Citation
Organ Dose Coefficients for Asian-Scaled Computational Phantoms Resulting from External Exposures at the Techa River Due to Ground Contamination

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Title:
Organ Dose Coefficients for Asian-Scaled Computational Phantoms Resulting from External Exposures at the Techa River Due to Ground Contamination
Creator:
Schwarz, Bryan C
Place of Publication:
[Gainesville, Fla.]
Florida
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University of Florida
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english
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1 online resource (94 p.)

Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Biomedical Engineering
Committee Chair:
BOLCH,WESLEY EMMETT
Committee Co-Chair:
HINTENLANG,DAVID ERIC
Committee Members:
WU,CHANG-YU
Graduation Date:
8/9/2014

Subjects

Subjects / Keywords:
Asians ( jstor )
Dosage ( jstor )
Dosimetry ( jstor )
Human organs ( jstor )
Liver ( jstor )
Photons ( jstor )
Radionuclides ( jstor )
Teeth ( jstor )
Tooth enamel ( jstor )
Untranslated regions ( jstor )
Biomedical Engineering -- Dissertations, Academic -- UF
dosimetry -- mcnp -- techa
Genre:
bibliography ( marcgt )
theses ( marcgt )
government publication (state, provincial, terriorial, dependent) ( marcgt )
born-digital ( sobekcm )
Electronic Thesis or Dissertation
Biomedical Engineering thesis, M.S.

Notes

Abstract:
The objective of this research is to update the organ dose coefficients used in the Techa River Dosimetry System dose reconstruction efforts with Techa River specific organ dose coefficients. New gender and age specific adult and pediatric phantoms from the UF/NCI family of hybrid phantoms are being utilized in this study. The phantoms have been matched to standing height, sitting height, and chest circumference given in IAEA Technical Document 1005 on the Asian Reference Man. Chest circumferences are scaled to anthropometric data listed in that same document. Soil concentrations and densities specific to the Upper and Middle/Lower Techa River are employed in Monte Carlo simulations to generate organ dose coefficients. EPA Federal Guidance Report No. 12 (FGR 12) soil is utilized as reference soil to allow for quantitative comparisons to values given in FGR 12. The percent differences of the spectrum-weighted organ dose coefficients between the Asian-scaled phantoms and their stylized counterpart were on average between 5% and 20%. The maximum percent difference between these two sets of organ dose coefficients was 30% occurring in the esophagus for the 1-year-old Asian-scaled male. For distributed sources in the ground, Upper Techa River soil consistently yielded the highest dose coefficients, followed by Middle/Lower Techa River soil and FGR 12 soil following the trend of the lowest density soil yielding the highest dose coefficient because of less attenuation of the volumetric photon source. Differences in radionuclide-specific organ dose coefficients varied depending on decay scheme changes from ICRP 38 to ICRP 107. ( en )
General Note:
In the series University of Florida Digital Collections.
General Note:
Includes vita.
Bibliography:
Includes bibliographical references.
Source of Description:
Description based on online resource; title from PDF title page.
Source of Description:
This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Thesis:
Thesis (M.S.)--University of Florida, 2014.
Local:
Adviser: BOLCH,WESLEY EMMETT.
Local:
Co-adviser: HINTENLANG,DAVID ERIC.
Electronic Access:
RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2015-08-31
Statement of Responsibility:
by Bryan C Schwarz.

Record Information

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UFRGP
Rights Management:
Applicable rights reserved.
Embargo Date:
8/31/2015
Classification:
LD1780 2014 ( lcc )

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ORGAN DOSE COEFFICIENTS FOR ASIAN SCALED COMPUTATIONAL PHANTOMS RESULTING FROM EXTERNAL EXPOSURES AT THE TECHA RIVER DUE TO GROUND CONTAMINATION By BRYAN C. SCHWARZ A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2014

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© 2014 Bryan C. Schwarz

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To my parents, who have stood behind me and provided unwavering support throughout my life regardless of the path I have chosen. To my friends, without whom my life would be significantly less enjoyable.

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4 ACKNOWLEDGMENTS I thank Dr. Wesley Bolch for his direction and input during the course of this project , Dr. David Hintenlang and Dr. Chang Yu Wu for their critiques and input, Dr. Matthew Maynard for his continued assistance w ith this research especially with regards to his knowledge regarding MCNPX, Elliott Stepusin and David Borrego for their immense help in writing MATLAB scripts and submitting jobs to UF HPC , Amy Geyer for her assistance with the phantom scaling methods and her willingness to help edit this document, and Dr. Michael Bellamy for providing insight into the calculation methods utilized throughout this document. Lastly, I thank my friends and family for their love and support throughout the years.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 7 LIST OF FIGURES ................................ ................................ ................................ .......... 8 LIST OF ABBREVIATIONS ................................ ................................ ........................... 12 ABSTRACT ................................ ................................ ................................ ................... 14 CHAPTER 1 INTRODUCTI ON ................................ ................................ ................................ .... 16 Background and Significance ................................ ................................ ................. 16 Radiation Effects on the Body ................................ ................................ .......... 16 History of Releases along the Techa River ................................ ...................... 17 Computational Dosimetry Phantoms ................................ ................................ ...... 19 Mathematical Stylized Phantoms ................................ ................................ ..... 20 Voxel Computational Phantoms ................................ ................................ ....... 21 Hybrid Computational Phantoms ................................ ................................ ...... 22 Previous Studies Concerning External Environmental Exposures .......................... 22 EPA Federal Guidance Report No. 12 (Eckerman and Ryman 1993) .............. 22 Techa River Dosimetry System ................................ ................................ ........ 24 Purpose of Study ................................ ................................ ................................ .... 25 2 MATERIALS AND METHODS ................................ ................................ ................ 28 UF/NCI Hybrid Phantom Library ................................ ................................ ............. 28 Asian Scaled Phantoms ................................ ................................ .......................... 28 Phantom Matching and Scaling ................................ ................................ ........ 28 Delineation of Enamel and Dentin ................................ ................................ .... 31 Stylized Phantoms ................................ ................................ ................................ .. 32 Techa River Exposure Modeling ................................ ................................ ............. 32 Environmental and Phantom Radiation Transport ................................ .................. 35 Monoenergetic Photon Organ Dose Coefficients ................................ .................... 37 Radionuclide Specific Organ Dose Coefficients ................................ ..................... 38 3 RESULTS AND DISCUSSION ................................ ................................ ............... 43 Monoenergetic Photon Organ Dose Coefficients ................................ .................... 43 Radionuclide Specific Organ Dose Coefficients ................................ ..................... 48 4 CONCLUSIONS AND FUTURE WORK ................................ ................................ . 88

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6 Conclusions ................................ ................................ ................................ ............ 88 Future Work ................................ ................................ ................................ ............ 89 UF/NCI Phantom L ibrary Reference Phantoms ................................ ................ 89 Integration of Plane Sources ................................ ................................ ............ 89 Integration for Techa River Depth Profiles ................................ ........................ 90 LIST OF REFERENCES ................................ ................................ ............................... 91 BIOGRAPHIC AL SKETCH ................................ ................................ ............................ 94

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7 LIST OF TABLES Table page 2 1 Standing heights and weights for IAEA Reference Asian Man (RAM) and ICRP Reference Man. ................................ ................................ ........................ 40 2 2 Elemental composition of air. ................................ ................................ .............. 40 2 3 Elemental composition of UTR soil, MLTR soil, and FGR 12 soil. ...................... 40 2 4 X, Y, Z voxel resolution used in voxelization of Asian scaled phantoms. ........... 41 2 5 Organs investiga ted for both male and female phantoms of different ages. ....... 41 3 1 Comparison of photon spectrum for 144 Pr in ICRP 38 and ICRP 107. ................ 55

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8 LIST OF FIGURES Figure page 1 1 Schematic of the Techa River with its associated villages in 1949 (Degteva et al. 2011) ................................ ................................ ................................ ............. 27 1 2 External perspective and internal coronal views of the Cristy stylized phantom (Cris ty 1980). ................................ ................................ ....................... 27 2 1 Side views of the Asian scaled phantoms ................................ .......................... 42 2 2 Visualization of voxelized skull anatomy for the Asian scaled adult male phantom showing the delineation of dentin and enamel layers for the teeth. ..... 42 3 1 Monoenergetic dose coefficients for a source deposited on the soil surface for the liver in the Asian scaled adult male, Asian s caled adult female, and ORNL adult stylized phantoms ................................ ................................ ........... 56 3 2 Monoenergetic dose coefficients for a source deposited on the soil sur face for the liver in the Asian scaled 15 year old male, Asian scaled 15 year old female, and ORNL 15 year old stylized phantoms ................................ ............. 57 3 3 Monoenergetic dose coefficients for a source deposited on the soil surface for the liver in the Asian scaled 10 year old male, Asian scaled 10 year old female, and ORNL 10 year old stylized phantoms ................................ ............. 58 3 4 Monoenergetic dose coefficients for a source deposited on the soil surface for the liver in the Asian scaled 5 year old male, Asian scaled 5 year old female, and ORNL 5 year old stylized phantoms ................................ ............... 59 3 5 Monoenergetic dose coefficients for a source deposited on the soil surface for the liver in the Asian scaled 1 year old male, Asian scaled 1 year old female, and ORNL 1 year old stylized phantoms ................................ ............... 60 3 6 Age dependence of the monoenergetic dose coefficients for a source deposited on the soil surface for the liver in the Asian scaled male phantoms ... 61 3 7 Age dependence of the monoenergetic dose coefficients for a source deposited on the soil surface for the liver in the Asian scaled female phantoms ................................ ................................ ................................ ............ 62 3 8 Age dependence of the monoenergetic dose coefficients for a 1 cm uniformly distributed source for the liver in the Asian scaled male phantoms. ................... 63 3 9 Age dependence of the monoenergetic dose coefficients for a 1 cm uniformly distributed source for the liver in the Asian scaled female phantoms ................. 64

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9 3 10 Soil dependence of the monoenergetic dose coefficients for a source deposited on the soil surface for the live r ................................ ........................... 65 3 11 Soil dependence of the monoenergetic dose coefficients for a 1 cm uniformly distributed source for the liver ................................ ................................ ............. 66 3 12 Soil dependence of the monoenergetic dose coefficients for a source deposited on the soil surface for the liver ................................ ........................... 67 3 13 Soil dependence of the monoenergetic dose coefficients for a 1 cm uniformly distributed source for the liver ................................ ................................ ............. 68 3 14 Soil dependence for the monoenergetic dose coefficients for a 5 cm uniformly distributed source for the live r ................................ ............................. 69 3 15 Comparison of monoenergetic dose coefficients for the liver in the adult Asian scaled male, adult Asian scaled female, and ORNL adult stylized phantoms to those for the liver in FGR 12 for a surface source .......................... 70 3 16 Comparison of monoenergetic dose coefficients for the liver in the adult Asian scaled male, adult Asi an scaled female, and ORNL adult stylized phantoms to those for the liver in FGR 12 for a 1 cm uniform source . ............... 71 3 17 Compariso n of monoenergetic dose coefficients for the liver in the adult Asian scaled male, adult Asian scaled female, and ORNL adult stylized phantoms to those for the liver in FGR 12 for a 5 cm uniform source ................. 72 3 18 Comparison of monoenergetic dose coefficients for enamel, dentin, and liver in the adult Asian scaled male phantom for a source deposited on the soil surface. ................................ ................................ ................................ ............... 73 3 19 Age dependence of the monoenergetic dose coefficients for enamel in adult Asian scaled male, 15 year old Asian scaled mal e, 10 year old Asian scaled male, and 5 year old Asian scaled male phantoms for a surface source ........... 74 3 20 95 Zr dose coefficients fo r a source deposited on the surface for UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 95 Zr dose coefficients from FGR 12. ................................ ................................ ... 75 3 21 95 Zr dose coefficients for a 1 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 95 Zr dose coefficients from FGR 12. ................................ ................................ ... 75 3 22 95 Zr dose coefficients for a 5 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 95 Zr dose coefficients from FGR 12. ................................ ................................ ... 76

