Terrestrial-origin skyshine at sea level

Low-energy continuous gamma radiation with a maximum energy distribution at similar to 70 keV reaches the Earth's surface from the upper hemisphere. In addition to components resulting from cosmic-origin low-energy gamma radiation, there is also a prominent contribution arising from gamma photons emitted by environmental ra-dionuclides, which are backscattered by air above ground (commonly referred as skyshine radiation). Since both components are covering the same energy region of gamma radiation (mainly 30 keV-350 keV), it is not simple to determine the separate contributions of each radiation component to the total gamma flux. The effi-cient way to solve this long-standing problem is to study the backscattering of gamma radiation on the atmo-spheric air by Monte Carlo simulations. In this work, the simulations were performed in order to obtain air-backscattered spectra, as well as gamma photon fluxes which can be expected for specified activity concentra-tions of natural radionuclides (K-40, Ra-226, Th-232) distributed in the ground. The simulation results were compared with experimental measurements of low-energy photon flux in the open area from the upper hemi-sphere. Furthermore, the influence of height above ground and distance from the shore on the skyshine intensity reduction is explored.

Automated summary

Low-energy continuous gamma radiation from cosmic sources and skyshine radiation from environmental radionuclides contribute to the gamma flux on Earth's surface. Monte Carlo simulations were used to analyze the backscattering of gamma radiation and compare the results with experimental measurements. The study also investigates the effect of height and distance from the shore on the reduction of skyshine intensity.