Photonuclear Reactions in Lightning: 1. Verification and Modeling of Reaction and Propagation Processes. Issue 20 (13th October 2020)

• Record Type: Journal Article
• Authors: Wada, Y.; Enoto, T.; Nakazawa, K.; Odaka, H.; Furuta, Y.; Tsuchiya, H.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 20(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-10-13
• Subjects: photonuclear reaction -- lightning -- thunderstorm -- high‐energy atmospheric physics -- terrestrial gamma ray flash; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2020JD033193
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: We report simulation results of photonuclear reactions in the atmosphere triggered by a downward terrestrial gamma ray flash in lightning. Possible channels of reactions in the atmosphere and their cross‐sections are verified with the ENDF/B‐VII.1 library. Monte Carlo simulations with two stages are then performed with the Geant4 framework. In the first stage, electrons following the relativistic runaway electron avalanche spectrum are produced in a mass model of the atmosphere, and production of photoneutrons and β + ‐decay nuclei is calculated based on the nuclear data library. In total 1 × 10 13 neutrons and 4 × 10 12 β + ‐decay nuclei are produced by 10 18 energetic electrons above 1 MeV. In the second stage, propagation of the photoneutrons and positrons from the β + ‐decay nuclei in the previous stage is calculated. As a result, we model on‐ground distributions of fluxes and energy spectra for neutrons, neutron‐related gamma rays, and annihilation ones. The simulation model is to be compared with photonuclear events detected in low‐charge‐center winter thunderstorms. Plain Language Summary: Lightning discharges occasionally emit a powerful flash of gamma rays called terrestrial gamma ray flashes. Gamma rays in terrestrial gamma ray flashes have high energies enough to react with atmospheric nuclei such as nitrogen and oxygen. The nuclear reactions in the atmosphere produce neutrons and unstable isotopes that emit positrons. In this paper, we utilize a Monte Carlo simulation framework, calculate a series of reactions and processes in the atmosphere, and then construct a distribution model of neutrons, neutron‐related gamma rays, and positron‐related ones at ground level. The obtained model can be compared with recent observations of nuclear reactions during winter thunderstorms in Japan. Key Points: Possible channels of atmospheric photonuclear reactions in lightning are surveyed from a nuclear‐reaction data library Monte Carlo calculations are performed to simulate photoneutron and β + ‐decay‐nuclide productions in the atmosphere On‐ground distributions of fluxes and spectra for neutrons, neutron‐related gamma rays, and annihilation gamma rays are modeled