Neutron production in terrestrial gamma ray flashes

Terrestrial gamma ray flashes (TGFs) are brief bursts of photons with energies up to 20 MeV typically observed in association with lightning. Such energetic photons may undergo photonuclear reactions with nontrivial cross section in the vicinity of the giant dipole resonance. Pulses of neutrons have been observed experimentally in coincidence with lightning, suggesting such reactions are observable. We present simulations of expected photoneutron production based on initial conditions inferred from observations of TGFs. We predict an average of similar to 10(12) neutrons produced per TGF and give energy, time, and space distributions of neutrons produced and neutrons reaching ground and satellite altitude. The simulation results are consistent with some observations and suggest further experiments may be profitable.