Defense Threat Reduction Agency 

8725 John J. Kingman Road, MSC 6201 

Fort Belvoir, VA 22060-6201 

DTRA-TR-09-15 

Derivation of Effective Resuspension Factors in 

Scenarios for Inhalation Exposure Involving 

Resuspension of Previously Deposited Fallout 

by Nuclear Detonations at Nevada Test Site 

Approved for public release; distribution is unlimited 

November 2009 

 HDTRA1-07-C-0015 

 

 David C. Kocher , et al. 

 Prepared by: 

 SENES Oak Ridge, Inc. 

 102 Donner Drive 

TECHNICAL REPORT

 Oak Ridge, TN 37830

 
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1. REPORT DATE (DD-MM-YYYY)

30-11-2009 

2. REPORT TYPE

Technical report 

3. DATES COVERED (From - To)

5a. CONTRACT NUMBER

HDTRA1-07-C-0015 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

Derivation of Effective Resuspension Factors in Scenarios for 

Inhalation Exposure Involving Resuspension of Previously Deposited 

Fallout by Nuclear Detonations at Nevada Test Site 

5c. PROGRAM ELEMENT NUMBER

139D 

5d. PROJECT NUMBER

CS 

5e. TASK NUMBER

AH 

6. AUTHOR(S)

David C. Kocher, John R. Trabalka, and A. Iulian Apostoaei 

5f. WORK UNIT NUMBER

DH11146 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

SENES Oak Ridge, Inc. 

102 Donner Drive 

Oak Ridge, TN 37830 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)

Defense Threat Reduction Agency 

Nuclear Technologies Directorate 

8725 John J. Kingman Road, STOP 6201 

Fort Belvoir, VA 22060-6201

11. SPONSORING/MONITORING 

AGENCY REPORT NUMBER

DTRA-TR-09-15 

12. DISTRIBUTION AVAILABILITY STATEMENT

Approved for public release; distribution is unlimited. 

13. SUPPLEMENTARY NOTES

14. ABSTRACT

This report presents an evaluation of inhalation doses in scenarios for exposure of military participants at 

atmospheric nuclear-weapons tests at the Nevada Test Site that involved unusually high resuspension of 

radionuclides in previously deposited fallout by the thermal pulse or blast (shock) wave produced in an above-ground 

detonation. The purpose of this evaluation was to determine values of a resuspension factor, defined as the ratio of 

the concentration of resuspended radionuclides in air above ground to the areal concentration on the ground surface, 

that should be assumed in those scenarios to ensure that point estimates of inhalation dose obtained in dose 

reconstruction would be credible upper bounds, i.e., at least upper 95% credibility limits. 

15. SUBJECT TERMS

Nuclear Test Personnel Review, Veterans, Atmospheric Nuclear Weapons Testing, Fallout, Inhalation, Resuspension 

16. SECURITY CLASSIFICATION OF: 19a. NAME OF RESPONSIBLE PERSON 

Dr. Paul K. Blake 

a. EPORT R

U

b.

A TRACT BS

U

c. THIS 

P E AG

U

17. IMITATION 

OF BSTRACT 

 L

 A

UU

18. NUMBER 

OF AGES P

162

19b. TELEPONE NUMBER (Include area code) 

703 767-3384 
CONVERSION TABLE 

Conversion Factors for U.S. Customary to metric (SI) units of measurement. 

MULTIPLY BY TO GET 

 TO GET BY DIVIDE 

meters (m) 

kilo pascal (kPa) 

kilo pascal (kPa) 

meter2

 (m2) 

joule (J) 

joule (J) 

mega joule/m2

 (MJ/m2) 

*giga bacquerel (GBq) 

radian (rad) 

degree kelvin (K) 

joule (J) 

joule (J) 

watt (W) 

meter (m) 

joule (J) 

meter3

 (m3) 

meter (m) 

joule (J) 

Gray (Gy) 

terajoules 

newton (N) 

kilo pascal (kPa) 

newton-second/m2

 (N-s/m2) 

meter (m) 

meter (m) 

meter (m) 

kilogram (kg) 

newton (N) 

newton-meter (N-m) 

newton/meter (N/m) 

kilo pascal (kPa) 

kilo pascal (kPa) 

kilogram (kg) 

kilogram-meter2

 (kg-m

2

) 

kilogram-meter3

 (kg/m3) 

**Gray (Gy) 

coulomb/kilogram (C/kg) 

second (s) 

kilogram (kg) 

kilo pascal (kPa)

1.000 000 x E -10 

1.013 25 x E +2 

1.000 000 x E +2 

1.000 000 x E -28 

1.054 350 x E +3 

4.184 000 

4.184 000 x E -2 

3.700 000 x E +1 

1.745 329 x E -2 

tk

 = (tof + 459.67)/1.8 

1.602 19 x E -19 

1.000 000 x E -7 

1.000 000 x E -7 

3.048 000 x E -1 

1.355 818 

3.785 412 x E -3 

2.540 000 x E -2 

1.000 000 x E +9 

1.000 000 

4.183 

4.448 222 x E +3 

6.894 757 x E +3 

1.000 000 x E +2 

1.000 000 x E -6 

2.540 000 x E -5 

1.609 344 x E +3 

2.834 952 x E -2 

4.448 222 

1.129 848 x E -1 

1.751 268 x E +2 

4.788 026 x E -2 

6.894 757 

4.535 924 x E -1 

4.214 011 x E -2 

1.601 846 x E +1 

1.000 000 x E -2 

2.579 760 x E -4 

1.000 000 x E -8 

1.459 390 x E +1 

1.333 22 x E -1

angstrom 

atmosphere (normal) 

bar 

barn 

British thermal unit (thermochemical) 

calorie (thermochemical) 

cal (thermochemical/cm2

)

curie 

degree (angle) 

degree Fahrenheit 

electron volt 

erg 

erg/second 

foot 

foot-pound-force 

gallon (U.S. liquid) 

inch 

jerk 

joule/kilogram (J/kg) radiation 

 absorbed dose 

kilotons 

kip (1000 lbf) 

kip/inch2

 (ksi) 

ktap 

micron 

mil 

mile (international) 

ounce 

pound-force (lbs avoirdupois) 

pound-force inch 

pound-force/inch 

pound-force/foot2

pound-force/inch2

 (psi) 

pound-mass (lbm avoirdupois) 

pound-mass-foot2

 (moment of inertia) 

pound-mass/foot3

rad (radiation dose absorbed) 

roentgen 

shake 

slug 

torr (mm Hg, 00

 C) 

 *The becquerel (Bq) is the SI unit of radioactivity; 1 Bq = 1 event/s.

**The gray (Gy) is the SI unit of absorbed dose. 
iii

ABSTRACT

 This report is concerned with inhalation doses in scenarios for exposure of military 

participants at atmospheric nuclear-weapons tests at the Nevada Test Site that involved high 

resuspension of previously deposited fallout by an above-ground detonation. The purpose is to 

derive values of a resuspension factor, defined as the ratio of the concentration of resuspended 

radionuclides in air above ground to the areal concentration on the ground surface, that should be 

assumed in those scenarios to ensure that point estimates of inhalation dose that are obtained in 

dose reconstructions would be credible upper bounds, i.e., at least upper 95% credibility limits, 

when point values of all other parameters that are normally used in estimating inhalation doses in 

any resuspension scenario are assumed. The other parameters include the areal concentrations of 

radionuclides in previously deposited fallout, the breathing rate, and dose coefficients for 

inhalation, which give equivalent doses to specific organs or tissues per unit activity of 

radionuclides inhaled. The desired resuspension factors, which are called “effective” 

resuspension factors, are derived on the basis of an analysis of uncertainty in the model currently 

used to estimate inhalation doses in any resuspension scenario that takes into account subjective 

estimates of uncertainty in all parameters, including the resuspension factor. Results of the 

uncertainty analysis indicate that effective resuspension factors for all radionuclides in 

previously deposited fallout that should be assumed to ensure that point estimates of equivalent 

dose to any organ or tissue are credible upper bounds when the usual point values of other 

parameters are assumed are 10−3

 m−1 in the region closest to ground zero where the thermal pulse 

that was produced in a detonation was an important cause of resuspension and 10−4

 m−1 in the 

region farther from ground zero where resuspension was caused only by the blast wave. These 

effective resuspension factors were determined mainly by the assumed uncertainties in dose 

coefficients for inhalation of radionuclides, resuspension factors that apply to all fallout on the 

ground surface, and the inhalable fraction of resuspended radionuclides. The extent of the 

thermal-pulse and blast-wave regions and the time periods after a detonation over which 

effective resuspension factors should be applied in those regions are discussed. 
iv

TABLE OF CONTENTS 

Page

ABSTRACT................................................................................................................................... iii 

LIST OF FIGURES ...................................................................................................................... vii 

LIST OF TABLES....................................................................................................................... viii 

1. INTRODUCTION ......................................................................................................................1 

2. DESCRIPTION OF THERMAL-PULSE AND BLAST-WAVE REGIONS............................5 

2.1 Thermal-Pulse Region ..................................................................................................5 

2.2 Blast-Wave Region .......................................................................................................6 

3. APPROACH TO ASSESSMENT OF INHALATION DOSES IN RESUSPENSION 

 SCENARIOS ............................................................................................................................11 

3.1 Description of Model to Estimate Inhalation Dose.....................................................11 

3.2 Approach to Derivation of Effective Resuspension Factors.......................................16 

4. ANALYSIS OF UNCERTAINTIES IN ESTIMATED INHALATION DOSES DUE 

 TO RESUSPENSION BY NUCLEAR DETONATIONS AT NTS ........................................19 

4.1 Assumed Probability Distributions of Model Parameters ..........................................19 

4.1.1 Photon Exposure Rate Due to Deposited Fallout ........................................20 

4.1.2 Concentrations of Radionuclides on Ground Surface Per Unit 

 Exposure Rate ..............................................................................................22 

4.1.2.1 Uncertainty in Calculated Exposure Rates from Infinite, 

 Uniformly Contaminated Plane Source ........................................24 

4.1.2.2 Uncertainty in Calculated Exposure Rates Due to Finite 

 Extent of Source Region ...............................................................24 

4.1.2.3 Uncertainty in Shielding Effect of Ground Roughness ................25 

4.1.2.4 Uncertainty in Relative Activities of Radionuclides in 

 Fallout at NTS...............................................................................26 

 4.1.2.4.1 Effects of fractionation of fission and activation 

 products.........................................................................28 

 4.1.2.4.2 Effects of enhancement of plutonium...........................35 

4.1.2.5 Summary of Uncertainties in Concentrations of 

 Radionuclides in Fallout Deposited on Ground Surface...............37 
v

Page

4.1.3 Resuspension Factors...................................................................................38 

4.1.3.1 Resuspension of Previously Deposited Fallout.............................39 

 4.1.3.1.1 Resuspension factor in thermal-pulse region................39 

 4.1.3.1.2 Resuspension factor in blast-wave region.....................42 

 4.1.3.1.3 Discussion of resuspension factors for previously 

 deposited fallout............................................................44 

4.1.3.2 Respirable and Nonrespirable Fractions of Resuspended 

 Radionuclides................................................................................46 

 4.1.3.2.1 Gravitational settling of resuspended material .............47 

 4.1.3.2.2 Particle-size distributions of activity in fallout.............50 

 4.1.3.2.3 Discussion of data on particle-size distributions ..........55 

 4.1.3.2.4 Implications and use of available data..........................58 

 4.1.3.2.5 Estimation of inhalable fraction....................................59 

 4.1.3.2.6 Estimation of respirable fraction...................................63 

 4.1.3.2.7 Estimation of nonrespirable fraction.............................65 

4.1.3.3 Summary of Uncertainties in Resuspension Factors ....................66 

4.1.4 Breathing Rate .............................................................................................68 

4.1.5 Dose Coefficients for Inhalation of Radionuclides......................................69 

4.1.5.1 Sources of Uncertainty in Dosimetric and Biokinetic Models .....69 

4.1.5.2 Overview of Approach to Evaluating Uncertainty in Dose 

 Coefficients...................................................................................71 

4.1.5.3 Assessments of Uncertainty in Dose Coefficients........................73 

 4.1.5.3.1 Assessment by NCRP ...................................................73 

 4.1.5.3.2 Assessment in EPA’s federal guidance.........................74 

 4.1.5.3.3 Assessment in NRC-CEC expert elicitation .................76 

 4.1.5.3.4 Assessments by ICRP ...................................................78 

 4.1.5.3.5 Other assessments .........................................................78 

4.1.5.4 Present Assessment of Uncertainties in Dose Coefficients ..........82 

 4.1.5.4.1 Uncertainty in ICRP’s dose coefficients for fission 

 and activation products .................................................83 

 4.1.5.4.2 Uncertainty in ICRP’s dose coefficients for 

 plutonium ......................................................................85 

 4.1.5.4.3 Bias in ICRP’s dose coefficients...................................88 

4.1.5.5 Summary of Uncertainties in Dose Coefficients ..........................90 

4.1.6 Summary of Uncertainties in Estimates of Inhalation Dose........................92 

4.2 Calculated Probability Distributions of Inhalation Dose............................................92 

4.2.1 Approach to Combining Parameter Uncertainties .......................................93 

4.2.2 Probability Distributions of Dose from Inhalation of Fission and 

 Activation Products......................................................................................94 

4.2.3 Probability Distributions of Dose from Inhalation of Plutonium ................96 

4.2.4 Comparison of Results for Fission/Activation Products and Plutonium .....98 

4.2.5 Consideration of Parameter Correlations.....................................................99 
vi

Page

5. DERIVATION OF EFFECTIVE RESUSPENSION FACTORS ..........................................125 

6. DISCUSSION OF RESULTS.................................................................................................129 

6.1 Importance of Judgment and Credibility of Results .................................................129 

6.2 Applicability of Effective Resuspension Factors......................................................135 

6.2.1 Extent of Thermal-Pulse and Blast-Wave Regions ...................................135 

 6.2.2 Time Periods for Applying Effective Reuspension Factors ......................137 

7. SUMMARY OF RESULTS ...................................................................................................139 

REFERENCES ............................................................................................................................140 

DISTRIBUTION LIST.................................................................................DL-1
vii

LIST OF FIGURES

Figure Page

2-1 Photograph of Shot EASY in Operation BUSTER-JANGLE (AFLML, 1951) 

 showing region closest to ground zero where thermal pulse was important cause of 

 resuspension of surface soil and blast-wave region extending beyond region 

 impacted by thermal pulse where height of resuspended dust cloud was lower .................8 

2-2 Dependence of peak overpressure at ground level in pounds per square inch (psi) 

 on height of burst and distance from ground zero for 1-kiloton (kt) detonation 

 (Glasstone and Dolan, 1977; Figure 3.73c). Burst height and distance of a given 

 peak overpressure from ground zero both scale as the cube root of the yield in kt.............9 

4-1 Distribution of activity with particle diameter in fallout sample at distance of 

 1.1 miles from ground zero at Shot DIABLO in Operation PLUMBBOB at NTS 

 (Miller, 1969; Figure 8). Activity distribution of large particles is shown at 

 one-tenth of actual particle diameter................................................................................103 
viii

LIST OF TABLES

Table Page

2-1 Calculated maximum wind speed at various peak overpressures associated with 

 blast-wave produced in above-ground nuclear detonations...............................................10 

4-1 Summary of assumed uncertainties in estimates of concentrations of radionuclides 

 in fallout deposited on ground surface at NTS ................................................................104 

4-2 Summary of reported resuspension factors associated with mechanical stresses at 

 sites where nuclear weapons were tested.........................................................................105 

4-3 Percentages of total activities in smallest size fractions of fallout samples from 

 tower shots in Operation UPSHOT-KNOTHOLE at NTS..............................................106 

4-4 Percentages of total activities in smallest size fractions of fallout samples from 

 tower shots in Operation TEAPOT at NTS .....................................................................107 

4-5 Percentages of total activities in smallest size fractions of on-site fallout samples 

 from tower Shot SHASTA in Operation PLUMBBOB at NTS ......................................109 

4-6 Percentages of total activities in various size fractions of 0−104 μm magnetic 

 particles in on-site fallout samples from tower Shot SHASTA in Operation 

 PLUMBBOB at NTS .......................................................................................................110 

4-7 Summary of assumed uncertainties in parameters to estimate resuspension factors 

 that apply to respirable and nonrespirable radionuclides in inhalable form in 

 thermal-pulse and blast-wave regions near nuclear detonations at NTS .........................111 

4-8 Estimates by NCRP of reliability of effective dose coefficients for intakes of 

 radionuclides relative to values calculated by ICRP........................................................112 

4-9 Uncertainty categories in assessment of uncertainties in risk coefficients for intakes 

 of radionuclides in the environment in EPA’s current federal guidance.........................113 

4-10 Estimates of uncertainty in risk coefficients for intakes of selected radionuclides in 

 the environment in EPA’s current federal guidance........................................................114 

4-11 Summary of results of NRC-CEC expert elicitation on uncertainties in dose 

 coefficients for intakes of radionuclides by adults calculated by ICRP ..........................115 
ix

Table Page

4-12 Summary of 90% credibility intervals of dose coefficients for selected 

radionuclides, routes of intake, and organs or tissues in adults estimated by 

 experts in NRC-CEC expert elicitation............................................................................117 

4-13 Estimates by ICRP task group of uncertainty in GI-tract absorption fraction (f1) 

for radionuclides in adults and effect of uncertainty in f1 on uncertainty in 

 committed effective dose from ingestion calculated by ICRP.........................................120 

4-14 Summary of assumed uncertainties in estimated dose coefficients for inhalation 

 of radionuclides in resuspended fallout at NTS...............................................................121 

4-15 Summary of assumed uncertainties in parameters to estimate dose from inhalation 

 of radionuclides in fallout resuspended by nuclear detonation at NTS ...........................122 

4-16 Summary of results of analysis of uncertainties in estimated organ-specific 

 equivalent doses from inhalation of mixtures of fission and activation products in 

 fallout resuspended by nuclear detonations at NTS.........................................................123 

4-17 Summary of results of analysis of uncertainties in estimated organ-specific 

 equivalent doses from inhalation of plutonium in fallout resuspended by nuclear 

 detonations at NTS...........................................................................................................124 
1

 

1. INTRODUCTION

 This report presents an assessment of certain scenarios for inhalation exposure of military 

participants in the atmospheric nuclear-weapons testing program at the Nevada Test Site (NTS) 

that involved unusually high resuspension of previously deposited fallout by above-ground 

detonations.1 The purpose of this assessment is to derive values of a resuspension factor, defined 

as the ratio of the concentration of resuspended radionuclides in air above ground to the areal 

concentration on the ground surface, that should be assumed in reconstructing inhalation doses in 

those scenarios when standard methods of inhalation dose reconstruction for military participants 

that were developed by the Defense Threat Reduction Agency (DTRA) are used. 

 Resuspension of previously deposited fallout by a nuclear detonation is a potential 

concern at NTS whenever participants were located within a few miles of ground zero at times 

shortly after detonation and fallout from one or more previous shots had been deposited at those 

locations. Such exposure scenarios occurred only at certain above-ground detonations at NTS, 

beginning with Shot FOX in Operation TUMBLER-SNAPPER in 1952; they did not occur at 

surface or underground shots at times earlier in the period of atmospheric testing at NTS, 

because there was no previously deposited fallout in areas where resuspension by a detonation 

could have occurred or participants were not located in those areas at times shortly after a 

detonation (Dancz and Chehata, 2006).2

 The potential importance of inhalation of radionuclides in previously deposited fallout 

that was resuspended by nuclear detonations at NTS was considered in a report by the National 

Research Council (NRC, 2003). An analysis in that report was prompted by a finding that 

resuspension of previously deposited fallout by nuclear detonations had not been considered in 

1

 Radioactive materials that were resuspended by an above-ground detonation at NTS generally 

included neutron activation products in soil from that detonation as well as fallout from previous 

detonations that was present in areas near ground zero. The presence of soil activation products in 

resuspended materials is not considered explicitly in this analysis. However, their inclusion would have a 

negligible effect on our results (Trabalka and Kocher, 2007). 

