不撹乱土壌中の過剰の²¹⁰Pb移動速度の簡易推定法

抄録

Two simple methods were developed to calculate migration rates of excess radioactive ²¹⁰Pb from undisturbed soil profiles. The migration of excess ²¹⁰Pb was described by one-dimensional differential equation with decay term under steady state. One method (method 1) assumes a constant migration rate of excess ²¹⁰Pb in the ground. This assumption gives resultantly the constant initial concentration of excess ²¹⁰Pb per unit bulk volume at the ground surface. The other method (method 2) assumes that the migration flux of ²¹⁰Pb through the ground decreases only by radioactive decay. The latter method can estimate the travel time of ²¹⁰Pb from the ground surface to any horizon of interest.
Undisturbed soil samples were taken at Kyoto City, Japan. ²¹⁰Pb and ²²⁶Ra contents were analyzed to get an excess ²¹⁰Pb profile in the ground. Each method was applied to the observed profile. The resultant migration rate was respectively found to be 0.70 and 0.25-1.00mm/y for methods 1 and 2. These results could be applied well to evaluate the stable Pb migration through the ground.