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10 3 23 95 Nb dose coefficients for a source deposited on the surface for UTR soil, MLTR soil, and F GR 12 soil for the adult Asian scaled male normalized to 95 Nb dose coefficients from FGR 12. ................................ ................................ .. 76 3 24 95 Nb dose coefficients for a 1 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 95 Nb dose coefficients from FGR 12. ................................ ................................ .. 77 3 25 95 Nb dose coefficients for a 5 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 95 Nb dose coefficients from FGR 12. ................................ ................................ .. 77 3 26 137m Ba dose coefficients for a source deposited on the surface for UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 137m Ba dose coefficients from FGR 12 ................................ ................................ 78 3 27 137m Ba dose coefficients for a 1 cm uniformly distributed source in UTR soil, MLTR soil, an d FGR 12 soil for the adult Asian scaled male normalized to 137m Ba dose coefficients from FGR 12. ................................ ............................... 78 3 28 137m Ba dose coefficients for a 5 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 137m Ba dose coefficients from FGR 12 . ................................ ............................... 79 3 29 144 Ce dose coefficients for a source deposited on the surface for UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 144 Ce dose coefficients from FGR 12 ................................ ................................ .. 79 3 30 144 Ce dose coefficients for a 1 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scale d male normalized to 144 Ce dose coefficients from FGR 12. ................................ ................................ . 80 3 31 144 Ce dose coefficients for a 5 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 144 Ce dose coefficients from FGR 12 . ................................ ................................ 80 3 32 144 Pr dose coefficients for a source deposited on the surface for UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 144 Pr dose coefficients from FGR 12. ................................ ................................ .. 81 3 33 144 Pr dose coefficients for a 1 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 144 Pr dose coefficients from FGR 12. ................................ ................................ .. 81 3 34 144 Pr dose coefficients for a 5 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 144 Pr dose coefficients from FGR 12. ................................ ................................ .. 82

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11 3 35 106 Rh dose coefficients for a source deposited on the surface for UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 106 Rh dose coefficients from FGR 12 . ................................ ................................ . 82 3 36 106 Rh dose coefficients for a 1 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 106 Rh dose coeffi cients from FGR 12 . ................................ ................................ . 83 3 37 106 Rh dose coefficients for a 5 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 106 Rh dose coefficients from FGR 12 . ................................ ................................ . 83 3 38 91 Y dose coefficients for a source deposited on the surface for UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 91 Y dose coefficients from FGR 12 . ................................ ................................ .... 84 3 39 91 Y dose coefficients for a 1 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 91 Y dose coefficients from FGR 12 . ................................ ................................ .... 84 3 40 91 Y dose coefficients for a 5 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 91 Y dose coefficients from FGR 12. ................................ ................................ .... 85 3 41 Adult Asian scaled male, adult Asian scaled female, and adult stylized phantom organ dose coeff icients normalized to the adult stylized phantom for a surface deposition for 137m Ba. ................................ ................................ .......... 85 3 42 15 year old Asian scaled male, 15 year old Asian scaled female, and 15 year old stylized phantom organ dose coefficients normalized to the 15 year old st ylized phantom for a surface deposition for 137m Ba. ................................ ... 86 3 43 10 year old Asian scaled male, 10 year old Asian scaled female, and 1 0 year old stylized phantom organ dose coefficients normalized to the 10 year old stylized phantom for a surface deposition for 137m Ba. ................................ ... 86 3 44 5 year old Asian scaled male, 5 year old Asian scaled female, and 5 year old stylized phantom organ dose coefficients normalized to the 5 year old stylized phantom for a surface deposition for 137m Ba. ................................ ......... 87 3 45 1 year old Asian scaled male, 1 year old Asian scaled female, and 1 year old stylized phantom organ dose coefficients normalized to the ORNL 1 year old s tylized phantom for a surface deposition for 137m Ba. ................................ ... 87

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12 LIST OF ABBREVIATIONS ALRADS Advanced Laboratory for Radiation Dosimetry Studies BEIR VII Biological Effects of Ionizing Radiation Report VII EPA Environmental Protection Agency EPR electron paramagnetic resonance ETRC Extended Techa River Cohort FGR 12 Federal Guidance Report No. 12 IAEA International Atomic Energy Agency ICRP International Commission on Radiological Protection ICRU International Commission on Radiation Units and Measurements LET linear energy transfer LSS Life Span Study MATLAB Matrix L aboratory MCNPX Monte Carlo n particle extended MLTR Middle/Lower Techa River MIRD Medical Internal Radiation Dose NCI National Cancer Institute NIST National Institute of Standards and Technology NURBS non uniform rational b splines ORNL Oak Ridge National Laboratory RAM Reference Asian Man SSR surface source read SSW surface source write STY stylized

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13 TRC Techa River Cohort TRDS Techa River Dosimetry System TROC Techa River Offspring Cohort UF University of Florida UF HPC University of Florida High Performance Computing Center UTR Upper Techa River

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14 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science ORGAN DOSE COEFFICIENTS FOR ASIAN SCALED COMPUTATIONAL PHANTOMS RESULTING FROM EXTERNAL EXPOSURES AT THE TECHA RIVER DUE TO GROUND CONTAMINATION By Bryan C. Schwarz August 2014 Chair: Wesley Bolch Major: Biomedical Engineering The objective of this research is to update the organ dose coefficients used in the Techa River Dosi metry System dose reconstruction efforts with Techa River sp ecific organ dose coefficients. New gender and age specific adult and pediatric phantoms from the UF/NCI family of hybrid phantoms ar e being utilized in this study. The phantoms have been matched to standing height, sitting height , and chest circumference given in IAEA Technical Document 1005 on the Asian Reference Man. Chest circumferences are scaled to anthropometric data listed in that same document. Soil concentrations and densities specific to the Upper and Middle/Lower Techa River are employed in Monte Carlo simulations to generate organ dose coefficients. EPA Fede ral Guidance Report No. 12 (FGR 12) soil is utilized as reference soil to allow for quantitative comparisons to values given in FGR 12. The percent differences of the spectrum weighted organ dose coefficients between the Asian scaled phantoms and their st ylized counterpart were on average between 5% and 20%. The maximum percent difference between these two sets of organ dose coefficients was 30% occurring in the esophagus for the 1 year old Asian -

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15 scaled male. For distributed sources in the ground, Upper Te cha River soil consistently yielded the highest dose coefficients, followed by Middle/Lower Techa River soil and FGR 12 soil following the trend of the lowest density soil yielding the highest dose coefficient because of less attenuation of the volumetric photon source. Differences in radionuclide specific organ dose coefficients varied depending on decay scheme changes from ICRP 38 to ICRP 107.

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16 CHAPTER 1 INTRODUCTION Background and Significance Radiation Effects on the Body Biological effects of ionizing radiation incident from either internal or external sources manifest themselves principally as damage to DNA molecules within cells. As ioni zing radiation enters the tissue and interacts with the cell, electrons can be liberated by either Compton scattering or photoelectric absorption within the cell material. The incoming particles can either interact directly with the DNA molecule to cause excitations and ionizations, or the incoming particles may interact with another material in the cell to produce free radicals, which then interact with the DNA molecule (Hall and Giaccia 2012) . These processes are referred to as direct action and indirect action, respectively. Direct action is the dominant mode of DNA damage in particles with high linear energy transfer (LET) , such as alpha particles, while indirect action is more common when the incident particles have low LET , such as photons and electrons . The proceeding discussion will focus on DNA damage resu lting from indirect action. When this DNA damage is not repaired by inherent molecular mechanisms for DNA repair, mutations can occur which can lead to the biological effects including cell killing and cancer incidence. In the event of cell killing, the b iological effects resulting from incident radiation are seen relatively soon after exposure , often presenting themselves within hours or days of exposure . In the event of cancer incidence, it may be years before the biological effects are seen (Hall and Giaccia 2012) . Data used in c alculation s of risk estimates from exposure to ionizing radiation comes primarily from Japanese atomic bomb survivor data. The Life Span Study (LSS)

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17 cohort contains approximately 120,000 survivors who lived within 2 10 km of hypocenter of the atomic bombs that were detonated by the United States above Hiroshima, Japan and Nagasaki, Japan at the end of World War II (BEIR 2005) . The LSS cohort has been carefully followed for decades, and it is a valuable cohort for estimating risk from ionizing radiation exposures because of the large amount of exposed indivi duals, variety in ag e and gender among members, and long follow up period . However, the LSS cohort lacks in the ability to accurately characterize the effects from chronic , low dose rate radiation exposure s because of the acute , high dose rate exposures r esulting from atomic bomb explosions (Kossenko et al. 19 97) . Currently, risk estimates for chronic, low dose rate exposures are based on extrapolations from the LSS data. Combining the data from the atomic bomb survivors with data from cohorts specifically exposed to chronic, low dose rate exposures allows for more comprehensive data in estimating the risk from radiation exposures. History of Releases along the Techa River The Techa River is located in southern Russia near the Ural Mountains. The river is a section of the Techa Isset Tobol Irtysh Ob River system that flows out of Lake Irtyash (Akleyev e t al. 2000) . The soil composition in the middle and lower section of the Techa River is more mineralized than the upper section, and therefore, the middle and lower Techa River soil is of higher density. A schematic map of the Techa River showing the river and sett lements in 1949 is seen in Figure 1 1. In 1948, the Mayak Production Association, a plutonium processing facility akin to the Hanford site along the Columbia River in Washington, was put into operation in the Chelyabinsk Region of the former U.S.S.R (Akleyev et al. 2000, Degteva et al.

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18 2000) . Similar to the Hanford site, the main purpose of Mayak was to produce In the late 1940s and e arly 1950s , radioactive contamination of the Techa River occurred as a result of liquid, radioactive waste releases from the plutonium processing facility of the Mayak Production Association (Mokorov et al. 2000, Degteva et al. 2006) . These releases occurred due to lack of knowledge with regards to radioactive waste and flawed technological processes . Because many villages bordered the Techa Ri ver, residents residing on the river during those years were subjected to radiation exposure in a multitude of pathways, the mo re prominent being river drinking water and external gamma exposure due to village proximity to the shoreline . In addition to rad ioactive releases into the Techa River, individuals were also exposed to gase ous aerosol releases from Mayak (Degteva et al. 2000) . From 1949 1956, approximately 110 petabecquerels ( P Bq) of liquid wastes were released in the upper portion of the Techa River which then contaminated sites downstream of the waste release (Seligman 2000, Degteva et al. 2009) . With respect to external exposures, the radionuclides released by Mayak of most concern are 137 Cs, 137m Ba, 95 Zr, 95 Nb, 144 Ce, 144 Pr, 106 Ru, 106 Rh, and 91 Y (Degteva et al. 2011) . With respect to internal exposures, 89 Sr, 90 Sr, and 90 Y are of most concern. T he situation has produced a population of people who were exposed to chronic, low dose rate radiation over an extended period of time that can be studied. In 1968, the Techa River Registry was created at the Urals Research Center for Radiation Medicine (URCRM) to attempt to create a cohort population of residents along the Techa River from 1949 1952, the peak exposure time period (Degteva et al. 2009) .

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19 Approxima tely 26,500 individuals compris e the Techa River Cohort (TRC) , and there has been an increase in both leukemia and solid cancers among members of the cohort (Kossenko et al. 1997) . Recently, approximately 5,000 individuals who migrated to the Techa River after 1952, but before the radioact ive releases stopped , have been added to the TRC. The original TRC and the additional 5,000 migration individuals comprise the Extended Techa River Cohort (ETRC) . In addition, URCRM retains information on approximately 30,000 individuals who were exposed in utero and/or are the children of exposed parents (Degteva et al. 2009) . The Techa River Offspring Cohort (TROC) includes information from 12,000 of those individuals. The TROC has the unique ability to be utilized in studies regarding exposed pregnant females and the effects of in utero low dose rate radiation exposure. Sim ilar to the LSS cohort, the ETRC is a useful cohort for epidemiological study because of the variety in age and gender among members, the relatively large doses received by the members, and the relatively old age of the members . However, the ETRC can be d irectly utilized to study the effects and estimate the risk from chronic, low dose rate radiation exposure. Computational Dosimetry Phantoms To study the magnitude of the doses received by individuals in these cohorts, accurate models of the human anatomy are necessary. Computational dosimetry phantoms are computer generated mo dels of human anatomy that are utilized by radiation transport codes. The phantoms are then used to calculate the dose to any organ defined in the phantom from a defined radiation s ource. There are three primary types of com putational dosimetry phantoms: s tylized phantoms, voxel phantoms, and hybrid phantoms.

