“Isotopic footprints” of gamma-ray and proton events and anomalous signal in radiocarbon in 775 AD

The production of the cosmogenic radionuclides 14 C, 10 Be, and 36 Cl in the Earth’s atmosphere under the action of powerful impulsive proton and gamma-ray events (superpowerful solar flares and Galactic gamma-ray bursts) is considered. The possible “isotopic footprint” in natural archives (the concentrations of these isotopes in dated polar ice cores and annual tree rings) has been calculated by taking into account geophysical processes. The results obtained have been applied to analyzing the anomalous increase in the concentration of radiocarbon measured in tree rings dated 774–775 AD. Arguments for the fact that the most likely cause of this increase is the high-energy emission from a Galactic gamma-ray burst are adduced.