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Title: Effective dose rate coefficients for exposure to contaminated soil

Abstract

The Oak Ridge National Laboratory Center for Radiation Protection Knowledge has undertaken calculations related to various environmental exposure scenarios. A previous paper reported the results for submersion in radioactive air and immersion in water using age-specific mathematical phantoms. This paper presents age-specific effective dose rate coefficients derived using stylized mathematical phantoms for exposure to contaminated soils. Dose rate coefficients for photon, electron, and positrons of discrete energies were calculated and folded with emissions of 1252 radionuclides addressed in ICRP Publication 107 to determine equivalent and effective dose rate coefficients. The MCNP6 radiation transport code was used for organ dose rate calculations for photons and the contribution of electrons to skin dose rate was derived using point-kernels. Bremsstrahlung and annihilation photons of positron emission were evaluated as discrete photons. As a result, the coefficients calculated in this work compare favorably to those reported in the US Federal Guidance Report 12 as well as by other authors who employed voxel phantoms for similar exposure scenarios.

Authors:
ORCiD logo [1];  [2]; ORCiD logo [3]; ORCiD logo [3]; ORCiD logo [3];  [2];  [4];  [5]
  1. Easterly Scientific, Knoxville, TN (United States); Y-12 National Security Complex, Oak Ridge, TN (United States)
  2. Easterly Scientific, Knoxville, TN (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Georgia Inst. of Technology, Atlanta, GA (United States)
  5. Univ. of California San Diego, La Jolla, CA (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1410952
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Radiation and Environmental Biophysics
Additional Journal Information:
Journal Volume: 56; Journal Issue: 3; Journal ID: ISSN 0301-634X
Publisher:
Springer
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; 63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.; Environmental; Dose coefficients; Soil; Phantoms; Effective dose; Organ dose; Tissue dose; Photon; Electron; Positron

Citation Formats

Veinot, Kenneth G., Eckerman, Keith F., Bellamy, Michael B., Hiller, Mauritius M., Dewji, Shaheen A., Easterly, Clay E., Hertel, Nolan E., and Manger, Ryan P.. Effective dose rate coefficients for exposure to contaminated soil. United States: N. p., 2017. Web. doi:10.1007/s00411-017-0692-7.
Veinot, Kenneth G., Eckerman, Keith F., Bellamy, Michael B., Hiller, Mauritius M., Dewji, Shaheen A., Easterly, Clay E., Hertel, Nolan E., & Manger, Ryan P.. Effective dose rate coefficients for exposure to contaminated soil. United States. doi:10.1007/s00411-017-0692-7.
Veinot, Kenneth G., Eckerman, Keith F., Bellamy, Michael B., Hiller, Mauritius M., Dewji, Shaheen A., Easterly, Clay E., Hertel, Nolan E., and Manger, Ryan P.. Wed . "Effective dose rate coefficients for exposure to contaminated soil". United States. doi:10.1007/s00411-017-0692-7. https://www.osti.gov/servlets/purl/1410952.
@article{osti_1410952,
title = {Effective dose rate coefficients for exposure to contaminated soil},
author = {Veinot, Kenneth G. and Eckerman, Keith F. and Bellamy, Michael B. and Hiller, Mauritius M. and Dewji, Shaheen A. and Easterly, Clay E. and Hertel, Nolan E. and Manger, Ryan P.},
abstractNote = {The Oak Ridge National Laboratory Center for Radiation Protection Knowledge has undertaken calculations related to various environmental exposure scenarios. A previous paper reported the results for submersion in radioactive air and immersion in water using age-specific mathematical phantoms. This paper presents age-specific effective dose rate coefficients derived using stylized mathematical phantoms for exposure to contaminated soils. Dose rate coefficients for photon, electron, and positrons of discrete energies were calculated and folded with emissions of 1252 radionuclides addressed in ICRP Publication 107 to determine equivalent and effective dose rate coefficients. The MCNP6 radiation transport code was used for organ dose rate calculations for photons and the contribution of electrons to skin dose rate was derived using point-kernels. Bremsstrahlung and annihilation photons of positron emission were evaluated as discrete photons. As a result, the coefficients calculated in this work compare favorably to those reported in the US Federal Guidance Report 12 as well as by other authors who employed voxel phantoms for similar exposure scenarios.},
doi = {10.1007/s00411-017-0692-7},
journal = {Radiation and Environmental Biophysics},
number = 3,
volume = 56,
place = {United States},
year = {Wed May 10 00:00:00 EDT 2017},
month = {Wed May 10 00:00:00 EDT 2017}
}

