Analytical method for calculating external exposure of biota above radioactively contaminated soil

Unified method for calculating internal absorbed fractions and doses to convex bodies was extended for analytical estimating external doses to biota. Analytical formulae were developed for external exposure in the air above infinite plane soil, and surface soil layer, uniformly contaminated with photon emitter. Values of air kerma were calculated at various heights above contaminated soil. Dose coefficients for external exposure of biota above soil were calculated. Values of air kerma and dose coefficients were in adequate agreement with independent test data obtained with Monte Carlo computer codes. The presented analytical method can be readily employed for calculating absorption of ionizing radiation within air layers and external exposure of biota above contaminated soil.