Scientists Create Di-positronium Molecules 160
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."
Re:Sharks (Score:5, Informative)
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/ [imdb.com]
Re:And doxology ruins the whole thread (Score:3, Informative)
The "optics" of a gamma laser (Score:5, Informative)
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.
Re:Not fair! (Score:4, Informative)
Chris Mattern
Re:Why is this an "atom?" (Score:5, Informative)
As for what's keeping them from annihilating each other...well, at first it's angular momentum and the Pauli exclusion principle [wikipedia.org]. 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.
Re:non-shark-related (Score:5, Informative)
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...
Re:The "optics" of a gamma laser (Score:5, Informative)
Re:The "optics" of a gamma laser (Score:4, Informative)
Now the gamma laser may well be highly collimated without any additional focusing. But we don't know that for a laser that's not been built and is only theoretically posssible!
Re:non-shark-related (Score:2, Informative)
Re:Why is this an "atom?" (Score:1, Informative)
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.