2

 Dancz and Chehata (2006) identified nine shots in Operations TUMBLER-SNAPPER (1952), 

UPSHOT-KNOTHOLE (1953), and TEAPOT (1955) at which exposure to previously deposited fallout 

that was resuspended by a nuclear detonation could have occurred. The potential for such exposures at 

Operation PLUMBBOB (1957) was not considered in that analysis. 
2

 

dose reconstructions at NTS. Consequently, there was a concern that inhalation doses to affected 

participants, including forward observers and maneuver troops, could have been underestimated 

substantially.3

 An example analysis in the NRC report suggested that, depending on the 

concentrations of radionuclides in previously deposited fallout, inhalation doses to some organs 

or tissues could have been significant. The example analysis indicated that organs or tissues that 

could have received significant doses include those at the major sites of deposition of inhaled 

radionuclides in the body (e.g., lung, bone surfaces, red bone marrow, liver). However, the 

example analysis also suggested that doses to organs or tissues at minor sites of deposition of 

inhaled radionuclides (e.g., prostate and many other soft tissues) were insignificant even if 

exposure to the highest concentrations of radionuclides in previously deposited fallout that could 

have been resuspended by a detonation occurred. 

 The assessment of the high-resuspension scenarios of concern to this report involves an 

analysis of uncertainty in the model that is used to estimate inhalation doses to military 

participants in any resuspension scenario. On the basis of assumptions about uncertainties in all 

model parameters, we derive point values of a resuspension factor that should be assumed in 

dose reconstructions for the scenarios of concern to ensure that point estimates of inhalation dose 

are credible upper bounds—i.e., that estimated inhalation doses to any organ or tissue are at least 

upper 95% credibility limits,4 as required by applicable regulations on methods of estimating 

dose in Title 32, Part 218 of the Code of Federal Regulations (32 CFR Part 218) and standard 

operating procedures and policies of the NTPR Program (DTRA, 2007; Case et al., 2008). 

 More specifically, we derive point values of resuspension factors that should be assumed 

in estimating inhalation doses in the high-resuspension scenarios of concern to ensure that 

credible upper bounds of doses are obtained when point estimates of other parameters that are 

normally assumed in dose reconstructions for any resuspension scenario (e.g., resuspension by 

3

 Dose reconstructions at NTS have considered resuspension of previously deposited fallout by 

such activities as marching or vehicular traffic through a fallout field. However, only fallout from 

previous shots in the same test series has been been taken into account, and fallout from shots in previous 

test series has not been included. 

4

 In this report, the term “credibility limit” is used, rather than “confidence limit,” to indicate that 

such a limit is based on highly subjective assessments of uncertainties in model parameters, rather than a 

rigorous statistical analysis of outcomes that might be obtained by repeated measurement. 
3

walking, vehicular traffic, or the wind) are used. The derived resuspension factors are referred to 

as “effective” resuspension factors to indicate that they do not necessarily correspond to actual 

resuspension factors that applied to old fallout that could have been inhaled at locations and 

times of exposure. Rather, they are resuspension factors that should be assumed to ensure that 

credible upper bounds of inhalation doses are obtained in dose reconstructions for the scenarios 

of concern. The analysis in this report does not provide estimates of inhalation dose. Such 

estimates, which could be based on data on concentrations of radionuclides in fallout from 

various shots, are not needed to derive effective resuspension factors. 

 Effective resuspension factors derived in this report are intended to be applied to all 

radionuclides in previously deposited fallout and at any location in one of two broadly defined 

regions near ground zero of nuclear detonations, which are referred to as the thermal-pulse and 

blast-wave regions. The former is the region closest to ground zero where the initial intense 

pulse of thermal radiation had an important effect on resuspension, and the latter is the region 

beyond the thermal-pulse region where resuspension was caused only by the blast wave 

(Glasstone and Dolan, 1977) and presumably was substantially lower than in the thermal-pulse 

region. Separate effective resuspension factors that should be applied in estimating inhalation 

doses in the two regions at times shortly after a detonation are derived. 

 Inhalation of resuspended fallout potentially involved many radionuclides that varied in 

importance depending on the times prior to exposure when fallout from previous shots occurred 

and the organ or tissue of interest. Furthermore, especially in the blast-wave region, the 

resuspension factor probably decreased with increasing distance from ground zero. Therefore, in 

principle, effective resuspension factors that would ensure that credible upper bounds of 

inhalation dose are obtained in dose reconstructions could depend on the shot at which exposure 

to resuspended fallout occurred, the organ or tissue of interest, and the distances from ground 

zero where participants were exposed. However, it is impractical and unnecessary to derive 

effective resuspension factors that would apply to specific shots, organs or tissues, and distances 

from ground zero. Rather, the objective is to derive effective resuspension factors that should be 

assumed in all cases of exposure to fallout that was resuspended by a nuclear detonation in the 

thermal-pulse or blast-wave region, without regard for the organ or tissue of interest, the 
4

radionuclides that are important contributors to inhalation doses at a given shot, and the specific 

locations in those regions where participants were exposed. Use of effective resuspension 

factors for the high-resuspension scenarios of concern that apply to all inhalation exposures in 

the two broadly defined regions is consistent with the approach to estimating inhalation doses to 

military participants in other resuspension scenarios (Egbert et al., 1985; NRC, 2003; Raine et 

al., 2007), where a single resuspension factor is assumed in all cases where a particular type of 

resuspension scenario applies. 

In above-ground detonations at NTS, resuspension of previously deposited fallout also 

could have been caused by the so-called “afterwind,” which is a strong updraft that sucked dirt 

and debris into the stem of the fireball produced in a detonation as the fireball rose (Glasstone 

and Dolan, 1977). Resuspension by the afterwind, which occurred after the thermal pulse and 

blast wave passed, or any other perturbations of surface winds that might have occurred as the 

fireball rose, is not considered this report. 

 This report is organized as follows. Section 2 describes the thermal-pulse and blast-wave 

regions near ground zero of above-ground nuclear detonations at NTS. Section 3 describes the 

model that is used in dose reconstructions for military participants to estimate inhalation doses 

due to resuspension of radionuclides and the approach that is used in this report to assess 

uncertainties in that model when it is applied to resuspension of previously deposited fallout by 

nuclear detonations. Section 4 presents the analysis of uncertainty in estimated inhalation doses 

in scenarios that involved resuspension of previously deposited fallout by nuclear detonations. 

In Section 5, results of our analysis are used to derive effective resuspension factors that should 

be assumed in the thermal-pulse and blast-wave regions. Section 6 discusses (1) the importance 

of judgment in deriving effective resuspension factors and the credibility of the results and 

(2) the applicability of the results, including the extent of the thermal-pulse and blast-wave 

regions and the time periods after a detonation when effective resuspension factors should be 

applied in those regions. The concluding section summarizes the results of this analysis. 
5

 

2. DESCRIPTION OF THERMAL-PULSE AND BLAST-WAVE REGIONS

 Nuclear detonations at NTS of interest to this study occurred at heights above ground of 

about 1,500 ft or less (Hawthorne, 1979). Those detonations produced high levels of 

resuspended surface soil in two distinct regions near ground zero, which we refer to as the 

thermal-pulse and blast wave regions.5 Resuspension of surface soil in those regions is 

illustrated by the photograph in Figure 2-1 at Shot EASY in Operation BUSTER-JANGLE, 

which was an airdrop test at a height of 1,314 ft (Hawthorne, 1979). 

2.1 Thermal-Pulse Region

 The thermal-pulse region is the region closest to ground zero where the initial intense 

pulse of thermal radiation that was produced in a nuclear detonation had an important effect on 

resuspension (Glasstone and Dolan, 1977). In that region, absorption of thermal radiation that 

was incident on surface soil produced a layer of hot air near the surface, which also included soil 

particles that were injected into the air as a result of boiling of water in surface soil. The 

presence of the layer of hot air resulted in the formation of an auxiliary wave, called the 

“precursor,” that preceded the main blast wave and resulted in intense scouring of surface soil 

(Snow, 1981). Some of the energy in the precursor propagated upward, which resulted in lofting 

of resuspended soil particles (dust) and other materials to considerable heights. Additional 

resuspension in the thermal-pulse region was caused by the main blast wave, which lagged the 

initial thermal pulse by as much as a few seconds at the outer boundary of that region. 

 In Figure 2-1, the thermal-pulse region is the region where the height of the cloud of 

resuspended surface soil extends farther above ground than in the region beyond. The height of 

the dust cloud in the thermal-pulse region is approximately uniform, and there is a clear 

distinction between the outer edge of this region and the region just beyond where the thermal 

5

 In this report, the term “resuspension” is used to describe transfer of surface soil, as well as 

previously deposited fallout, into the air by any stress of concern, even though this term strictly applies 

only to the latter materials. The proper term to describe transfer of surface soil that was not deposited on 

the ground from the atmosphere is “suspension.” 
6

 

pulse was not sufficiently intense to affect resuspension of material on the ground surface. These 

characteristics of a dust cloud in the thermal-pulse region are seen in photographs of other 

detonations at NTS (AFLML, 1951).6

 The thermal-pulse region in which the precursor was formed extended to a distance from 

ground zero where the peak overpressure at ground level associated with the blast wave was 

about 6 pounds per square inch (psi) (Glasstone and Dolan, 1977). At any shot, the distance at 

which the peak overpressure was 6 psi can be estimated from Figure 2-2, which gives the 

distances of various peak overpressures as a function of the height of burst of a 1-kiloton (kt) 

detonation (Glasstone and Dolan, 1977; Figure 3.73c).7 The burst height and distance of a given 

peak overpressure both scale as the cube root of the yield (Glasstone and Dolan, 1977). For 

example, at Shot EASY in Figure 2-1, which had a burst height of 1,314 ft and yield of 31 kt 

(Hawthorne, 1979), the corresponding burst height for a 1-kt detonation, which is called the 

scaled height-of-burst, is 1,314/(31)1/3, or 418 ft, and the distance at which the peak overpressure 

from a 1-kt detonation at that height was 6 psi, as estimated from Figure 2-2, is about 1,700 ft. 

By scaling this distance by the yield of 31 kt, the estimated distance of the 6-psi line at Shot 

EASY is about 5,300 ft, or 1 mile. From the known burst heights and yields of above-ground 

detonations at NTS (Hawthorne, 1979), we estimate that the greatest distance of the 6-psi line 

from ground zero at any shot was about 1.4 miles. This estimate applies at Shot HOOD in 

Operation PLUMBBOB, which was detonated at a height of 1,500 ft with a yield of 74 kt. 

2.2 Blast-Wave Region

 Beyond the thermal-pulse region, resuspension was caused by the high wind associated 

with the blast wave that was produced in a nuclear detonation. The high wind, which was 

6

 Examples include Shot CHARLIE in Operation BUSTER-JANGLE, Shot CHARLIE in 

Operation TUMBLER-SNAPPER, Shot MET in Operation TEAPOT, and Shots BOLTZMANN and 

PRISCILLA in Operation PLUMBBOB. 

7

 Calculations represented in Figure 2-2 apply under nearly ideal conditions where effects of 

terrain, surface properties, and meteorological conditions are unimportant. Although the ground surface 

at NTS is thermally nonideal, these calculations are considered to be appropriate for general use. 
7

directed away from a detonation, persisted for a few seconds at a given location and was 

followed by a much weaker and much less important wind that lasted for several seconds and 

was directed toward the detonation (Glasstone and Dolan, 1977). As indicated in Figure 2-1, the 

blast-wave region extended well beyond the thermal-pulse region, and the height of the dust 

cloud was substantially lower than in the thermal-pulse region. 

 It is difficult to define the outer boundary of the blast-wave region, essentially because 

the maximum wind speed associated with the blast wave decreased with increasing distance from 

a detonation and the lowest wind speed that would cause unusually high resuspension when the 

wind persisted for no more than a few seconds is not well defined. If we assume, for example, 

that the blast-wave region extended to a distance from ground zero where the maximum wind 

speed was about 40−70 miles per hour (mph), calculations summarized in Table 2-1 (Glasstone 

and Dolan, 1977; Table 3.07 and Figure 3.55) indicate that the corresponding peak overpressure 

was about 1−2 psi. By using the curves in Figure 2-2, with the burst height and distance from 

ground zero both scaled by the cube root of the yield as discussed in the previous section, we 

then estimate that the blast-wave region at Shot EASY in Figure 2-1 extended to a distance of 

about 2−3 miles. At Shot HOOD, which was the worst case noted in the previous section, we 

estimate that the blast-wave region extended to a distance of about 2.5−4 miles. This estimate is 

roughly consistent with reports of military activities at Shot HOOD (Maag et al., 1983; USMC, 

1957), which indicated that a dense dust cloud probably was formed to a distance of at least 

5 miles. At yields of about 10−40 kt and burst heights of 300−500 ft, which were common in 

detonations at NTS (Hawthorne, 1979), the blast-wave region should have extended to a lesser 

distance than at Shot HOOD, perhaps by about 20−50%. As at Shot HOOD, it may be possible 

to define the extent of the blast-wave region at particular shots on the basis of reports of actual 

conditions at times shortly after detonation. 

Estimates of the extent of the blast-wave region given above are intended only as 

illustrative examples. The issue of defining the extent of the blast-wave region is discussed 

further in Section 6.2. 
8

Figure 2-1. Photograph of Shot EASY in Operation BUSTER-JANGLE (AFLML, 1951) 

showing region closest to ground zero where thermal pulse had an important effect on 

resuspension of surface soil and blast-wave region extending beyond region impacted by 

thermal pulse where height of resuspended dust cloud was lower. 
9

Figure 2-2. Dependence of peak overpressure at ground level in pounds per square inch (psi) on 

height of burst and distance from ground zero for 1-kiloton (kt) detonation (Glasstone 

and Dolan, 1977; Figure 3.73c). Burst height and distance of a given peak overpressure 

from ground zero both scale as the cube root of the yield in kt. 
10

Table 2-1. Calculated maximum wind speed at various peak overpressures associated 

with blast wave produced in above-ground nuclear detonationsa

Peak overpressure 

(pounds per 

square inch) 

Maximum wind speed 

(miles per hour)b

Peak overpressure 

(pounds per 

square inch) 

Maximum wind speed 

(miles per hour)b

200 2,100 20 500 

150 1,800 10 290 

100 1,400 5 160 

72 1,200 2 70 

50 930 1 40 

30 670 

a

 Estimates are obtained from Table 3.07 of Glasstone and Dolan (1977), except maximum wind 

speed at peak overpressure of 1 psi is obtained from Figure 3.55. 

b

 Values are rounded to two significant figures at wind speeds above 100mph and to one 

significant figure at lower wind speeds. 
11

 

3. APPROACH TO ASSESSMENT OF INHALATION DOSES 

IN RESUSPENSION SCENARIOS

 In this report, the assessment of exposure scenarios that involved inhalation of 

radionuclides in previously deposited fallout that was resuspended by above-ground detonations 

at NTS is based on an analysis of uncertainty in the model that is currently used to estimate 

inhalation doses to military participants in any resuspension scenario. The following sections 

describe the model and our approach to an uncertainty analysis for the purpose of deriving 

effective resuspension factors in the thermal-pulse and blast-wave regions that should be 

assumed in dose reconstructions to obtain inhalation doses that are credible upper bounds (at 

least upper 95% credibility limits). 

3.1 Description of Model to Estimate Inhalation Dose

 The model that is currently used to estimate inhalation doses to military participants in 

any scenario that involved resuspension of radionuclides on the ground surface is described by 

Barrett et al. (1986) and in Section IV.C.2 of the NRC (2003) report. 

 In any scenario for inhalation exposure, the dose from inhalation of a particular 

radionuclide is estimated as: 

 D = AA × BR × DF × T , (1) 

where 

D = equivalent dose to specific organ or tissue (rem),8

AA = activity concentration of radionuclide in air (Ci m−3), 

8

 Until recently, the dosimetric quantity that was calculated in dose reconstructions for military 

participants was called “dose equivalent.” The term “equivalent dose” is now used in the NTPR Program 

(DTRA, 2007; Raine et al., 2007) to conform to a recommendation by the International Commission on 

Radiological Protection (ICRP, 1991) and National Council on Radiation Protection and Measurements 

(NCRP, 1993). 
12

 

BR = breathing rate (m3 h−1), 

DF = equivalent dose to specific organ or tissue per unit activity of radionuclide 

inhaled (rem Ci−1

),9

T = duration of exposure (h). 

The dose from inhalation of mixtures of radionuclides is the sum of calculated doses from each 

radionuclide. The dose from all radionuclides combined is calculated using radionuclide-specific 

values of the concentration in air, AA, and dose coefficient, DF. 

 The model in eq. (1) incorporates an assumption that airborne radionuclides are attached 

to particles of size sufficiently small that they can be inhaled; i.e., the concentration in air, AA, is 

a value that applies to inhalable materials only. The concentration in air also is time-dependent 

in most scenarios. Thus, the term AA in eq. (1) represents an average concentration of a 

radionuclide in inhalable form during the period of exposure, T. 

 The dose coefficient, DF, depends on the particle size of inhaled material, which is 

expressed in terms of the activity median aerodynamic diameter (AMAD) of a distribution of 

particle sizes (ICRP, 1979; 1994). Until recently, an AMAD of 1 or 20 μm was assumed in dose 

reconstructions for military participants (Egbert et al., 1985), and the assumption that gave the 

higher dose to an organ or tissue of interest for the assumed mixture of inhaled radionuclides was 

used. On the basis of the model of the respiratory tract that was used to calculate those dose 

coefficients (ICRP, 1979), dose coefficients for inhalation of 20-μm particles were essentially the 

same as dose coefficients for ingestion, because the model assumed that 95% of all inhaled 

particles with an AMAD of 20 μm are deposited in the nasal passages and that 99% of the 

deposited material is transferred to the gastrointestinal (GI) tract by swallowing. Therefore, the 

dose coefficient in eq. (1) was either the value for inhalation of respirable 1-μm particles, which 

were assumed to be deposited to some extent in all regions of the respiratory tract (ICRP, 1979), 

or the value for ingestion, which represented the dose coefficient for inhalation of larger particles 

9

 Until recently, the quantity DF was referred to as a “dose conversion factor” in dose 

reconstructions for military participants (Egbert et al., 1985). The term “dose coefficient” is now used in 

the NTPR Program (DTRA, 2007; Raine et al., 2007) to conform to terminology currently recommended 

by ICRP; e.g., see ICRP (1996a). 
13

 

that were assumed to be essentially nonrespirable and were not deposited to a significant extent 

in regions of the respiratory tract other than the nasal passages. 

 Dose reconstructions for military participants now use dose coefficients for inhalation of 

radionuclides by adult members of the public that are currently recommended by ICRP [(1996a; 

2002) and references therein]; see Raine et al. (2007).10 These dose coefficients replace those 

used previously (Egbert et al., 1985), which were based in large part on recommended dosimetric 

and biokinetic models for workers in ICRP Publication 30 (ICRP, 1979). ICRP’s current model 

of the respiratory tract assumes that about 50% of all large, essentially nonrespirable particles 

that are inhaled are deposited in the nose and throat and that about 50% of the deposited material 

is transferred to the GI tract by swallowing, with the deposited material that is not swallowed 

assumed to be expelled by nose-blowing or -wiping; i.e., about 25% of all large particles that are 

inhaled are assumed to be swallowed (ICRP, 1994). Therefore, ingestion dose coefficients that 

were used previously in dose reconstructions probably overestimated doses from inhalation of 

large, nonrespirable particles by a factor of about 4 in cases where there were no other significant 

changes in internal dosimetry models for radionuclides of concern. Dose coefficients for 

inhalation that are now used in dose reconstructions are calculated by assuming a particle size 

(AMAD) of 1, 3, 5, or 10 μm, and the assumption that gives the highest equivalent dose to an 

organ or tissue of interest for the assumed mixture of inhaled radionuclides in a particular case is 

used (Raine et al., 2007). Particles with an AMAD of 10 μm or greater are assumed to be 

essentially nonrespirable and are either expelled or swallowed (ICRP, 1994). 

 In this analysis, the inhalation dose per unit exposure time (rem h−1

) is assessed, because 

the duration of exposure, T, is an extrinsic factor that is determined by an individual’s activities 

and the uncertainty in T is negligible compared with uncertainties in other parameters in the 

model, especially the average concentration in air during the period of exposure, AA, and the 

dose coefficient, DF. The inhalation dose per unit exposure time is given by: 

 ΔD/Δt = AA × BR × DF . (2) 

10 A requirement to use dose coefficients currently recommended by ICRP is contained in the 

Policy & Guidance Manual of the NTPR Program (DTRA, 2007). 
14

 

 Airborne concentrations of radionuclides were not measured during periods of exposure 

of military participants. In scenarios that involved resuspension of radionuclides, the 

concentration of a radionuclide in air above ground (Ci m−3

) is estimated on the basis of an 

estimate of its concentration on the ground surface and a resuspension-factor model given by: 

 AA = SA × K , (3) 

where 

SA = activity concentration of radionuclide on ground surface (Ci m−2

), 

K = resuspension factor (m−1

). 

