A study of Cs-137 spatial distribution in soil thin sections by digital autoradiography and microscopy

•137Cs in thin sections of the contaminated podzolic sandy soil was studied.•Radiography showed cluster and dispersion patterns of 137Cs on microscale level.•Organic matter, micas, K-feldspars, Fe oxides identified in 137Cs fixation zones

Digital autoradiography with imaging plates and microprobe analysis was used to study 137Cs micro-distribution in thin sections of the podzolic sandy soil typical for the Chernobyl remote impact zone 25 years after the accident. The zone is notable for contamination of the so-called condensation type where the contribution of the “hot” fuel particles was comparatively low. The initial 137Cs contamination level of the study plot located on the Iput river terrace ca. 20 km to the east of the town of Novozybkov, Bryansk region, was approx. 40 Ci/km2. According to the modern soil core data the main portion of cesium radioisotopes is still concentrated in the 10–20 cm thick surface layer. Thin sections were prepared from the top 0–10 cm layer of the soil profile located on the shoulder of the relatively steep northern slope of the forested hill. Autoradiography of the thin sections has clearly shown both cluster and dispersed patterns of 137Cs distribution presumably reflecting initial radiocesium accumulation in the surficial organic layer with mineral admixture and subsequent lateral and vertical propagation due to water movement and filtration. The propagation was accompanied by fixation of 137Cs ions on surfaces of soil particles. High sensitivity (0.03 Bq/cm2) and resolution (ca 40 μm) of the applied technique enable us to reveal concentration and dispersion zones in soil thin sections on microscale level. Soil micro-morphology and microprobe analysis have shown to be helpful in deciphering soil chemical and mineral composition assumed to be responsible for 137Cs retention in the soil top layer.