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20 Mathematical Stylized Phantoms Stylized phantoms were the first computational phantom s utilized for radiation transport studies. Stylized phantoms are modeled using mathematical shapes and the surface equations that describe them. The first generation of stylized phantoms was developed in the mid 1960s by Fisher and Snyder for use in esti mating organ doses from internal photon sources (Cristy 1980) . The Fisher Snyder phantom was included in the Medical Internal Radiation Dose (MIRD) Committee Pamphlet No. 5 in 1969 and its revision in 1978. In this phantom, elliptical cylinders represented th e arms, torso, hips, and neck while truncated circular cones represented legs and feet (Snyder et al. 197 8) . Three types of tissues were assigned in the phantom: Skeletal, lung, and other soft tissue. In 1980, Mark Cristy of ORNL developed the Cristy phantom and a set of pediatric phantoms for use in radiation transport codes. While creating this set of pediatric phantoms, Cristy made many changes to the Fisher Snyder phantom. Female breast tissue and an improved heart model were added to the Cristy phantom, and the lungs were redesigned to allow for the inclusion of the new heart model (Cristy 1980) . Small changes in the position of the thyroid, adrenals, gall bladder, and the thymus were all included to allow for consistency between the adult and pediatric phantoms (Cristy 1980) . Additionally, densities and chemical compositions were adjusted for lung, skeleta l, and soft tissues (Cristy and Eckerman 1987) . A perspective and coronal view of the Cristy phantom is seen in Figure 1 2. These phantoms were again updated by Mark Cr isty and Keith Eckerman in the late 1980 s. These updates included size and position changes of the lungs and liver along with slight modifications to the density and elemental composition of lung, skeletal, and soft tissues. The Fisher Snyder phantom,

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21 Cristy phantom, and all subsequent updated phantoms are hermaphroditic. The ORNL phantoms have been updated multiple times since their creation, most recently to update organ densities and elemental compositions to that of Publi cation 89 of the International Commission on Radiological Protection (ICRP) and Report 46 of the International Commission on Radiation Units and Measurements (ICRU) (Han et al. 2006) . The benefit of stylized phantoms is their ea se in adjusting both organ size and organ shape and their subsequent inclusion in radiation transport codes. However, stylized phantoms lack in anatomical accuracy as the orga ns are defined by geometric surface equations (Bolch et al. 2010) . Additionally, organ size, organ shape, tissue density, and tissue composition can vary between genders. Therefore, more accurate repre sentations of the human body are necessary. Voxel Computational Phantoms Voxel phantoms are created through segmentation methods by delineating the computed tomography ( CT ) or magnetic resonance ( MR ) image set organs by three dimension arrays of rectangular prism voxels at a resolution desired by the user (Bolch et al. 2010) . Organs are tagged by number for identification purposes. By doing this, one can assign specific values for density and elemental composition for a tagged organ and have high anatomical accuracy , because the resulting phantom is essentially a direct copy of the individual scanned. However, the process to create a voxel phantom can be arduous. The segmentation process is gene rally manual and time consuming , and the voxel phantom must then be changed into a format that a radiation transport code can utilize (Hurtado

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22 et al. 2012) . The ideal phantom construction combines the anatomical realism of voxel phantoms with the flexibility of stylized phantoms. Hybrid Computational Phantoms Hybrid phantoms combine the anatomical accuracy of voxel phantoms with the flexibility to alter organ and body contours available in stylized phantoms. As in voxel phantoms, CT or MR image sets are used in combination with a segmentation program to delineate the organs for inclusion in the hyb rid phantom. Three dimensional rendering of the anatomy resul ts in contours defined by triangular surface array which are then converted to non uniform rational B spline (NURBS) surfaces (Bolch et al. 201 0) . NURBS surfaces have control points which the user can use to adjust the morphometry of organ and body contours . Hybrid phantoms have the inherent accuracy of voxel phantoms as they are derived from patient image data sets. However, unlike voxel phantoms, they allow for scaling of the organ and body contours, and t herefore contain the advantages of both stylized and voxel phantoms (Hurtado et al. 2012) . Previous Studies Concerning External Environmental Exposures EPA Federal Guidance Report No. 12 (Eckerman and Ryman 1993) U.S. Environmental Protection Agency Federal Guidance Report No. 12 (FGR 12) published in 1993 by Oak Ridge National Laboratory (ORNL) provides organ dose coefficients and effective dose coefficients for an adult hermaphrodite stylized phantom exposed t o an external radiation source distributed in air, water, and soil (Eckerman and Ryman 1993) . For the air submersion scenario, a semi infinite cloud source containing a monoenergetic photon emitter of 1 Bq m 3 was used with the phantom completely

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23 surrounded by the air cloud . In the water immersion scenario, an infinite pool source containing a monoenergetic photon emitter of 1 Bq m 3 was utiliz ed. In this scenario, the phantom is placed in the middle of the pool so as to be completely immersed. The source for the ground contamination scenario was an infinite plane source containing a monoenergetic photon emitter of 1 Bq m 2 at either the surfac e of the soil or at a specific depth in the soil. This depth was specified in terms of mean free paths in the soil at the source energy. In the ground contamination scenario, the phantom is standing on the surface of the soil at the air ground interface (Eckerman and Ryman 1993) . For the ground contamination scenario, organ d ose co efficients from a monoenergetic photon emitter of 1 Bq m 2 at six source depths (0, 0 .04, 0.2, 1.0, 2.5, and 4.0 mean free paths ) were calculated. Calculations at multiple depths allowed for integration over the different plane sources to calculate organ do se coefficients from uniformly distributed volume sources in the ground. The depths of the plane sources were chosen to allow for accurate integration as one must interpolate between these plane sources to calculate the dose coefficients from volu me sources (Eckerman and Ryman 1993) . Regardless of the exposure scenari o , t he calculation of organ dose coefficients in FGR 12 can be broken down into two steps. The first step involves the simulation of environmental exposure to a surface that completely surrounds the phantom , Whi le direct radiation transport from the environment to the phantom can be completed, the process is both more time intensive and statistically weaker due to the complex geometry of the phantom and the size/depth of the sources (Eckerman and Ryman 1993) . Once a particle strikes the coupling

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24 cylinder, the angular and energy inform ation of the particle is saved to a separate file . This separate file is read in during a separate transport simulation as a cylindrical area source with the phantom placed inside the coupling cylinder . It should be noted that the phantom is not present during the initial e nvironmental simulation to the coupling cylinder . The calculations described above result in monoenergetic dose coefficients for air, water, and soil contamination. T o estimate the dose to an individual exposed to one of these sources, the results of the simulations must be spectrum weighted for the specific radionuclide to which the individual was exposed. The monoenergetic dose coefficients were spectrum weighted using the energies and yields for all radionuclides l isted in ICRP Publi cation 38 (Eckerman and Ryman 1993) . The resulting data from the study ar e organ dose coefficients and effective dose coefficients (Sv m 3 Bq 1 s 1 ) normalized to unit activity strength for specific radionuclides from a multitud e of exposure pathways. The dose coefficients can be scaled to calculate organ dose and effective dose for actual exposure scenarios knowing the activity concentration of radionuclide and the amount of time an individual was exposed. Techa River Dosimetry System The Techa River Dosimetry System (TRDS) has been developed to reconstruct the doses for the re sidents that lived on the Techa River during the years of exposure from Mayak. TRDS utilizes the information garnered from members of the TRC, ETRC, and TROC to provide estimates of the external doses and internal doses for members of the cohort (Degteva et al. 2006) . At the onset of TRDS, the estimates prov ided by the code were a village averaged quantity, but the code has been improved over the

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25 years to provide estimates of dose for specific members of the cohort (Degteva et al. 2011) . TRDS utilizes the organ dose coefficients from FGR 12 described in the previous section. T hese dose coefficie nts are calculated for an adult hermaphrodite stylized phantom standing on soil with a density of 1.6 g cm 3 (Eckerman and Ryman 1993 , Degteva et al. 2011) . These external organ dose coefficients are for sources of infinite extent; therefore, organ dose coefficients are scaled by dose reduction factors for finite sho reline widths. Future TRDS studies plan to utilize hybrid phantoms on Techa River specific soil for more specific estimates of the organ dose coefficients for individuals who lived along the Techa River. Purpose of Study Since the goal of TRDS is to provi de accurate estimates of the dose received by individuals along the Techa River, it follows that studies concerning the Techa River should be as specific to the region as possible. In the scope of external dosimetry, phantoms that accurately portray the T echa River cohort combined with the densities and elemental compositions of the different soils along the Techa River should be used in concert to calculate external dose coefficients for the organs of interest from contaminated soil. The resulting dose c oefficients will be specific to the Techa River and will allow for more accurate quantification of the dose received by an individual living along the Techa River during the 1950 s. With the use of soils and hybrid computational phantoms specific to the T echa River, one would expect a deviation of the organ dose coefficients for the Techa River as compared to the organ dose coefficients listed in FGR 12. The hypothesis is that the monoenergetic photon organ dose coefficients for the Asian scaled phantoms will be

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26 greater than the monoenergetic photon organ dose coefficients from FGR 12. Additionally, the hypothesis is that the monoenergetic photon organ dose coefficients for the Asian scaled phantoms will be greater than the monoenergetic photon organ dose coefficients from the stylized phantoms. If one were to utilize the decay schemes from ICRP 38 for the spectrum weighted organ dose coefficients, the resulting spectrum weighted organ dose coefficients would be higher. However, since updated decay scheme s from ICRP 107 are utilized in this study, it is difficult to estimate how the spectrum weighted organ dose coefficients will differ to those from FGR 12. In general, small increases or decreases in the photon yield for higher frequency emissions associa ted with a radionuclide are expected to have a profound effect on the spectrum weighted organ dose coefficients.

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27 Figure 1 1. Schematic of the Techa River with its associated villages in 1949 (Degteva et al. 2011) Figure 1 2 . External perspective and internal coronal views of the Cristy stylized phantom (Cristy 1980) .

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28 CHAPTER 2 MATERIALS AND METHODS UF/NCI Hybrid Phantom Library In the Advanced Laboratory for Radiation Dosimetry Studies (ALRADS) at the University of Florida (UF ), an extensive library of hybrid computational phantoms have been developed for computational radiation dosimetry. The first UF hybrid phantoms developed were male and female newborn hybrid phantoms that represented reference newborn male and female as d efined by ICRP Publication 89 (Lee et al. 2007, Lee et al. 2010) . Hybrid computational phantoms representing the reference 15 year old male and female were then included in the library (Lee et al. 2008) . In 2010, reference 1 year old , 5 year old , and 10 year old reference male and female hybrid phantoms were reported (Lee et al. 2010) . In 2012, reference adult male and adult female hybrid computational phantoms were reported (Lee et al. 2010, Hurtado et al. 2012) . Recent work comple ted within ALRADS has resulted in a large array of hybrid compu tational phantoms totaling over 350. This library represents males and females of both adult and pediatric ages covering a wide range of body morphometries seen within the US population (Geyer et al. in press) . A sian Scaled Phantoms Phantom Matching and Scaling To provide an accurate assessment of the dose coefficients for the Techa River, phantoms representing the population residing along the Techa River are nec essary. A nthropometric data described in International Atomic Energy Agency (IAEA) Technical Document 1005

