Following the observation of neutrons and gamma rays in association with lightning, a new study reports evidence that lightning also triggers specific nuclear reactions. On 6 February 2016, Teruaki Enoto of Kyoto University in Japan and colleagues observed a gamma-ray flash lasting less than 1 ms followed by an exponentially decaying gamma-ray spectrum and then prolonged line emission around 0.511 MeV (indicative of electron–positron annihilation). The process is well-explained by photo-dissociation processes such as 14N + γ 13N + n with emission of de-excitation gamma rays, followed by positron decay of the nucleus to 13C, and finally the positron annihilating with an electron. In addition to its intrinsic interest, the result reveals a new source of isotopes, including 14C, used for carbon dating.