22.011 Radiocarbon dating

Das Wissensmagazin (The knowledge magazine)
Also lightning produces antimatter, 06.12.2017
scinexx.de, Radiocarbon dating

Also lightning produces antimatter

First proof of lightning induced nuclear reaction in the air

Even atomic nuclei decay: Lightning does not only produce energy rich radiation, but even triggers nuclear reactions in the surrounding air. With these decay reactions antimatter is released – positrons are produced, as researchers have now proven for the first time. New also: The nuclear reactions produce carbon isotope C 14 – a decisive atom variant for the radiocarbon dating.

Lightning not only produces energy rich radiation, but also antimatter and new isotopes.

A thunderstorm with lightning and thunder is a dramatic natural spectacle. Lightning, produced through charge differences in the thunderstorm cloud, can reach an intensity of current of several ten thousands ampere and in a fraction of a second heat up the surrounding air to up to 30,000 degrees. Its explosive expansion then produces the thunder.

Where do positrons come from?

But still more happens: In the year 2011 the gamma radiation telescope Fermi registered above large thunderstorm clouds a surprising gamma ray surplus. The energy of this radiation was at 0.511 megaelectronvolt – and thus exactly that value, which comes into being with the reaction of positrons with matter. Somewhere therefore antimatter had to be materialized in the thunderstorm.

But where? Researchers suspect already for some time that lightning can produce nuclear reactions of the air molecules and on that occasion also positrons. But a proof for it was up to now outstanding. Exactly this Teruaki Enoto of the University Kyoto and his colleagues succeeded to do. For their study they had installed four highly sensible gamma ray detectors near the power station Niigata in Japan - in the hope to catch some time a lightning "in the act."

Lightning walks "into the trap"

On the 6th of February 2017 at last it was ready: A couple of lightning flashes discharged only a few hundreds of metres away from the measuring instruments. "All four detectors and even sensors of the nuclear power station registered on that occasion an about 200 millisecond lasting gamma ray release", reported the researchers.

Within these results the detectors registered three different phases: First came a strong gamma discharge lasting less than one second. After that followed a weaker gamma ray after glowing, this went on some dozens milliseconds. The end formed a hardly one minute lasting phase, in which increased gamma radiation of energy of 0.511 megaelectronvolt was released

Gamma pulse and neutron catapult

"We knew that the first gamma lightning had to come from the flash of lightning itself", explained Enoto. The electric discharge is so energy rich that not only photons of the visible light and X-rays are released on that occasion, but also the still more energy rich gamma radiation. "Through further analyses we could then determine, what was behind the second and third phase of this gamma ray release", so Enoto.

Therefore the second ray thrust occurred through a nuclear reaction of the air nitrogen: The energy of the lightning knocked a neutron out of the nucleus of the atom and so produced the short lived isotope nitrogen 13. The on that occasion released neutron collides with further gas atoms in the air and produces gamma radiation on that occasion.

Antimatter through decay reactions

But the third phase is exciting: In it the unstable nitrogen 13 isotope decays to carbon, by one proton of the atomic nucleus changing to one neutron through beta decay, as the researchers report. On that occasion, next to a neutrino, also the antimatter equivalent of the electron is released: one positron. As soon as this gets into contact with electrons, both particles extinguish each other and release gamma radiation typical for this annihilation reaction.

With this it seems clear: The puzzling gamma ray surplus above thunderstorm clouds has its origin in the lightning. It triggers the nuclear reactions in the air, which produce the antimatter and the gamma radiation. "Antimatter is therefore something, which can, on stormy days, originate directly above our heads", says Enoto.

Thunderstorms as isotopes "factory"

Surprising also: With their measurements the researchers unveil one of the up to now unknown source of isotopes in the earth atmosphere. Element variances like nitrogen 15, carbon 13 and carbon 14 therefore originate not only through cosmic radiation or at other exotic sources, but also in thunderstorms.

"Therefore Enoto and his colleagues have supplied the first clear proof for a thunderstorm induced nuclear reactions", says Leonid Babich of the Russian nuclear centre in Nischni Nowgorod in an accompanying commentary. Important is this knowledge for example because the carbon isotope C 14 plays a decisive role for the radiocarbon dating of fossils and archaeological finds.

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