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29 (IAEA TEC DOC 1005) was utilized to scale phantoms from the UF/NCI phantom library . This document contains anthropometric data for eight Asian nations along with averaged anthropometric data for equal country weighting, population weight, and range midpoint values f or each of the measurements. In this study, the range midpoint value parameters were used in scaling as they provide the most reasonable single value to be used in practice (IAEA 1998) . Table 2 1 provides a comparison of heights and weights between ICRP and IAEA TECDOC 1005 reference individuals . The data from IAEA TECDOC 1005 was used to match to phantoms in the UF/NCI phantom library with regards to standing height, sitting height, and chest ci rcumference. These three parameters were then scaled to precisely match the data in IAEA TECDOC 1005. The smaller chest circumferences given for the Asian body morphometries listed in IAEA TECDOC 1005 y ield s higher dose coefficients for internal organs du e to less adipose/skeletal muscle shielding of internal organs (Eckerman and Ryman 1993) . Scaling to IAEA TECDOC 1005 anthropometric data was completed using the modeling software Rhinoceros® v5 for the male and female adult, 15 year old , 10 year old , 5 year old , and 1 year old Asian scaled phantoms. In the UF library, sitting height is defined as the distance from the crown of the skull to just below the pubic bone, directly inferior to the ischial tuberosity. After this distance was matched and confirmed with the data from IAEA TECDOC 1005, the legs were either shortened or lengthened to conform to the targeted total phantom height. While scaling for height is straightforward, scaling the chest circumference was more problematic for the smaller phantoms of the Asian series. Chest circumference was scaled by selecting the tor so of the phantom and adjusting the appropriate

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30 collection of NURBS control points. These control points were adjusted manually to increase/decrease the chest circumference. This process effectively adds/removes d back. Once the correct chest circumference was attained, the control points were used to smooth the body contours to re establish a normal appearance. While IAEA TECDOC 1005 provides a measurement for chest circumference, it does not define the locati on of the measurement. Consequently, chest circumference was defined as the base of the sternum for males and the bottom of the breast for females. In all cases, the Asian scaled phantom chest circumferences were less than the matched UF hybrid phantom. In most cases, the difference between the Asian scaled phantom and UF hybrid phantom was not sufficiently large enough to induce problems with internal anatomy when reducing the amount of adipose tissue on the chest and back. However, this issue arose wit h the 5 year old male and 5 year old female Asian scaled phantom s . The difference between IAEA TECDOC 1005 chest circumference and UF hybrid phantom chest circumference was approximately 10 cm for both the male and female. In this situation, as the chest circumference was manually reduced using NURBS control points, issues arose with the positioning of the ribs and scapula of the phantom because the internal anatomy remains fixed during body contour adjustment of the phantom. Therefore, a 2D scaling of t he torso was applied to scale the adipose layer in lieu of using manual control points. Side views of the male and female Asian scaled phantoms are shown in Figure 2 1 . It should be noted that the internal organs of the Asian scaled phantoms have not been scaled to reference values. The decision to not scale the internal organs to reference values was made because the

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31 reduced chest circumferences did not allow for scalin g of the organs due to space considerations. Delineation of Enamel and Dentin For all phantoms in the UF/NCI phantom library, the teeth are modeled as a uniform polysurface in Rhinoceros TM . In this study, a separate tally of radiation dose to the tooth en amel is needed for comparison to electron paramagnetic resonance (EPR) dose estimates. EPR dosimetry is a method based on the stable, induced radicals present in tooth enamel after exposure to a radiation source. Each radical species formed in the enamel has a unique spectrum, and the peak to peak width in the spectrum is proportional to the absorbed dose (IAEA 2002, Vestad et al. 2004) . Consequently, to add a 1 mm layer of enamel to the surface of the teeth, the teeth were transformed into a mesh layer , and the OffsetMesh command in Rhinoceros TM was utilized. OffsetMesh allows the user to choose an offset distance for uniform expansion/contraction of a mesh object. This process was completed for each Asian scaled phantom except the 1 year old , because the 1 year old UF hybrid phantoms do not have te eth included in their anatomy . Figure 2 2 shows the enamel layer on the teeth as visualized in the visualization program ImageJ. In this image, the teal layer represents the body of the teeth while the red layer represents a 1 mm layer of enamel surroundi ng the teeth. This modification to the phantoms was requested to support dose coefficients for comparison to EPR measurements of TRC members . The end product of the OffsetMesh method effectively delineates the teeth into a section of enamel and a section of dentin in the Asian scaled phantom . Elemental compositions and densities of tooth enamel and dentin varied widely between sources. Therefore, the data for elemental composition and density of tooth enamel and dentin were taken

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32 from IAEA TECDOC 1331 (IAEA 2002) as this document provided the most comprehensive information regarding dentin and enamel . The densities of enamel and dentin were taken as 2.9 g cm 3 and 2.5 g cm 3 , respectively. S tylized Phantoms Stylized phantoms received from Michael Bellamy at ORNL are utilized in this study as a comparison to the Asian scaled phantoms and FGR 12 stylized data. These hermaphroditic stylized phantoms allow for direct comparisons of hybrid phantoms and stylized phantoms for external dose coefficient calculation. The O RNL stylized phantoms allow for a more comprehensive representation of dose coefficients in stylized phantoms than in FGR 12 because FGR 12 utilized a single adult hermaphroditic stylized phantom while the new series of ORNL stylized phantoms a re divided i nto five age groups: 1 year, 5 year, 10 year, 15 year, and adult. Techa River Exposure Modeling The modeling of infinite plane sources in the soil as completed in FGR 12 was utilized to model the exposures at the Techa River. The model used in FGR 12 was used because TRDS currently uses dose coefficients calculated in FGR 12 for inclusion in their code and is considered an industry standard procedure for calculating dose coeff icients from external exposures. Unless otherwise specified, the unit used for d escribing the absorbed do se to an organ is the gray (Gy), which is defined as the absorption of one joule (J) of energy by 1 kg of matter. As described in FGR 12, the source for the contaminated soil exposure scenario is an infinite isotropic plane source of monoenergetic photons of 1 Bq m 2 areal activity concentration with the phantom standing at the air ground interface (Eckerman and Ryman 1993) . The soil was modeled as a cylinder with each plane source in the soil

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33 modeled as a disk in the soil medium. The air medium above the soil was modeled as a cylinder with a heig ht of three mean free paths in air at the source energy. The height of the cylinder was defined in FGR 12 as three mean free paths because any photon that scatters at three mean free paths or greater in the air must travel a minimum of six mean free paths to contr ibute to the organ dose and any contribution to organ dose from a particle traveling this distance is negligible (Eckerman and Ryman 1993) . The density of air (1.2 kg m 3 ) and the elemental composition of air were taken from FGR 12 (Eckerman and Ryman 1993) . The elemental composition of air is listed in Table 2 2 . In this study, three soils were utilized to calculate organ dose coefficients to both Asian scaled phantoms and stylized phantoms. The three soils used in organ dose coefficient calculati ons were Upper Techa River (UTR) soil (1.0 g cm 3 ), Middle/Lower Techa River (MLTR) soil (1.5 g cm 3 ), and a typical soil (1.6 g cm 3 ). The densi ties and elemental compositions for the UTR and MLTR soils were provided by Russian colleagues. The density and elemental composition for the typical silt soil was taken from FGR 12 (Eckerman and Ryman 1993) of this document . The elemental compositions of UTR soil , MLTR soil , and FGR 12 soil are seen in Table 2 3 . Calculations were made for monoenergetic photons at 25 source energies from 10 keV to 10 MeV as a function of depth for 0, 0.04, 0.2 , 1.0, 2.5, and 4.0 mean free paths in soil at the source energy . These depths were chosen to allow for accurate integration over the source planes for volume sources (Eckerman and Ryman 1993) . For source s at depths of 0, 0.04, 0.2, and 1.0 mean free paths, the soil medium thickness was defined as three mean free paths at the source energy. For the depths of

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34 2.5 and 4 mean free paths, the soil mediu m thickness was taken as 3.5 and 5 mean free paths, respectively. These depths were chosen in a similar fashion as the depth of the air medium. Any photon that scatters at the soil boundary and travels back to the air ground interface would have traveled at least six mean free paths, and the contribution to the organ dose from the photon is negligible (Eckerman and Ryman 1993) . T hough the sources in FGR 12 are defined as infinite, a distance must be defined for the plane sources. The air medium and soil medium cylinders were assigned radii of two mean free paths in air at the source energy. This distance was chosen because radii greater than two mean free paths in air resulted in negligible increases of particles striking the coupling cylinder. The attenuation coefficients used to calculate the mean free paths were taken fro m the National Institute of Standards and Technology (NIST) XCOM photon cross section database. The coupling cylinder was placed at the origin with a height of 200 cm and radius of 40 cm. This height and radius allows for the placement of any phantom in the UF/NCI phantom library inside the coupling cylinder. To avoid geometry errors, the air and soil cylinder were offset from the coupling cylinder; however, this offset was less than 0.1 µ m and does not affect the calculation of organ dose coefficients. Additionally, for the surface contamination scenario, the source was placed at 1 nm depth in the soil to avoid geometry errors. Consequently, while there may be small variations in the org an dose coefficients from each of the three soils because of this source depth definition , the field above the soil from a surface contamination scenario should be insensitive to soil density and composition (Eckerman and Ryman 1993) .

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35 Environmental and Phantom Radiation Transport Radiation transport for both the environmental tr ansport and phantom transport was completed using the general purpose , radiation transport code Monte Carlo N Particle Code Extended Version 2.7.0 (MCNPX TM V2.7). MCNP is a general purpose , time dependent, probabilistic radiation transport code developed by Los Alamos National Laboratory. Effectively, MCNP randomly samples to determine the events a simulated particle experiences in the course of its transport using radiation transport data. In MCNP, the user defines the transport environment through the u se of simple surfaces in the MCNP input file to accurately reflect the geometry of the system. Additionally, descriptions of the materials constituting the geometry are included in the input deck including densities and elemental compositions. The descri ption of the materials is necessary because MCNP accesses cross section libraries during transport for the materials of interest, and the cross section libraries govern the processes by which these transported particles interact. The probabilistic sampling is based on the selection of random numbers between 0 and 1. The random numbers generated determine the interactions and the locations of those interactions based on the associated probabilities ting (HPC) Center has been employed for all radiation transport simulations in this study. Recently, UF HPC the amount of wall time declarations for simulations from 99 hours to 672 hours. Because of this increase in wall clock availability, an increase in the amount of source particles declared in an MCNPX input deck was possible.

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36 To construct the cylindrical area source around the phantom, the surface source write (SSW ) capability of MCNPX was utilized. In a SSW calculation, as particles cross regarding starting energy, collision energy, Cartesian coordinate position, and direction cos ines are saved to a binary file for use in subsequent MCNP calculations. To save computing time, the inside of the cylinder was set to zero importance and defined as a void so that any particle entered from the envi ronment and struck the cylinder was kill ed and not followed by the program after its information was saved to the SSW file . SSW files can become large as you increase the amount of particles (10 keV SSW for 100 billion particles is approximately 180 gigabytes ). Because of space considerations on UF HPC, limits existed on the amount of particles that could be simulated. Environmental simulations were completed using 100 billion source particles. The wall time required for each of these 100 billion particle simulations ranged from approximately one day (10, 15 keV source particles) to approximately six days (10 MeV source particles). UF HPC reinstalled MCNP in an unsigned 8 byte format to allow for a larger amount of source particles. Phantom transport from the SSW files was completed using the surface source read (SSR) capability of MCNPX. SSR utilizes the SSW file created in a previous MCNPX simulation and continues transporting particles based on the information saved to the SSW file. To be utilized by MCNPX, phantoms must be voxelized and placed into a lattice form that MCNPX is capable of reading. A MATLAB script provided by ALRADS members Matthew Maynard and Elliott Stepusin carried out the voxelization process. The Asian scaled phantoms have been voxelized at the resolutions listed in

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37 Table 2 4. Elliott Stepusin also provided a MATLAB script that created the MCNPX input files for phantom transpor t which assigned materials and densities for all organs of interest and utilizes the phantom lattice file . The organs investigated in this st udy for both the Asian scaled phantoms and stylized phantoms are listed in Table 2 5. In the input file MATLAB script, organ numbers and densities had to be adjusted accordingly for the inclusion of tooth enamel to the phantoms. Monoenergetic Photon Organ Dose Coefficients In MCNPX, *F6 tallies were utilized to calculate organ dose coefficients. *F6 tallies the average energy deposition over a defined cell in units of jerks g 1 . Since organ dose coefficients are typically in units of Gy m 2 Bq 1 s 1 for a plane source , a conversion from jerks g 1 to Gy is neces sary. To convert from jerks g 1 to Gy, one multiples the resulting tally by 1 x 10 12 , and the resulting tally value is in units of Gy per source particle . T o normalize each of the plane sources to 1 Bq m 2 , one assumes an areal activity concentration of 1 Bq m 2 . Because the radius of the soil source was defined by the user, the area can be calculated based on the radius of the soil disk at each energy. Multiplying the areal activity concentra tion by the area of the plane source results in an activity that is equal to the area of the plane source (i.e. if the area of the plane source is 10 m 2 , the assumed activity would be 10 Bq). The activity calculated (Bq) is then multiplied by the tally re sult (Gy photon 1 ) which results in a monoenergetic photon organ dose coefficient (Gy m 2 Bq 1 s 1 ) for each plane source. To calculate organ dose coefficients for uniformly distributed volume sources, integration over the plane sources is completed accordi ng to Equation 2 1 (Eckerman and Ryman 1993)