A resuspension factor thus is defined as the ratio of the concentration of a radionuclide in air to 

its areal concentration on the ground surface. Reported resuspension factors often are based on 

measured concentrations in air at a height of 1 m above ground.11 Since the concentration in air 

should be a value that applies to inhalable materials, resuspension factors should represent 

airborne concentrations of radionuclides in inhalable form relative to total areal concentrations 

on the ground surface. 

 Concentrations of radionuclides on the ground surface, SA, also were not measured 

during periods of exposure. In dose reconstructions, concentrations of radionuclides in deposited 

fallout are estimated on the basis of (1) measured photon exposure rates in air above ground 

(R h−1

) at various locations and times shortly after each detonation, (2) calculated exposure rates 

per unit activity concentration of each radionuclide on the ground surface (R h−1

 per Ci m−2), and 

(3) the relative activities of each radionuclide in fallout, which are estimated on the basis of 

calculated yields in fission, cloud-sampling data, and an assumption that fallout was 

11 When surface soil is resuspended by relatively gentle stressors, such as walking or light 

vehicular traffic, resuspension factors may decrease substantially with increasing height above ground 

(Sehmel, 1984; Tables 12.7 and 12.9). Thus, if an individual is standing on the ground, a resuspension 

factor that applies at the location of the head under those conditions could be substantially lower than a 

resuspension factor at 1 m. However, the stressors that occurred in nuclear detonations are much more 

vigorous, and it is not expected that resuspension factors in the thermal-pulse and blast-wave regions 

varied significantly over the height of an individual standing on the ground. 
15

 

unfractionated.12 Photon exposure rates per unit activity concentration of radionuclides on the 

ground surface are calculated at a height of 1 m by assuming that the source region is a plane of 

infinite extent (Egbert et al., 1985; Raine et al., 2007). Calculated exposure rates also account 

for the shielding effect of ground roughness, which is assumed to reduce exposure rates to about 

70% of the exposure rates above an unshielded plane source (Egbert et al., 1985; Raine et al., 

2007).13 Thus, activity concentrations of radionuclides on the ground surface are estimated from 

measured photon exposure rates, I (R h−1), as: 

 SA = (SA/I) × I , (4) 

where SA/I is the reciprocal of a calculated exposure rate at a height of 1 m per unit activity 

concentration on the ground surface (Ci m−2

 per R h−1). For mixtures of radionuclides with 

assumed relative activities, SA/I represents the concentration of each radionuclide on the ground 

per unit exposure rate in air above ground from all radionuclides combined, and SA calculated 

from eq. (4) represents the concentrations corresponding to a measured exposure rate, I. 

 By combining eqs. (2), (3), and (4), the equivalent dose to an organ or tissue of interest 

from inhalation of resuspended radionuclides per unit exposure time is given by: 

 ΔD/Δt = I × (SA/I) × K × BR × DF . (5) 

When resuspension scenarios are included in dose reconstructions, point estimates of all 

parameters in the model in eq. (5) are used. As noted in Section 1, the assumed parameters 

should result in credible upper bounds (at least upper 95% credibility limits) of estimated 

inhalation doses. To comply with this requirement, the selection of resuspension factors that are 

expected to substantially overestimate concentrations of radionuclides in air relative to 

concentrations on the ground surface in an assumed scenario is emphasized (Egbert et al., 1985; 

12 Only fission and activation products normally contributed significantly to measured photon 

exposure rates. Activity concentrations of plutonium in fallout relative to concentrations of fission and 

activation products in weapons debris are estimated from cloud-sampling data. 

13 To account for the shielding effect of ground roughness, exposure rates in air above ground are 

calculated by assuming that the source region consists of two plane sources with equal activity 

concentrations, one source located at a depth of 0.25 cm in soil and the other at a depth of 0.75 cm. 
16

Barrett et al., 1986; NRC, 2003; Raine et al., 2007). Selected values of other parameters in the 

model are intended to be more realistic. 

3.2 Approach to Derivation of Effective Resuspension Factors

 The purpose of our assessment of exposure scenarios that involved inhalation of 

radionuclides in previously deposited fallout that was resuspended by above-ground detonations 

at NTS is to derive point values of effective resuspension factors that should be used in the 

model in eq. (5) to ensure that credible upper bounds (at least upper 95% credibility limits) of 

inhalation doses are obtained when point estimates of other parameters that are normally 

assumed in dose reconstructions for other resuspension scenarios (i.e., concentrations of 

radionuclides on the ground surface, the breathing rate, and dose coefficients for inhalation) are 

used. Effective resuspension factors are derived in the following way. 

 First, probability distributions that are assumed to represent uncertainty in all parameters 

in eq. (5), including the resuspension factor in the thermal-pulse or blast-wave region, are 

propagated through the model to obtain a probability distribution that represents uncertainty in 

model output, and the upper 95% credibility limit of that distribution is identified. Then, by 

comparing the upper 95% credibility limit with a point estimate of model output obtained by 

using point estimates of all other parameters that are normally assumed in estimating inhalation 

doses in other resuspension scenarios, an effective resuspension factor that would give a model 

output equal to the upper 95% credibility limit obtained in the probabilistic uncertainty analysis 

is calculated. Effective resuspension factors so derived are rounded to the nearest power of 10 to 

be consistent with assumed resuspension factors in other scenarios for inhalation exposure at 

NTS and in the Pacific (Barrett et al., 1986; Phillips et al., 1985). This level of precision is 

appropriate when resuspension factors in any scenario are highly uncertain. 

 It is important to emphasize that comparisons of probability distributions of outputs of 

the model in eq. (5) with point estimates that are obtained in dose reconstructions do not require 

assumptions about concentrations of radionuclides on the ground surface or inhalation dose 

coefficients. As indicated by an example analysis in Section V.C.3.3 of the NRC (2003) report, 
17

such comparisons can be based on a unit concentration on the ground surface and a unit 

inhalation dose coefficient for all radionuclides combined. The key to understanding the analysis 

in this report is to recognize that it is concerned only with relative comparisons of inhalation 

doses that are calculated using probability distributions of model parameters with doses that are 

calculated using point estimates of all parameters. 

 Uncertainty in output of the model in eq. (5) is estimated using a Monte Carlo sampling 

method. A probability distribution of each model parameter, which is assumed to represent its 

uncertainty, is defined, values of each parameter are selected from those probability distributions 

by repeated random sampling, and parameter values in each random sample are propagated 

through the model to generate a probability distribution of model output, which represents 

uncertainty in estimated inhalation doses. We emphasize that assumed probability distributions 

of model parameters are subjective representations of uncertainty that are based on scientific 

judgment, rather than distributions that might be obtained by repeated measurement; i.e., they are 

intended to represent the current state of knowledge. Therefore, estimates of uncertainty in 

calculated inhalation doses also represent subjective scientific judgment. The need for judgment 

is a consequence of the paucity of data that can be used to quantify uncertainty in important 

model parameters. Approaches to uncertainty analysis used in this report, including the 

importance of judgment, are discussed elsewhere (NCRP, 1996). 

 The method of Monte Carlo sampling used in this analysis is a form of stratified random 

sampling called Latin Hypercube sampling (McKay et al., 1979). In this method, probability 

distributions of model parameters are divided into N intervals of equal probability, where N is the 

number of random samples used in calculating a probability distribution of model output. In the 

first iteration, one interval and one value in that interval are selected at random for each 

parameter, and the model output corresponding to the selected values of all parameters is 

calculated. In each subsequent iteration, parameters are selected at random in the same way, 

except intervals previously sampled are excluded. Latin Hypercube sampling thus ensures that 

the entire probability distribution of each parameter is sampled, thereby providing more robust 

estimates of probability distributions of model output for a given number of samples than 

conventional Monte Carlo methods in which parameters are sampled at random in each iteration 
18

 

without regard for previously sampled values. Sampling over entire probability distributions of 

parameters is important when upper tails of probability distributions of model output (e.g., upper 

95% credibility limits) are of interest, as is the case in the analysis presented in this report. 

 All probability distributions of model output described in this report were calculated 

using Crystal Ball® software (Decisioneering, 2001). In all calculations, the number of samples 

from probability distributions of input parameters was 10,000, and the initial seed value for the 

random number generator was set to 0. At that number of samples, changes in the initial seed 

value or the sequence of random numbers for a given initial seed result in variations in upper 

95% credibility limits of model output of no more than a few percent.14 Such variations are 

unimportant when assumed probability distributions of model parameters are highly subjective 

and effective resuspension factors that are derived from upper 95% credibility limits of 

probability distributions of model output are rounded to the nearest power of 10. Crystal Ball®

also allows correlations between different parameters to be taken into account in propagating 

probability distributions of uncertain parameters through a model. The potential importance of 

parameter correlations to results of our analysis is considered in Section 4.2.5. 

 The approach to assessing resuspension scenarios at NTS presented in this report is 

similar to approaches that were used in example analyses in Section V.C.3.3 and Appendix E of 

the NRC (2003) report. However, the assessment in this report is independent of those analyses, 

which were intended as hypothetical illustrative examples only, in that we performed our own 

assessment of uncertainties in model parameters. Some parameter uncertainties developed in 

this report differ substantially from assumptions used in the NRC report. 

14 Crystal Ball® also allows use of the same sequence of random numbers for a given initial seed 

value in all calculations. If that option is chosen, the same probability distribution of model output is 

obtained each time a calculation is performed using the same number of random samples. 
19

4. ANALYSIS OF UNCERTAINTIES IN ESTIMATED INHALATION DOSES 

DUE TO RESUSPENSION BY NUCLEAR DETONATIONS AT NTS

 This section presents an analysis of uncertainties in the model in eq. (5) (see Section 3.1) 

when it is used to estimate inhalation doses in scenarios that involved resuspension of 

radionuclides in previously deposited fallout by nuclear detonations at NTS. Probability 

distributions that are assumed to represent uncertainty in each model parameter are developed. 

Results of propagating those distributions through the model using techniques of random 

sampling to obtain probability distributions that represent uncertainty in estimated inhalation 

doses are presented. As described in Section 3.2, these results are used to derive point values of 

effective resuspension factors that should be assumed in the thermal-pulse and blast-wave 

regions near ground zero of nuclear detonations to ensure that estimates of inhalation dose are 

credible upper bounds (at least upper 95% credibility limits) of possible doses to military 

participants; effective resuspension factors are derived in Section 5. 

4.1 Assumed Probability Distributions of Model Parameters

 With reference to the model in eq. (5), parameters for which subjective probability 

distributions to represent uncertainty are developed in this analysis include: 

• the photon exposure rate in air due to fallout deposited on the ground (I), 

• areal concentrations of radionuclides in deposited fallout per unit exposure rate in air 

above ground (SA/I), 

• the resuspension factor (K), 

• the breathing rate (BR), and 

• dose coefficients for inhalation of radionuclides (DF). 

An accounting of uncertainties in the photon exposure rate (I), the resuspension factor (K), the 

breathing rate (BR), and dose coefficients for inhalation (DF) is straightforward, since doses 
20

 

from inhalation of resuspended radionuclides are directly proportional to those parameters. 

However, an accounting of uncertainty in the areal concentrations of radionuclides in deposited 

fallout per unit exposure rate (SA/I) is more complex when several factors that affect estimates of 

inhalation dose in different ways must be considered. 

4.1.1 Photon Exposure Rate Due to Deposited Fallout

 All estimates of inhalation dose in resuspension scenarios are based on measurements of 

exposure rates in air due to photons emitted by radionuclides on the ground at various locations 

and times shortly after each detonation. Those measurements are used to generate contour plots 

of exposure rates at a fixed time after detonation, usually one hour. At any location where 

exposure occurred, the exposure rate at the fixed time after detonation is estimated using spatial 

interpolation or extrapolation. The exposure rate, I, at any location at the fixed time after 

detonation is uncertain as a consequence of measurement uncertainty and uncertainty in spatial 

interpolation or extrapolation of measured exposure rates. Extrapolation of measured exposure 

rates in time to generate exposure-rate contours at the fixed time is not an additional source of 

uncertainty when relative activities of radionuclides on the ground are known, because those 

extrapolations are based on known decay rates (half-lives) of radionuclides (Egbert et al., 1985; 

Raine et al., 2007). However, there is uncertainty in extrapolations in time that arises from 

uncertainty in the relative activities of radionuclides in fallout; this uncertainty is addressed in 

assessing uncertainty in the concentrations of radionuclides in fallout deposited on the ground 

per unit exposure rate (SA/I) in the following section. 

 In this analysis, estimates of photon exposure rates at any location at a fixed time after 

detonation that are based on measurements at times shortly after each detonation are assumed to 

be uncertain by a factor of 3.15 We represent this uncertainty by a lognormal probability 

15 In this report, a statement that a parameter is uncertain by a factor of x means that the ratio of 

an upper bound to the median (50th percentile) is x, unless otherwise noted. When an unbounded 

probability distribution (e.g., lognormal or normal) is assumed, the upper bound is the 95th percentile 

(upper 95% credibility limit). When a bounded distribution (e.g., log-triangular or uniform) is assumed, 

the upper bound is the maximum value, and the 95th percentile is somewhat less. 
21

 

distribution with a 90% credibility interval between 1/3 and 3 times the exposure rate that is 

assumed in dose reconstructions—i.e., point estimates of exposure rates at a fixed time after 

detonation that are used in dose reconstructions are assumed to be median values (50th

percentiles) of lognormal probability distributions, and the probability that the true exposure rate 

is within a factor of 3 of the median is assumed to be 90%. The assumed uncertainty is based on 

a finding in the NRC (2003) report that the uncertainty in reconstructed external photon doses to 

participants whose exposures were not recorded by film badges usually should be about a factor 

of 3. The assumed uncertainty is due mainly to the uncertainty in interpolating or extrapolating 

measurements at a few locations to other locations where exposure occurred, and it is intended to 

account for any variations in radionuclide concentrations on the ground surface that affect 

estimates of external exposure rates at locations of exposure.16

 Uncertainties in measurements of exposure rates using field instruments should be no 

more than a few tens of percent (Brady and Nelson, 1985) and, thus, should be unimportant.17 

Measurement uncertainty is assumed to be incorporated in the subjective estimate of uncertainty 

of a factor of 3 that we have assigned to estimated photon exposure rates at locations of exposure 

to account for uncertainty in extrapolating or interpolating measured values. 

 An additional consideration in scenarios that involved resuspension of radionuclides by a 

nuclear detonation is the following. The model used to estimate inhalation doses in resuspension 

scenarios (see Section 3.1) incorporates an assumption that airborne concentrations of 

radionuclides at any location resulted from resuspension of radionuclides on the ground at that 

location. This is a reasonable assumption in many scenarios, such as resuspension by walking or 

16 The uncertainty in the photon exposure rate at many locations could be substantially less than a 

factor of 3. This could be the case, for example, at locations where exposure rates in fallout fields at NTS 

that were well characterized are relatively high. However, for purposes of this analysis, a single estimate 

of uncertainty that applies at any location in a fallout field is needed, and we believe that a factor of 3 is a 

reasonable representation of that uncertainty. An uncertainty of a factor of 3 also is specified in the 

Policy & Guidance Manual of the NTPR Program (DTRA, 2007). Use of an unbounded lognormal 

probability distribution gives a small weight (2.5%) to an assumption that the exposure rate was more 

than a factor of 3 higher than the value assumed in dose reconstructions. 

17 For example, if measurement uncertainty is represented by a normal distribution with a 90% 

credibility interval between 0.7 and 1.3 times a reported exposure rate, combining this uncertainty with 

the assumed uncertainty of a factor of 3 in interpolating or extrapolating measured exposure rates to 

locations of exposure would increase the overall uncertainty by only about 3%. 
22

vehicular traffic. However, nuclear detonations at NTS resulted in resuspension over large areas, 

and mixing of airborne radionuclides from areas away from a location of exposure by turbulent 

diffusion and the wind associated with a blast wave, which was initially directed away from a 

detonation but then reversed direction (see Section 2.2), presumably occurred. Thus, airborne 

concentrations of radionuclides at any location may have resulted from resuspension over an area 

in which concentrations on the ground varied substantially. 

 The issue of concern to our analysis is whether the effect described above is a significant 

source of additional uncertainty in using measured photon exposure rates to estimate airborne 

concentrations of resuspended radionuclides. We believe that resuspension over large areas is 

not a significant source of additional uncertainty if the uncertainty in photon exposure rates due 

to uncertainty in interpolation and extrapolation of measurements to locations where exposure 

rates were not measured is represented adequately. Widespread mixing of resuspended material 

should tend to reduce variations in airborne concentrations in the thermal-pulse and blast-wave 

regions that would result if concentrations at a given location were due only to resuspension at 

that location and concentrations on the ground varied substantially with location—i.e., an 

averaging of airborne concentrations over large areas presumably occurred. Consequently, 

airborne concentrations over a large area could be estimated based primarily on estimated 

concentrations on the ground in areas of higher concentration, where the uncertainty in estimated 

photon exposure rates should be lower. On the basis of this reasoning, we have not included an 

additional uncertainty to account for resuspension over large areas and widespread mixing of 

resuspended radionuclides. 

4.1.2 Concentrations of Radionuclides on Ground Surface Per Unit Exposure Rate

 Uncertainty in the areal concentrations of radionuclides in deposited fallout per unit 

exposure rate in air above ground (SA/I) arises from several factors that affect estimates of 

inhalation dose in different ways. In assessing uncertainty in the quantity SA/I, it is important to 

bear in mind that the quantity of interest in estimating inhalation doses is the concentration of 

radionuclides on the ground surface, SA, which is calculated as (SA/I) × I [see eq. (4)], rather 
23

than SA/I itself, and that we are interested in the effect of uncertainty in SA on estimated doses 

from inhalation of small, respirable particles or larger, nonrespirable particles (see Section 3.1). 

 The contribution to uncertainty in the concentrations of radionuclides on the ground 

surface, SA, due to uncertainty in measured exposure rates, I, is treated separately in the previous 

section. The exposure rate essentially is a scaling factor in estimating concentrations of 

radionuclides on the ground surface—i.e., an over- or underestimate of I by some factor will 

result in an over- or underestimate of SA for all radionuclides by the same factor. 

 Other sources of uncertainty in calculating SA/I and, thus, concentrations of radionuclides 

on the ground surface, SA, and doses from inhalation of resuspended radionuclides include: 

• uncertainty in calculations of photon exposure rates in air above ground per unit 

concentration of radionuclides on the ground surface, which assume that the source 

region is an infinite and uniformly contaminated plane surface; 

• uncertainty in calculated photon exposure rates per unit concentration of radionuclides on 

the ground surface due to the finite extent of the source region; 

• uncertainty in the shielding effect of ground roughness; 

• uncertainty in the relative activities of radionuclides in fallout as that uncertainty affects 

estimates of dose from inhalation of small, respirable particles or larger, nonrespirable 

particles. 

A probability distribution to represent uncertainty in the concentrations of radionuclides on the 

ground surface, SA, due to uncertainty in estimated concentrations per unit exposure rate, SA/I, is 

obtained by combining probability distributions that describe each of these uncertainties. 

 The first three uncertainties listed above are similar to the uncertainty in the exposure 

rate, I, in that they are scaling factors in estimating concentrations of radionuclides on the ground 

surface, SA, and doses from inhalation of resuspended radionuclides. However, uncertainty in 

the relative activities of radionuclides in deposited fallout affects estimates of SA and doses from 

inhalation of respirable or nonrespirable particles differently, and this source of uncertainty does 
24

not act as a scaling factor when exposure to mixtures of radionuclides occurs, as is generally the 

case in exposures to resuspended fallout. 

