Distributions of fallout Cs, Pu and Am in a soil core from South Central China.

The source and vertical distribution of Cs,Pu and Am activity concentrations in a soil core from Hunan Province, China were investigated. The maximum Cs and Pu activity concentrations were 15.45 ± 0.76 mBq/g and 0.819 ± 0.066 mBq/g, respectively. While the maximum Am activity concentration in samples obtained from the core was 0.341 ± 0.019 mBq/g. The Pu/Pu atom ratio and the Cs/Pu activity ratio were 0.183 ± 0.011 and 19.5 ± 1.8, respectively, and both were consistent with the characteristic value of global fallout. The integrated Am/Pu activity ratio for global fallout was also re-estimated. The measured Am/Pu activity ratio (average 0.43 ± 0.07) in the samples was very close to the estimated value (0.45), which suggested their Am also came from the global fallout. Regarding the vertical distribution of Cs, Pu and Am in these red soil samples, all these radionuclides had higher concentrations in upper layers of several centimeters of soil while they had slightly lower concentrations in lower soil layers down to 30 cm. Vertical distributions of Cs/Pu and Am/Pu activity ratios indicated the migration velocity was Am ≈ Pu > Cs. The intrinsic chemical properties of the radionuclides as well as soil type and properties (acidic, nutrient-deficient and low in organic matter and cation exchange capacity) might be reasons for the differences in their migration behaviors.