?

[mistermack]

What would you guys say to someone who thinks the money which has been spent on this should go an something more frivolous like cancer research?

I'm thinking of Marie Curie. You know, discovering radioactivity and that stuff, is linked in a way to discovering antimatter?

I would have to answer that the Earth is overpopulated as it is. More people need more energy. So what is more important? Finding ways to create clean energy, or finding ways to make people live longer?
Not that there's a direct link to producing energy in this, but eventually that knowledge might pay off big-time.
What I'd like to know is, is it true that every particle of matter has a matching particle of antimatter, somewhere in the universe?
And does antimatter produce gravity, in the same way as matter?

[lpetrich]

I've done graduate-level work in physics, so I hope I know what I'm talking about.

Antimatter 101:

Every elementary particle has an antiparticle, which is a sort-of mirror image of it. Antimatter might be called mirror matter. Some particles are their own antiparticles, like photons. Antimatter has positive mass, just as ordinary matter does.

The antiparticle of an electron is an antielectron or positron. As far as can be determined, it has the same mass, opposite electric charge, and otherwise identical properties to within some sign changes. The Particle Data Group has some stuff on tests of matter-antimatter comparisons for various particles, and so far, they are consistent with an important symmetry called CPT. Electrons and positrons having different masses, magnetic moments, and some other such properties would violate CPT. But from the PDG's page on electrons, that's been tested to VERY high accuracy.

An antimatter counterpart of a macroscopic object would have identical macroscopic properties, as far as can be determined. There'd be a few differences in the weak interactions, like spin directions and "CP violation effects" in particles like kaons, but even there, no big difference.

Those 38 antihydrogen atoms were just like 38 ordinary hydrogen atoms, but with a positron and antiproton instead of an electron and proton. Physicists hope to make enough enough of them to be able to measure their spectra, to see if they are the same as ordinary-hydrogen spectra. Differences would violate CPT.


The antihydrogen atoms were contained by using their magnetic fields. Though electrically neutral, their electron and proton have built-in spins, which make built-in magnetic-dipole moments (electron's one ~ 700 * proton's one). This gives these hydrogen atoms magnetic moments, meaning that they can be moved around with magnetic fields.

If enough antihydrogen atoms are produced, they may combine to make antihydrogen molecules. They are even more difficult to manipulate, since their positrons will form antiparallel, spin-0 pairs, reducing their magnetic moments by a large factor. If their antiprotons' spins are also antiparallel, like the ground state of ordinary hydrogen molecules, then they have zero magnetic moment. However, hydrogen molecules are diamagnetic, repelling about 10-5 of an external magnetic field. So it will still be possible to use magnetic fields to hold antihydrogen molecules.


It must be pointed out that production of antimatter is typically VERY inefficient. I tracked down some stuff on how particle-accelerator labs make positrons and antiprotons for use in their experiments.

For positrons, shoot an electron beam with an energy of about 250 MeV at a metal target. It will produce about 5*10[sup]-3[/sup] positrons per electron, or a relative efficiency of 5*10-5.

For antiprotons, shoot a proton beam with an energy of about 120 GeV at a metal target. it will produce about 2.5*10[sup]-5[/sup] antiprotons per proton, or a relative efficiency of 4*10-7.

This is relative to all the energy going into pair production, which means that only half the energy goes into positrons or antiprotons.

Sources:
SpringerLink - Hyperfine Interactions, Volume 44, Numbers 1-4 -- Positron production for particle accelerators - positrons
Build a (Virtual) Particle Accelerator - antiprotons


Accelerator operation is an additional source of inefficiency, and I haven't been able to find good numbers for that.

[JimC]

From the New Scientist article I read, the key goal of the research is to have enough anti-hydrogen, trapped for a long enough time, to study in great detail how they absorb and emit photons of specific frequencies, which will provide a useful test of some predictions made by the Standard Model.

[mistermack]

I know zilch about antimatter, so I have only questions.
Does antihydrogen destruct when it meets any particle of matter, or does it have to encounter hydrogen?
And if the Universe were in a state where it will stop expanding, and eventually contract in a big crunch, does that fit in with the laws of thermodynamics, of increasing entropy? ( presumable all the matter and antimatter would have to eventually meet up, in that case ).

[lpetrich]

From the New Scientist article I read, the key goal of the research is to have enough anti-hydrogen, trapped for a long enough time, to study in great detail how they absorb and emit photons of specific frequencies, which will provide a useful test of some predictions made by the Standard Model.

In particular, that it should have the exact same spectrum as ordinary hydrogen. That's an outcome of CPT symmetry, which is an outcome of certain rather plausible postulates. It's not just the Standard Model that obeys CPT, it's just about every plausible quantum field theory.

I know zilch about antimatter, so I have only questions.
Does antihydrogen destruct when it meets any particle of matter, or does it have to encounter hydrogen?

It doesn't have to meet an atom of ordinary hydrogen. What's likely to happen:

It runs into an atom, and its positron annihilates with an electron in that atom, producing some gamma rays.

The now-bare antiproton runs into a nucleus, and it annihilates with either a proton or a neutron, producing some pions. These will either escape or run into the rest of the nucleus, breaking it up. Antiproton-nucleus annihilation at rest describes some experiments in sending antiprotons into various nuclei.

And if the Universe were in a state where it will stop expanding, and eventually contract in a big crunch, does that fit in with the laws of thermodynamics, of increasing entropy? ( presumable all the matter and antimatter would have to eventually meet up, in that case ).

Yes, entropy will continue to increase in it.