Antimatter In Lightning

AMESN writes "The Fermi Gamma-ray Space Telescope, launched last year, detects gamma rays from light years away, but recently it detected gamma rays from lightning on Earth. And the energy of the gamma rays is specific to the decay of positrons, which are the antimatter flavor of electrons. Finding antimatter in lightning surprised researchers and suggests the electric field of the lightning somehow got reversed."

Comments

Crossover

[gmuslera]

Now the monster of frankenstein (powered by lightning) was in fact the first asimovian positronic robot (ok, the alpha one, without any law). With that much discussion about who could be the author to write Asimov's stories, maybe the original Mary Shelley could be the one worthy for that task.

Not that surprising

[tylersoze]

Apparently they've detected gamma ray energies up to 20 MeV from thunderstorms, so given that amount of energy involved I wouldn't think it's that surprising that electron-positron pairs might be created in the process since an electron only has a mass of .511 MeV. The thunderstorms are basically operating like natural linear accelerators.

Re:what exactly did they detect?

[TheSHAD0W]

then for that energy we would need 2 electrons, not one.

511 KeV is the mass-equivalent energy of a single electron or positron, and annihilation results in two gamma photons heading off in different directions.

well isn't fusion a way of matter-to-energy conversion power generator?

Yes, but it's not as clean as direct annihilation would be. It generates neutrons which make the materials used for containment radioactive.

Whoa there, cart before horse?

[Ancient_Hacker]

Could it be the other way around, that cosmic rays trigger lightning? So the timing is just a coincidence?

Re:clean fusion

[jeffb (2.718)]

Well, some of the polywell/Farnsworth enthusiasts hope to harness boron-11/proton fusion. In the most common case, that produces three energetic He nuclei (alpha particles), each carrying two positive charges at several MeV. Surround the reaction zone with collector plates, and you extract the energy directly as high-voltage, low-current DC.

In practice, of course, it's not that simple.

Re:reversal schmersal

[John Hasler]

Fusion reactions seem more likely.

Cross section of lightning?

[jasno]

Does anyone know what the cross section of a lightning bolt looks like? I've always wondered if forces akin to the skin-effect are trying to spread out the electrons while it's constrained in a tube of plasma. Is it round? Is it a sheet? What's the electron density like? What sorts of pressures would you expect in the center of a bolt?

Just curious... but I'm unable to find a google hit and too dumb to simulate it.

Re:Cross section of lightning?

[TropicalCoder]

what I wonder though is do you end up with a tube of electrons surrounding a vacuum, or a more uniform distribution of electrons. What is the environment like that's created inside the plasma, and what happens to other high energy particles, say cosmic rays, that enter this region?

I think we have a pretty good understanding of plasma. Just look at a florescent or neon lamp. A lightening bolt is a tube of mostly positively-charged nitrogen ions in a cloud of electrons. The super-heated gas glows brightly as the electrons pass through it. Of course it wants to expand as fast as it can, leaving a vaccuum at the centre. As the gas expands, it cools and the light it generated is extinguished as it moves away from the core, so we see tube of light. The bulk of the current preferentially remains at the centre - the path of least resistance. Of course the negatively charged electrons want to repel each other, but they are partially constrained to the core where there are fewer gass molecules to bump into by the intense magnetic field they generate. The "skin effect" is not significant. That is a function of frequency, and we are dealing with more of a direct current here.

Now we think about a cosmic ray particle passing through that rarefied super-charged gas, and it goes flying right on through as if there was nothing there. These are mostly protons, sometimes traveling in pairs, flying at a good fraction of the speed of light. Their path may be barely deflected as they pass through the magnetic field becuase they have so much mass. If one did happen to collide with an electron or ion, we will get a shower of charged mesons much the same as during any kind of collision, and maybe even a black hole or two.

Disclosure: I am not a physicist, but I saw one on TV once.

Re:This was first observed in 1971

[calidoscope]

And, considering that lightning / thunderstorm related gamma rays are routinely observed with energies up to 10 MeV, there is plenty of energy to create positrons, and so I wouldn't be surprised if all of these reports included the positron annihilation line (or, at least the ones with sensitivity in that energy range).

Considering that pair production starts becoming significant at gamma energies above 5 MeV (threshold 1.022 MeV), I would be very surprised if there weren't some 0.511 MeV gammas from thunderstorms. It is also likely that the positrons could be formed by interaction between high energy electrons and matter.

I would think that the gammas are produced in conjunction with sprites (cloud to ionosphere) rather than normal cloud to ground strokes.