4.1.2.1 Uncertainty in Calculated Exposure Rates from Infinite, Uniformly Contaminated 

Plane Source. Exposure rates per unit concentration of radionuclides on the ground surface are 

calculated at a height of 1 m above ground, based on an assumption that exposure rates were 

measured at that height (Egbert et al., 1985; Raine et al., 2007). There are three sources of 

uncertainty in photon exposure rates per unit concentration of radionuclides that are calculated 

by assuming a uniform distribution on an infinite plane surface: 

• uncertainty in calculations of photon transport from the source region to a location at a 

height of 1 m above ground; 

• uncertainty in the height above ground where photon exposure rates were measured; 

• uncertainty in the energies and intensities of photons emitted by radionuclides. 

For photons of energy about 0.1 MeV or greater, which are the most important contributors to 

external exposure, comparisons of various calculations indicate that the uncertainty in 

calculations of photon transport to a location 1 m above ground is less than 20% (Eckerman and 

Ryman, 1983). If we assume that the height above ground where photon exposure rates were 

measured ranged from 0.5 to 1.5 m, calculations by Beck and de Planque (1968; Figure 9) 

indicate that the uncertainty in calculated exposure rates per unit concentration of radionuclides 

on the ground surface is about 10%. Uncertainties in the energies and intensities of important 

photons emitted by radionuclides in fallout are less than 10% (Kocher, 1981; ICRP, 1983). 

 On the basis of the uncertainties summarized above, we assume an uncertainty of 20% in 

calculated photon exposure rates per unit concentration of radionuclides on an infinite and 

uniformly contaminated plane surface. We represent this uncertainty by a normal probability 

distribution with a median at 1.0 and a 90% credibility interval between 0.8 and 1.2. 

4.1.2.2 Uncertainty in Calculated Exposure Rates Due to Finite Extent of Source Region. 

An assumption of an infinite source region, which is incorporated in all calculations of photon 

exposure rates per unit concentration of radionuclides on the ground surface (Egbert et al., 1985; 
25

Raine et al., 2007), results in overestimates of exposure rates per unit concentration from a finite 

source. Thus, radionuclide concentrations that correspond to a measured exposure rate are 

underestimated when the source region is finite but an infinite source region is assumed. 

 Calculations of external dose rates from finite sources that are uniformly distributed on 

the ground surface (Apostoaei et al., 2000) indicate that reductions in exposure rates compared 

with the exposure rate from an infinite source could exceed 10% only if the distance to the 

boundary of the source region is less than about 200 m. Data on fallout patterns at NTS 

(Hawthorne, 1979) indicate that source regions of concern to this analysis were substantially 

larger. Therefore, possible reductions in photon exposure rates due to the finite extent of regions 

of deposited fallout at NTS are assumed to be negligible, and a probability distribution to 

represent this reduction and its uncertainty is not included in our analysis. 

4.1.2.3 Uncertainty in Shielding Effect of Ground Roughness. Calculations of photon 

exposure rates per unit concentration of radionuclides on the ground surface used in dose 

reconstructions incorporate an assumption that the shielding effect of ground roughness reduces 

the exposure rate to about 70% of the exposure rate from an unshielded plane source (Egbert et 

al., 1985; Raine et al., 2007). If the shielding effect of ground roughness and other terrain 

irregularities reduced exposure rates by a greater amount than assumed in dose reconstructions, 

for example, concentrations of radionuclides on the ground surface would be underestimated. 

 On the basis of measurements and calculations reviewed by Burson and Profio (1977), 

which apply to various types of contaminated surfaces (paved areas, lawns, gravelled areas, 

plowed fields, hills, and washes), we assume that the shielding effect of ground roughness at 

NTS reduced photon exposure rates compared with exposure rates above an unshielded plane 

source by an uncertain factor that is represented by a uniform probability distribution between 

0.5 and 0.9. A reduction in exposure rates by a factor outside this range seems highly unlikely 

(Burson and Profio, 1977). Since a reduction in exposure rates by a factor of about 0.7 is 

assumed in dose reconstructions, as noted above, the uncertainty in estimated concentrations of 

radionuclides on the ground surface, SA, due to uncertainty in the shielding effect of ground 

roughness is assumed to be represented by a uniform probability distribution with a minimum at 

0.7/0.9 = 0.78 and a maximum at 0.7/0.5 = 1.4. Thus, we assume that, on average, the shielding 
26

 

effect of ground roughness that is incorporated in dose reconstructions results in slight 

underestimates (by about 10%) of concentrations of radionuclides on the ground surface. 

 Penetration of deposited fallout into surface soil over time, which is often referred to as 

weathering, would result in reductions in photon exposure rates per unit concentration of 

radionuclides on the ground compared with exposure rates assumed in dose reconstructions. 

However, we assume that weathering of fallout had a negligible effect on the uncertainty in 

exposure rates per unit concentration, because exposure rates that are used to estimate 

radionuclide concentrations on the ground surface at NTS were measured within a few days of 

each shot and weathering at an arid site should not be important over such short times. 

4.1.2.4 Uncertainty in Relative Activities of Radionuclides in Fallout at NTS. Activity 

concentrations of radionuclides in deposited fallout that are assumed in dose reconstructions are 

estimated from measured photon exposure rates in air above ground and an assumption that there 

was no fractionation of radionuclides, except for removal of noble gases (NRC, 2003). That is, 

the relative activities of radionuclides in fallout are estimated on the basis of estimates of their 

abundances or abundances of their precursor radionuclides in weapons debris shortly after a 

detonation, before chemical and physical separation of different elements, a process referred to 

as fractionation, occurred;18 fractionation of fallout from detonations at NTS is discussed, for 

example, by Hicks (1982; 1990). Abundances of specific radionuclides in weapons debris are 

estimated on the basis of calculations and data from cloud sampling. Relative activities of 

fission products that resulted from a known fission mode in a weapon (e.g., fission of 239Pu or 

235U by an unmoderated spectrum of fission neutrons) are calculated from known fission yields 

(atoms per fission) of each mass chain produced by that fission mode and radionuclide half-lives 

and parent/decay-product relationships in each mass chain. Contributions to the activities of 

fission products from different fission modes in a weapon and the relative activities of activation 

18 The FIIDOS computer code that is used to calculate doses from inhalation or ingestion of 

radionuclides (Egbert et al., 1985; Raine et al., 2007) includes an option to account for fractionation in 

estimating concentrations of radionuclides other than noble gases in fallout on the basis of data provided 

by the user. That option has not been used in dose reconstructions (NRC, 2003). 
27

 

products and unfissioned weapons material (e.g., plutonium) are estimated from cloud-sampling 

data. We assume that plutonium is the most important unfissioned weapons material in fallout.19

 Fractionation of radionuclides in fallout is a complex phenomenon (Freiling et al., 1965), 

and data on fractionation in fallout from specific shots are not extensive. A simplified and 

idealized description of fractionation is given by Hicks (1982) and in Section IV.C.2.1.2 of the 

NRC (2003) report. For purposes of this analysis, the important effect of fractionation is that, 

compared with unfractionated weapons debris in an atmospheric cloud immediately after an 

above-ground detonation, fallout at locations close to ground zero (e.g., within the boundary of 

NTS) was enhanced in refractory elements that have relatively high boiling points (e.g., 

zirconium, cerium, plutonium) or whose short-lived precursors have high boiling points, due to a 

tendency of those elements to be dissolved in liquid droplets that formed soon after detonation 

and, thus, to be dispersed in the volume of larger particles that fell to Earth relatively rapidly. 

Fallout from above-ground detonations at locations close to ground zero also was depleted in 

volatile elements that have substantially lower boiling points (e.g., strontium, iodine, cesium) or 

whose precursors are volatile, due to a tendency of those elements to condense from the gaseous 

phase at later times and, thus, to be attached to the surface of smaller particles that fell to Earth 

more slowly and were carried farther from ground zero by the winds. 

 In this analysis, effects of fractionation of fallout on doses from inhalation of plutonium 

are considered separately from effects on doses from inhalation of fission and activation 

products. This distinction is made, in part, because fission and activation products include many 

radionuclides, some of which are considered to be refractory and others volatile, whereas 

plutonium is considered to be highly refractory (Freiling et al., 1965; Hicks, 1982), and only 

fission and activation products contributed to measured photon exposure rates (I) that are used to 

estimate concentrations of radionuclides in fallout deposited on the ground (SA). A separate 

19 In this report, the term “plutonium” refers to 239Pu and 240Pu combined, because these two 

isotopes have essentially the same radiological properties (Kocher, 1981; ICRP, 1983). Many weapons 

that were detonated at NTS also contained uranium that was highly enriched in 235U. However, since the 

half-life of 235U exceeds the half-lives of 239Pu and 240Pu by more than a factor of 10,000 (Kocher, 1981; 

ICRP, 1983), 235U was radiologically insignificant unless its mass in fallout was about 10,000 times 

higher than the mass of plutonium, which is highly unlikely. We also note that 235U was not reported in 

later measurements of radionuclides in surface soil at NTS (McArthur, 1991). 
28

 

consideration of plutonium also is warranted when there are sources of uncertainty in internal 

dosimetry models that are more important for alpha-emitting radionuclides than for fission and 

activation products. Measurements in surface soil at NTS after the period of weapons testing 

(McArthur, 1991) indicated that other alpha-emitting radionuclides in fallout (e.g., 241Am and 

238Pu) were unimportant compared with plutonium. 

4.1.2.4.1 Effects of fractionation of fission and activation products. An assessment of 

the effects of fractionation of fission and activation products on estimates of inhalation dose due 

to resuspension of previously deposited fallout requires two considerations. The first is the 

effect of fractionation on estimates of concentrations of radionuclides on the ground surface, 

which are based on measured photon exposure rates and a calculated exposure rate per unit 

concentration of each radionuclide. The second is the effect of fractionation on estimates of dose 

from inhalation of small, respirable particles or larger, nonrespirable particles at concentrations 

of radionuclides on the ground that correspond to a given exposure rate.20

 Although fallout from above-ground detonations at NTS generally was enhanced in 

refractory radionuclides compared with unfractionated weapons debris (Hicks, 1982; Miller, 

1969), the extent of fractionation in fallout from particular detonations is not well known and 

presumably was shot-specific. However, the effects of fractionation of fission and activation 

products on estimates of inhalation dose due to resuspension of radionuclides in previously 

deposited fallout can be bounded by assuming an extreme case in which only refractory 

radionuclides, but none of the volatile radionuclides, were present in fallout at NTS. 

 A bounding analysis of the effects of fractionation of fission and activation products on 

doses from inhalation of resuspended radionuclides in respirable or nonrespirable form at NTS 

was performed by Trabalka and Kocher (2007). That analysis was based on the following 

assumptions and data sets: 

20 The effect of fractionation on the relative concentrations of radionuclides in fallout probably is 

correlated to some degree with the effect of fractionation on inhalation doses when it is considered that 

the greater the degree of fractionation, the greater the fraction of the activity that is attached to larger 

particles and, thus, the lower the fraction of the activity that is attached to inhalable particles. The 

importance of such a correlation is considered in Section 4.2.5. 
29

 

• The dominant fission modes in detonations at NTS were fission of 235U or 239Pu by 

spectra of fission neutrons, but in unknown proportions.21 Thus, it was assumed that 

uncertain contributions from 235U and 239Pu fission each could range from 0 to 100%. 

• Fission yields (atoms per fission) of radioisotopes in each mass chain produced in fission 

of 235U or 239Pu were obtained from England and Rider (1994). 

• Production of 237U and 239U/239Np by neutron activation of 238U was included in some 

calculations but not others. When uranium activation products were assumed to be 

present in fallout, intermediate yields (atoms per fission) and higher yields that should be 

bounding were assumed.22

• Fission products were assumed to be refractory or volatile on the basis of a classification 

scheme developed by Hicks (1982; Appendix 2). For the few radionuclides that were 

classified by Hicks as having both volatile and refractory precursors in their decay chains 

(e.g., 91Y, 140Ba, 140La, and 141Ce), half of the fission yield was assumed to be present in 

refractory material and half in volatile material.23

• Effects of fractionation can be assessed by ignoring the presence of activation products 

other than the uranium activation products 237U and 239U/239Np.24

• All radionuclides in fallout at NTS were resuspended to the same extent. 

21 Relative abundances of fission products from fission of 239Pu or 235U at each shot at NTS have 

been estimated on the basis of 137Cs/90Sr ratios in cloud-sampling data and data on the yields of those 

radionuclides in the two fission modes (H.L. Beck, personal communication). Such estimates are not 

needed in a bounding analysis of the effects of fractionation. 

22 Intermediate yields were 15 atoms of 237U and 30 atoms of 239U/239Np per 100 fissions, and 

higher yields were 50 and 100 atoms per 100 fissions, respectively. 

23 Hicks (1982) assumed different proportions of refractory and volatile materials in mass chains 

91, 140, and 141. However, since supporting data are limited and highly variable, Trabalka and Kocher 

(2007) assumed equal proportions of refractory and volatile materials in those mass chains. 

24 Other potentially important activation products include those that were produced by neutron 

activation of weapons casings, shot towers, and soil (e.g., 60Co, 56Mn, and 152,154Eu). Such activation 

products can be ignored for purposes of a bounding analysis of effects of fractionation when most are 

considered to be refractory and including them would reduce differences in external exposure rates and 

inhalation doses from exposure to refractory radionuclides only compared with exposure to an 

unfractionated mixture of refractory and volatile radionuclides (Trabalka and Kocher, 2007). 
30

 

• Calculated photon exposure rates per unit concentration of radionuclides on the ground 

surface can be represented by effective dose-equivalent rates per unit concentration 

calculated by Eckerman and Ryman (1993).25

• Doses from inhalation or ingestion of radionuclides can be represented by the effective 

dose (ICRP, 1991),26 augmented by calculations of equivalent dose to a limited number 

of organs and tissues (i.e., doses to the lung, red marrow, and pancreas from inhalation; 

doses to the colon, red marrow, and pancreas from ingestion).27 Dose coefficients for 

inhalation or ingestion of radionuclides in oxide form by workers currently recommended 

by ICRP (2002) were used in all calculations.28

• Possible differences in absorption of radionuclides from the lungs or GI tract due to the 

lower biological availability of refractory radionuclides, which tend to be dispersed in the 

volume of insoluble fallout particles, compared with volatile radionuclides, which tend to 

be attached to the surface of particles (Miller, 1964), are not taken into account.29

 On the basis of these assumptions, the ratio of the photon exposure rate per unit 

concentration of fission products and uranium activation products on the ground when only 

25 At photon energies of about 0.1 MeV or greater, which are the most important in determining 

exposure rates, differences between exposure (R) and effective dose equivalent are no more than a few 

tens of percent (ICRP, 1987; 1996b). Such differences are unimportant for purposes of this analysis. 

26 The effective dose is a weighted average of equivalent doses to many organs and tissues (ICRP, 

1991), which replaced the effective dose equivalent (ICRP, 1977). Effective dose equivalents or effective 

doses have been calculated in dose reconstructions when results are provided for information only, but 

they are not calculated in dose reconstructions that are used in adjudicating claims for compensation for 

cancer or other radiogenic diseases. 

27 A rigorous analysis would require consideration of equivalent doses to all organs and tissues. 

However, such an analysis is impractical when there are many radionuclides in fallout and distributions of 

dose among various organs and tissues are radionuclide-specific. The lung, red marrow, and colon were 

selected because they often receive relatively high doses, and the pancreas was selected to represent soft 

tissues at minor sites of deposition of radionuclides in the body. 

28 Oxide forms are among the least soluble chemical forms of all elements of concern except 

strontium, and dose coefficients for radionuclides in oxide form are considered appropriate for intakes of 

relatively insoluble fallout particles (Egbert et al., 1985; Raine et al., 2007). 

29 Such differences are considered in evaluating uncertainties in dose coefficients for inhalation of 

larger, nonrespirable fallout particles (see Section 4.1.5.4.3). 
31

refractory radionuclides are assumed to be present to the exposure rate per unit concentration 

when fission products (except noble gases) and activation products are assumed to be 

unfractionated can be estimated at any time after detonation. Similar ratios of doses from 

inhalation of respirable or nonrespirable particles per unit concentration of refractory or 

unfractionated fission products and uranium activation products can be estimated. As discussed 

in Section 3.1, doses from inhalation of larger, nonrespirable particles can be calculated using 

dose coefficients for ingestion. These ratios were estimated at times after detonation of 2 days 

and 4 years to represent the effects of fractionation in fresh fallout at early times and in aged 

fallout (Trabalka and Kocher, 2007). Only the calculations at 2 days are relevant in assessing 

effects of fractionation on estimates of the concentrations of radionuclides in deposited fallout, 

since photon exposure rates used to estimate those concentrations were measured at times shortly 

after each detonation. However, calculations at both times are relevant to evaluating effects of 

fractionation on estimates of inhalation dose. 

 Results obtained from Trabalka and Kocher (2007) of importance to this analysis are 

summarized as follows: 

Time after detonation of 2 days – 

• When all volatile radionuclides are assumed to be removed from an unfractionated 

mixture of fission products and uranium activation products in deposited fallout and only 

refractory radionuclides are assumed to be present, the external dose rate above ground is 

reduced by a factor between 0.37 (fission of 239Pu, fission products only) and 0.62 

(fission of 235U, fission products plus higher yields of uranium activation products). 

Thus, to give a known exposure rate at 2 days, concentrations of refractory radionuclides 

need to be increased by a factor between 1/0.62 = 1.6 and 1/0.37 = 2.7 compared with 

their concentrations in an unfractionated mixture, depending on the fission mode and the 

yields of uranium activation products. 

• When only refractory fission and activation products are assumed to be present and their 

concentrations are increased by a factor that would give a known exposure rate at 2 days, 

as described above, the effective dose from inhalation of respirable particles would 
32

change compared with the effective dose from an unfractionated mixture by a factor 

between 1.0 (fission of 239Pu, fission products only) and 1.3 (fission of 235U or 239Pu, 

fission products plus either yields of uranium activation products). Changes in the 

effective dose from inhalation of nonrespirable particles varied by a factor between 0.64 

(fission of 239Pu, fission products only) and 0.94 (fission of 235U or 239Pu, fission products 

plus higher yields of uranium activation products). When calculations of equivalent dose 

to a limited number of organs and tissues are included, changes in the effective dose or 

equivalent dose to a specific organ or tissue ranged from a factor of 0.96 to 1.7 for 

inhalation of respirable particles and 0.64 to 1.7 for inhalation of nonrespirable particles. 

Time after detonation of 4 years – 

• When only refractory fission and activation products are assumed to be present and their 

concentrations are increased by a factor that would give a known exposure rate at 2 days, 

as described above, the effective dose from inhalation of respirable particles would 

change compared with the effective dose from an unfractionated mixture by a factor 

between 0.50 (fission of 239Pu, fission products plus higher yields of uranium activation 

products) and 1.4 (fission of 235U, fission products only). Changes in the effective dose 

from inhalation of nonrespirable particles varied by a factor between 0.19 (fission of 235U 

or 239Pu, fission products plus higher yields of uranium activation products) and 0.29 

(fission of 239Pu, fission products only). When calculations of equivalent dose to a 

limited number of organs and tissues are included, increases in the effective dose or 

equivalent dose to a specific organ or tissue could be as high as a factor of 1.9 for 

inhalation of respirable particles and 1.1 for inhalation nonrespirable particles. 

In the calculations at 4 years, reductions of more than a factor of 100 in equivalent doses to 

specific organs or tissues were obtained in some cases when only refractory fission and 

activation products are assumed to be present, including doses to red marrow and the pancreas 

from inhalation of nonrespirable particles (Trabalka and Kocher, 2007). Those results are not 

used in this analysis, because our primary concern is the extent to which fractionation could 
33

increase inhalation doses compared with doses calculated in dose reconstructions. Furthermore, 

if fractionation reduced doses to specific organs or tissues from inhalation of fission and 

activation products by a large factor, it is all the more likely that plutonium was the most 

important radionuclide in fallout that had been aged a few years (NRC, 2003) and, thus, that 

uncertainties in doses from fission and activation products would be unimportant. 

 If fallout at NTS consisted of refractory radionuclides only, results of the calculations at 

2 days and 4 years after detonation summarized above indicate the following. At times shortly 

after detonation, doses from inhalation of fission and activation products in respirable form 

would change by a factor between 1.0 and 1.7 and doses from inhalation of fission and activation 

products in nonrespirable form would change by a factor between 0.6 and 1.7 compared with the 

corresponding doses from inhalation of an unfractionated mixture of fission and activation 

products. At times long after detonation, changes in doses would be a factor between 0.5 and 1.9 

for inhalation of respirable particles and between 0.2 and 1.1 for inhalation of nonrespirable 

particles. Thus, the largest potential change in inhalation dose due to fractionation of fission and 

activation products is assumed to be a factor of 5 (i.e., 1/0.2). 

