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Dose-rate conversion factors have been calculated for external exposure above ground to monoenergetic photon emitters in soil. These factors give external dose rates per unit source concentration in soil. The calculations are based on the point-kernel integration method and assume that the source concentration at any depth in soil is uniform over an infinite surface parallel to the ground plane. Dose-rate factors in air at a height of 1 m above ground are tabulated for discrete photon energies between 0.01 and 10 MeV and for source depths in soil between 0 and 300 cm. Application of the results for plane sources in soil to the calculation of photon dose rates from distributions of sources with depth in soil is described, and dose-rate factors are tabulated for the particular cases of uniform slab sources of finite thickness and sources which are exponentially distributed with depth. We also demonstrate how dose-rate factors in air for monoenergetic photon sources are used to estimate dose-rate factors for body organs of exposed individuals and for the spectrum of photons from radioactive decay. The calculations in this paper show that allowing for downward migration of radionuclides in soil can result in significant reductions in external dose compared with the usual assumption that radionuclides which are deposited on the ground surface remain there until removal by radioactive decay.

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We conducted a sensitivity analysis using a numerical model of fractured porous media to find out how porous media and fracture parameters affect solute transport. The 2‐dimensional, saturated fracture flow and transport code FRACTRAN was used to conduct the simulations. Seven parameters were considered: matrix hydraulic conductivity, matrix porosity, retardation of the matrix, gradient of the flow field, fracture retardation, fracture aperture, and fracture probability (which incorporates fracture spacing and fracture length). A Latin‐hypercube design was used to select a matrix of parameter values that minimized correlations among the design parameters. The results were summarized by examining least square fit of the relationship between the seven parameters and 50% breakthrough time and spread of the breakthrough curves, with nearly identical results. The matrix parameters, in particular hydraulic conductivity and porosity, had the greatest effect. As expected, fracture probability was nearly equivalent in importance. These results indicate that field characterization in fractured porous media should not only emphasize fracture location, which strongly influences directions of contaminant transport, but also matrix properties, which have a major influence on contaminant residence times and breakthrough concentrations.

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