Table Of ContentNCRP REPORT No. 94
Exposure of the Population
in the United States and
Canada from Natural
Background Radiation
Recommendations of the
NATIONAL COUNCIL ON RADIATION
PRO'TECTION AND MEASUREMENTS
Issued December 30,1987
First Reprinting September 30, 1992
Second Reprinting August 15, 1998
National Council on Radiation Protection and Measurements
7910 WOODMONT AVENUEIBethesda, MD 20814
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Library of Congress Cataloging-in-Publication Data
Exposure of the population in the United States and Canada from natural bac~ground
radiation.
(NCRP report ; no. 94)
Bibliography: p.
Includes index.
1. Radiation, Background-United States-Measurement. 2. Radioactive pollution-
United States. 3. Radiation-Dosage. I. National Council on Radiation Protection and
Measurements. 11. Series.
RA.569.E97 1987 363.1'79 87-24688
ISBN 0-913392-93-6
Copyright O National Council on Radiation
Protection and Measurements 1987
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Preface
The NCRP has long recognized the need for a clear assessment of
the magnitude of doses from various sources of radiation to which the
population of the U.S. is exposed. In anticipation of the need to gather
basic data for input into this process five assessment committees, each
addressing a different source category, were established in 1971. NCRP
reports assessing exposures from natural background and from con-
sumer products were produced (NCRP, 1975a; 1977).
In 1985, the NCRP reconsidered its overall effort in this area and,
with the further support and stimulation of the Committee on Inter-
agency Radiation Research and Policy Coordination (Office of Science
and Technology Policy, Executive Office of the President of the United
States), undertook to evaluate the exposure of the U.S. population
from all sources. This resulted in the reconstitution of an NCRP
committee to re-assess the radiation exposure of the population from
natural background radiation. The present report updates and
supersedes NCRP Report No. 45 (NCRP, 1975a) and includes the
absorbed doses to the population due to radiation from cosmic sources,
radionuclides in the earth, internally deposited radionuclides, inhaled
radioactivity and fallout from nuclear weapons tests. Notable additions
to the earlier report are an emphasis on the radon contribution to
population exposures and the inclusion of Canadian data. This report
represents one important source of information for the overall sum-
mary effort, NCRP Report No. 93, Ionizing Radiation Exposure of the
Population of the United States.
In general, the International System of Units (SI) is used in this
report followed by conventional units in parentheses in accordance
with the procedure set forth in NCRP Report No. 82, SI Units in
Radiation Protection and Measurements. However, some figures which
were taken from the previously published NCRP Report No. 45,
Natural Background Radiation in the United States, are presented in
their original format using conventional units.
iii
iv / PREFACE
This report was prepared by the Council's Scientific Committee 43
on Natural Background Radiation. Serving on the Committee during
the preparation of this report were:
John H. Harley, Chairman
Hoboken, New Jersey
Richard B. Holtzman Wayne M. Lowder
U.S. Nuclear Regulatory Commission U.S. Department of Energy
Glen Ellyn, Illinois New York, New York
Allan B. Tanner Ned A. Wogman
U.S. Geological Survey Battelle Pacific Northwest Labora-
Reston, Virginia tories
Richland, Washington
Dorothy P. Meyerhof
Bureau of Radiation and Medical Devices
Ottawa. Ontario
Bernard S. Pasternack Joseph K. Soldat
New York University Medical Center Battelle Pacific Northwest Labora-
New York, New York tories
Richland, Washington
James A. Young
Battelle Pacific Northwest Laboratories
Fhchland, Washington
Secretariat-Thomas M. Koval
The Council wishes to express its appreciation to the members of the
Committee and reviewers for the time and effort they devoted to the
preparation of this report.
Warren K. Sinclair
President, NCRP
Bethesda, Maryland
9 September 1987
Contents
.
1 Introduction .......................................
1.1 Structure of the Report ........................
1.2 Dosimetric Considerations ......................
1.3 Natural Radiation .............................
1.3.1 Primordial Radionuclides ...............
1.3.2 Cosmogenic Radionuclides ..............
1.3.3 Cosmic Radiation .....................
.
2 Cosmic Radiation ..................................
2.1 Introduction ..................................
2.2 Cosmic-Ray Particle Flux Densities ..............
2.3 Cosmic-Ray Absorbed Dose Rates in Air .........
2.4 Cosmic-Ray Dose Rates in Tissue at Ground
Altitudes ...................................
2.5 Cosmic-Ray Dose Rates in Tissue at Aircraft
Altitudes ...................................