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38 (2 1) where h T,L (Gy m 3 Bq 1 s 1 ) is the dose coefficient for tissue T for a volumetric source extending from the surface to depth L (cm) , h T,P is the dose coefficient for tissue T for a plane source at energy E and depth (mean free paths) . The integration bound µL is equal to the thickness of the v olume source in mean free paths. The values for the monoenergetic dose coefficients for plane sources were interpolated using spline interpolation in MATLAB. These interpolated dose coefficients were then numeri cally integrated using MATLAB to calculate the organ dose coefficients for a volume source of defined depth L . For the lowest energy cases (primarily 10 and 15 keV sources) and smaller organs , tallies for internal organs were primarily zero. Therefore, log log extrapolations of the data sets were completed for 10 and 15 keV sources (Eckerman and Ryman 1993) . Since 10 and 15 keV photons have little penetration ability, the absorbed doses from these sources are effectively zero. Therefore, extrap olations from the higher energy cases to the lower energy cases results in conservative values for monoenergetic dose coefficients (Eckerman and Ryman 1993) . Additionally, radionuclide photon yields below 15 keV are small and do not contribute greatly to calculated radionuclide specific organ dose coefficients. R adionuclide Spe cific Organ Dose Coefficients To calculate radionuclide specific organ dose coefficients, monoenergetic dose coefficients were spe ctrum weighted using the decay schemes provided by ICRP Publication 107 publi shed in 2008 (ICRP 2008) .

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39 Spectrum weighted organ dose coefficients can be calculated using Equation 2 2 (Petoussi Henss et al. 2012) (2 2) where y j (E i ) is the yield of radiation from discrete lines with energies E i , and y j (E) represents the yield of continuous radiation per nuclear transformation with energy between E and E + dE . This total summation is over all electron and photon radiation. Dose coefficients for photon irradiation for 137 Cs, 137m Ba, 95 Zr, 95 Nb, 144 Ce, 144 Pr, 106 Ru, 106 Rh, and 91 Y were provided as these radionuclides are the most prominent with respect to external exposures along the Techa River. It is important to note that the values obtained from Equation 2 2 are the spectrum weighted dose coefficients for the single radionuclide whose decay information is used, not the subsequent daughter radionuclides from fu rther decays. As an example, using 137 Cs decay data provides the spectrum weighted dose coefficient for 137 Cs. However, the most prominent gamma component from 137 Cs is a 662 keV photon that is released by its daughter , 137m Ba. Consequently, the most pr udent application of these dose coefficients would be combining the calculated spectrum weighted dose coefficients and utilizing the decay schemes and branching fractions of particular radionuclides along with the spectrum weighted dose coefficients of its daughter radionuclides. However, in this paper, only the single radionuclide spectrum weighted dose coefficients are provided.

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40 Table 2 1 . Standing heights and weights for IAEA Reference Asian Man (RAM) and ICRP Reference Man (IAEA 1998, ICRP 2002) . Age RAM Height (cm) ICRP 89 Height (cm) RAM/ICRP Height RAM Weight (kg) ICRP 89 Weight (kg) RAM/ICRP Weight 30M 167 176 0.949 58 73 0.795 30F 155 163 0.951 50 60 0.833 15M 161 167 0.964 48 56 0.857 15F 153 161 0.950 45 53 0.849 10M 133 138 0.964 28 32 0.875 10 F 130 138 0.942 26 32 0.813 0 5 M 108 109 0.991 17 19 0.895 0 5 F 107 109 0.982 16 19 0.842 0 1 M 74 76 0.974 8.7 10 0.870 0 1 F 73 76 0.961 8.4 10 0.840 Table 2 2 . Elemental composition of air (Eckerman and Ryman 1993) . Element Atomic Number Mass Fraction H 1 0.00064 C 6 0.00014 N 7 0.75086 O 8 0.23555 Ar 18 0.01281 Table 2 3 . Elemental composition of UTR soil, MLTR soil, and FGR 12 soil (Eckerman and Ryman 1993, Degteva et al. 2011) . Element Atomic Number UTR Mass Fraction MLTR Mass Fraction FGR 12 Soil M ass Fraction H 1 0.0296 0.0235 0.021 C 6 0.0154 0.0166 0.016 N 7 0.0008 0.0008 O 8 0.5819 0.5590 0.577 Na 11 0.0046 0.0050 Mg 12 0.0046 0.0050 Al 13 0.0547 0.0586 0.050 Si 14 0.2541 0.2731 0.271 P 15 0.0006 0.0007 S 16 0.0006 0.0007 K 19 0.0100 0.0107 0.013 Ca 20 0.0100 0.0107 0.041 Ti 22 0.0035 0.0038 Mn 25 0.0006 0.0007 Fe 26 0.0285 0.0306 0.011 Ba 56 0.0004 0.0004

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41 Table 2 4 . X, Y, Z voxel resolution used in voxelization of Asian scaled phantoms. Age/ Gender X (cm) Y (cm) Z (cm) 01MF 0.0663 0.0663 0.1400 05MF 0.0850 0.0850 0.1928 10MF 0.0990 0.0990 0.2425 15M 0.1250 0.1250 0.2832 15F 0.1200 0.1200 0.2828 30M 0.1580 0.1580 0.2207 30F 0.1260 0.1260 0.2700 Table 2 5 . Organs investigated for both male and female phantoms of different ages. Organs 30M , 15M, 10M, 05M 30F, 15F, 10F,05F 01M 01F Esophagus x x x x Stomach Wall x x x x Small Intestine Wall x x x x Lungs x x x x Liver x x x x Kidneys x x x x Pancreas x x x x Urinary Bladder Wall x x x x Spleen x x x x Adrenals x x x x Thymus x x x x Thyroid x x x x Brain x x x x Skin x x x x Dentin x x Enamel x x Right Colon Wall x x x x Left Colon Wall x x x x Rectosigmoid x x x x Breast x x x x Testes x x Ovaries x x Uterus x x Active Marrow x x x x Shallow Marrow x x x x

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42 A B Figure 2 1. Side views of the Asian scaled phantoms. A) Male Asian scaled phantoms (30M, 15M, 10M, 05M, and 01M left to right), B) Female Asian scaled phantoms (30F, 15F, 10F, 05F, and 01F left to right). Figure 2 2 . Visualization of voxelized skull anatomy for the Asian scaled adult male phantom showing the del ineation of dentin and enamel layers for the teeth.

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43 CHAPTER 3 RESULTS AND DISCUSSION Monoenergetic Photon Organ Dose Coefficients With the multitude of parameters studied, it would not be prudent to show data for all organs investigated in this study. Con sequently, the fig ures comparing the data for the monoenergetic photon organ dose coefficients in this document are for the liver unless otherwise specified . In the following figures, acronyms are frequently utilized in is for the Asian the data is for the ORN L stylized phantoms. When subscripts are utilized, the number can be seen in the following figures that the data for the stylized phantoms do not contain subscripts with regards to gender because the phantoms are hermaphroditic. Figure 3 1 show s monoenergetic photon dose coefficients for surface deposition (0 cm) in the adult Asian scaled male, adult Asian scaled female, and ORNL adult stylized phantoms for UTR soil, MLTR soil, and FGR 12 soil as a function of source energy. Figures 3 2 through 3 5 show the same data for the 15 year old, 10 year old, 5 year old, and 1 year old phantoms , respectively. Figures 3 1 through 3 5 show good agreement between genders for th e Asian scaled phantoms . As expected, the monoenergetic photon dose coefficients for the Asian scaled phantoms are greater than those for the stylized phantoms. The stylized phantoms are intended to represent a n ICRP reference individual and contain more adipose/skeletal muscle than the Asian scaled phantoms. This additional adipose/skeletal muscle provides more shielding for the internal organs and yields lower dose coefficients for the stylized phantoms

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44 (Eckerman and Ryman 1993) . Additionally, one can see the effect of different soils for the surface deposition scenario is negligible because the source sits atop the soil at the air ground interface and therefore experiences no attenuation with in the soil. The effect of soil composition and soil density on the organ dose coefficients is discussed later in this section. Figure s 3 6 and 3 7 show the age dependence of the monoenergetic dose coefficients for surface deposition in both the Asian scaled male and female phantoms for UTR soil, MLTR soil, and FGR 12 soil as a function of source energy. As phantom age increases, the do se coefficient decreases. This disparity occurs because as the phantom age increases, both height and chest circumference of the phantom increases. If a taller phantom is placed inside the coupling cylinder, one would expect the dose coefficient to decre ase because the organ of interest is now positioned further from the photon source. As explained before, a smaller chest circumference results in a higher dose coefficient due to less shielding by the body. Figures 3 8 and 3 9 show the age dependence of the monoenergetic dose coefficients for a 1 cm uniformly distributed source in both the Asian scaled male and female phantoms for UTR soil, MLTR soil, and FGR 12 soil as a function of source energy. The same trend as in Figures 3 6 and 3 7 is visible as the dose coefficient decreases with increasing phantom age. It should be noted that the monoenergetic dose coefficient decreases by two orders of magnitude between the surface deposition scenario and the 1 cm uniformly distributed source scenario. This o ccurs because the soil is now attenuating the source, and the 1 cm source does not take into account surface deposition of the radionuclide. Therefore, for a complete scenario involving

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45 surface deposition and contamination down to 1 cm, the dose coefficie nts for those two scenarios should be summed. Figures 3 10 compares the monoenergetic dose coefficients for UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male, adult Asian scaled female, and ORNL adult stylized phantoms as a function of t he source energy. Although it can be seen in previous figures, one can see there is little difference between soils for the surface deposition scenario. In the MCNPX input deck, the source was placed at a distance of 1 nm below the soil surface to avoid geometry errors. While this distance could play a small role in the minor differences between the three soils for the surface deposition scenario, the majority of the monoenergetic dose coefficients for the liver in this scenario are within the error prov ided by MCNPX for the surface source scenario (< 1%). Figure 3 11 shows the same data for a 1 cm uniformly distributed source in the soil. In this figure, clear differences between the soils are visible. As expected, UTR soil consistently yielded the hi ghest monoenergetic dose coefficients, followed by MLTR soil and then FGR 12 soil due to differential attenuation between the soils . Since the density of MLTR soil and FGR 12 soil are quite similar, one would expect their curves to remain quite close while the curve representing UTR soil should begin to diverge. Figures 3 12 through 3 14 show the soil dependence of the monoenergetic dose coefficients at multiple phantom ages for Asian scaled male phantoms for surface deposition, 1 cm uniformly distri buted source, and 5 cm uniformly distributed source , respectively . The trend of UTR soil yielding the highest dose coefficients, followed by MLTR soil and FGR 12 soil, was visible in all ages for each phantom data set. In the 5 cm source data set, the ML TR soil dose coefficient periodically increases above the

