Long-term study (1987–2023) on the distribution of ¹³⁷Cs in soil following the Chernobyl nuclear accident: a comparison of temporal migration measurements and compartment model predictions.

This article focuses on a long-term study (1987–2023) of the vertical migration and distribution of cesium-137 (^137Cs) in soil at a designated ~1000 m² area within the Aristotle University of Thessaloniki farm in Northern Greece, following the Chernobyl nuclear accident. Soil samples were collected in 5-cm layers down to 30 cm depth and analyzed using gamma spectroscopy to monitor ^137Cs activity, with total deposition backdated to the accident estimated at approximately 18.6–20 kBq/m². The study employed a compartment model assuming equal transfer rates between soil layers to describe the temporal evolution of ^137Cs distribution, finding good agreement with measured data over 36 years, while a model with increasing transfer rates (consistent with diffusion) did not fit the observations. These results suggest that diffusion is unlikely the primary mechanism for ^137Cs migration in soil over the long term, indicating that other processes such as advection may play a significant role.