Flashes generate radioactive isotopes in atmosphere via nuclear reactions. This suspicion, already expressed in 1925, could now be confirmed for first time by a research team in Japan. With aid of four detectors for gamma radiation, team observed a thunderstorm immediately after lightning, a radiation resulting from pairwise destruction of electrons and positron.
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The positron originate from decay of radioactive isotopes, which in turn form by nuclear reactions after a flash. Thunderstorms could refore be a non-negligible source of isotopes used for archaeological age determination, according to scientists in journal Nature (Enoto et al. 2017).
“Lightning is a natural particle accelerator,” explains Teruaki Enoto from University of Kyoto and his colleagues. They trigger entire cascades of high-energy electrons, which emit gamma rays as in a synchrotron. “The energy of this gamma radiation is high enough to trigger nuclear reactions in atmosphere.”
This conjecture had already been expressed by Scottish physicist Charles Wilson in 1925. Previous attempts to observe se reactions, however, were unsuccessful or did not allow any distinction between reactions by lightning or cosmic high-altitude radiation.
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The gamma radiation produced by lightning can in particular trigger a neutron from stable isotope nitrogen-14. The resulting isotope nitrogen-13 is extremely unstable and immediately decays under release of a positron into more stable carbon-13. Previous experiments focused on detection of neutrons produced in first reaction.
Enoto and his colleagues have now taken a different route: y observed only gamma rays in a thunderstorm on February 6 in Japan. After each flash, researchers first registered an outbreak of high-energy gamma radiation less than a millisecond. But this was followed by a one-minute continuous lighting with an energy of 511 kilos of Elektronenvolt. And this is precisely energy of gamma quanta that occur in pair destruction of electrons and positron.
The short-term gamma outbreak is braking radiation of electron cascade generated by Lightning. The paarvernichtungs radiation, on or hand, shows decay of secondary radioactive isotopes produced by gamma rays. Furr investigations would now have to show, says Enoto and his colleagues, which isotopes can be produced precisely in thunderstorms.
This question could be particularly important for archaeologists. For so far, in age determination of decay of radioactive isotopes, y assume that se are exclusively caused by cosmic high-radiation. In some regions, for example, production of carbon 14 could be by thunderstorms of same magnitude as those caused by cosmic radiation – thus distorting age determination accordingly.