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46 UTR soil dose coefficient. This consistently occurs at 800 keV and periodically also occurs at 1 MeV. When reviewing t he raw data before integration over the plane source data , the order of the mo noenergetic dose coefficient from highest to lowest was UTR soil, MLTR soil, and FGR 12 soil as expected. Therefore, the integration over the plane source must be the reason for the discrepancy at higher depths. Integration for these data sets was comple ted using spline integration in MATLAB. However, in FGR 12 cubic Hermite spline inte rpolation was utilized for integration over the different plane sources. Cubic Hermite spline interpolation is a more rigorous interpolation technique that attempts to be tter preserve monotonicity over an interval by constructing a piecewise cubic interpolant and produces a smoother curve (Fritsch and Carlson 1980) . Experimenting with this integration technique in MATLAB with the raw data resulted in s moother cu rves. It should also be noted that the dose coefficients for the 5 cm distributed source are greater than the dose coefficients for the 1 cm distributed source. This physically makes sense because more source is being added below the phantom so one would expect the dose coefficients to increase. Figures 3 15 through 3 17 compare the monoenergetic dose coefficients for the liver in the adult Asian scaled male, adult Asian scaled female, and ORNL adult stylized phantoms for a surface deposition, 1 cm distributed source, and 5 cm distributed source to the original data in FGR 12 for UTR soil, MLTR soil, and FGR 12 soil . It should be noted that FGR 12 only considered 12 source energies while 25 source energies have been considered in this study. In Figure 3 15, the dose coefficients from FGR 12 for a surface deposition are consistently greater than the dose coefficients for UTR soil, MLTR soil, and FGR 12 soil. Figure 3 16 shows that for a 1 cm distributed source, the

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47 dose coefficients from FGR 12 are still greater than the dose coefficients using MLTR soil and FGR 12 soil; however, dose coefficients for UTR soil start to dominate dos e coefficients from FGR 12, especially at energies greater than 1 MeV. Figure 3 17 shows that for a 5 cm distributed source, the dose coefficients for UTR soil, MLTR soil, and FGR 12 soil are greater than the dose coefficients from FGR 12 at lower energie s. However, at higher energies (> 2 MeV), the dose coefficients from FGR 12 begin to dominate once again. Additionally, the spikes in organ dose coefficients at 800 keV for MLTR soil can be seen in Figure 3 17. This issue will be addressed in the next c hapter of this document. Figures 3 15 through 3 17 demonstrate that the methods for calculating the dose coefficients yield trends consistent with what was seen in FGR 12. Figure 3 18 compares the organ dose coefficients for enamel, dentin, and liver in t he adult Asian scaled male for UTR soil, MLTR soil, and FGR 12 soil in a surface deposition scenario as a function of source energy. It should be noted that while the source energy in other figures varied from 10 keV to 10 MeV, the source energy in Figure 3 18 varies from 10 keV to 1 MeV to highlight the differences between the three organs. Calculated dose coefficients for enamel and dentin are greater than in the liver due to the density and composition of the organs. The densities of enamel and dentin were taken as 2.9 g cm 3 and 2.5 g cm 3 , respectively , while the density of the liver was taken as 1.05 g cm 3 . Enamel and dentin have elemental compositions with high percentages of calcium which makes their effective atomic number larger than that of soft tissue organs (organs with effective atomic number similar to water). Therefore, one would expect to see much higher dose coefficients in enamel and dentin than in liver at diagnostic x ray energies (approximately 30 keV to 150 keV) because

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48 photoelec tric absorption is proportional to Z 3 E 3 . This can be seen in Figure 3 18. However, at energies beyond the diagnostic x ray range, the E 3 term begins to dominate, and the differences in the dose coefficients of enamel and dentin to liver should reduce. This trend can also be seen in Figure 3 18. The age dependence on the enamel dose coefficient for a surface deposition scenario for UTR soil, MLTR soil, and FGR 12 soil can be seen in Figure 3 19. As phantom age increases, the dose coefficient for the en amel decreases due to increased distance between the source and the enamel. Radionuclide Specific Organ Dose Coefficients 95 Zr spectrum weighted organ dose coefficients for 17 organs in the adult Asian scaled male phantom for a surface deposition, 1 cm di stributed source, and 5 cm distributed source for UTR soil, MLTR soil, and FGR 12 soil normalized to the spectrum weighted organ dose coefficients from FGR 12 are presented in Figures 3 20 through 3 22, respectively. In Figure 3 20 , the percent differenc e between 95 Zr organ dose coefficients for the adult Asian scaled male data and FGR 12 data for a surface source ranged from approximately 16% to 5%. The majority of the percent differences ranged from approximately 5% to 5%, with the sole outlier being the dose coefficient for the shallow marrow. It will be shown in this section that this trend with the shallow marrow is seen in all spectrum weighted dose coefficient data sets. One would expect the percent differences of the Asian scaled dose coeffici ents relative to FGR 12 to be quite close for surface deposition because differences in soil attenuation characteristics are not taken into accou nt.

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49 In Figure 3 21, the percent difference between 95 Zr organ dose coefficients for a 1 cm distributed source ranged from approximately 25% to 12%. For the 1 cm source, the difference in soil attenuation is visible. For each organ, UTR soil provides a greater dose coefficient than MLTR soil or FGR 12 soil. Figure 3 22 shows the same data for the 5 cm distribu ted source. For the 5 cm source, the percent difference between 95 Zr organ dose coefficients and FGR 12 organ dose coefficients ranged from approximately 5% to 45%. Contrary to what was expected, the 5 cm source yielded higher organ dose coefficients fo r MLTR soil than for UTR soil or FGR 12 soil. This can be explained by studying the decay spectrum for 95 Zr. The primary photon components of 95 Zr spectrum are 756 keV and 724 keV gamma rays occurring at 54.4% and 44.3%, respectively. The e nergies of th ese gamma rays lie in the middle of the quick spike in the organ dose coefficients occurring around 800 keV for the 5 cm distributed source in MLTR soil referenced in Figures 3 14 and 3 17. 95 emission to 95 Nb. 95 Nb spectrum weighted organ dose coefficients for 17 organs in the adult Asian scaled male phantom for a surface deposition, 1 cm distributed source, and 5 cm distributed source for UTR soil, MLTR soil, and FGR 12 soil normalized to the spectrum weighted or gan dose coefficients from FGR 12 are presented in Figures 3 23 through 3 25 , respectively. Similar trends are seen in the 95 Nb spectrum weighted dose coefficients as in the 95 Zr spectrum weighted dose coefficients. The percent differences ranged from ap proximately 15% to 7%, 25% to 12%, and 3% to 45% for the surface source, 1 cm source, and 5 cm sources, respectively. For the surface source, the differences in the organ dose coefficients are relatively negligible and can be attributed to statistical variations. UTR soil yields higher

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50 organ dose coefficients for the 1 cm source, while MLTR soil yields higher organ dose coefficients for the 5 cm source. Investigation of the 95 Nb decay scheme shows that primary photon component is a 766 keV gamma ray oc curring at 99.8%. This energy is in the energy range of the spike in the organ dose coefficients occurring around 800 keV for the 5 cm distributed source in MLTR soil. Figures 3 26 through 3 28 display 137m Ba spectrum weighted organ dose coefficients for 17 organs in the adult Asian scaled male phantom for a surface deposition, 1 cm distributed source, and 5 cm distributed source for UTR soil, MLTR soil, and FGR 12 soil normalized to the spectrum weighted organ dose coefficients from FGR 12. As with previ ous radionuclides, Figure 3 26 shows that differences in organ dose coefficients between soils for the surface deposition scenario are visible. However, these differences are small and can mostly be attributed to the statistical nature of the simulations. A few of the organs (e.g. adrenals) show larger differences between the soils for a surface source. This is a consequence of the size of the organs as smaller organs deeper in the body will have worse statistics associated with their dose coefficients. For the 1 cm source displayed in Figure 3 27 , the order of the organ dose coefficients from highest to lowest is UTR soil, MLTR soil, and FGR 12 soil as expected. In Figure 3 28, f or the 5 cm source, this order from highest to lowest continues with the e xception of a few outliers (i.e. shallow marrow, adrenals, and bladder). The primary photon component for 137m Ba is a 662 keV gamma ray at 89.7 % frequency. For this reason, one does not see the abnormal spikes in MLTR soil for 137m Ba because 662 keV is f urther away from the spike in dose coefficients around 800 keV. However, since

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51 these organ dose coefficients are interpolated based on the radionuclide energy, the spike at 800 keV may still be affecting the organ dose coefficients for 137m Ba and artifici ally increasing the organ dose coefficients . The percent difference in the organ dose coefficients ranged from approximately 17% to 8%, 27% to 12%, and 3% to 40% for the surface source, 1 cm source, and 5 cm source, respectively. 144 Ce spectrum weig hted organ dose coefficients for 17 organs in the adult Asian scaled male phantom for a surface deposition, 1 cm distributed source, and 5 cm distributed source for UTR soil, MLTR soil, and FGR 12 soil normalized to the spectrum weighted organ dose coeffic ients from FGR 12 are presented in Figures 3 29 through 3 31, respectively. The percent differences for the organ dose coefficients to those from FGR 12 ranged from approximately 22% to 10%, 22% to 12%, and 20% to 50% for the surface source, 1 cm sourc e, and 5 cm source, respectively, with the exception of the shallow marrow. The shallow marrow ranged from approximately 65% to 59%, 65% to 57%, and 55% to 40% for the surface source, 1 cm source, and 5 cm source, respectively. For the 1 cm and 5 c m distributed sources, UTR soil organ dose coefficients dominate MLTR soil and FGR 12 organ dose coefficients. There are no issues with the dose coefficient spike at 800 keV in this data set because all photon emissions by 144 Ce are well below 800 keV. Th e most prominent photon component of the 144 Ce decay scheme is a 133.5 keV gamma ray occurring at 11.1% frequency. 144 emission to 144 Pr. 144 Pr spectrum weighted organ dose coefficients for 17 organs in the adult Asian scaled male phantom f or a surface deposition, 1 cm distributed source, and 5 cm distributed source for UTR soil, MLTR soil, and FGR 12 soil normalized to the spectrum weighted organ dose coefficients from

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52 FGR 12 are presented in Figures 3 32 through 3 34, respectively. The tr ends for expected differential soil attenuation are visible in the data for 144 Pr. The percent differences in the organ dose coefficients varied from approximately 45% to 24% for surface deposition, 50% to 17% for a 1 cm distributed source, and 35% to 12% for a 5 cm distributed source. While differences in organ dose coefficients between those in this study and those in FGR 12 can often be attributed to difference between phantoms, often the differences comes from updates in the decay schemes for t he radionuclides themselves. FGR 12 utilized ICRP Publication 38 (1983) while this study utilizes ICRP Publication 107 (2007) . Many of the radionuclide decay schemes have been updated since ICRP 38. As an example, Table 3 1 shows the gamma ray componen ts to the photon spectrum in ICRP 38 and ICRP 107 for 144 Pr. 144 Pr had 10 gamma rays contributing to the photon spectrum ranging from 625 keV to 2.65 MeV in ICRP 38 (ICRP 1983) . In ICRP 107, 144 Pr has 16 gamma rays contributing to the photon spectrum ranging from 625 keV to 2.65 MeV; however, the yield for gamma rays common to both spectrums were greater in ICRP 38 and the additional gamma rays included in ICRP 107 occur with low frequency and have a low effect on the dose coefficient (ICRP 2008) . The three largest yields for 144 Pr come from photons of energies 697 keV, 1.49 MeV, and 2.19 MeV. For the 697 keV photon emission of 144 Pr , the yield was reduced from 1.48% in ICRP 38 to 1.342% in ICRP 107, a 9.32% percent reduction in the yield. For the 1.49 MeV photon, the yield was reduced from 0.3004% to 0.2778%, a 7.52% reduction in the photon yield. Lastly, the 2.19 MeV photon yield was reduced from 0.774% to 0.6938%, a 10.4% reduction in the photon yield. This difference in photon

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53 yields between ICRP 38 and ICRP 107 for 144 Pr accounts for the differences seen between organ dose coefficients in this study and FGR 12 in Figures 3 32 through 3 34 as lower yields for radionuclide photon emissions will r esult in lower dose coefficients . 106 Rh spectrum weighted organ dose coefficients for 17 organs in the adult Asian scaled male phantom for a surface deposition, 1 cm distributed source, and 5 cm distributed source for UTR soil, MLTR soil, and FGR 12 soil n ormalized to the spectrum weighted organ dose coefficients from FGR 12 are presented in Figures 3 35 through 3 37, respectively. The percent differences between the organ dose coefficients for the Asian scaled phantoms and FGR 12 ranged from approximately 25% to 2% for surface deposition, 35% to 8% for a 1 cm distributed source, and 10% to 32% for a 5 cm distributed source. As the depth of the source is increased, UTR soil dose coefficients begin to dominate over MLTR soil and FGR 12 soil dose coeffici ents. Figures 3 38 through 3 40 show the spectrum weighted organ dose coefficients for 17 organs in the adult Asian scaled male phantom for a surface deposition, 1 cm distributed source, and 5 cm distributed source for UTR soil, MLTR soil, and FGR 12 soil normalized to the spectrum weighted organ dose coefficients from FGR 12. The percent differences between the organ dose coefficients for the Asian scaled phantoms and FGR 12 ranged from approximately 65% to 38% for surface deposition, 67% to 32% for a 1 cm distributed source, and 55% to 25% for a 5 cm distributed source. Similar to 144 Pr, 91 Y decay spectrum changed from ICRP 38 to ICRP 107. The primary photon component of its spectrum in ICRP 38 was a 1.2 MeV gamma ray with a 0.32% frequency. In ICR P 107, this frequency is 0.25%, a 28% reduction in the yield from ICRP 38 to ICRP 107.

