Monte Carlo Calculation of Dose Rate Conversion Factors for External Exposure to Photon Emitters in Soil

Abstract

The dose rate conversion factors D(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(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.

Radium equivalent activity in the light of UNSCEAR report

“…The conversion factors calculated by Clouvas et al (2000) by using the GEANT, MC, and MCNP simulation codes have slightly lower values than those presented by Beck et al (1972) and Saito and Jacob (1995). The reports of the UNSCEAR (1982,1988) used the dose conversion factors of Beck et al (1972), whereas in the reports of UNSCEAR (1993,2000), the conversion coefficients of Saito and Jacob (1995) have been adopted.…”

Long-term investigation of anthropogenic and naturally occurring radionuclides at reference sites in western Sweden

“…Measurements made over water, approximately 1000 m away from the coast, are consistent with the UNSCEAR estimation. To determine the dose rate from a measured activity density, conversion factors from Clouvas et al (2000) and Finck (1992) were used for the naturally occurring radionuclides and for 137 Cs, respectively. The calculated dose rates for the thorium and uranium series assumed radioactive equilibrium in the ground.…”

Natural Radioactivity at an Uraniferous Site

“…Monte Carlo methods have been widely used for exposure calculation (Clouvas et al, 2000;Conti et al, 1999;Jacob and Paretzke, 1987;Meckbach et al, 1996;Salinas et al, 2006a;2006b;2007;LANL, 2003) and have also been used in this study to perform the radiation transport calculation.…”