22.012 Age dating

planeterde Welt der Geowissenschaften
Particle accelerator in clouds, 24.11.2017
planeterde.de, Age dating

Thunderstorms obviously bring electrons to such speeds that they can knock neutrons out of atomic nuclei and so trigger decay chains in the atmosphere, which are like those of the hard cosmic radiation. Japanese high-energy physicists have now observed this and communicated it in "Nature" with a thunderstorm over the Japanese west coast. The thunderstorms are therefore, next to cosmic radiation, the second natural source for unstable isotopes in the atmosphere.

On the 6th of February 2017 a violent thunderstorm raged over the nuclear power station Kashiwazaki-Kariwa in the Japanese Prefecture Niigata. The region is known for its violent winter thunderstorms and that of the 6th of February was no exception. A particular strong flash of lightening has now made into the science magazine "Nature", because with it the researchers of the University Kyoto have followed the production of unstable isotopes of the elements nitrogen, oxygen and carbon. With this thunderstorms are now considered as source for radioactive isotopes in the atmosphere. The only other natural source is the high energy part of cosmic radiation.

"We are actually astrophysicists, but one application of our X-ray astronomy instruments is the observation of high energy phenomena in the atmosphere", reports Teruaki Enoto. Since 2006 the working group at the University Kyoto, in which Enoto researches, operates four of the compact instruments on the ground of the nuclear power station. Normally the instruments are used on board of satellites, but at the Japanese See they monitor the sky from the ground. And on the 6th of February the high energy physicists were lucky. All four detectors recorded the ray eruptions, which were triggered by a particular strong flash of lightning. "We could make out three types of gamma radiation during this event: First we registered a very intensive, extremely short eruption, which almost coincided with the flash of lightning. Then we recorded an about half a second long "afterglow" of the gamma rays – and finally staggered time wise, 35 seconds after the flash of lightning the third gamma ray type", so Enoto.

The three ray eruptions reflect the following cascade in the thunderstorm cloud. Russian high energy physicists had formulated them about ten years ago, but up to now they could neither be adjusted in the laboratory nor observed in nature. High energy electrons hit upon atmosphere molecules, above all therefore nitrogen. On the basis of their high energy they knock a neutron out of the stable nitrogen isotope N 14, so that unstable nitrogen 13 is produced. Gamma radiation is released with this reaction, the first very intensive eruption. The neutron buzzes through the atmosphere and is finally caught by another atomic nucleus. Also on that occasion gamma radiation occurs, the "afterglow". The unstable N 13 has in the meantime decayed to carbon 13 and has thereby released a neutrino and a positron. Positrons are the antimatter equivalences to our electrons. Sometime such a positron hits upon an electron and both are destroyed in an energy eruption, the third gamma ray event.

Electrons supply the impulse for this chain reaction, which are accelerated to nearly the speed of light in the thunderstorm clouds and so show the sufficient high energy, to drive neutrons out of atomic nuclei. "There are in the meantime a number of studies", says Teruaki Enoto, "which show that thunderstorm clouds work like particle accelerators.

Beyond the narrow circle of high energy physicists and lightning researchers the new discovered mechanism has possibly clear consequences. Because one of the isotopes, which occur with the strong thunderstorms, is the radioactive carbon 14. It is employed by numerous disciplines in age dating. Basis of the method is the assumption that radiocarbon atoms exist uniformly in the whole earth atmosphere. That is correct, as long as it is assumed, that only cosmic radiation can produce the radioactive carbon isotope. Indeed there exist correction tables, which store the changing intensity of the cosmic radiation, but the basic assumption remains: Everywhere the upper layers of the earth atmosphere remain exposed to this energy rich radiation in the same measure.

The thunderstorms as second source for C 14 bring uncertainty. "Thunderstorms can in some regions possess a share in the C 14 production, which is about as high as that of cosmic radiation", thinks for example Leonid Babych of the All Russian Research Institute for Experimental Physics in Nischni Nowgorod in an accompanying article in "Nature". Teruaki Enoto on the other hand estimates that the share of thunderstorms will not be considerable. "But that is my personal view; no-one knows what the case is." That can confidently be judged as invitation to a more exact check over.

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