 A result that fractionation of fission and activation products could change doses from 

inhalation of radionuclides in previously deposited fallout at NTS by no more than a factor of 5, 

when large reductions in equivalent doses to some organs or tissues noted above are excluded, is 

reasonable when many refractory and volatile fission products were present in fallout and their 

radiological properties (energies and intensities of emitted radiations) and biokinetic behavior in 

the body are independent of their fractionation characteristics. Effects of fractionation on doses 

from individual radionuclides, which can be large and are highly variable, tend to be averaged 

when many fission products of both types are inhaled. If we consider calculated effective doses, 

for example, the largest changes are seen in doses from inhalation of nonrespirable particles at 

4 years after detonation. Relatively large reductions in effective doses in that case are a 

consequence of the few refractory fission products that are present in significant activities at that 

time, compared with the number of volatile fission products, and the relatively low effective dose 

coefficients for ingestion of longer-lived refractory fission products. Smaller changes are seen in 

effective doses from inhalation of respirable particles at 4 years, even though only a few 
34

refractory fission products are present at that time, essentially because the effective dose 

coefficient for nearly all fission products is determined primarily by the dose to the lung when all 

radionuclides are assumed to be in oxide form and oxide forms of most elements are insoluble. 

 We assume that the bounding analysis of the effects of fractionation of fission and 

activation products on inhalation doses at 2 days and 4 years after detonation described above 

can be used to bound these effects at any time after detonations that produced fallout at NTS. 

We use results of the bounding analysis to develop probability distributions of factors to adjust 

estimates of inhalation dose that are obtained by assuming no fractionation of fission and 

activation products in fallout to account for an enhancement of refractory relative to volatile 

radionuclides in fallout at NTS. We assume that these factors can be represented by uniform 

probability distributions with ranges that are defined by the highest and lowest bounding 

estimates of the effects of fractionation given above. An assumption of uniform probability 

distributions between those bounding estimates is based on considerations that (1) the relative 

importance of the assumed fission modes (fission of 235U or 239Pu by spectra of fission neutrons) 

is unknown to us and was shot-specific, (2) the degree of fractionation of fission and activation 

products in fallout at NTS is largely unknown (i.e., the effects of fractionation could range from 

a bounding value obtained by assuming that only refractory radionuclides were present to the 

value 1.0 if very little fractionation occurred), and (3) the use of single adjustment factors that 

apply to inhalation of respirable or nonrespirable particles separately at any time after detonation 

from a few days to a few years is desirable in estimating doses due to resuspension of 

radionuclides by a subsequent nuclear detonation when fallout at any location of interest at NTS 

may have resulted from multiple detonations at various times. 

 On the basis of the analysis summarized above, we assume that factors to account for the 

uncertain effects of fractionation of fission and activation products on doses from inhalation of 

those radionuclides in respirable or nonrespirable form can be represented by the following 

probability distributions: 

• Inhalation of fission and activation products in respirable form – Uniform distribution 

between 0.5 and 1.9; 
35

• Inhalation of fission and activation products in nonrespirable form – Uniform distribution 

between 0.2 and 1.7. 

Thus, fractionation is assumed to increase or decrease doses from inhalation of fission and 

activation products compared with doses from an unfractionated mixture. The median and mean 

of the assumed distributions are 1.2 and 0.95, and the maximum values are less than 2. Thus, we 

assume that the extent to which fractionation could increase doses from inhalation of fission and 

activation products, compared with doses from inhalation of unfractionated mixtures, is small. 

4.1.2.4.2 Effects of enhancement of plutonium. As noted in Section 4.1.2.4, plutonium 

was the most important alpha-emitting radionuclide in fallout at NTS, and it probably was the 

most important radionuclide in resuspended fallout that had been aged a few years (NRC, 2003). 

Plutonium is highly refractory (Freiling et al., 1965; Hicks, 1982) and its concentrations in 

fallout at NTS thus were enhanced compared with concentrations in unfractionated weapons 

debris. In contrast to fission and activation products, which include many radionuclides, an 

enhancement in the concentrations of plutonium in fallout by some factor results in an increase 

in inhalation doses by the same factor. Since concentrations of plutonium in fallout that are 

assumed in dose reconstructions are based on cloud-sampling data and an assumption that fallout 

was unfractionated (except for removal of noble gases), doses from inhalation of resuspended 

plutonium presumably have been underestimated. 

 The extent to which concentrations of plutonium in fallout at NTS were enhanced due to 

fractionation of weapons debris presumably was shot-specific, and we did not have access to 

data that could be used to estimate the extent of enhancement compared with an assumption of 

no fractionation. On the basis of measured volatile-to-refractory mass ratios in off-site fallout 

from Shots DIABLO, SHASTA, and SMOKY in Operation PLUMBBOB at distances up to 

160 miles, Hicks (1982) concluded that about half of the mass of refractory radionuclides from 

tower shots was present in off-site fallout, which implies that about half of the mass of refractory 

radionuclides was deposited closer to ground zero. At the closest distance to ground zero of 

about 5 miles at which data reported by Hicks (1982) were obtained, the volatile-to-refractory 

mass ratio was about 1.1. When that ratio is compared with an estimated ratio of about 1.4 in 
36

 

unfractionated fallout (Hicks, 1982), an enhancement in refractory radionuclides by less than a 

factor of 2 is indicated. However, data used by Hicks (1982) show increasing enhancements of 

refractory radionuclides with decreasing distance from ground zero, and only one measurement 

at distances closer than 15 miles was reported. Therefore, substantially greater enhancements of 

refractory radionuclides in fallout at distances closer than 5 miles are not ruled out. In addition, 

data used by Hicks may not apply to fallout from other tower shots at NTS. 

 In the absence of definitive data from all shots and at various distances close to ground 

zero of interest in dose reconstructions, a bounding estimate of the extent of enhancement of 

plutonium in fallout at NTS can be obtained from the analysis of the effect of fractionation on 

external dose rates in air above ground (Trabalka and Kocher, 2007) described in the previous 

section. That analysis indicated that concentrations of refractory fission and activation products 

that would give a known external dose rate when all volatile radionuclides are removed are a 

factor between 1.6 and 2.7 higher than the concentrations in an unfractionated mixture that 

would give the same external dose rate. Thus, if there were no uncertainty in cloud-sampling 

data that were used to estimate activities of plutonium relative to activities of fission and 

activation products, fractionation would enhance the concentrations of plutonium in fallout by no 

more than a factor of 2.7. Since the extent of fractionation is unknown, its effect on 

concentrations of plutonium in fallout is represented by a uniform probability distribution 

between 1.0 and 2.7 in the absence of uncertainty in cloud-sampling data. 

 There also is uncertainty in the activities of plutonium relative to the activities of fission 

and activation products due to uncertainty in cloud-sampling data. This uncertainty is assumed 

to be represented by a standard deviation of 30%.30 To account for this uncertainty, we increase 

the upper bound of the uniform probability distribution given above from 2.7 to 3.3.31

 On the basis of considerations described above, we assume that the enhancement in the 

concentrations of plutonium in fallout at NTS due to fractionation is represented by a uniform 

probability distribution between 1.0 and 3.3. The median and mean of this distribution of 2.2 is 

30 H.L. Beck, personal communication. 

31 This increase was obtained by combining a uniform distribution between 1.0 and 2.7 with a 

normal distribution with a mean at 1.0 and standard deviation of 0.3 and setting the upper 95% credibility 

limit of the resulting distribution at the 95th percentile of a uniform distribution with a lower bound at 1.0. 
37

consistent with data from three tower shots in Operation PLUMBBOB that were used by Hicks 

(1982), as discussed above. The assumed probability distribution also represents the uncertainty 

in increases in doses from inhalation of plutonium in respirable or nonrespirable form compared 

with doses obtained by assuming that fallout was unfractionated. 

4.1.2.5 Summary of Uncertainties in Concentrations of Radionuclides in Fallout 

Deposited on Ground Surface. Table 4-1 summarizes assumed uncertainties in the different 

factors that contribute to uncertainty in estimated concentrations of fission and activation 

products or plutonium in deposited fallout at NTS per unit exposure rate in air above ground, 

SA/I, in eq. (5) and, thus, uncertainty in estimated activity concentrations, SA. Table 4-1 also 

gives the assumed uncertainty in the exposure rate, I, discussed in Section 4.1.1. 

 Representations of uncertainties in concentrations of fission and activation products or 

plutonium in deposited fallout, which are used as input to calculations of dose from inhalation of 

resuspended radionuclides in respirable or nonrespirable form, are obtained by combining 

(multiplying) the probability distributions of relevant parameters in Table 4-1. When probability 

distributions are combined using Latin Hypercube sampling as discussed in Section 3.2, the 

following medians and 90% credibility intervals of probability distributions of concentrations of 

radionuclides on the ground as they affect estimates of inhalation dose are obtained: 

• Inhalation of fission and activation products in respirable form – Median at 1.2 and 90% 

credibility interval between 0.32 and 4.4; 

• Inhalation of fission and activation products in nonrespirable form – Median at 0.93 and 

90% credibility interval between 0.19 and 3.5; 

• Inhalation of plutonium in respirable or nonrespirable form – Median at 2.2 and 90% 

credibility interval between 0.60 and 7.7. 

Thus, we estimate that upper 95% credibility limits of concentrations on the ground surface, SA, 

in eq. (5) exceed point estimates used in dose reconstructions by factors of 4.4 for inhalation of 

fission and activation products in respirable form, 3.5 for inhalation of fission and activation 

products in nonrespirable form, and 7.7 for inhalation of plutonium in either form. 
38

The importance of the assumed uncertainty in a parameter to the total uncertainty in SA

can be represented by its contribution to the variance. The uncertainty of a factor of 3 in 

estimated exposure rates that are based on measurement contributes 72% and 56% of the total 

uncertainty in SA for fission and activation products in respirable and nonrespirable form, 

respectively, and 76% for plutonium; this source of uncertainty thus is the most important. 

Uncertainty in the effects of fractionation contributes 22% and 39% of the total uncertainty for 

fission and activation products in respirable and nonrespirable form, respectively, and 18% for 

plutonium. The other two sources of uncertainty contribute 5−7% of the total uncertainties for 

fission and activation products or plutonium. 

 All probability distributions of radionuclide concentrations on the ground, SA, described 

above are represented reasonably well by lognormal distributions with the indicated 90% 

credibility intervals. This is an expected result when the parameter with the largest uncertainty 

in each case (the exposure rate, I) is assumed to be lognormally distributed. The greatest 

deviation from a lognormal distribution occurs in the case of inhalation of fission and activation 

products in nonrespirable form, where the probability distribution of SA is the most influenced 

by the uniform probability distribution that represents uncertainty in the effects of fractionation. 

Geometric standard deviations (GSDs) of lognormal probability distributions with the indicated 

90% credibility intervals are about 2.2 for fission and activation products in respirable form, 2.4 

for fission and activation products in nonrespirable form, and 2.2 for plutonium in either form. 

 In these results and all other results presented in this report, 90% credibility intervals of 

calculated probability distributions have greater significance than medians. This conclusion is 

based on the consideration that assumed shapes of probability distributions of input parameters 

are highly subjective in many cases. 

4.1.3 Resuspension Factors

 Quantities of interest in estimating inhalation doses due to resuspension of previously 

deposited fallout by nuclear detonations at NTS are the concentrations of radionuclides in air that 

could be inhaled at times and locations of exposure. Estimation of those concentrations requires 
39

assumptions about (1) the extent of resuspension of all previously deposited fallout in the 

thermal-pulse or blast-wave region, which is described by a resuspension factor, and (2) the 

inhalable fraction of resuspended radionuclides. The latter assumption takes into account that 

some radionuclides in resuspended fallout presumably were attached to particles that were too 

large to be inhaled or to be present in air at times after a detonation when exposure occurred. 

 Inhalation doses also depend on whether inhalable radionuclides were in respirable or 

nonrespirable form (see Section 3.1). Thus, the inhalable fraction of resuspended radionuclides 

needs to be separated into respirable and nonrespirable fractions. 

 In estimating inhalation doses in the thermal-pulse or blast-wave region, the appropriate 

resuspension factor is the product of the resuspension factor that applies to all fallout on the 

ground surface and the respirable or nonrespirable fraction of resuspended radionuclides. As 

discussed in Section 3.1, a resuspension factor that applies to radionuclides in respirable form is 

appropriate when doses to military participants are estimated by assuming inhalation of small 

particles with an AMAD less than about 10 μm, and a resuspension factor that applies to 

radionuclides in nonrespirable form is appropriate when doses are estimated by assuming 

inhalation of larger particles that are either swallowed or expelled. 

4.1.3.1 Resuspension of Previously Deposited Fallout. Resuspension of radionuclides in 

previously deposited fallout by the thermal pulse/precursor and blast wave in nuclear detonations 

at NTS presumably was higher than resuspension by less vigorous disturbances. However, we 

are not aware of any data on resuspension factors associated with the stressors of interest. 

Therefore, judgment is required in developing a probability distribution of the resuspension 

factor that applies to all previously deposited fallout in the thermal-pulse or blast-wave region. 

We develop separate probability distributions of resuspension factors in the two regions on the 

basis of data on resuspension factors associated with several types of less vigorous disturbances 

and other assumptions. 

4.1.3.1.1 Resuspension factor in thermal-pulse region. Data on resuspension factors 

associated with a variety of mechanical stresses were reviewed by Sehmel (1984; Table 12.9); 

see also Sehmel (1980; Figure 2). The most relevant data for purposes of this analysis were 

obtained at various sites where nuclear weapons were tested, including NTS. Those data are 
40

 

summarized in Table 4-2. Data on resuspension factors in indoor environments reviewed by 

Sehmel (1984) are not considered, because surfaces of floors are different in texture from surface 

soil and resuspension into confined air spaces occurred. Data in Table 4-2 indicate, for example, 

that at a height of 1 m, a resuspension factor associated with vehicular traffic as high as about 

10−4

 m−1 is plausible.32

 We assume that the highest resuspension factor at a height of 1 m associated with 

vehicular traffic of about 10−4

 m−1 provides a lower credibility limit of the resuspension factor 

that applies to all previously deposited fallout in the thermal-pulse region. Data in Table 4-2 and 

other data on resuspension of plutonium from safety shots at NTS (Anspaugh et al., 1975) 

suggest that penetration of fallout into surface soil over time could have reduced the 

resuspension factor that should be applied to aged fallout to lower values. However, 

measurements at NTS also suggested that more than 95% of all plutonium in fallout was retained 

in the top quarter inch (about 0.6 cm) at 1.5 years after deposition (Dick and Baker, 1961). 

Therefore, since stressors in the thermal-pulse region, including the thermal pulse, precursor, and 

blast wave with associated wind speeds that exceeded 200 mph (see Table 2-1), presumably were 

more effective than vehicular traffic in resuspending material located within about 1 cm of the 

ground surface, we assume that penetration of fallout into surface soil over time was not an 

important factor in determining resuspension in the thermal-pulse region during time periods 

after deposition of concern in dose reconstructions. The earliest shots that produced fallout at 

NTS occurred in 1951 (Hawthorne, 1979), and exposures in the thermal-pulse or blast-wave 

region occurred as late as 1957 (NRC, 2003). Therefore, the time period between deposition and 

subsequent resuspensions of concern is about 6 years or less. 

 We then assume that an upper credibility limit of the resuspension factor that applies to 

all previously deposited fallout in the thermal-pulse region is 10−2

 m−1. This assumption is 

supported by the following argument. On the basis of an estimate that the diameter of the 

32 Resuspension factors at a height of 0.3 m in Table 4-2, which are as high as 10−3

 m−1, should be 

interpreted with caution, because values at a height of 1 m associated with wind-driven resuspension may 

be substantially less than resuspension factors at 0.3 m (Stewart, 1967). Data summarized in Table 4-2 do 

not indicate whether resuspension factors associated with mechanical stresses were substantially lower at 

the normal height of the head of an individual standing on the ground than at 1 m. 
41

fireball produced in a 20-kt detonation was about 500 m [Glasstone and Dolan (1977), as 

summarized by Walker (2004)] and photographs of fireballs and dust clouds at times shortly 

after above-ground detonations at NTS (AFLML, 1951), such as shown in Figure 2-1, we 

estimate that the height of the dust cloud in the thermal-pulse region was in the range of about 

100−300 m. At the lower height of 100 m, a resuspension factor of 10−2

 m−1 corresponds to an 

assumption that all fallout on the ground surface was resuspended, which clearly is an upper 

bound. At a height of 300 m, the maximum resuspension factor obtained by assuming that all 

fallout was resuspended is (1/3) × 10−2

 m−1. However, a somewhat higher resuspension factor 

could still apply within a few meters of the ground surface if airborne concentrations of 

resuspended material were lower near the top of the dust cloud in the thermal-pulse region than 

near the ground. 

 On the basis of the considerations described above, we assume that the resuspension 

factor that applies to all previously deposited fallout in the thermal-pulse region of nuclear 

detonations at NTS is represented by a lognormal probability distribution with a 90% credibility 

interval between 10−4 and 10−2 m−1. The median of this distribution is 10−3 m−1 and the GSD is 

about 4.1. If we assume a nominal height of a resuspended dust cloud in that region of 100 m 

and a uniform distribution of dust with height, the median resuspension factor corresponds to an 

assumption that 10% of all fallout on the ground surface was resuspended. At the lower 

credibility limit of the resuspension factor, 1% of all fallout on the ground is assumed to be 

resuspended; we believe that this is a reasonable result given the violent nature of stressors in the 

thermal-pulse region. 

 Support for the assumed 90% credibility interval of the resuspension factor that applies to 

all previously deposited fallout in the thermal-pulse region is provided by measurements of 

airborne concentrations of resuspended dust at Operation TEAPOT, Shot MET (Gordon et al., 

1957), which was a 22-kt tower shot at a height of 400 ft (Hawthorne, 1979). At distances from 

ground zero of 2,000 and 2,500 ft, which were within the thermal-pulse region that extended to a 

distance of about 3,900 ft as estimated from Figure 2-2, concentrations of airborne dust at 

heights of 3 and 10 ft ranged from 0.05 to 2 mg cm–3. If we assume somewhat arbitrarily that the 

top 1 cm of soil of density about 1.5 g cm–3 was subject to resuspension, the concentrations of 
42

 

airborne dust correspond to a resuspension factor of about 0.003–0.13 m–1. Given the substantial 

uncertainties in the measured concentrations of airborne dust and the depth of surface soil that 

was subject to resuspension, we believe that the estimated range of the resuspension factor based 

on measurement provides some support for our assumed 90% credibility interval. 

4.1.3.1.2 Resuspension factor in blast-wave region. In the blast-wave region, the 

resuspension factor that applies to all previously deposited fallout presumably was less than in 

the thermal-pulse region, due to the absence of a thermal pulse and precursor and the lower wind 

speeds associated with a blast wave. In addition to the lack of measurements under conditions of 

a high-speed burst of wind of short duration, estimation of a resuspension factor is complicated 

by (1) the decrease in the maximum wind speed associated with a blast wave with increasing 

distance from ground zero (see Section 2.2 and Table 2-1) and (2) the likely dependence of the 

resuspension factor on the maximum wind speed, given that concentrations of resuspended 

material in arid environments typically increase with increasing wind speed at wind speeds lower 

than maximum values associated with a blast wave (Sehmel, 1984; Table 12.10). Therefore, the 

resuspension factor at the inner boundary of the blast-wave region, where the peak overpressure 

was about 6 psi and the maximum wind speed associated with a blast wave was nearly 200 mph 

(see Table 2-1), probably was substantially higher than at greater distances from ground zero, 

where the maximum wind speed that could have caused unusually high resuspension perhaps 

was in the range of about 40–70 mph (see Section 2.2).33

 For purposes of this analysis, we believe that it is appropriate to develop a single 

probability distribution to represent an average resuspension factor that applies to all previously 

deposited fallout throughout the blast-wave region. This approach takes into account that 

participants who entered the blast-wave region shortly after a detonation were exposed to 

resuspended radionuclides over a range of distances from ground zero and for varying durations 

33 If the resuspension factor is assumed to increase with wind speed, u, as u

2.5, where the exponent 

is a nominal value based on data reported by Sehmel (1984; Table 12.10), the resuspension factor in the 

outermost portions of the blast-wave region would be about 1–2 orders of magnitude less than at the inner 

boundary, depending on the assumption about the lowest maximum wind speed in the blast-wave region. 

