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Scientists Create Di-positronium Molecules
doxology writes "The BBC reports that scientists have been able to create di-positronium molecules. A di-positronium molecule consists of two positronium atoms, exotic atoms which are made from an electron and a positron (the anti-particle of the electron). A potential use of these molecules is to make extremely powerful gamma-ray lasers, possibly on sharks."
Dr. Evil: You know, I have one simple request. And that is to have sharks with frickin' laser beams attached to their heads! Now evidently my cycloptic colleague informs me that that cannot be done. Ah, would you remind me what I pay you people for, honestly? Throw me a bone here! What do we have?
Its an Austin Powers joke. http://www.imdb.com/title/tt0118655/quotes/
The original article was posted by someone called "doxology"!
A gamma-ray laser would certainly have many applications. Maybe the energy density is so high that it becomes irrelevant, but the problem that jumps out at me is that you really can't refract high-energy photons. About all you can do is stop them. I don't see this type of "laser" being used in most applications where you traditionally think lasers would be useful, since you wouldn't be able to easily focus these beams, guide them in fiber, or anything like that. The most useful thing you could do with this type of laser, I would guess, would be ablation--THAT it should be pretty darn good at.
Anyhow, it'll be interesting to see the radiometry for these lasers in however many years it'll take for them to be in a position where they can even think about that sort of thing. From that, you can figure out the dosimetry if you were to turn one onto a person. In this situation, a medical linac should be to this sort of thing what a flashlight is to a laser in terms of photon flux. When you're talking about gamma photons instead of visible ones, I imagine you could give someone a pretty serious radiation dose in pretty short order. From a military perspective I don't think that putting that in a hand-held weapon would exactly rival bullets (which are pretty good at disabling people quickly, something that radiation couldn't do reliably barring stupidly high doses over large areas of the brain or GI), especially considering the cost. Putting one on a satellite and blasting ICBMs in orbit, however, could be a very different story--you don't have nearly as much atmosphere to get through, and you ought to be able to put an awful lot more energy in that missile with similar fluxes of gamma photons versus lower-energy photons. The gammas would probably significantly penetrate the housing of the missile, too, which could be good or bad--bad in that it spreads out the heating effect you'd get, good in that you can significantly heat things that are behind a few layers of metal.
Come to think of it, considering that medical linacs have caused serious burns (and then death from ARS) in the past, turning a gamma laser on someone would probably basically burn right through them--so maybe dosimetry really isn't an issue (for the target--for the operators, on the other hand...)
Anyhow, that's way in the future. For now, all we have are jokes about sharks that can turn people into the Hulk from ten meters.
Dude, I know you don't read the article, but you should at least read the summary. Positronium isn't anti-hydrogen; it's an electron and a positron, not a positron and an anti-proton.
Chris Mattern
Calling an electron-positron pair an 'atom' is a bit suspect, but not too bad. Any semi-stable collection of elementary particles can be referred to as an 'atom'. They took the analogy even further, saying that when these 'atoms' met each other they formed 'molecules' -- large, electromagnetically bound accumulations of electron-positron pairs. Kinda cool.
As for what's keeping them from annihilating each other...well, at first it's angular momentum and the Pauli exclusion principle. Both the electron and the positron are fermions, and they must occupy discrete states. Give the pair enough energy and they will occupy a semi-stable state that does not allow them to contact and destroy each other.
But before long they *do* annihilate each other. That's why it's called an 'annihilation laser'. The matter-antimatter pair collapses, liberating enormous amounts of energy in the form of gamma rays.
I think 'matter-antimatter annihilation laser' sounds cooler, but there's a certain mad scientist flavor to the 'gamma ray' bit, too.
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First of all, the electrons orbiting around the atom's nucleus is an atomic model that was valid during the first couple of decades of the 20th century. Our atomic models of the last 80 years are not as simple as that.
You are right about the electron and the positron being able to annihilate each other (producing a couple of photons IIRC, I guess your "explosion" of radiation). However, you are limited to high school level (particles orbiting each other) and Hollywood level (matter-antimater explosions) physics, but you are getting in quantum physics territory, where the particle-antiparticle annihilation does not exactly happen when the particles "touch". In fact we cannot even say that two particles "touch" in the traditional sense of the word.
Anyway, without being a particle physicist and without RTFA (leaving for work now), I can tell you that I don't see a reason that a positron-electron pair could not survive for a brief time. Where "brief" in physics is measured in ps or at least ns. When you hear physics news like "we created the xxx exotic particle" they are usually referring to something that existed in their accellerator for a picosecond or so...
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I am a physicist but not a particle physicist. Electrons and positrons are attracted to each other because one is negatively charged and one is positively charged. When they come together they can form a stable state which is a lot like a hydrogen atom, instead of a proton and an electron you have a positron and electron. The stable state is called "positronium". "Stable" is a relative term here, positronium lasts maybe 100 nanoseconds, which is a "long" time in some sense. After that the electron and positron do annihilate one another. When they do, they produce gamma rays of about 1 MeV. I'm not sure how you would make this into a gamma ray "laser", but you could at least produce gamma rays this way.
I was going to write a long post speculating on the decay of positronium, but I just got owned by Wikipedia.
But you're right that the Pauli exclusion principle doesn't apply to the stability of positronium.
The wikipedia article has some good information on lifetimes of various states; I find it interesting that the triplet state (parallel spins) has roughly 1000 times the lifetime of the singlet state (antiparallel spins). I think this is due to angular momentum: the net angular momentum in the singlet state is 0, so the easier two-photon decay is possible. The triplet (spin 1) requires the three-photon decay to carry away the angular momentum, as photons have spin +-1. However, none of the lifetimes is much more than about a microsecond, so it doesn't make very good rocket fuel.