An alternative methodology to determine ²¹⁰Pb activity soil profiles

Unsupported ²¹⁰Pb (Pb_exc) is generated in air and is subsequently deposited on soil surface. The Pb_exc can be used for sediment dating, soil erosion/sedimentation and air mass studies. In many cases, ²¹⁰Pb activity determination (gamma ray 46.5 keV) cannot be performed due to the lack of efficiency calibration curve, especially when radioactive patron source is not available. This work presents an alternative methodology to obtain the ²¹⁰Pb activity values, based on the activity definition and the attenuation coefficient determinations and assuming that soil samples coming from depth higher than 25 cm only contain ²¹⁰Pb generated in the soil (Pb_exc free, i.e., for those soil layers the ²¹⁰Pb activity is equal to the ²²⁶Ra activity, at secular equilibrium). The proposed methodology was evaluated using soils from La Plata region, Argentina. The same soil samples were also analyzed in a second laboratory by the conventional methodology. The obtained results indicated that the proposed procedure can be used as a good alternative in cases where a calibration sample is not available.