However, observed dependencies of the resuspension factor on wind speed, which are highly variable, 

may not apply at higher wind speeds in the blast-wave region, in part because available data apply mainly 

to resuspension of small, respirable particles, whereas larger particles presumably were resuspended to a 

greater extent at higher wind speeds, especially near the thermal-pulse region. 
43

at different distances, and that there are no data on the dependence of the resuspension factor on 

wind speed at the maximum wind speeds of short duration in the blast-wave region. Thus, it is 

difficult to justify the use of a resuspension factor in the blast-wave region that varies with 

distance from ground zero. 

 Data on resuspension factors associated with wind stresses were reviewed by Sehmel 

(1984; Table 12.7); see also Sehmel (1980, Figure 2), Shinn et al. (1986), and Nicholson (1988). 

Reported resuspension factors range from about 10−10 to 3 × 10−4

 m−1. As in the data on 

resuspension factors associated with mechanical stresses summarized in Table 4-2, the highest 

value in that range applied at a height of 0.3 m, and the highest value at a height of 1 m is lower 

(about 5 × 10−5

 m−1). However, available data on wind-driven resuspension probably have 

limited relevance to this analysis when they apply at wind speeds less than 25 mph, which are 

much lower than maximum wind speeds in the blast-wave region. In addition, most of the data 

apply under conditions of chronic wind stress, and some of the data, including some data on 

resuspension of plutonium at NTS (Shinn et al., 1986), apply at times of a few decades after 

deposition, when long-term weathering probably reduced resuspension by the wind. 

 Data on resuspension factors associated with mechanical stresses, as discussed in the 

previous section and summarized in Table 4-2, also may be relevant in developing a 

resuspension factor in the blast-wave region. In particular, we believe that it is reasonable to 

assume that the resuspension factor in areas of the blast-wave region closest to the thermal-pulse 

region, where the maximum wind speed was the highest, could have been substantially higher 

than resuspension factors associated with vehicular traffic. 

 A 90% credibility interval of the resuspension factor in the blast-wave region is estimated 

on the basis of the following considerations: 

• The resuspension factor in the blast-wave region should be substantially lower than in 

the thermal-pulse region. 

• The concentration of resuspended material at the inner boundary of the blast-wave 

region should be about the same as the concentration in the thermal-pulse region (i.e., the 

concentration should not be grossly discontinuous at that boundary). Thus, if the height 
44

of the dust cloud at the inner boundary of the blast-wave region is less than the height of 

the cloud in the thermal-pulse region by some factor, the resuspension factor at the inner 

boundary of the blast-wave region would be less than the resuspension factor in the 

thermal-pulse region by about the same factor. 

• The uncertainty in the resuspension factor in the blast-wave region should be 

substantially higher than the uncertainty in the thermal-pulse region, due to the likely 

dependence of the resuspension factor on the maximum wind speed, which decreases 

with increasing distance from ground zero, and the likelihood that the resuspension 

factor decreases with increasing age of the previously deposited fallout, especially in 

areas of the blast-wave region where the maximum wind speed was relatively low. 

On the basis of these considerations, we assume that the resuspension factor that applies to all 

previously deposited fallout in the blast-wave region can be represented by a lognormal 

probability distribution with a 90% credibility interval between 10−7

 to 10−3 m−1. The median of 

this distribution is 10−5 m−1 and the GSD is about 16. Since the height of the dust cloud in the 

blast-wave region was substantially lower than in the thermal-pulse region and perhaps was a 

few tens of meters at most (see Figure 2-1), the upper 95% credibility limit of the assumed 

probability distribution corresponds to an assumption that no more than a few percent of fallout 

was resuspended to a height of at least 1 m by a blast wave. The assumed probability 

distribution overlaps higher resuspension factors associated with mechanical stresses (e.g., 

vehicular traffic; see Table 4-2) and higher resuspension factors associated with wind stresses 

(Sehmel, 1984). We believe that these comparisons provide support for our assumption. 

4.1.3.1.3 Discussion of resuspension factors for previously deposited fallout. Assumed 

probability distributions of resuspension factors that apply to all previously deposited fallout in 

the thermal-pulse or blast-wave region developed in the previous two sections are based in part 

on observations and assumptions about the extent of resuspension of surface soil in the two 

regions, especially the height of the resulting dust clouds. Thus, those probability distributions 

incorporate an implicit assumption that resuspension factors that apply to fallout and surface soil 

are similar. 
45

 Several studies, including studies of plutonium and other radionuclides at NTS, have 

shown that, under certain conditions, resuspension of previously deposited radioactive material 

can be significantly different from resuspension of surface soil (Shinn et al., 1986; Shinn, 1992; 

NCRP, 1999, and references therein). In models of resuspension, such differences are 

represented by an enhancement factor, which is defined as the ratio of the activity per unit mass 

of airborne particles to the activity per unit mass in surface soil (NCRP, 1999). Studies reviewed 

by NCRP (1999) have shown the following. First, enhancement factors that applied to 

undisturbed surface soil ranged from about 0.2 to slightly greater than 1.0, thus indicating that 

the resuspension factor that applied to the deposited material was somewhat less than the 

resuspension factor that applied to soil. Second, in cases where surface soil was recently 

disturbed (e.g., by soil thawing, bulldozer blading, vacuum cleaning, a wildfire, and raking), the 

enhancement factor that applied to redeposited radioactive material over the first few days 

following a disturbance ranged from about 2 to more than 8, thus indicating a substantially 

higher resuspension factor for the redeposited material compared with soil. Finally, in the case 

of a surface nuclear detonation at NTS, where some of the radioactive material at locations close 

to ground zero was incorporated in an amorphous silicate glass, referred to as “shot glass,” the 

enhancement factor ranged from about 0.002 to 0.024, thus indicating a much lower 

resuspension factor for the radioactive material compared with soil. Most of the glass particles 

were large, with diameters on the order of 1 mm or higher (Lee and Tamura, 1981). 

 We do not believe that the studies of enhancement factors summarized above indicate 

that our assumed probability distributions of resuspension factors that apply to all previously 

deposited fallout in the thermal-pulse or blast-wave region need to be modified. Since the 

assumed probability distributions were based in large part on data on resuspension of plutonium 

by mechanical stressors or the wind at NTS and other sites where nuclear weapons were tested 

[see Table 4-2 and Sehmel (1984; Table 12.7)], these data already incorporate any enhancement 

factor. Furthermore, large enhancement factors that apply in cases where surface soil was 

significantly disturbed, especially by human activity, probably are not relevant to resuspension 

by nuclear detonations at NTS, where most of the land was undisturbed prior to resuspension. 
46

The possibility that the assumed probability distributions of resuspension factors 

significantly overestimate resuspension of larger fallout particles, as suggested by data on an 

enhancement factor for shot glass noted above, is potentially important when, as discussed in 

Section 4.1.3.2.2 below, fallout at NTS consisted mainly of larger particles of diameter greater 

than 100 μm. This concern could be especially important in the blast-wave region, given that 

such larger particles usually are not resuspended by the wind (Sehmel, 1980; 1984). However, 

as indicated by the development of assumptions about the respirable and nonrespirable fractions 

of resuspended fallout in inhalable form in the following section, the possibility that we have 

greatly overestimated resuspension of larger fallout particles is unimportant in estimating 

inhalation dose, essentially because larger particles are assumed not to be inhalable or they 

would not have remained in the air for a significant period of time even if they were inhalable. 

That is, an overestimate of resuspension of larger fallout particles is unimportant when those 

particles do not contribute significantly to inhalation doses. 

4.1.3.2 Respirable and Nonrespirable Fractions of Resuspended Radionuclides. In the 

model currently used to estimate inhalation dose in any resuspension scenario, all resuspended 

radionuclides are assumed to be inhalable (see Section 3.1). However, it is virtually certain that 

only a fraction of fallout particles that were resuspended by nuclear detonations at NTS were 

sufficiently small that they were present in air and could have been inhaled at times shortly after 

a detonation when exposure in the thermal-pulse or blast-wave region occurred. 

 As noted previously, quantities of interest to this analysis are resuspension factors that 

apply to the respirable and nonrespirable, but still inhalable, fractions of radionuclides in fallout 

that was resuspended in the thermal-pulse or blast-wave region. To estimate those fractions, we 

first estimate the inhalable fraction of resuspended radionuclides and the respirable fraction of 

inhalable radionuclides; the product of those fractions gives the respirable fraction of 

resuspended radionuclides. The nonrespirable fraction of inhalable radionuclides then is 

estimated from the relationship that the sum of the respirable and nonrespirable fractions of 

inhalable radionuclides must be unity. The product of that fraction and the inhalable fraction of 

resuspended radionuclides gives the nonrespirable fraction of resuspended radionuclides. This 

approach ensures that a proper correlation between the respirable and nonrespirable fractions of 
47

 

resuspended radionuclides in inhalable form is preserved when all fractions are described by 

probability distributions to represent their uncertainty; i.e., it ensures that the sum of the 

respirable and nonrespirable fractions is equal to the inhalable fraction. 

 Development of probability distributions of the respirable and nonrespirable fractions of 

resuspended radionuclides in the thermal-pulse and blast-wave regions is described in the 

following sections. We first discuss the importance of maximum dust loadings in air that can be 

tolerated while breathing in establishing that most resuspended soil particles in the two regions 

must have been redeposited on the ground quickly by gravitational settling. The next three 

sections discuss available data on particle-size distributions of activity in fallout from tower 

shots at NTS and the use of those data to estimate the fraction of resuspended radionuclides that 

remained airborne at times of exposure. The last two sections present and discuss the assumed 

probability distributions of the inhalable and respirable fractions of resuspended radionuclides in 

the thermal-pulse and blast-wave regions and the nonrespirable fractions of resuspended 

radionuclides that were derived from those distributions. 

4.1.3.2.1 Gravitational settling of resuspended material. In estimating doses from 

inhalation of radionuclides in fallout that was resuspended in the thermal-pulse or blast-wave 

region, an important consideration is that the dust loading in air during prolonged exposures had 

to be less than levels that are intolerable while breathing.34 Consider, for example, resuspension 

in the thermal-pulse region. If we assume that the top 1 mm of surface soil was resuspended in 

that region, the height of the dust cloud was 300 m, and the density of soil was1.5 g cm−3

, the 

average dust loading in air would be 5 g m−3

. An assumption of a greater depth of resuspended 

surface soil or a lower height of the dust cloud would increase the estimated dust loading. This 

estimate can be compared with a dust loading of about 0.1 g m−3

 that was identified by Stewart 

(1967) as barely tolerable while breathing. The barely tolerable dust loading is nearly two orders 

of magnitude less than the estimated dust loading in the thermal-pulse region. Therefore, if a 

34 This consideration is based on an assumption that participants who were exposed to 

resuspended material in the thermal-pulse or blast-wave region at NTS did not wear respiratory protection 

during their entire period of exposure. Forward observers who were located in the blast-wave region at 

the time of a detonation may have taken some action to limit inhalation of airborne dust for a short time 

after detonation (e.g., a few minutes or less), but not for long periods of time. 
48

 

substantial fraction of surface soil was resuspended in the thermal-pulse region, it is reasonable 

to conclude that only a small fraction of the resuspended soil could have remained in the air 

when significant inhalation exposure occurred. 

 A similar consideration should apply in the blast-wave region. Although a smaller 

fraction of surface soil presumably was resuspended in that region than in the thermal-pulse 

region, the dust loading still could have been intolerably high when the lower height of the dust 

cloud in the blast-wave region is taken into account, especially at locations near the boundary of 

the thermal-pulse region. 

 Large reductions in concentrations of resuspended dust to levels that are tolerable while 

breathing can be obtained by assuming that most material that was resuspended by nuclear 

detonations consisted of larger particles that fell to Earth quickly by gravitational settling. 

Consider, for example, gravitational settling of soil particles of diameter 100 μm, which is the 

largest diameter at which the inhalability of particles has been studied (ICRP, 1994; NCRP, 

1997); i.e., particles of diameter greater than 100 μm are assumed to be too large to be inhaled. 

Gravitational settling of particles in air occurs under the influence of frictional (viscous) 

and inertial forces. At a particle diameter of 100 μm, neither force is dominant. In such cases, 

the settling velocity can be estimated using an approach described by Hinds (1982; Section 3.7 

and Table 3.4).35 For an assumed density of soil particles of 1.5 g cm–3 and an assumed dynamic 

shape factor of 1.57, the estimated settling velocity is 24 cm s–1. The dynamic shape factor takes 

into account that nonspherical particles have lower settling velocities than spherical particles; a 

dynamic shape factor of 1.57 is a representative value for sand (Hinds, 1982; Table 3.2). At this 

settling velocity, the time required for a soil particle to fall to Earth from an assumed maximum 

height of the dust cloud in the thermal-pulse region of 300 m is about 20 minutes. Thus, unless 

35 In this approach, the quantity CDRe2

, where CD is the coefficient of drag and Re is the Reynolds 

number, is calculated as CDRe2

 = 4d3ρpρag/3η2χ, where d is the particle diameter (i.e., diameter of an 

equivalent volume sphere for a nonspherical particle) in cm, ρp is the particle density in g cm–3, ρa is the 

density of air (1.2 × 10–3 g cm–3), g is the acceleration due to gravity (981 cm s–2), η is the viscosity of air 

(1.81 × 10–4 g cm–1 s–1) and χ is the dynamic shape factor; CDRe2

 thus depends on the particle diameter 

and density but does not depend on the settling velocity. From the calculated value of CDRe2

, the 

corresponding Reynolds number is obtained from Table 3.4, and the settling velocity, V, is calculated 

from the Reynolds number as V = (Re)η/ρad. This approach overcomes the problem that although V can 

be expressed in terms of CD, estimation of CD requires knowledge of Re, which depends on V. 
49

exposure occurred in the thermal-pulse region shortly after a detonation, the largest inhalable soil 

particles, as well as soil particles that were too large to be inhaled, would not have remained in 

the air at times of exposure. 

In contrast, consider a 10-μm diameter soil particle, which is sufficiently small that the 

frictional (viscous) force is dominant and Stokes Law can be applied (Hinds, 1982). At that 

diameter and again assuming a dynamic shape factor of 1.57, the estimated settling velocity is 

about 0.3 cm s–1, and the fall time from a height of 300 m is about 28 hours. 

If the maximum height of a dust cloud in the blast-wave region was about one-tenth of 

the maximum height in the thermal-pulse region, as discussed previously, the maximum fall time 

for soil particles of diameter 100 or 10 μm would be one-tenth of the maximum fall times in the 

thermal-pulse region estimated above. Thus, in the blast-wave region, where some forward 

observers were located at the time of a detonation, the largest inhalable soil particles would have 

remained airborne for no more than about two minutes, or less if the maximum height of the dust 

cloud was less than 30 m at locations of exposure, whereas smaller particles remained airborne 

for a much longer time. 

Similar calculations can be performed for fallout particles from tower shots at NTS, 

which have a density of about 2.7 g cm–3 (Miller, 1969). If we assume a dynamic shape factor of 

1.3, which is representative of values for clusters of spheres (Hinds, 1982; Table 3.2), the 

estimated settling velocity of fallout particles of diameter 100 μm is 48 cm s–1, and the fall time 

from a height of 300 m is about 10 minutes. At a particle diameter of 10 μm, the settling 

velocity is about 0.6 cm s–1, and the fall time from a height of 300 m is about 13 hours. 

 Actual fall times of larger particles may have been somewhat longer than the values 

estimated above, due to the effects of turbulence in the atmosphere following passage of the blast 

wave. However, since the highest wind speeds at a given location persisted for only a few 

seconds and winds thereafter were much weaker (Glasstone and Dolan, 1977), it is not expected 

that turbulence greatly increased the fall times of larger particles. Furthermore, the estimated fall 

times of larger particles given above apply to particles that are assumed to fall from the 

maximum height of the dust cloud, and fall times from that height should have been affected by 

turbulence to a lesser extent than shorter fall times from lower heights. 
50

 

4.1.3.2.2 Particle-size distributions of activity in fallout. Fall times of larger fallout 

particles given in the previous section are relevant when particle-size distributions of activity in 

fallout are considered. Tower shots produced most of the fallout at NTS to which participants 

could have been exposed in the thermal-pulse or blast-wave region after a subsequent detonation 

(Hawthorne, 1979; Dancz and Chehata, 2006).36 The first tower shot that resulted in significant 

on-site fallout was Shot EASY in Operation TUMBLER-SNAPPER in 1952. As discussed 

below, larger particles contained most of the activity in on-site fallout from tower shots; a 

preponderance of larger particles is expected on the basis of considerations of fractionation of 

radionuclides in fallout from above-ground detonations (see Section 4.1.2.4). 

 Data on particle-size distributions of activity in on-site fallout from tower shots at NTS 

appear to be limited. Data on fallout within about 10 miles of ground zero are of greatest interest 

to this analysis, because fallout at greater distances did not impact areas where exposure in the 

thermal-pulse or blast-wave region occurred at subsequent detonations (Dancz and Chehata, 

2006; Goetz et al., 1979; Hawthorne, 1979). Data that we are aware of are described below. 

Data on fallout at distances between 10 and 20 miles also are included to provide additional 

information that may be useful in interpreting data at closer distances of interest. 

Particle diameters in reported particle-size distributions of activity in fallout presumably 

represent physical diameters as estimated, for example, from sieve analysis of samples. A 

physical diameter is not the same as an aerodynamic equivalent diameter, which is the diameter 

of a unit density sphere that has the same settling velocity as the particle of interest and is used in 

estimating the AMAD of a particle-size distribution for purposes of estimating dose from 

inhalation of radionuclides (ICRP, 1994; NCRP, 1997). The aerodynamic diameter of a fallout 

particle of density 2.7 g cm–3 (Miller, 1969) with an assumed dynamic shape factor of 1.3 is 

about 40–50% greater than the physical diameter (Hinds, 1982). However, the distinction 

36 Fallout from surface or underground shots (e.g., Shots SUGAR and UNCLE in Operation 

BUSTER-JANGLE and Shot ESS in Operation TEAPOT) or airdrop shots (e.g., Shots WASP and WASP 

PRIME in Operation TEAPOT and Shots WILSON and PRISCILLA in Operation PLUMBBOB) was 

unimportant, because there was little fallout at NTS or on-site fallout did not significantly impact areas 

where exposure in the thermal-pulse or blast-wave region occurred after a subsequent detonation. On-site 

fallout from the few safety shots through Operation PLUMBBOB in 1957 also was unimportant, because 

those shots did not occur in the same areas as above-ground detonations or they did not impact locations 

where subsequent exposures of participants occurred. 
51

between the physical and aerodynamic diameter of particles is not important to this report when 

the objective is to derive effective resuspension factors to the nearest power of 10 only. We also 

note that: (1) the uncertainty in distributions of physical diameters of fallout particles at NTS is 

large, as indicated in the following discussions; (2) it is difficult to estimate an AMAD of fallout 

particles and its uncertainty when data are limited and those quantities depend on particle shapes, 

which are irregular and variable, as well as their sizes. 

Data at Operation TUMBLER-SNAPPER. Particle-size distributions of activity in 

fallout that was present in surface soil at the end of Operation TUMBLER-SNAPPER in 1952 

were reported by Olafson et al. (1953). All data were obtained at locations beyond the boundary 

of NTS, and only two locations were within 20 miles of a tower shot at that operation. At a 

distance of 12 miles from Shot HOW, which was detonated at a height of 300 ft with a yield of 

14 kt (Hawthorne, 1979), reported percentages of the total activity in the smallest size fractions 

of fallout were as follows: 0–44 μm, 12%; 44–73 μm, 23%, and 74–149 μm, 13%. At 18 miles 

from Shots FOX and GEORGE, which were detonated at a height of 300 ft with yields of 11 kt 

and 15 kt, respectively, percentages in those size fractions were 1.6%, 39%, and 21%. Thus, 

particles of diameter less than 150 μm contained about half or more of the total activity. 