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54 To compare organ dose coefficients for stylized phantoms to the organ dose coefficients for the Asian scaled phantoms, 137m Ba spectrum weighted organ dose coefficients were utilized. Using monoenergetic dose coefficients for this comparison is not prudent because they are binned by energy and would be difficult to compare while the spectrum weighted dose coefficients are summ ed over the photon spectrum and give a single value for a radionuclide for each organ for any given phantom . Figures 3 41 through 3 45 show the 137m Ba spectrum weighted organ dose coefficients for a certain set of organs for the Asian scaled male, Asian sc aled female, and ORNL stylized phantoms normalized to the organ dose coefficients for the ORNL stylized phantoms for a surface source . Figures 3 41 through 3 45 are for the adult, 15 year old, 10 year old, 5 year old, and 1 year old, respectively. These f igures show that for the majority of organs and ages, the Asian scaled phantoms yield higher dose coefficients than the stylized phantoms. This is expected because of less adipose/skeletal muscle on the phanto ms available as shielding. Taking into accoun t all ages and percent differences, the minimum percent difference between the Asian scaled phantoms and ORNL styli zed phantoms was approximately 5 % and the maximum percent difference was approximately 30%. The largest percent differences were seen in the 1 year old and 5 year old. When scaling the Asian scaled phantoms, these ages were the most problematic as they required the largest downward scaling of the contours. Therefore, one would expect these phantoms to have the largest percent difference with regards to the stylized phantoms as they have significantly less adipose tissue to act as shielding against incoming photons.

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55 Table 3 1 . Comparison of photon spectrum for 144 Pr in ICRP 38 and ICRP 107 (ICRP 1983, ICRP 2008) . Energy (MeV) ICRP 38 Yield (%) ICRP 107 Yield (%) 0.625 0.0013 0.0011 0.675 0.0031 0.0030 0.697 1.4800 1.3420 0.814 0.0036 0.0032 0.864 0.0029 0.0024 1.180 0.0001 1.380 0.0004 1.390 0.0066 0.0067 1.490 0.3004 0.2778 1.560 0.0003 0.0002 1.980 0.0009 2.050 0.0003 2.070 0.0002 2.190 0.7740 0.6938 2.370 0.0002 0.0001 2.650 0.0001

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56 Figure 3 1. Monoenergetic dose coefficients for a source deposited on the soil surface for the liver in the Asian scaled adult male, Asian scaled adult female, and ORNL adult stylized phantoms for A) UTR soil, B) MLTR soil, and C) FGR 12 soil.

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57 Figure 3 2. Monoenergetic dose coefficients for a source deposited on the soil surface for the liver in the Asian scaled 15 year old male, Asian scaled 15 year old female, and ORNL 15 year old stylized phantoms for A) UTR soil, B) MLTR soil, and C) FGR 12 soil.

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58 Figure 3 3. Monoenergetic dose coefficients for a source deposited on the soil surface for the liver in the Asian scaled 10 year old male, Asian scaled 10 year old female, and ORNL 10 year old stylized phantoms for A) UTR soil, B) MLTR soil, and C) FGR 12 soil.

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59 Figure 3 3 . Monoenergetic dose coefficients for a source deposited on the soil surface for the liver in the Asian scaled 5 year old male, A sian scaled 5 year old female, and ORNL 5 year old stylized phantoms for A) UTR soil, B) MLTR soil, and C) FGR 12 soil.

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60 Figure 3 4 . Monoenergetic dose coe fficients for a source deposited on the soil surface for the liver in th e Asian scaled 1 year old male, Asian scal ed 1 year old female, and ORNL 1 year old stylized phantoms for A) UTR soil, B) MLTR soil, and C) FGR 12 soil.

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61 Figure 3 5 . Age dependence of the monoenergetic dose coefficients for a s ource deposited on the soil surface for the liver in the Asian scaled male phantoms for A) UTR soil, B) MLTR soil, and C) FGR 12 soil.

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62 Figure 3 6 . Age dependence of the monoenergetic dose coefficients for a source deposited on the soil surface for the liver in the Asian scaled female phantoms for A) UTR soil, B) MLTR soil, and C) FGR 12 soil.

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63 Figure 3 8. Age dependence of the monoenergetic dose coefficients for a 1 cm uniformly distributed source for the liver in the As ian scaled male phantoms for A) UTR soil, B) MLTR soil, and C) FGR 12 soil.

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64 Figure 3 9. Age dependence of the monoenergetic dose coefficients for a 1 cm uniformly distributed source for the liver in the Asian scaled female phantoms for A) UTR soil, B) MLTR soil, and C) FGR 12 soil.

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65 Figure 3 10. Soil dependence of the monoenergetic dose coefficients for a source deposited on the soil surface for the liver in the A) Adult male Asian scaled phantom, B) Adult female Asian scaled phantom, C) ORNL adul t stylized phantom.

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66 Figure 3 11. Soil dependence of the monoenergetic dose coefficients for a 1 cm uniformly distributed source for the liver in the A) Adult male Asian scaled phantom, B) Adult female Asian scaled phantom, C) ORNL adult stylized phant om.

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67 Figure 3 12. Soil dependence of the monoenergetic dose coefficients for a source deposited on the soil surface for the liver in the A) Adult male Asian scaled phantom, B) 10 year old male Asian scaled phantom, and C) 1 year old male Asian scaled phantom.

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68 Figure 3 13. Soil dependence of the monoenergetic dose coefficients for a 1 cm uniformly distributed source for the liver in the A) Adult male Asian scaled phantom, B) 10 year old male Asian scaled phantom, and C) 1 year old male Asian scale d phantom.

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69 Figure 3 14. Soil dependence for the monoenergetic dose coefficients for a 5 cm uniformly distributed source for the liver in the A) Adult male Asian scaled phantom, B) 10 year old male Asian scaled phantom, and C) 1 year old male Asian scaled phantom.

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70 Figure 3 15. Comparison of monoenergetic dose coefficients for the liver in the adult Asian scaled male, adult Asian scaled female, and ORNL adult stylized phantoms to those for the liver in FGR 12 (1993) for a source deposited on the soil surface for A) UTR soil, B) MLTR soil, and C) FGR 12 soil.

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71 Figure 3 16. Comparison of monoenergetic dose coefficients for the liver in the adult Asian scaled male, adult Asian scaled female, and ORNL adult stylized phantoms to those for the liver in FGR 12 (1993) for a 1 cm uniformly distributed source in A) UTR soil, B) MLTR soil, and C) FGR 12 soil.

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72 Figure 3 17. Comparison of monoenergetic dose coefficients for the liver in the adult Asian scaled male, adult Asian scaled female, and ORNL adult stylized phantoms to those for the liver in FGR 12 (1993) for a 5 cm uniformly distributed source in A) UTR soil, B) MLTR soil, and C) FGR 12 soil.

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73 Figure 3 1 7 . Comparison of monoenergetic dose coefficients for enamel, dentin, and liver in the adult Asian scaled male phantom for a source deposited on the soil surface for A) UTR soil, B) MLTR soil, C) FGR 12 soil.

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74 Figure 3 19. Age dependence of the monoenergetic dose coefficients for enamel in adult Asian scaled male, 15 year old Asian scaled male, 10 year old Asian scaled male, and 5 year old Asian scaled male phantoms for a source deposited on the soil surface for A) UTR soil, B) MLTR soil, C) FGR 12 soil.

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75 Figure 3 20. 95 Zr spectrum weighted do se coefficients for a source deposited on the surface for UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 95 Zr spectrum weighted dose coefficients from FGR 12 (1993). Figure 3 21. 95 Zr spectrum weighted dose coefficie nts for a 1 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 95 Zr spectrum weighted dose coefficients from FGR 12 (1993).

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76 Figure 3 22. 95 Zr spectrum we ighted dose coefficients for a 5 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 95 Zr spectrum weighted dose coefficients from FGR 12 (1993). Figure 3 23. 95 Nb spectrum weighted dose coefficients for a source depos ited on the surface for UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 95 Nb spectrum weighted dose coefficients from FGR 12 (1993).

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77 Figure 3 24. 95 Nb spectrum weighted dose coefficients for a 1 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 95 Nb spectrum weighted dose coefficients from FGR 12 (1993). Figure 3 25. 95 Nb spectrum we ighted do se coefficients for a 5 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 95 Nb spectrum weighted dose coefficients from FGR 12 (1993).

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78 Figure 3 26. 137m Ba spectrum weighted dose coeff icients for a source deposited on the surface for UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 137m Ba spectrum weighted dose coefficients from FGR 12 (1993). Figure 3 27. 137m Ba spectrum weighted dose coefficients for a 1 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 137m Ba spectrum weighted dose coefficients from FGR 12 (1993).

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79 Figure 3 28. 137m Ba spectrum weighted do se coefficients for a 5 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 137m Ba spectrum weighted dose coefficients from FGR 12 (1993). Figure 3 29. 144 Ce spectrum weighted dose coefficients for a source d eposited on the surface for UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 144 Ce spectrum weighted dose coefficients from FGR 12 (1993).

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80 Figure 3 30. 144 Ce spectrum weighted dose coefficients for a 1 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 144 Ce spectrum weighted dose coefficients from FGR 12 (1993). Figure 3 31. 144 Ce spectrum we ighted dose coefficients for a 5 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 144 Ce spectrum weighted dose coefficients from FGR 12 (1993).

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81 Figure 3 32. 144 Pr spectrum weighte d dose coefficients for a source deposited on the surface for UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 144 Pr spectrum weighted dose coefficients from FGR 12 (1993). Figure 3 33. 144 Pr spectrum weighted dose coefficients for a 1 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 144 Pr spectrum weighted dose coefficients from FGR 12 (1993).

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82 Figure 3 34. 144 Pr spectru m we ighted dose coefficients for a 5 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 144 Pr spectrum weighted dose coefficients from FGR 12 (1993). Figure 3 35. 106 Rh spectrum weighted dose coefficients for a source deposited on the surface for UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 106 Rh spectrum weighted dose coefficients from FGR 12 (1993).

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83 Figure 3 36. 106 Rh spectrum weighted dose co efficients for a 1 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 106 Rh spectrum weighted dose coefficients from FGR 12 (1993). Figure 3 37. 106 Rh spectrum we ighted dose coefficients for a 5 cm uniformly distributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 106 Rh spectrum weighted dose coefficients from FGR 12 (1993).

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84 Figure 3 38. 91 Y spectrum weighted dose coefficients for a sou rce deposited on the surface for UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 91 Y spectrum w eighted dose coefficients from FGR 12 (1993). Figure 3 39. 91 Y spectrum weighted dose coefficients for a 1 cm uniformly dis tributed source in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 91 Y spectrum weighted dose coefficients from FGR 12 (1993).

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85 Figure 3 40. 91 Y spectrum we ighted dose coefficients for a 5 cm uniformly distributed sou rce in UTR soil, MLTR soil, and FGR 12 soil for the adult Asian scaled male normalized to 91 Y spectrum weighted dose coefficients from FGR 12 (1993). Figure 3 41. Adult Asian scaled male, adult Asian scaled female, and ORNL adult stylized phantom organ dose coefficients normalized to the organ dose coefficients for the ORNL adult stylized phantom for a surface deposition on FGR 12 soil spectrum weighte d for 137m Ba.

