Comparison of external dose coefficients used by the European Model for Inhabited Areas (ERMIN) and ICRP Publication 144

Hirouchi, Jun ; Charnock, T.*

The recent ICRP publication of dose coefficients for external exposures to environmental sources, ICRP Publ. 144, provided an opportunity to evaluate and improve the dose coefficients and dose conversion factors used by the European Model for Inhabited Areas (ERMIN). ERMIN contains several idealised built environments with the "open area" environment being very similar to the ICRP Publ. 144 "planar sources on and within the ground" situation. The study compares the values given in ERMIN with those derived from ICRP Publ. 144 for the external gamma dose coefficients, the dose conversion factors to convert from air kerma to effective dose and the beta dose coefficients. This study has enabled ERMIN to be improved in several ways. A new "open area" environment was developed based on ICRP Publ. 144. New dose conversion factors were developed moving from a single radionuclide specific one to nine that account for depth in the soil. The dose coefficients for Cs-137, Pr-143, Pr-144, Ru-106, Sr-89, Sr-90, Y-90, and Y-91 were significantly different between ERMIN and ICRP Publ. 144 because bremsstrahlung was not considered in ERMIN. 144, dose coefficients considering bremsstrahlung were developed using correction coefficients based on ICRP Publ. 144.