Radionuclide activity in cryoconite from glaciers of the Central Caucasus, Russia

This work presents the results of a study of radionuclide activity in cryoconite from glacier and glacial soil of the Central Caucasus. Cryoconite were sampled from the surface of the Garabashi glacier, and soil samples were taken from the humus horizon of periglacial mountain forest-meadow soil. Measurements were performed with low-background germanium gamma spectrometers located inside a passive shield consisting of ∼20 cm of copper, ∼15 cm of lead, and ∼8 cm of borated polyethylene. The specific activity of radionuclides (Be-7, K-40, Th-232, U-235, U-238, Cs-137) was established. It was revealed that all measured spectra contain γ-lines from decays of K-40, decay chains of U-238, U-235 and Th-232. In addition, the spectra of cryoconite samples from the Garabashi glacier show a 477.6 keV line from the decay of the cosmogenic isotope Be-7, and in the soil sample a 661.7 keV line from the radionuclide Cs-137. No radionuclide Be-7 was detected in the mountain forest-meadow soil. Radionuclide Cs-137 is present in the soil sample, while in cryoconite, is not detected. Radioisotope activities in the Garabashi glacier cryoconite, except for the cosmogenic isotope Be-7, do not differ significantly in terms of mass, i.e., the content of K-40, U-238, U-235 and Th-232 in them is approximately the same. The activity of all the studied radionuclides in the soil sample compared to cryoconite samples is lower, although the differences are not significant, except for Th-232, whose activity in soil is almost two times lower.