Contents of Radionuclides (Ra, Th, K, and Cs) in Soils on Moraine Deposits in the European Russia Sampled in 1926–2017

Abstract: The results of integrated studies of the contents of natural radionuclides (NRNs) Ra, Th, and K and technogenic Cs in soils on moraine deposits available from the Bioresource Collection at the Dokuchaev Central Soil Museum are reported. Soils were sampled before the commencement of nuclear tests, during intensive tests, and in recent years. The assayed soils belong to 11 reference soil groups according to the WRB system. Organic, humus (including formerly plow), humus-eluvial, eluvial, and subeluvial horizons and soil-forming rocks were analyzed. The NRNs contents in soil-forming rock amount to 13.4–36.0 Bq/kg (mean specific activity M = 22.2 Bq/kg and standard deviation σ = 7.4 Bq/kg) for Ra; 18.9–49.0 Bq/kg (M = 32.1 ± 10.4 Bq/kg) for Th; and 417–890 Bq/kg (M = 695 ± 151 Bq/kg) for K. In the organic horizons, NRNs are detectable only in the samples of 2004 and 2017 in the amounts of 7.0–43.0 Bq/kg Ra (M = 20.9 ± 14.4 Bq/kg), 10.0–21.2 Bq/kg Th (M = 14.0 ± 8.1), and 50–620 Bq/kg K (M = 291 ± 227 Bq/kg). Narrower ranges and lower mean content (except for K) in the humus and eluvial horizons are recorded in the former plow horizon (P) as compared with the AY horizon and in the EL horizon as compared with the AEL and BEL horizons. The NRN content correlates with the particle size fractions in a statistically significant manner. Technogenic Cs is detectable only in the recent soil samples. According to its content, the soils fall into two groups. The first group of soils (pits 261 and MLK-4, Lisino education and experimental forestry station) displays a relatively high Cs activity in the 0–5-cm layer and a penetration depth of 10 cm. The second group comprises the remaining soils. The cesium content there does not exceed 54 Bq/kg and penetration depth, 20 cm.