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  • External dose coefficients for environmental exposure scenarios are often computed using assumption on infinite or semi-infinite radiation sources. For example, in the case of a person standing on contaminated ground, the source is assumed to be distributed at a given depth (or between various depths) and extending outwards to an essentially infinite distance. In the case of exposure to contaminated air, the person is modeled as standing within a cloud of infinite, or semi-infinite, source distribution. However, these scenarios do not mimic common workplace environments where scatter off walls and ceilings may significantly alter the energy spectrum and dose coefficients.more » In this study, dose rate coefficients were calculated using the International Commission on Radiological Protection (ICRP) reference voxel phantoms positioned in rooms of three sizes representing an office, laboratory, and warehouse. For each room size calculations using the reference phantoms were performed for photons, electrons, and positrons as the source particles to derive mono-energetic dose rate coefficients. Since the voxel phantoms lack the resolution to perform dose calculations at the sensitive depth for the skin, a mathematical phantom was developed and calculations were performed in each room size with the three source particle types. Coefficients for the noble gas radionuclides of ICRP Publication 107 (e.g., Ne, Ar, Kr, Xe, and Rn) were generated by folding the corresponding photon, electron, and positron emissions over the mono-energetic dose rate coefficients. Finally, results indicate that the smaller room sizes have a significant impact on the dose rate per unit air concentration compared to the semi-infinite cloud case. For example, for Kr-85 the warehouse dose rate coefficient is 7% higher than the office dose rate coefficient while it is 71% higher for Xe-133.« less
  • Effective dose-equivalent responses have been calculated for external exposure from residual photon emitters in soil. The calculations are based on the assumption that the receptor is located 1 m above the contaminated ground. A Monte Carlo algorithm was developed to perform the photon transport calculation for the soil/air configuration, in which the soil constituents were assumed to be similar to those of the earth's crust. Photon cross-sections for soil were based on the latest cross-sectional information generated by the U.S. National Institute of Standards and Technology. For every incident photon at the receptor, an estimate of the air-absorbed dose wasmore » calculated first and then converted into the effective dose equivalent. The effective dose equivalent is based on the concept of weighted organ doses, as recommended by the ICRP. The ICRP's latest conversion coefficients were used to transform point air-absorbed doses into effective dose equivalents. Baseline effective dose responses were obtained for monoenergetic photon sources assumed to be distributed uniformly in soil for energies ranging from 0.01 to 10 MeV, soil thicknesses from 0 to 5 mean-free-path (mfp) lengths, and soil densities from 1 to 2 g cm-3. On the basis of the calculated dose responses, empirical relationships were obtained for correlating the dose responses with the soil depths and densities for each source energy. The derived correlations contain a convenient exponential form that describes the depth-dose relationship for an estimated accuracy within about 15%; soil densities show an inverse relationship with dose responses. Results of the effective dose-equivalent response can be used to calculate effective dose-equivalent responses for gamma-emitting radionuclides that are commonly identified as residual radioactive materials in soil.« less
  • The dose rate conversion factors {dot D}{sub CF} (absorbed dose rate in air per unit activity per unit of soil mass, nGy h{sup {minus}1} per Bq kg{sup {minus}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 bymore » 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 {dot D}{sub 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.« less