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86 Figure 3 42. 15 year old Asian scaled male, 15 year old Asian scaled female, and ORNL 15 year old stylized phantom organ dose coefficients normalized to the organ dose coefficients for the ORNL 15 year old stylized phantom for a surface deposition on FGR 12 soil for 137m Ba. Figure 3 43. 10 year old Asian scaled male, 10 year old Asian scaled female, and ORNL 10 year old stylized phantom organ dose coefficients normalized to the organ d ose coefficients for the ORNL 10 year old stylized phantom for a surface deposition on FGR 12 soil 137m Ba .

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87 Figure 3 44. 5 year old Asian scaled male, 5 year old Asian scaled female, and ORNL 5 year old stylized phantom organ dose coefficients normalized to the organ d ose coefficients for the ORNL 5 y ear old stylized phantom for a surface deposition on FGR 12 soil 137m Ba . Figure 3 45. 1 year old Asian scaled male, 1 year old Asian scaled female, and ORNL 1 year old stylized phantom organ dose coefficients normalized to the organ dose coefficients fo r the ORNL 1 year old stylized phantom for a surface deposition on FGR 12 soil 137m Ba .

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88 CHAPTER 4 CONCLUSIONS AND FUTURE WORK Conclusions Organ dose coefficients were calculated for adult, 15 year old, 10 year old, 5 year old, and 1 year old Asian scaled male, Asian scaled female, and ORNL stylized phantoms using UTR soil, MLTR soil, and FGR 12 soil. Organ dose coefficients were calculated for 23 organs and 24 organs in the adult, 15 year old, 10 year old, and 5 year old male and female phantoms, respectively. Organ dose coefficients were calculated for 21 organs and 22 organs in the 1 year old male an d female phantoms, respectively . A tot al of 25 source energies from 10 keV to 10 MeV were utilized in this study to allow for accurate integration over the decay schemes for radionuclide specific organ dose coefficients. Sources were infinite plane sources in the ground at depths of 0, 0.04, 0.2, 1.0, 2.5, and 4.0 mean free paths (at the source energy in the soil of interest) to allow for accurate integration to a specified depth in the soil. The use of Asian scaled and stylized phantoms yielded similar results to FGR 12 organ dose coefficient s. FGR 12 only considered an adult stylized phantom, so benchmarking the data in this study with FGR 12 was completed using the adult Asian scaled male, adult Asian scaled female, and the ORNL adult stylized phantom. Data for the Asian scaled phantoms an d the stylized phantoms were found to follow the same trends. With regards to soil attenuation, organ dose coefficients were found to follow the expected trends, with the lowest density soil (UTR soil) yielding the highest organ dose coefficients and the highest density soils (MLTR soil, FGR 12 soil) yielding the lowest organ dose coefficients. This trend deviated when spectrum weighting for certain radionuclides at deeper depths (i.e. 95 Zr, 95 Nb) because of an unexpected spike

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89 in the organ dose coefficie nts around 800 keV. The method of integrating over the plane sources is the expected reasoning for this disconnect Overall, this study shows there is a clear dependence on the soil density for sources distributed at different depths in the soil. However , the greatest difference between spectrum weighted do se coefficients of different soi l s was approximately 25%. Therefore, while the soil density and composition clearly has an effect on the organ dose coefficient, it would be prudent to discuss whether o r not the additional accuracy from changing the soil composition and density is necessary. This is especially true considering the majority of soils are closer to a density of 1.6 g cm 3 of FGR 12 soil rather than the 1.0 g cm 3 of UTR soil. Future Work U F/NCI Phantom Library Reference Phantoms The next step of this project is to calculate organ dose coefficients for the adult, 15 year old, 10 year old, 5 year old, and 1 year old reference phantoms on the UF/NCI phantom library. After completion of these organ dose coefficients, organ dose coefficients will have been calculated for stylized reference phantoms, hybrid reference phantoms, and scaled hybrid phantoms. This data set will allow for quantifying differences between stylized reference phantoms and hybrid reference phantoms along with investigating differences in phantom variation with the availability of the Asian scaled phantom data. Integration of Plane Sources When completing the organ dose coefficients for the reference phantoms, cubic Hermite spline interpolation will be utilized in MATLAB. The reasoning for this is to

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90 eliminate the awkward spikes in the organ dose coefficients for larger soil sources at deeper depths. Integration for Techa River Depth Profiles When providing data in our final report, instead of integration from 0 5 cm, organ dose coefficients will be integrated over 2 cm increments from 0 20 cm. This will reduce the amount of time for interpolation and allow for more precise numerical integration. In this study, trapezoidal numerical integration was used with increments of 0.001 spacing. The spacing of the increments can be reduced further for enhanced accuracy with smaller integration bounds.

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91 LIST OF REFERENCES Akleyev AV, Kostyuchenko VA, Peremyslova LM , Baturin VA, Popova IY. Radioecological impacts of the techa river contamination. Health Physics 79: 36 47; 2000. BEIR. Health risks from exposure to low le vels of ionizing radiation: BEIR VII P hase 2. National Research Council, Washington D.C.; 2005. Bolch WE, Lee C, Wayson M, Johnson P. Hybrid computational phantoms for medical dose reconstruction. Radiation Environmental Biophysics 49: 155 168; 2010. Cristy M. Mathematical phantoms representing children of various ages for use in estimates of internal dose. ORNL/NUREG/TM 357. Oak Ridge, TN: Oak Ridge National Laboratory; 1980. Cristy M, Eckerman KF. Specific absorbed fractions of energy at various ages from internal photon sources. ORNL/TM 8381/V1. Metabolism and Dosimetry Research Group, Heal th and Safety Research Division, Oak Ridge National Laboratory, Oak Ridge, TN; 1987. Degteva M, Anspaugh L, Napier B. Enhancements in the techa river dosimetry system. U.S. Department of Energy; 2009. Degteva MO, Kozheurov VP, Tolstykh EI, Vorobiova MI, Anspaugh LR, Napier BA. The techa river dosimetry system: Dose reconstruction for population risk analysis. 2000. Degteva MO, Shagina NB, Vorobiova MI, Shishkina EA, Peremyslova LM, Tokareva EE, Anspaugh LR, Napier BA. Individualization and validation of external doses for individuals who lived in the upper techa river villages. US Russian Joint Coordinating Committee on Radiation Effects Research Project 1.1; 2011. Degteva MO, Tolstykh EI, Vorobiova MI, Shagina NB, Shishkina EA, Bougrov NG, Anspaugh LR, Napier BA. Techa river dosimetry system: Current status and the future. Radiation Safety Problems (Mayak Production Association Scientific Journal): 66 80; 2006. Eckerman KF, Ryman JC. External exposure to radionuclides in air, water, and soil. Oak Ridge National Laboratory, Oak Ridge, TN: U.S. Environmental Protection Agency; Federal Guidance Report No. 12, EPA 402 R 93 081; 1993. Fritsch FN, Carlson RE. Monotone piecewise cubic interpolation. Society for Industrial and Applied Mathematics Journal on Numerical Analysis 17: 238 246; 1980.

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92 Geyer AM, O'Reilly S, Lee C, Long DJ, Bolch WE. The uf/nci family of hybrid computational phantoms representing the current u.S. Population of male and female children, adolescents, and adults applications to ct do simetry. Physics in Medicine and Biology; in press. Hall EJ, Giaccia AJ. Radiobiology for the radiologist. 7th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2012. Han EY, Bolch WE, Eckerman KF. Revisions to the ornl series of adult and pediatric c omputational phantoms for use with the mird schema. Health Physics 90: 337 356; 2006. Hurtado JL, Lee C, Lodwick D, Goede T, Williams JL, Bolch W, E. Hybrid computational phantoms representing the reference adult male and adult female: Construction and ap plications for retrospective dosimetry. Health Physics 102: 292 304; 2012. IAEA. Compilation of anatomical, physiological, and metabolic characteristics for reference asian man. IAEA TECDOC 1005 Volume 1: Data summary and conclusions: 1 116; 1998. IAEA. Use of electron paramagnetic resonance dosimetry with tooth enamel for retrospective dose assessment. IAEA TECDOC 1331: 1 64; 2002. ICRP. Radionuclide transformations energy and intensity of emissions. ICRP Publication 38 Ann ICRP 11 13; 1983. ICRP. Ba sic anatomical and physiological data for use in radiological protection reference values. ICRP Publication 89 Ann ICRP 32 (3 4): 1 277; 2002. ICRP. Nuclear decay data for dosimetric calculations. ICRP Publication 107 Ann ICRP 38 (3): 1 119; 2008. Kossen ko MM, Degteva MO, Vyushkova OV, Preston DL, Mabuchi K, Kozheurov VP. Issues in the comparison of risk estimates for the population in the techa river region and atomic bomb survivors. Radiation Research 148: 54 63; 1997. Lee C, Lodwick D, Hasenauer D, Wi lliams JL, Lee C, Bolch WE. Hybrid computational phantoms of the male and female newborn patient: Nurbs based whole body models. Physics in Medicine and Biology 52: 3309 3333; 2007. Lee C, Lodwick D, Hurtado J, Pafundi D, Williams JL, Bolch WE. The uf fam ily of reference hybrid phantoms for computation radiation dosimetry. Physics in Medicine and Biology 55: 339 363; 2010.

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93 Lee C, Lodwick D, Williams JL, Bolch WE. Hybrid computational phantoms of the 15 year male and female adolescent: Applications to ct o rgan dosimetry for patients of variable morphometry. Medical Physics 35: 2366 2382; 2008. Mokorov Y, Glagolenko Y, Napier B. Reconstruction of radionuclide contamination of the techa river caused by liquid waste discharge from radiochemical production at the mayak production association. Health Physics 79: 15 23; 2000. Petoussi Henss N, Schlattl H, Zankl M, Endo A, Saito K. Organ doses from environmental exposures calculated using voxel phantoms of adults and children. Physics in Medicine and Biology 57: 5679 5713; 2012. Seligman PJ. The u.S. russian radiation health effects research program in the southern urals. Health Physics 79: 3 8; 2000. Snyder WS, Ford MR, Warner GG. Mird pamphlet no. 5, revised: Estimates of specific absorbed fractions for photon source uniformly distributed in various organs of a heterogeneous phantom. Journal of Nuclear Medicine: 5 67; 1978. Vestad TA, Malinen E, Olsen DR, Hole EO, Sagstuen E. Electron paramagnetic resonance ( EPR ) dosimetry using lithium formate in radiotherapy : Comparison with thermoluminescence (tl) dosimetry using lithium fluoride rods. Physics in Medicine and Biology 49: 4701 4715; 2004.

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94 BIOGRAPHICAL SKETCH Bryan Schwarz was born in Miami, Florida to Stephen and Ileana Schwarz. Until college, Bryan had lived his entire childhood in Key Largo, FL, the first island of the Florida Keys, a small island chain off the southern peninsula of Florida. He graduated f rom Coral Shores High School in Tavernier, FL in the spring of 2007 and began attending classes at the University of Florida in the fall of 2007. Bryan graduated cum laude with his B.S. in Nuclear Engineering from the University of Florida in December 201 1. Currently , he is completing his M.S. in biomedical engineering with a specialty in m edi c al p hysics at the University of Florida and has plans on continui ng on to complete his Ph.D. in medical p hysics at the University of Florida. Bryan maintains a s teady life outside of school, participating extensively in intramural sports with members of the Medical Physics department in flag football and basketball leagues. Dating back to elementary school, Bryan has been active in many sports including baseball, basketball, tennis, racquetball, football, and golf. While he enjoys playing all sports, his true love is golf, as he can be seen at the local golf courses three to four times a week on the driving range working on his golf swing. While many enjoy trave ling far distances, Bryan prefers to simply make the six hour drive back home to Key Largo from Gainesville and spend multiple days with his parents and his dogs. When home, he and his parents will spend most days fishing and lobstering on the reef. His parents have been instrumental in his life, standing beside him and providing unwavering support in all his endeavors. Stephen and Ileana made an effort early to bas eball practice or an event or much greater magnitude such as college graduation, his parents were there at every important moment in his life. This work is for them.