Slashdot Mirror
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."
It’s a surprise to have found the signature of positrons during a lightning storm, Briggs said.
No, it's not.
There is a long history of observations and theorizing about gamma ray flashes from lightning strikes and ball lightning, starting in the early 1970's :
Is Ball Lightning caused by Antimatter Meteorites?
D. E. T. F. ASHBY, C. WHITEHEAD, Nature 230, 180-182 (19 March 1971).
This has also been observed in connection with "sprites".
And from thunderclouds without lightning.
Oh, and it's also been observed from space before :
RHESSI Observations of Terrestrial Gamma-Ray Flashes
Now, not all of these reports include a positron annihilation signature at 511 KeV. But, 511 KeV emissions were explicitly reported from lightning in the 1970's. 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).
No, you don't get annihilation from electrons and protons.
You do get radiation, if things are energetic enough. If the electron becomes bound to the proton, you get emissions at one of the Hydrogen lines.
If, for example, the electron went all the way to the Hydrogen ground state, you would have emissions at the limit of the Lyman Series, up in the hard UV at 91 nanometers.
If things are more energetic, you will get electrons and protons combining to form free neutrons. These will decay (this decay is called beta decay) and release gamma rays at 782 KeV, but since the half life of free neutrons is 10.3 minutes, this will be really spread out in time and hard to see. Free neutrons have been directly detected from lightning strikes, so some of this is presumably going on.