When gamma rays strike

On 6 January earlier this year, one of the strongest thunderstorms in livin’ memory a-crashed and a-roared its way across the Sea of Japan, rattlin the daylights outta the Kashiwazaki-Kariwa nuclear power plant on the coast.

This power plant is fitted with one of the most advanced radiation detectors on the planet and durin’ the storm it collected some extraordinary data. After a lil number crunchin, a team of physicists led Kazuo “Tiger” Makishima at the Cosmic Radiation Lab RIKEN, are publishing details of what they saw.

That night the nuclear power station was bombarded with gamma rays with energies of at least 10 MeV (that was the limit of the detectors).

Now gamma rays bursts ain’t commonly detected on the ground cos they ain’t easy to make (if you spot any it’s a good sign your local nuclear power station ain’t workin properly. It’s also why n-plants have the kit to detect ’em) .

The RIKEN team says the gamma rays were probably caused by the sudden deceleration of high energy electrons as they smashed into atoms in the thunderclouds above, forcing the electrons to given up their energy in the form of gamma ray photons. But how did the electrons get accelerated to energies of 10 MeV or higher?

That’s a bit of mystery cos our ground-based accelerators require a near perfect vacuum to get particles a-movin and a-groovin at any kinda decent energy. Without a vacuum, particles start a-crashin and a-bangin into atoms and molecules in the air before they can get going.

Thunderclouds are known to have hugely powerful electric fields of more than 400 kiloVolts per meter so getting to 10 MeV from scratch requires quite a few metres of acceleration.

Unless the electrons start off with a fairly high energy, that is. The RIKEN team speculates that the gamma ray bursts in the thunderstorm were triggered by cosmic rays– high energy particles from outta space that come a-smashin and a-bargin their way through the atmosphere, creatin a shower of energetic electrons in their wake, a well known phenomenon.

So it’s quite possible that high energy electrons were created by a cosmic ray shower in the thundercloud and then accelerated to even higher energies by the electric field.

That seems to be backed up, at least in part, by the fact that the gamma ray bursts did not occur at the same time as visible lightning strikes so the mechanism behind that kinda discharge don’t seem to be responsible.

Fascinatin’ stuff, huh?

Ref: arxiv.org/abs/0708.2947:Detection of High-Energy Gamma Rays from Winter Thunderclouds

One Response to “When gamma rays strike”

  1. Speedy says:

    Runaway relativistic breakdown avalanche? Or maybe something else (http://www.physorg.com/news3959.html)
    …this group also observed a disconnect between the gamma rays and the lightning strike…of an average of 1.24 milliseconds…