Distribution and migration of ^239,240 Pu in soil profiles in North China

The source, vertical distribution and migration behavior of plutonium in five soil profiles (from forest, grassland and desert areas) in northern China were investigated. The average ²⁴⁰Pu/²³⁹Pu atomic ratio of 0.184 ± 0.022 observed in these samples is in good agreement with the reported value of global fallout, suggesting that the global fallout is the major source of plutonium in northern China. The ^239,240Pu inventories in five soil profiles ranges from 43.3 Bq/m² to 175 Bq/m², lying in the reported range for global fallout in the similar latitude band. The effective convection velocity (0.04–0.16 cm/y) and effective dispersion coefficient (0.13–0.41cm²/y) of plutonium in different soil profiles derived using the CDE model varies significantly, attributed to multi-factors including location, topography, climate and soil types. The results showed that the migration of plutonium in grassland soil is significantly slow compared to other type of soil, especially desert soil.