Abstract: The distribution of radioisotopes in soil of small particle size is very important for the evaluations of the resuspension and personal radiation protection, as well as the research of nuclides migration. According to Stokes sedimentation law, the soil of a particle size less than 50 μm, from a radioactive pollution area, was classified in a barrel which was specifically designed. ²⁴¹Am of the classified samples were detected by HPGe γ spectrometer. The results showed that the quality purity of different granular size was larger than 50% by using optimized density of soil and 1.25 times′ the theoretical sedimentation time. For the suspensible fine grain from the radioactive pollution area, the fraction of the quality and ²⁴¹Am was less than 6% and 2% respectively.

Key words: Stokes' law, radioactive, soil, granular size classification