Thunderbolts and lightning are more than just frightening 鈥� they also create radiation. For the first time, we have definitive proof that lightning sparks radiation and even clouds of antimatter, though it鈥檚 not clear how or if this will affect the health of people on the ground.
鈥淣ature still has a lot of mysteries, even with very familiar phenomena like lightning,鈥� says at Kyoto University in Japan. Enoto and his colleagues put one mystery to rest earlier this year, when four radiation detectors picked up neutron and positron signals during a thunderstorm.
杏吧原创s had long predicted that this might be the case. Back in 1994, NASA made a strange discovery. The agency鈥檚 space-based Compton Gamma Ray Observatory, which was designed to detect the most energetic photons in nature from distant astrophysical objects, instead spotted bright bursts of gamma rays radiating upwards from Earth.
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Now, we understand that these so-called terrestrial gamma ray flashes occur within the intense electric fields generated by lightning. Those fields accelerate electrons to ultra-high energies, which can emit gamma rays.
Predictions suggested those gamma rays could then slam into molecules in the atmosphere, like nitrogen, and cause a long list of chemical reactions that create neutrons and radioactive elements. As radioactive decay kicks in, positrons, the antimatter cousins of electrons are produced.
But between the dangers of directly observing thunderstorms and the lack of appropriate instruments, proof wasn鈥檛 forthcoming, until now.
Final piece to the puzzle
Though several pieces of the nuclear-reaction puzzle have been observed before, this was the first time all the pieces fell into place. 鈥淲hat鈥檚 really new here is that it鈥檚 all been wrapped up together very nicely and everything has been seen in one event,鈥� says at the University of California, Santa Cruz. 鈥淚t really cements our understanding of what a downward terrestrial gamma ray flash looks like.鈥�
鈥淏ut something like this always makes you step back and say, 鈥榳ow, it鈥檚 kind of amazing that something as聽common and garden-variety as lightning is actually doing something this energetic,鈥欌�� says at Duke University in Durham, North Carolina.
Cummer is referring to all those chemical reactions that follow a flash of lightning. Not only do they produce radiation and antimatter, they ultimately transform nitrogen-14 into carbon-13 鈥� alchemy that only occurs in extreme environments. 鈥淚t鈥檚 so powerful that on a small scale it does things that only fusion in stars and supernovae do.鈥�
That power could have wild implications for the kinds of health hazards lightning poses.
Unexpected implications
Physicists have long worried about the radiation hazard that lightning might pose for aircraft flying by a storm. Luckily, aircraft tend to dodge bad weather, and as long as they do, we can be relatively confident that lightning storms don鈥檛 pose a serious risk.
But this proof that the gamma rays emanating from lightning鈥檚 powerful electric field can spark radiation is prompting Smith to ask the question again.
鈥淣one of us have actually sat down to ask, 鈥榦kay, what radiation dose would a person immediately below these events receive鈥�?鈥� Smith says. 鈥淲e know that if you go right to the point where the gamma ray flash is actually made, that is a dangerous amount of radiation. But if it鈥檚 a mile up or half a mile up? You probably shouldn鈥檛 be worried.鈥�
He argues that the terrestrial gamma ray flash would need to be extremely low, much less than 1 kilometre above ground, to have a bad effect on health. Still, he says, scientists need to do more calculations to determine if these powerful flashes pose a radiation risk to people on the ground, especially given the fact that this area in Japan tends to produce extremely low-lying thunderstorms.
Journal reference: Nature, DOI:
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