Thunderstorm neutrons

To assess the current state of studies of nuclear reactions in thunderstorms, observational data are reviewed on the neutron flux enhancement in thunderclouds and during thunderstorms related to photonuclear reactions because of the bremsstrahlung of the avalanches of high-energy runaway electrons that can develop in thunderstorm electric fields. Selecting thunderstorm neutrons is a challenging problem, since detectors are affected by a mixed field of various penetrating radiations that also includes, apart from neutrons, primary high-energy electrons and their bremsstrahlung. Special attention is given to the discovery of the electron-positron annihilation line with the photon energy of 0.511 MeV in a thundercloud and on Earth's surface during thunderstorms, providing trustworthy evidence of neutron production by thunderstorms and the photonuclear origin of thunderstorm neutrons. The consequences of this discovery are discussed. "New is a carefully forgotten old." Favorite proverb of Dr L V Tarasova from VNIIEF, who was the first to detect high-energy runaway electrons and their bremsstrahlung in electric discharges in the open atmosphere [1, 2].