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

Abstract

This publication presents radionuclide-specific organ and effective dose rate\ncoefficients for members of the public resulting from environmental external exposures to\nradionuclide emissions of both photons and electrons, calculated using computational\nphantoms representing the ICRP reference newborn, 1-year-old, 5-year-old, 10-year-old, 15-\nyear-old, and adult males and females. Environmental radiation fields of monoenergetic\nphoton and electron sources were firstly computed using the Monte Carlo radiation transport\ncode PHITS (Particle and Heavy Ion Transport code System) for source geometries\nrepresenting environmental radionuclide exposures including planar sources on and within\nthe ground at different depths (representing radionuclide ground contamination from fall-out\nor naturally occurring terrestrial sources), volumetric sources in air (representing a\nradioactive cloud), and uniformly distributed sources in simulated contaminated water. For\nthe above geometries, the exposed reference individual is considered to be completely within\nthe radiation field. Organ equivalent dose rate coefficients for monoenergetic photons and\nelectrons were next computed employing the PHITS code thus simulating photon and\nelectron interactions within the tissues and organs of the exposed reference individual. For\nquality assurance purposes, further cross-check calculations were performed using GEANT4,\nEGSnrc, MCNPX, MCNP6, and the Visible Monte Carlo radiation transport codes. From the\nmonoenergetic values, nuclide-specific effective and organ equivalent dose rate coefficients\nfor several radionuclides for the above environmental exposures were computed using the\nnuclear decay data from Publication 107. The coefficients are given as dose rates normalised\nto radionuclide concentrations in environmental media, such as radioactivity concentration, in\nunits of nSv h-1 Bq-1 m-2 or nSv h-1 Bq-1 m-3 and can be re-normalised to ambient dose\nequivalent (Sv Sv-1) or air kerma (Sv Gy-1). The findings showed that, in general, the smaller\nthe body mass of the phantom, the higher the organ and effective dose due to (1) closer\nproximity to the source (in the case of ground contamination) and (2) the smaller amount of\nbody shielding of internal organs in the younger and smaller reference phantoms. The\ndifference in effective dose between an adult and an infant is 60-140% at a photon energy of\n50 keV, while it is less than 70% above a photon energy of 100 keV, where the smaller\ndifferences are observed for air submersion and the largest differences are observed for soil\ncontamination on the surface of the ground. For realistic exposure situations of radionuclide\nenvironmental contamination, the difference was found to be more moderate. For example,\nfor radioactive caesium (134Cs, 136Cs, 137Cs/137mBa) deposited on and in the ground, the\ndifference in effective dose between an adult and an infant was in the range of 20-60%,\ndepending on the radioactivity deposition depth within the soil.\n\n \n \n\n \n \n \n \n ICRP \nroutinely solicits comments on most draft documents prior to \npublication, with the exception of those that are basically compilations\n of computed values such as specific absorbed fraction values or dose \nconversion factors.View comments Draft Document