Precipitation-related increase events of the electromagnetic component of secondary cosmic rays: Spectral analysis

We report the measurement results of differential spectra of electromagnetic radiation in the range 0.1–4 MeV, which occurs in the atmosphere as a component of secondary cosmic rays. Spectral monitoring was performed using a spectrometer based on the Nai (TL) crystal in 2022–2023. The main purpose of the measurements was to determine spectral characteristics of the electromagnetic radiation during increase events, when the electromagnetic radiation flux from the atmosphere rises by tens of percent with respect to the background level. From a thorough analysis of the spectra of many dozens of events, we have drawn a conclusion that although the lines of natural radionuclides are present on the spectra and contribute their share, their total contribution to the increase events is ~0.1 of the total energy supplied during an increase. We unambiguously conclude that the effect of increasing electromagnetic radiation during precipitation is not due to the presence of radionuclides in precipitation.