The high percentages of the total activities in the size fraction less than 150 μm noted 

above may be anomalous, given that the reported percentages in that size fraction at two other 

locations more than 25 miles from any tower shot in Operation TUMBLER-SNAPPER were 

12% and 15% (Olafson et al., 1953). In addition, both measurement locations probably received 

fallout from the prior underground Shot UNCLE in Operation BUSTER-JANGLE, and the 

location at 12 miles from Shot HOW probably received fallout from Shot FOX (Hawthorne, 

1979). Particle-size distributions of activity in fallout from Shot UNCLE probably did not 

resemble distributions from tower shots, and Shots HOW and FOX were detonated at different 

distances from the measurement location closest to Shot HOW. Therefore, it is questionable 

whether the reported particle-size distributions of activity described above apply to fallout at a 

known distance from a tower shot. 

Data at Operation UPSHOT-KNOTHOLE. Particle-size distributions of activity in 

fallout from tower Shots NANCY, BADGER, and SIMON in Operation UPSHOT-KNOTHOLE 
52

in 1953 were reported by Rainey et al. (1954). Those shots were detonated at a height of 300 ft 

with yields of 24 kt at Shot NANCY, 23 kt at Shot BADGER, and 43 kt at Shot SIMON. 

Reported percentages of the total activities in the smallest size fractions of fallout at distances 

within 20 miles of those shots are given in Table 4-3. Only the data at the closest distance at 

each shot apply to on-site fallout. On the basis of these data, we estimate that fallout particles of 

diameter less than 100 μm, which is the largest diameter at which particles are assumed to be 

inhalable (ICRP, 1994; NCRP, 1997), contained the following percentages of the total activities 

in samples closest to ground zero: 51% at Shot NANCY, 9% at Shot BADGER, and 0.3% at 

Shot SIMON. These estimates were obtained by assuming that particles of diameter less than 

100 μm contained one-third of the activity in the 88−125 μm size fraction; i.e., the distribution of 

activity in that size fraction was assumed to be uniform. 

The data at a distance of 3.5 miles from Shot NANCY appear to be anomalous, given that 

the percentage of the total activity in the size fraction less than 125 μm is much higher than at 

greater distances. At a distance of about 3 miles from Shot BADGER, the percentage of the total 

activity in that size fraction also is higher than at greater distances, but differences are not as 

pronounced as in the data at Shot NANCY. The lower exposure rate at the closest distance at 

Shot BADGER compared with the three highest exposure rates at greater distances suggests that 

the closest measurement location was some distance from the centerline of the fallout plume. 

However, the percentage of the total activity in the size fraction less than 125 μm did not vary 

greatly at greater distances even though the exposure rate varied by more than a factor of 30. 

Only the data at Shot SIMON conform to an expectation that the percentage of the total activity 

in the size fraction less than 125 μm should be smallest at the location closest to ground zero. In 

addition, in contrast to the data at Shot BADGER, the percentages of the total activities in that 

size fraction at greater distances were much higher at locations where the exposure rate was 

relatively low than at locations where the exposure rate was much higher. 

Data at Operation TEAPOT. Particle-size distributions of activity in fallout from tower 

Shots TESLA, TURK, APPLE I, MET, and APPLE II in Operation TEAPOT in 1955 were 

reported by Baurmash et al. (1958). The heights of detonation and yields were 300 ft and 7 kt at 

Shot TESLA, 500 ft and 43 kt at Shot TURK, 500 ft and 14 kt at Shot APPLE I, 400 ft and 22 kt 
53

at Shot MET, and 500 ft and 29 kt at Shot APPLE II (Hawthorne, 1979). Reported percentages 

of the total activities in the smallest size fractions of fallout at distances within 20 miles of those 

shots are given in Table 4-4. Especially at Shots TESLA, MET, and APPLE II, fallout was 

collected at several locations at the same distance. These data give information on variations in 

particle-size distributions at different distances from the centerline of a fallout plume. Only the 

data at Shot APPLE II apply to on-site fallout. The 0−44 μm size fraction in samples from that 

shot contained between 0.15% and 2.5% of the total activity, with an average of about 0.9%. By 

again assuming a uniform distribution of activity in the 88−125 μm size fraction, we estimate 

that inhalable particles of diameter less than 100 μm in the samples at Shot APPLE II contained 

between 0.25% and 3.2% of the total activity, with an average of 1.6%. 

 When compared with the data at other shots in Table 4-4, data at Shot APPLE II conform 

to an expectation that the percentages of the total activities in the size fraction less than 125 μm 

were comparable to or less than the percentages in fallout at greater distances. Data at the 

different shots do not show any evident anomalies. 

Data at Operation PLUMBBOB. Data on particle-size distributions of activity in on-site 

fallout from tower Shots DIABLO and SHASTA in Operation PLUMBBOB in 1957 were 

reported by Miller (1969). Both shots were detonated at a height of 500 ft with a yield of 17 kt 

(Hawthorne, 1979). Data on fallout from those shots were obtained at several distances from 

ground zero between 1.1 and 4.7 miles. These data are more extensive than data on fallout at 

locations close to tower shots in previous operations. 

A particle-size distribution of activity in fallout at a distance of 1.1 miles from Shot 

DIABLO is shown in Figure 4-1 (Miller, 1969; Figure 8); the separate distributions for large and 

small particles are discussed later in this section. This figure and the more detailed data on this 

sample in Table 14 of Miller (1969) indicate that inhalable particles of diameter less than 

100 μm contained about 0.7% of the total activity and the 0–44 μm size fraction contained about 

0.5%. Similar particle-size distributions of activity in fallout at distances of 2.5 and 4.2 miles 

from Shot SHASTA are shown in Figures 11 and 13 of Miller (1969) and discussed below. 

 Fallout from Shot SHASTA was collected at seven locations at distances between 2.2 and 

4.7 miles. Reported percentages of the total activities in the smallest size fractions of fallout at 
54

those locations (Miller, 1969; Table 16) are given in Table 4-5. In the five samples with the 

highest total activities, inhalable particles of diameter less than 100 μm contained between 0.42% 

and 0.75% of the total activity, with an average of 0.57%. In the two samples with much lower 

total activities, inhalable particles contained between 2.8% and 6.2% of the total activity. The 

masses of those samples also were much lower than the masses of the other five samples. 

 In the seven samples of fallout from Shot SHASTA discussed above, Miller (1969) 

analyzed particle-size distributions of activity in magnetic and nonmagnetic particles separately. 

In the five samples with the highest total activities, reported percentages of the total activities in 

various size fractions of 0−104 μm magnetic fallout particles (Miller, 1969; Table 17) are given 

in Table 4-6. Data in Table 16 of Miller (1969) indicate that nonmagnetic particles in these five 

samples had a much higher percentage of their activity in the 0−104 μm size fraction than 

magnetic particles even though the activity in nonmagnetic particles in that size fraction was 

substantially less than the activity in magnetic particles. Table 16 of Miller (1969) also gives 

data on the two samples from Shot SHASTA with the lowest total activities. In these samples, 

magnetic particles contained 73% and 82% of the total activity in all particle sizes, the 

percentage of the activity in nonmagnetic particles in the 0−104 μm size fraction was much 

higher than the percentage of the activity in magnetic particles, and the activity in nonmagnetic 

particles in that size fraction was much higher than the activity in magnetic particles. 

 Miller (1969) also analyzed particle-size distributions of activity in small and large 

particles separately. In the sample at a distance of 1.1 miles from Shot DIABLO for which these 

activity distributions are shown in Figure 4-1, small particles included all size fractions up to 

420 μm and some particles of diameter as large as 1,300 μm, whereas all large particles had 

diameters greater than 420 μm (Miller, 1969; Table 14). Median diameters in the distributions of 

activity in small and large particles were 150 and 860 μm, respectively, and small particles 

contained 3% of the total activity in all particles. In the five samples from Shot SHASTA with 

the highest total actitivies, small particles included all size fractions in Table 4-5 and some 

particles of diameter as large as 420, 830, or 1,200 μm, depending on the sample, whereas all 

large particles had diameters greater than 250, 300, or 420 μm (Miller, 1969; Table 17). Median 

diameters in the distributions of activity in small particles ranged from 73 to 300 μm, and small 
55

particles contained between 1% and 2.6% of the total activity in all particles, with an average of 

2%. Median diameters in the distributions of activity in large particles, which contained an 

average of 98% of the activity in all particles, ranged from 470 to 900 μm. 

 Additional data on fallout at a distance of 1 mile from Shot DIABLO were reported by 

Schuert (1959). However, the particle-size distribution of activity was studied for larger 

particles (> 200 μm) only; no data were given for smaller particles of interest to our analysis. 

 Finally, a particle-size distribution of activity in fallout at an off-site location 10 miles 

from Shot WHITNEY, which was detonated at a height of 500 ft with a yield of 19 kt, was 

reported by Larson et al. (1966). Data plotted in Figure 3.11 of that report indicate the following 

percentages of the total activity in the smallest size fractions: 0–44 μm, 6%; 44–88 μm, 1%; and 

88–105 μm, <1%. Thus, inhalable particles of diameter less than 100 μm contained about 8% of 

the total activity. 

Particle-Size Distributions of Activity in Off-Site Fallout. Data on particle-size 

distributions of activity in fallout discussed above were obtained at NTS or at off-site locations 

within about 20 miles of ground zero of a detonation. Data on particle-size distributions of 

activity in off-site fallout at locations farther from NTS, such as data reported by Larson et al. 

(1966) and Cederwall et al. (1990), also could be considered. However, those data are of limited 

relevance to our analysis when a much higher fraction of the activity in off-site fallout was 

attached to smaller, inhalable particles, compared with on-site fallout, due primarily to the 

pronounced decrease in fall times to Earth with increasing particle size. 

Data on particle-size distributions of activity in off-site fallout perhaps could be used to 

estimate an upper bound of the fraction of the activity in on-site fallout that was attached to 

smaller, inhalable particles. However, given that this fraction is highly variable in the data on 

fallout at or near NTS, as discussed above and summarized in Tables 4-3 through 4-6, and is also 

variable in the data at more distant locations, due in part to the variability in distances from 

ground zero where data were obtained, any such estimate would be difficult to justify. We have 

not considered data at distances beyond 20 miles in our analysis. 

4.1.3.2.3 Discussion of data on particle-size distributions. In principle, it should be 

possible to predict whether the inhalable fraction in particle-size distributions of activity in 
56

 

fallout at locations close to ground zero of a detonation was large or small.37 A key parameter is 

the scaled height-of-burst, which is the burst height divided by the cube root of the yield (see 

Section 2.1). When the fireball does not reach the ground and melt a significant amount of soil, 

the greater the scaled height-of-burst, the more difficult it is for larger soil particles to be sucked 

into the fireball and, thus, the smaller the size of soil particles that will form part of fallout, along 

with other materials (e.g., the shot tower and weapon casing). Conversely, the smaller the scaled 

height-of-burst, the easier it is for larger soil particles to be sucked into the fireball and, thus, the 

larger the size of soil particles that will form part of fallout. Once fallout particles have formed 

as the fireball cools, distances from ground zero at which particles of different sizes deposit 

depend on the stabilization height of the cloud and the wind speeds between the ground surface 

and the height of the cloud. The scaled height-of-burst also may be an important factor in 

determining the importance of early fallout of larger particles from the stem.38

 The principles outlined above suggest that particle-size distributions of activity in fallout 

at a given distance from ground zero should be similar at detonations with about the same scaled 

height-of-burst if wind speeds between the ground surface and the stabilization heights of the 

clouds were not greatly different. Of interest to this analysis is an expectation that, at a given 

distance close to ground zero (i.e., within the boundary of NTS), the fraction of the total activity 

in smaller particles often should be about the same. However, data on fallout at distances of 

about 3–3.5 miles from Shots NANCY, BADGER, and SIMON in Table 4-3 do not conform to 

this expectation. In those cases, the size fraction less than 125 μm contained widely varying 

percentages of the total activities even though (1) the scaled heights-of-burst at Shots NANCY 

and BADGER (104−105 ft) are nearly identical and are not greatly different from the scaled 

height-of-burst at Shot SIMON (86 ft) and (2) wind speeds up to the stabilization heights of the 

clouds at those shots varied by less than a factor of 2 (Hawthorne, 1979). 

37 Discussions on the formation of fallout and expected particle-size distributions in fallout are 

based mainly on personal communications from J. Dancz of Science Applications International 

Corporation (SAIC); see also Glasstone and Dolan (1977) and Ferlic (1983). 

38 On-site deposition of fallout from the stem at locations close to ground zero probably occurred, 

for example, at Shot SIMON in Operation UPSHOT-KNOTHOLE (Goetz et al., 1981) and Shot SMOKY 

in Operation PLUMBBOB (NRC, 2003).
57

 

 Some differences in particle-size distributions of activity in on-site fallout from the three 

shots in Table 4-3 could be due to differences in the lateral distance of sampling locations from 

the centerline of the plumes. The fraction of smaller particles in fallout should be larger near the 

edges of a plume, where the total activity would be relatively low, than near the center of the 

plume, where the total activity is the highest, due to the greater diffusion and dispersion of 

smaller particles during atmospheric transport. Evidence of this effect in fallout at NTS is seen 

in the data at Shot SHASTA in Table 4-5, where the percentages of the total activities in the size 

fraction less than 150 μm in the two samples with the lowest activities are at least a factor of 4 

higher than the percentages in that size fraction in the five samples with much higher total 

activities.39 This effect might be a partial explanation of the high percentage of the total activity 

in smaller particles in on-site fallout from Shot NANCY in Table 4-3. An inability to separate 

the 0−5 μm size fraction from the 0−44 μm size fraction in that sample, when the 0−5 μm size 

fraction was separated in a fallout sample from Shot BADGER, which had a substantially 

smaller percentage of the total activity in smaller particles, suggests that the total mass and 

activity were low and, thus, that fallout was not collected near the centerline of the plume where 

fallout should have consisted mainly of larger particles.40 However, it is difficult to assess the 

meaning and importance of differences in the percentages of the total activities in small particles 

in different fallout samples in any detail when available data are limited and uncertainties in the 

measurements were not reported. 

39 Clearer evidence of the effect of distance from the centerline of a fallout plume on the fraction 

of the activity in small particles is seen in the data at distances greater than 10 miles from Shot SIMON in 

Table 4-3 (but not in the data from Shot BADGER at about the same distances) and Shots TESLA and 

MET in Table 4-4, as well as the data at a distance of 35 miles from Shot BOLTZMANN in Operation 

PLUMBBOB (Larson et al., 1966; Figure 3.12). 

40 Another factor that could have affected the particle-size distribution of activity in the sample of 

on-site fallout from Shot NANCY is the meandering of the plume at times shortly after detonation, which 

probably delayed the arrival time of fallout at the location 3.5 miles from ground zero compared with the 

arrival times of fallout from the other shots in Table 4-3 at about 3 miles (J. Dancz, SAIC, personal 

communication). A delay in the arrival time of fallout could have significantly increased the fraction of 

smaller particles (Ferlic, 1983). This effect is shown, for example, by an increase in the percentage of the 

total beta activity in the 0–44 μm size fraction in fallout from Shot SMOKY in Operation PLUMBBOB 

as the arrival time increased from 1 to 15 hours (Larson et al., 1966; Figure 3.14 and Table 3.2). 
58

 Given the kinds of inconsistencies noted above, it is difficult to estimate particle-size 

distributions of activity in fallout on the basis of principles of fallout formation. Rather, we have 

relied on available data and attempted to take the variability in the data into account. 

4.1.3.2.4 Implications and use of available data. The considerations of a maximum dust 

loading in air that is barely tolerable while breathing, fall times of fallout particles of different 

sizes in dust clouds produced in nuclear detonations, and data on particle-size distributions of 

activity in on-site fallout from tower shots at NTS described above indicate that, on average, 

only a small fraction of the activity of radionuclides in fallout that was resuspended in the 

thermal-pulse or blast-wave region could have been inhaled by participants; i.e., most of the 

resuspended fallout must have fallen to Earth before significant inhalation exposure could have 

occurred. This conclusion applies even in cases of exposure of participants who were present in 

the blast-wave region at the time of a detonation, because larger particles remained in the air for 

only a short time. For example, the estimated fall time of a 100-μm diameter fallout particle that 

was resuspended to a height of 10 m is about 20 s (see Section 4.1.3.2.1). 

 A confounding factor, however, is the variable data on particle-size distributions of 

activity in on-site fallout, as discussed in Section 4.1.3.2.2. Data on some samples indicate that 

smaller particles that could have remained in the air to be inhaled by participants contained a 

substantial fraction of the total activity. 

 We are unaware of any published information on particle-size distributions of airborne 

activity in fallout that was resuspended by nuclear detonations at NTS. Therefore, the fraction of 

the activity in resuspended fallout that could have been inhaled when effects of particle size on 

potential exposures are considered is highly uncertain. 

In the absence of data, we use assumptions described in the following three sections to 

estimate upper and lower bounds of the fractions of the activity of resuspended radionuclides in 

respirable or nonrespirable form that could have been inhaled by participants. These estimates 

are assumed to apply throughout the thermal-pulse and blast-wave regions. As noted previously, 

respirable and nonrespirable fractions of resuspended radionuclides in inhalable form are 

estimated on the basis of estimates of the inhalable fraction of resuspended radionuclides and the 

respirable fraction of inhalable radionuclides. Respirable particles are assumed to have a 
59

diameter (AMAD) of about 10 μm or less (ICRP, 1994), and we assume that inhalable particles 

have a diameter less than 100 μm (ICRP, 1994; NCRP, 1997). Since fallout particles of diameter 

greater than 100 μm have fall times to Earth from a height of 300 m (the assumed maximum 

height of resuspended material in the thermal-pulse region) of about 10 minutes or less and fall 

times in the blast-wave region should not exceed 1 minute if the maximum height of resuspended 

material in that region was a few tens of meters (see Section 4.1.3.2.1), exposure times and 

inhalation doses in the thermal-pulse and blast-wave regions would be unimportant even if such 

particles were inhalable. 

 In using available data on particle-size distributions of activity in fallout at NTS, rather 

than modeling, to estimate the inhalable fraction of resuspended radionuclides and the respirable 

and nonrespirable fractions of resuspended radionuclides in inhalable form, it is important to 

recognize limitations in the data. At many shots that produced fallout that could have been 

resuspended by subsequent detonations, data either were not obtained or were not known to us. 

In addition, data that were known to us were obtained at very few locations. This is an important 

consideration when participants often were exposed to resuspended fallout at various distances 

and directions from ground zero of a previous shot as they moved through the fallout field from 

that shot (e.g., in carrying out a maneuver or moving toward a display area), particle-size 

distributions in fallout from a given prior shot presumably depended on the distance from ground 

zero and the lateral distance from the centerline of the plume, and exposure to fallout from more 

than one previous shot with ground zeros at different locations occurred in some cases. Thus, 

available data on particle-size distributions are not definitive, and estimation of credibility 

intervals of the inhalable and respirable fractions of fallout that was resuspended by nuclear 

detonations necessarily involves a high degree of subjective judgment. 

4.1.3.2.5 Estimation of inhalable fraction. Given the limited data on particle-size 

distributions of activity in fallout at NTS, we believe that upper and lower bounds (credibility 

limits) of the inhalable fraction of radionuclides in fallout that was resuspended by nuclear 

detonations should be specified to powers of 10 only, as was done in defining the probability 

distributions of resuspension factors that apply to all fallout (see Section 4.1.3.1). We develop 

the assumed credibility limits of the inhalable fraction as described below. 
60

 

A lower credibility limit of the inhalable fraction of resuspended radionuclides is 

estimated on the basis of two assumptions: (1) all inhalable radionuclides were attached to 

particles of diameter about 44 μm or less, and (2) particle-size distributions of activity in 

resuspended fallout were the same as the distributions in on-site fallout from tower shots at 

locations of higher total activity where the smallest particles had the lowest percentages of the 

total activity. A maximum diameter of about 44 μm often defines the smallest size fraction that 

was used in specifying particle-size distributions of activity (see Tables 4-3 through 4-6). 

 An assumption that the maximum particle size of inhalable material was about 44 μm for 

the purpose of estimating a lower credibility limit of the inhalable fraction of resuspended 

radionuclides, rather than 100 μm (ICRP, 1994; NCRP, 1997) as discussed previously, is 

supported by the following argument. First, if the maximum height of resuspended material in 

the thermal-pulse region is assumed to be 300 m, fallout particles of diameter greater than 44 μm 

in that region have estimated fall times to Earth of about 40 minutes or less.41 Since participants 

(i.e., forward observers or maneuver troops) did not enter the thermal-pulse region for some time 

after a detonation (perhaps a few tens of minutes or more), any exposures to inhalable particles 

of diameter greater than 44 μm that might have occurred should have been of short duration. 