. 2.6 Dose Equivalent Rates from Cosmic Radiation ....
3 Cosmogenic Radioactivity ..........................
3.1 Introduction ..................................
3.2 Atmospheric Production .......................
3.3 Atmospheric Distribution and Transport .........
3.4 Variations in the Average Cosmogenic Radionuclide
Concentrations with Time and Location ........
3.5 Nuclear Weapons Testing ......................
3.6 Releases by Nuclear Reactors ...................
3.7 Terrestrial Distributions .......................
3.8 Dose Estimates ...............................
.
4 Radionuclides in the Earth .........................
4.1 Introduction ..................................
4.2 Primordial Radionuclides ......................
4.2.1 Series Radionuclides ...................
4.2.2 Non-Series Radionuclides ..............
4.2.3 Spontaneous Fission ...................
4.3 Distribution of Natural Terrestrial Radionuclides in
Rocks .......................................
v
v; 1 CONTENTS
4.3.1 Concentration of Radionuclides Within Ig-
neousRocks ........................
4.3.2 Redistribution by Weathering and
Sedimentation ........................
4.3.3 Formation of Sedimentary Rocks ........
4.3.4 Concentrations of Radionuclides in Sedi-
mentary Rocks ......................
4.4 Soil Radioactivity .............................
4.4.1 Distribution of Radioactivity ............
4.4.2 Transfer to Plants .....................
4.4.3 Transfer to the Hydrosphere ............
4.4.4 Transfer to the Atmosphere .............
4.4.5 Radon Entry into Buildings .............
. 4.5 Summary of Major Radionuclide Concentrations . .
5 External Terrestrial Radiation .....................
5.1 Introduction ..................................
5.2 Sources of Terrestrial Exposure .................
5.3 Extercal Exposures Outdoors ...................
5.4 IndoorExposures .............................
5.5 Variations in Terrestrial Radiation ..............
5.5.1 Influence of Soil Moisture ..............
5.5.2 Influence of Snow Cover ................
5.5.3 Annual and Seasonal Variations .........
5.6 Summary of Population Dose Rates .............
.
6 Inhaled Radionuclides .............................
6.1 Introduction ..................................
6.2 Atmospheric Aerosols ..........................
6.3 Uranium. Radium and Thorium .................
6.4 Short-lived Decay Products of Radon ............
6.4.1 Units ................................
6.4.2 Outdoor Air ..........................
6.4.3 Indoor Air ............................
6.5 Lead-210 and Polonium-210 ....................
6.6 Thoron and its Decay Products .................
6.7 Dosimetry ....................................
6.7.1 UraniumT238 and 234. Thorium-230 and
Radium-226 ..........................
6.7.2 Radon and its short-lived decay products .
6.7.3 Lead-210 and Polonium-210 ............
6.7.4 Thorium-232 and Thorium-228 ..........
6.7.5 Thoron and its decay products ..........
. 6.8 Summary ....................................
7 Internally Deposited Radionuclides .................
CONTENTS /
7.1 Introduction ..................................
7.2 Sources ......................................
7.2.1 Diet and Drinking Water ...............
7.2.2 Atmospheric Contribution ..............
7.3 Levels in Tissues ..............................
7.3.1 Potassium-40 and Rubidium-87 .........
7.3.2 Uranium Series .......................
7.3.3 Thorium Series .......................
7.4 Doses to Tissues ..............................
7.4.1 Beta-Gamma Emitters .................
7.4.2 Alpha Emitters .......................
7.4.3 Uranium Seiies .......................
7.4.4 Thorium Series .......................
7.4.5 Summary of Dose Equivalent Rates to
Tissues ............................
.
8 UnusualExposures ................................
8.1 Sites of unusual radiation exposures .............
8.1.1 Denver. CO ...........................
8.1.2 Grand Junction. CO ...................
8.1.3 Uravan. CO ..........................
8.1.4 Phosphate Lands. FL ..................
8.1.5 Butte. MT ............................
8.1.6 The Reading Prong ....................
8.1.7 Port Hope. Ontario ....................
8.1.8 Scarborough. Ontario ..................
8.1.9 Elliot Lake. Ontario ...................
8.2 Summary of Unusual Exposures .................
8.3 Epidemiological Considerations .................
.
