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 × 10¹³ neutrons and 4 × 10¹² β⁺‐decay nuclei are produced by 10¹⁸ 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.

中文翻译：

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闪电中的光核反应：1.反应和传播过程的验证和建模

我们报告了由向下的地面伽马射线闪光触发的大气中光核反应的模拟结果。ENDF / B-VII.1库验证了大气中可能的反应通道及其横截面。然后使用Geant4框架执行两个阶段的蒙特卡洛模拟。在第一阶段，在大气质量模型中产生遵循相对论失控电子雪崩谱的电子，并根据核数据库计算光中子和β ⁺衰变核的产生。总共1×10 ¹³中子和4×10 ¹² β ⁺衰变核通过产生101 MeV以上的^18个高能电子。在第二阶段，计算前阶段来自β ⁺衰变核的光中子和正电子的传播。结果，我们对中子，与中子有关的伽马射线和an灭的通量和能谱的地面分布进行了建模。将模拟模型与在低电荷中心冬季雷暴中检测到的光核事件进行比较。