Spectral Hardness of X- and Gamma-Ray Emissions From Lightning Stepped and Dart Leaders

During the 2022 New Mexico monsoon season, we deployed two X-ray scintillation detectors, coupled with a 180 MHz data acquisition system to detect X-rays from natural lightning at the Langmuir Lab mountain-top facility, located at 3.3 km above mean sea level. Data acquisition was triggered by an electric field antenna calibrated to pick up lightning within a few km of the X-ray detectors. We report the energies of over 240 individual photons, ranging between 13 keV and 3.8 MeV, as registered by the LaBr3(Ce) scintillation detector. These detections were associated with four lightning flashes. Particularly, four-stepped leaders and seven dart leaders produced energetic radiation. Importantly, the reported photon energies allowed us to confirm that the X-ray energy distribution of natural stepped and dart leaders follows a power-law distribution with an exponent ranging between 1.09 and 1.96, with stepped leaders having a harder spectrum. Characterization of the associated leaders and return strokes was done with four different electric field sensing antennas, which can measure a wide range of time scales, from the static storm field to the fast change associated with dart leaders.. Authors: Contreras‐Vidal, Luis [New Mexico Institute of Mining and Technology, Socorro, NM (United States)] (ORCID:0000000154617047); Sanchez, James T. [New Mexico Institute of Mining and Technology, Socorro, NM (United States); Univ. of California, Santa Cruz, CA (United States). Santa Cruz Institute for Particle Physics] (ORCID:0009000569605256); da Silva, Caitano L. [New Mexico Institute of Mining and Technology, Socorro, NM (United States)] (ORCID:0000000337283035); Sonnenfeld, Richard G. [New Mexico Institute of Mining and Technology, Socorro, NM (United States)] (ORCID:000000030364850X); Aulich, Graydon [New Mexico Institute of Mining and Technology, Socorro, NM (United States)]. DOE Contract: 89233218CNA000001. Subjects: 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; leaders; lightning; plasma; runaway electrons; spectrum; x-rays