ICRP Publication 144: Dose Coefficients for External Exposures to Environmental Sources

Abstract

This publication presents radionuclide-specific organ and effective dose-rate coefficients for members of the public resulting from environmental external exposures to radionuclide emissions of both photons and electrons, calculated using computational phantoms representing the International Commission on Radiological Protection's (ICRP) reference newborn, 1-year-old, 5-year-old, 10-year-old, 15-year-old, and adult males and females. Environmental radiation fields of monoenergetic photon and electron sources were first computed using the Monte Carlo radiation transport code PHITS for source geometries representing environmental radionuclide exposures including planar sources on and within the ground at different depths (representing radionuclide ground contamination from fallout or naturally occurring terrestrial sources), volumetric sources in air (representing a radioactive cloud), and uniformly distributed sources in simulated contaminated water. For the above geometries, the exposed reference individual is considered to be completely within the radiation field. Organ equivalent dose-rate coefficients for monoenergetic photons and electrons were next computed employing the PHITS code, thus simulating photon and electron interactions within the tissues and organs of the exposed reference individual. For quality assurance purposes, further cross-check calculations were performed using GEANT4, EGSnrc, MCNPX, MCNP6, and the Visible Monte Carlo radiation transport codes. From the monoenergetic values, nuclide-specific effective and organ equivalent dose-rate coefficients were computed for 1252 radionuclides of 97 elements for the above environmental exposures using the nuclear decay data from ICRP Publication 107. The coefficients are given as dose-rates normalised to radionuclide concentrations in environmental media, such as radioactivity concentration (nSv h−1 Bq−1 m2 or nSv h−1 Bq−1 m3), and can be renormalised to ambient dose equivalent (Sv Sv−1) or air kerma free in air (Sv Gy−1). The main text provides effective dose-rate coefficients for selected radionuclides; details including age- and sex-dependent organ dose-rate coefficients are provided as an electronic supplement to be downloaded from the ICRP and SAGE websites. The data show that, in general, the smaller the body mass of the phantom, the higher the organ and effective dose due to: (1) closer proximity to the source (in the case of ground contamination); and (2) the smaller amount of body shielding of internal organs in the younger and smaller reference phantoms. The difference in effective dose between an adult and an infant is 60–140% at a photon energy of 0.05 MeV, while it is less than 70% above a photon energy of 0.10 MeV, where smaller differences are observed for air submersion and the largest differences are observed for soil contamination on the surface of the ground. For realistic exposure situations of radionuclide environmental contamination, the difference is found to be more moderate. For example, for radioactive caesium (134Cs, 136Cs, 137Cs/137mBa) deposited on and in the ground, the difference in effective dose between an adult and an infant is in the range of 30–60%, depending on the radioactivity deposition depth within the soil.