Nuclear Technology Laboratory
|Health Physics Society : Volume 78, Number 3, March 2000
MONTE CARLO CALCULATION OF DOSE RATE CONVERSION FACTORS FOR EXTERNAL
EXPOSURE TO PHOTON EMITTERS IN SOIL
A. Clouvas, S. Xanthos, M. Antonopoulos-Domis, and J. Silva
Abstract-The dose rate conversion factors D(dot)CF
(absorbed dose rate in air per unit activity per unit of soil mass, nGy
h-1 per Bq kg-1) are calculated 1 m above ground
for photon emitters of natural radionuclides uniformly distributed in
the soil. Three Monte Carlo codes are used: 1) The MCNP code of Los Alamos;
2) The GEANT code of CERN; and 3) a Monte Carlo code developed in the
Nuclear Technology Laboratory of the Aristotle University of Thessaloniki.
The accuracy of the Monte Carlo results is tested by the comparison of
the unscattered flux obtained by the three Monte Carlo codes with an independent
straightforward calculation. All codes and particularly the MCNP calculate
accurately the absorbed dose rate in air due to the unscattered radiation.
For the total radiation (unscattered plus scattered) the D(dot)CF
values calculated from the three codes are in very good agreement between
them. The comparison between these results and the results deduced previously
by other authors indicates a good agreement (less than 15% of difference)
for photon energies above 1,500 keV. Antithetically, the agreement is
not as good (difference of 20-30%) for the low energy photons.