Effective dose conversion coefficients for radionuclides exponentially distributed in the ground

Abstract

In order to provide fundamental data required for dose evaluation due to environmental exposures, effective dose conversion coefficients, that is, the effective dose rate per unit activity per unit area, were calculated for a number of potentially important radionuclides, assuming an exponential distribution in ground, over a wide range of relaxation depths. The conversion coefficients were calculated for adults and a new-born baby on the basis of dosimetric methods that the authors and related researchers have previously developed, using Monte Carlo simulations and anthropomorphic computational phantoms. The differences in effective dose conversion coefficients due to body size between the adult and baby phantoms were found to lie within 50 %, for most cases; however, for some low energies, differences could amount to a factor of 3. The effective dose per unit source intensity per area was found to decrease by a factor of 2-5, for increasing relaxation depths from 0 to 5 g/cm(2), above a source energy of 50 keV. It is also shown that implementation of the calculated coefficients into the computation of the tissue weighting factors and the adult reference computational phantoms of ICRP Publication 103 does not significantly influence the effective dose conversion coefficients of the environment. Consequently, the coefficients shown in this paper could be applied for the evaluation of effective doses, as defined according to both recommendations of ICRP Publications 103 and 60.

Fig. 1

Effective dose conversion coefficients for exponentially distributed ground sources emitting mono-energetic photons

Fig. 2

Effective dose conversion coefficients for several selected radionuclides exponentially distributed in ground

Fig. 3

Distribution of effective dose ratios between Baby and adults for a a submersion source in air and b an exponential source in ground. The dose coefficients for the submersion source in air were taken from Petoussi-Henss et al.

Fig. 4

Comparison of effective doses defined in ICRP 103 to those defined in ICRP 60, for a plane source at a depth of 0.5 g/cm² in ground. The data for ICRP 103 were taken from Petoussi-Henss et al.