9 Summary of Natural Background Exposure .........
9.1 MeanExposures ..............................
9.1.1 Cosmic Radiation .....................
9.1.2 Radiation from Cosmogenic Radionuclides
9.1.3 External Gamma Radiation .............
9.1.4 Inhalation ............................
9.1.5 Radionuclides in the Body ..............
9.1.6 Total ................................
9.2 Variability in Exposure ........................
9.2.1 Cosmic Radiation .....................
9.2.2 Cosmogenic Radionuclides ..............
9.2.3 External Gamma Radiation .............
9.2.4 Inhalation ............................
9.2.5 Radionuclides in the Body ..............
9.2.6 Total Exposure to Natural Background ...
viii / CONTENTS
9.3 International Standard (SI) Units ............... 145
9.4 The Effective Dose Equivalent Concept .......... 146
9.5 Need for Additional Data ....................... 149
.
Appendix A Glossary .................................. 150
.
Appendix B Fallout from Nuclear Weapons Tests ....... 153
References ............................................ 164
The NCRP ............................................. 190
NCRP Publications ...................................... 197
Index 209
1. Introduction
In 1975, the National Council on Radiation Protection and Meas-
urements (NCRP) issued Report No. 45, N~turalB ackground Radia-
tion in the United Stutes (NCRP, 1975a). That report stated that it
resulted from an effort by the NCRP to present a more comprehensive
picture of exposure to natural background radiation in the United
States. The present report is designed to add information developed
in the last decade and to extend the geographic span to include data
from Canada.
Natural radiation and radioactivity in the environment provide the
major source of human radiation exposure. For this reason, natural
radiation is frequently used as a standard of comparison for exposure
to various man-made sources of ionizing radiation. In addition, there
have been many epidemiological studies which have attempted to
relate health effects to exposures from elevated natural radiation as
well as to exposures from medical uses, weapons test fallout and
nuclear power generation. Such epidemiological uses of the data make
it highly desirable to define the average exposures of the population
and to determine the distribution of natural exposures expected under
various conditions.
Summary reports on exposures to natural radiation are available
from a number of sources. The most comprehensive are those prepared
by the United Nations Scientific Committee on the Effects of Atomic
Radiation (UNSCEAR, 1966, 1972, 1977, 1982). Oakley (1972) au-
thored a report "Natural Radiation Exposure in the United States,"
which covered external radiation. This was published by the Environ-
mental Protection Agency (EPA) and was used extensively in the 1975
NCRP report. Also, the Committee on the Biological Effects of Ion-
izing Radiation under the National Academy of Science has included
data on natural background radiation in its 1972 and 1980 reports
(NAS-NRC, 1972,1980).
In the years since the previous NCRP report, it has become apparent
that the inhalation of the short-lived decay products of radon-222
indoors is the most significant source of natural exposure. Also, the
quality factor (Q)f or alpha radiation is generally accepted as 20 at
this time rather than the value of 10 used in 1975. Some additional
information has also become available for other sources, so it appears
that a new summary of natural background is desirable.
1
2 / 1. INTRODUCTION
The present report is intended to give a broad picture of exposure
to natural background radiation. It will include considerable descrip-
tive material in the introductory chapters to aid in understanding
natural background radiation. The data presented will summarize the
available information on the levels of natural radiation in the environ-
ment, the consequent average exposures and radiation doses to the
population and, wherever possible, the distribution or at least the
variability of these factors will be indicated. With such information it
should be possible to estimate the exposures for various population
groups.
As a cautionary note, it must be considered that not all of the
available measured data are of high quality. While there has been an
attempt to be selective, not all of the faulty information can be
objectively discarded. In looking at the recent references, the absence
of valid quality assurance data may be a warning to the reader.
1.1 Structure of the Report
People are subjected to all types of natural radiation in the environ-
ment. As in the previous report, it seems appropriate to divide the
types into two classes, the first arising from terrestrial radioactivity
and the other comprising exposures to radiation from extra-terrestrial
sources. Both of these have an external component of radiation im-
pinging on man from outside the body and an internal component
where radioactive materials are taken into the body by inhalation or
ingestion.
The terrestrial and extra-terrestrial exposures will be described
separately and then brought together to provide the total dose equiv-
alent to man, based on our best estimates of the dose equivalents to a
few of the important body organs. Those considered here, in particular
cases, are the gonads, skeleton, lungs, gastrointestinal tract and thy-
roid. These various doses will be qualified as necessary in the appro-
priate place in the report. The final result will be a tabulation of dose
equivalent rates to the organs described from the various sources of
radiation having a natural origin and an estimate of the total effective
dose equivalent.
Definitions of many technical terms used in this report are given in
the Glossary (Appendix A).
Since this report is one of a group intended to cover all of the
radiation exposures to the population-namely, those arising from
medical uses, occupational exposures, nuclear power production and
