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.