Neutron generation in lightning bolts

Abstract

Intense electrical discharges through polymer fibres have been shown¹ to produce 2.45-MeV neutrons, probably by deuteron–deuteron fusion. Noting broad similarities between discharges in polymer fibres and natural lightning, Libby and Leukens² have suggested that neutrons are also generated in lightning flashes, as a result of the fusion of deuterium contained in the atmospheric water vapour; by rescaling the plasma parameters of polymer fibres to those involved in natural lightning, they have predicted a yield of ∼10¹⁵ neutrons per lightning flash. An experiment by Fleischer³, however, using fission track detectors placed near lightning arrestors, has failed to ascertain the neutron production in lightning discharges. Based on the number of background cosmic-ray tracks accumulated in these detectors during seven months of observations, Fleischer estimated an upper limit of 2.5×10¹⁰ neutrons per lightning stroke. In our experiment, we have attempted to keep the cosmic-ray neutron background at a negligible level by searching for neutrons from individual lightning strokes, for a time-interval comparable with the duration of the lightning stroke. Here we present the first experimental evidence that neutrons are generated in lightning discharges, with 10⁷–10¹⁰ neutrons per stroke. Whether these neutrons are thermonuclear in origin, or are generated by non-thermal processes, remains to be determined.