Draft Report for Consultation: Dose Coefficients for External Exposures to Environmental Sources
The draft Dose Coefficients for External Exposures to Environmental Sources is now available for public consultation. We welcome comments from individuals and organisations. The draft document can be downloaded from the ICRP website. Comments must be submitted through the ICRP website no later than October 12, 2018.
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 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 firstly computed using the Monte Carlo radiation transport
code PHITS (Particle and Heavy Ion Transport code System) for source geometries
representing environmental radionuclide exposures including planar sources on and within
the ground at different depths (representing radionuclide ground contamination from fall-out
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
for several radionuclides for the above environmental exposures were computed using the
nuclear decay data from Publication 107. The coefficients are given as dose rates normalised
to radionuclide concentrations in environmental media, such as radioactivity concentration, in
units of nSv h-1 Bq-1 m-2 or nSv h-1 Bq-1 m-3 and can be re-normalised to ambient dose
equivalent (Sv Sv-1) or air kerma (Sv Gy-1). The findings showed 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
50 keV, while it is less than 70% above a photon energy of 100 keV, where the 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 was 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 was in the range of 20-60%,
depending on the radioactivity deposition depth within the soil.