Second, since the height of resuspended material in the blast-wave region was less than in the 

thermal-pulse region, fall times would be reduced in proportion to reductions in the height of the 

cloud. The photograph in Figure 2-1 and other similar photographs (AFLML, 1951) indicate that 

the maximum height of resuspended material in the blast-wave region was no more than a few 

tens of meters, and estimated fall times of fallout particles of diameter greater than 44 μm from 

such heights are less than 5 minutes. Consequently, inhalation of those particles should not have 

occurred when participants entered the blast-wave region after a detonation, and inhalation of 

those particles should not have been important when forward observers were located in the blast41 Fallout particles of diameter 44 μm are sufficiently small that the Reynolds number (Re) is 

substantially less than 1.0 and, therefore, frictional (viscous) forces are dominant and the settling velocity, 

V, can be calculated using Stokes Law as V = ρpd2

g/18ηχ (Hinds, 1982), where ρp is the particle density 

(2.7 g cm–3), d is the particle diameter in cm, g is the acceleration due to gravity (981 cm s–2), η is the 

viscosity of air (1.81 × 10–4 g cm–1 s–1), and χ is the dynamic shape factor, which is assumed to be 1.3 for 

fallout particles (see Section 4.1.3.2.1). 
61

 

wave region at the time of a detonation, due to the short exposure time before such particles fell 

to Earth.42

 On the basis of the assumptions described above, we assume that a lower credibility limit 

(5th percentile) of the inhalable fraction of radionuclides in resuspended fallout is 0.001 (0.1%). 

This credibility limit represents the lowest percentages of the total activities in particles of 

diameter less than 44 μm at locations of relatively high total activity in on-site fallout from Shots 

APPLE II and SHASTA (see Tables 4-4 and 4-5). An estimate of 0.01% in a sample at Shot 

SIMON (see Table 4-3) was excluded, mainly on the grounds that the exposure rate at the 

location of that sample was not reported and only one sample of on-site fallout from that shot 

was analyzed. In addition, the estimate of 0.01% is an order of magnitude lower than any other 

estimate in the data we reviewed and, thus, may be anomalous. By assuming an unbounded 

probability distribution, as described later in this section, we also have assumed that there is a 

small probability that the inhalable fraction of radionuclides in resuspended fallout was 

substantially less than 0.001. 

 We then assume that an upper credibility limit (95th percentile) of the inhalable fraction 

of radionuclides in resuspended fallout is 0.1 (10%). This assumption is based mainly on the 

reported percentages of the total activities in particles of diameter less than 100 μm in on-site 

42 As an example, we consider an extreme case in which the concentration of plutonium on the 

ground surface is assumed to be 3 × 103

 nCi m–2, the resuspension factor that applies to all fallout in the 

blast-wave region is assumed to be 10–3 m–1, all resuspended plutonium is assumed to be inhalable, and 

the breathing rate is 2 m3

 h–1. The assumed concentration of plutonium represents the highest 

concentration over a substantial area at NTS after the period of atmospheric testing (McArthur, 1991; 

Figure 2) and, thus, should overestimate concentrations at locations of exposure to fallout that was 

resuspended by nuclear detonations; the assumed resuspension factor is the upper 95% credibility limit in 

the blast-wave region developed in Section 4.1.3.1.2; the assumption that all resuspended plutonium is 

inhalable should overestimate airborne concentrations of inhalable plutonium in regions of high fallout 

depositions at NTS, where most fallout particles should have been too large to be inhaled; and the 

assumed breathing rate applies under conditions of moderately strenuous activity (EPA, 1997). Using 

these assumptions and current dose coefficients for ingestion (ICRP, 2002) that are adjusted by the 

fraction of inhaled material that would be swallowed (see Section 3.1), which apply when inhaled 

material is nonrespirable, the highest equivalent dose to any organ or tissue from a 5-minute exposure to 

airborne plutonium is about 4 mrem to bone surfaces. Such a low dose under conditions that should 

greatly overestimate actual exposures shows that doses from intakes of larger inhalable particles with 

short fall times to Earth must have been very low. This conclusion also applies in the thermal-pulse 

region where the resuspension factor that applies to all fallout on the ground surface is assumed to be an 

order of magnitude higher and exposure times may have been longer (a few tens of minutes at most). 
62

 

fallout from Shot BADGER (see Table 4-3) and fallout at a distance of 10 miles from Shot 

WHITNEY noted in Section 4.1.3.2.2. The assumed upper credibility limit is more than an order 

of magnitude higher than the percentages of the total activities in particles of diameter less than 

44 μm in the five samples with the highest total activity in fallout from Shot SHASTA (see 

Table 4-5) and the average percentage of the total activity in that size fraction in fallout from 

Shot APPLE II (see Table 4-4). In estimating an upper credibility limit of the inhalable fraction 

on the basis of percentages of the total activities in particles of diameter up to 100 μm, we have 

assumed implicitly that the particle-size distributions of activity in resuspended fallout included a 

substantially higher fraction of smaller particles than the distributions of resuspended soil 

particles, because the dust loading in air presumably was intolerable while breathing unless most 

of the resuspended soil consisted of larger particles that fell to Earth within a short time (see 

Section 4.1.3.2.1). An estimate of about 50% in a sample of on-site fallout from Shot NANCY 

(see Table 4-3) was excluded on the grounds that the high percentage of the total activity in 

small particles in that sample appears to be anomalous when compared with estimates of less 

than 10% in two samples at greater distances from ground zero (see Section 4.1.3.2.2). By 

assuming an unbounded probability distribution, as described below, we also have assumed that 

there is a small probability that the inhalable fraction of radionuclides in resuspended fallout was 

substantially greater than 0.1. 

 We also believe that intermediate values of the inhalable fraction were more likely than 

the upper and lower credibility limits developed above. Therefore, we assume that the inhalable 

fraction of radionuclides in fallout that was resuspended in the thermal-pulse or blast-wave 

region is represented by a lognormal probability distribution with a 90% credibility interval 

between 0.001 and 0.1.43 The median of this distribution of 0.01 (1%) does not differ greatly 

from an average fraction of the total activity in particles of diameter less than 44 μm in on-site 

fallout, as estimated from data in Tables 4-3, 4-4, and 4-5 but excluding data at Shot NANCY in 

43 The assumed distribution assigns a small probability to an inhalable fraction greater than 1.0, 

which is not possible. However, that probability is less than 0.05% and, thus, is very small. The small 

probability of selecting a value greater than 1.0 by random sampling does not have a significant effect on 

an analysis of uncertainty in estimates of inhalation dose, and no correction is made to account for 

impossible values. 
63

Table 4-3. As noted previously, particles in 0–44 μm size fraction are expected to comprise 

most of the airborne materials that could have been inhaled in the thermal-pulse and blast-wave 

regions. The median of 0.01 also is consistent with an estimate obtained by assuming that about 

half of the activity in small particles with a median diameter of 75−300 μm in fallout from Shot 

SHASTA (Miller, 1969), but none of the activity in large particles, remained in the air for a 

sufficient time to be inhaled. 

 The probability distribution of the inhalable fraction of resuspended radionuclides 

developed above is intended to apply at any location where significant resuspension by a nuclear 

detonation at NTS occurred. In a more refined analysis, a smaller inhalable fraction could be 

assumed in regions of higher concentrations of fallout, where larger particles should have 

contained more of the total activity, and a larger inhalable fraction could be assumed in regions 

of lower concentrations, where smaller particles should have contained more of the total activity. 

These inhalable fractions would have a smaller uncertainty than the single inhalable fraction that 

is assumed to apply at all locations in the thermal-pulse and blast-wave regions. However, it is 

difficult to define regions of higher and lower concentrations of fallout when a continuum of 

concentrations occurred in fallout from any shot, and we do not believe that the available data on 

particle-size distributions are sufficient to justify such an approach even if those regions could be 

defined in a reasonable manner. 

Data in Tables 4-3, 4-4, and 4-5 indicate that the 95th percentile of the assumed 

probability distribution of the inhalable fraction of resuspended radionuclides of 0.1 is somewhat 

higher than needed to give a credible upper bound in regions of higher concentrations of fallout, 

where inhalation doses would be the highest—i.e., a credible upper bound in those regions could 

be somewhat less than 0.1. However, as noted previously, we believe that specifying an upper 

95% credibility limit more precisely than to the nearest power of 10 is difficult to justify, given 

the limited data on particle-size distributions of activity in fallout at NTS and the uncertainty in 

assuming that particle-size distributions of activity in resuspended fallout were the same. 

4.1.3.2.6 Estimation of respirable fraction. Data that can be used to estimate the 

respirable fraction of the total activity of radionuclides in fallout that was resuspended by a 

nuclear detonation (i.e., the activity in particles of diameter about 10 μm or less) are more limited 
64

than data on the inhalable fraction discussed in the previous section. However, the respirable 

fraction must have been less than the inhalable fraction when respirable particles are included in 

the larger size range of inhalable particles. On the basis of an argument in the previous section 

that most of the inhalable material in the thermal-pulse and blast-wave regions had a diameter of 

about 44 μm or less, we assume that the respirable fraction of resuspended radionuclides in 

inhalable form can be represented by the fraction of the activity in the 0−44 μm size fraction that 

occurred in particles of diameter up to 10 μm. 

 Data on particle-size distributions of activity in on-site fallout from Shots BADGER, 

APPLE II, and SHASTA in Tables 4-3, 4-4, and 4-6, respectively, indicate that the respirable 

fraction of the 0–44 μm size fraction could have been as low as about 0.01 and as high as 1.0. 

The lowest estimate is based on data from a sample of magnetic fallout particles at a distance of 

2.5 miles from ground zero at Shot SHASTA; an estimate of about 0.06 is obtained from data on 

another sample at a distance of 4.7 miles at that shot. The highest estimate is based on data from 

the sample at Shot APPLE II that had the lowest total activity. If the particle-size distribution of 

activity in all 5−20 μm size fractions at Shot APPLE II is assumed to be uniform, the average for 

all samples at that shot is about 0.7. The data at Shot BADGER give an estimate of about 0.2 if 

the particle-size distribution of activity in the 5−44 μm size fraction also is assumed to be 

uniform. An additional estimate of about 0.4 is obtained from the particle-size distribution of 

activity in small particles in a sample from Shot DIABLO (Miller, 1969; Table 14). 

 On the basis of the limited data summarized above, we assume that the respirable fraction 

of resuspended fallout particles of diameter 0–44 μm could range from 0.01 to 1.0. We also 

assume that the most likely value is 0.3, which is an estimate obtained by averaging the single 

estimates at Shots BADGER and DIABLO and averages of the multiple estimates at Shots 

APPLE II and SHASTA. We represent the respirable fraction of the 0–44 μm size fraction by a 

log-triangular distribution with a minimum at (ln 0.01) = −4.6, mode at (ln 0.3) = −1.2, and 

maximum at (ln 1.0) = 0. The median of this distribution is 0.17, the mean is 0.22, and the 90% 

credibility interval ranges from 0.024 to 0.59. 

 A bounded probability distribution, rather than an unbounded distribution (e.g., 

lognormal), is chosen to represent the respirable fraction of inhalable radionuclides because 
65

values greater than 1.0 are not possible, values well within an order of magnitude of the highest 

possible value appear to be the most likely, and a credible lower bound is much less than the 

upper bound. A lognormal distribution would not adequately represent the assumed upper and 

lower bounds and most likely value. A log-triangular, rather than a triangular, distribution is 

assumed on the grounds that log-transformed distributions are preferable when credible values 

could vary by more than an order of magnitude (NCRP, 1996). A log-uniform distribution is 

inappropriate when intermediate values appear to be much more likely than extreme values. 

 The respirable fraction of radionuclides in fallout that was resuspended by a nuclear 

detonation at NTS is represented by a probability distribution that is obtained by combining the 

probability distribution of the inhalable fraction of resuspended radionuclides developed in the 

previous section with the probability distribution of the respirable fraction of inhalable 

radionuclides given above. The resulting probability distribution of the respirable fraction of 

resuspended radionuclides has a median at 1.5 × 10−3

 and 90% credibility interval between 

8.2 × 10−5

 and 2.3 × 10−2. The uncertainty in the inhalable fraction of resuspended radionuclides 

contributes two-thirds of the total uncertainty. 

The assumed probability distribution of the respirable fraction of resuspended 

radionuclides may tend to overestimate actual values. If the inhalable fraction included particles 

of diameter substantially greater than 44 μm, the fraction of the activity in the inhalable size 

fraction that occurred in particles of diameter up to 10 μm would be overestimated. In addition, 

as noted in Section 4.1.3.2.2, reported diameters of fallout particles presumably are physical 

diameters that are less than the corresponding aerodynamic equivalent diameters. Thus, by 

assuming that fallout particles of physical diameter up to 10 μm are respirable, the respirable 

fraction should include some nonrespirable particles with an AMAD greater than 10 μm. 

However, we do not expect that a possible overestimation of the respirable fraction of 

resuspended radionuclides would be significant compared with the assumed uncertainty. 

4.1.3.2.7 Estimation of nonrespirable fraction. The nonrespirable fraction of 

radionuclides in inhalable form (i.e., the nonrespirable fraction of the 0−44 μm size fraction of 

resuspended radionuclides) is obtained from the relationship that the sum of the nonrespirable 

and respirable fractions of inhalable radionuclides is unity. The resulting probability distribution 
66

of the nonrespirable fraction of inhalable radionuclides has a median at 0.83 and 90% credibility 

interval between 0.41 and 0.98. The much smaller uncertainty in this fraction compared with the 

uncertainty in the respirable fraction of inhalable radionuclides is a consequence of an 

assumption of a high probability that the respirable fraction was much less than 1.0. 

By combining the probability distribution of the nonrespirable fraction of inhalable 

radionuclides given above with the probability distribution of the inhalable fraction of 

resuspended radionuclides that was developed in Section 4.1.3.2.5, the resulting probability 

distribution of the nonrespirable fraction of resuspended radionuclides has a median at 7.6 × 10−3

and 90% credibility interval between 7.0 × 10−4 and 8.0 × 10−2. As expected, this probability 

distribution is not greatly different from the assumed probability distribution of the inhalable 

fraction of resuspended radionuclides. The uncertainty in the inhalable fraction of resuspended 

radionuclides contributes 97% of the total uncertainty. 

The assumed probability distribution of the nonrespirable fraction of resuspended 

radionuclides may tend to underestimate actual values if the respirable fraction tends to be 

overestimated, as discussed in the previous section. However, any such tendency would be 

unimportant compared with the assumed uncertainty in the nonrespirable fraction when that 

fraction is much greater than the respirable fraction. We also note that the difference between 

the physical diameter of a fallout particle and the corresponding aerodynamic equivalent 

diameter, as discussed in Section 4.1.3.2.2, is unimportant in estimating the nonrespirable 

fraction, because the dose from inhalation of nonrespirable particles, which are either expelled or 

swallowed, is independent of particle size. 

 We also considered the possibility that the respirable and nonrespirable fractions of 

radionuclides in inhalable form might be correlated to some degree with the inhalable fraction of 

resuspended radionuclides. This correlation and its potential effects on our analysis of 

uncertainty are considered in Section 4.2.5. 

4.1.3.3 Summary of Uncertainties in Resuspension Factors. Overall uncertainties in 

resuspension factors that are used to estimate activity concentrations of radionuclides in 

respirable or nonrespirable form that could have been inhaled by military participants in the 

thermal-pulse and blast-wave regions of nuclear detonations at NTS relative to the 
67

concentrations in fallout on the ground surface are obtained by combining estimated 

uncertainties in (1) the resuspension factor that applies to all fallout, (2) the inhalable fraction of 

resuspended radionuclides, and (3) the respirable or nonrespirable fraction of resuspended 

radionuclides in inhalable form. Estimated uncertainties in the three parameters that were 

developed in Sections 4.1.3.1 and 4.1.3.2 are summarized in Table 4-7. We obtain the following 

medians and 90% credibility intervals of probability distributions of resuspension factors that 

apply to radionuclides in respirable or nonrespirable form in the two regions: 

• Radionuclides in respirable form in thermal-pulse region – Median resuspension factor at 

1 × 10–6 m

–1 and 90% credibility interval between 4 × 10–8 and 6 × 10–5 m–1; 

• Inhalable radionuclides in nonrespirable form in thermal-pulse region – Median 

resuspension factor at 8 × 10–6 m

–1 and 90% credibility interval between 3 × 10–7 and 

2 × 10–4 m

–1; 

• Radionuclides in respirable form in blast-wave region – Median resuspension factor at 

1 × 10–8 m

–1 and 90% credibility interval between 7 × 10–11 and 3 × 10–6 m–1; 

• Inhalable radionuclides in nonrespirable form in blast-wave region – Median 

resuspension factor at 8 × 10–8 m

–1 and 90% credibility interval between 4 × 10–10 and 

1 × 10–5 m

–1; 

These results are given to one significant figure only, to reflect the large uncertaintis and the 

subjective nature of assumed probability distributions of each parameter. We also reiterate that 

resuspension factors in the blast-wave region are intended to be averages of values that are 

expected to decrease with increasing distance from ground zero (see Section 4.1.3.1.2). 

In the thermal-pulse region, where the assumed uncertainties in the resuspension factor 

that applies to all radionuclides and the inhalable fraction of resuspended radionuclides both are 

a factor of 10, each of those uncertainties contributes 40% and 49% of the total uncertainties in 

the resuspension factors that apply to radionuclides in respirable and nonrespirable form, 

respectively. The uncertainty in the respirable fraction of inhalable radionuclides contributes the 

remaining uncertainties of 20% and 2%, respectively. In the blast-wave region, the assumed 
68

uncertainty of a factor of 100 in the resuspension factor that applies to all radionuclides 

contributes 74% and 80% of the total uncertainties in the resuspension factors that apply to 

radionuclides in respirable and nonrespirable form, respectively. For radionuclides in respirable 

form, the assumed uncertainties in the inhalable fraction of resuspended radionuclides and the 

respirable fraction of inhalable radionuclides contribute 18% and 9% of the total uncertainty, 

respectively, and for radionuclides in nonrespirable form, those contributions are 19% and 0.6%. 

 The probability distributions of resuspension factors summarized above are well 

represented by lognormal distributions with the indicated 90% credibility intervals. This is an 

expected result when the two parameters that contribute most of the total uncertainties are 

assumed to be lognormally distributed. In the thermal-pulse region, GSDs of lognormal 

probability distributions with the indicated 90% credibility intervals are about 9.2 and 7.2 for 

radionuclides in respirable and nonrespirable form, respectively. In the blast-wave region, the 

corresponding GSDs are about 26 and 22. 

4.1.4 Breathing Rate

 A breathing rate of 1.2 m3

 h−1 is assumed in most dose reconstructions (Egbert et al., 

1985; Raine et al., 2007). The assumed breathing rate is intended to be somewhat higher than a 

typical value during light activity. 

 If a breathing rate during light activity applies to participants in the thermal-pulse or 

blast-wave region shortly after a nuclear detonation, an analysis by the U.S. Environmental 

Protection Agency (EPA, 1997) indicates that the 90% credibility interval in adults ranges from 

0.6 to 1.4 m3

 h−1. We assume that the upper credibility limit should be increased to 2 m3 h−1 on 

the grounds that some activities, such as marching in full battle gear during post-shot maneuvers, 

were more strenuous than normal light activities. The excitement of being near ground zero 

shortly after a nuclear detonation also could have resulted in increased breathing rates. 

 On the basis of the considerations described above, we assume that the uncertainty in the 

breathing rate is represented by a lognormal probability distribution with a 90% credibility 
69

 

interval between 0.6 and 2.0 m3 h−1. The median breathing rate of 1.1 m3 h–1 is slightly less than 

the value assumed in most dose reconstructions. The GSD of this distribution is about 1.4. 

4.1.5 Dose Coefficients for Inhalation of Radionuclides

 This section considers uncertainties in dose coefficients for inhalation of radionuclides 

that are used in dose reconstructions. Assumptions about particle sizes of inhaled materials that 

have been used in calculating dose coefficients for inhalation (Egbert et al., 1985; Raine et al., 

2007) are described in Section 3.1. Doses from inhalation of nonrespirable particles can be 

estimated using dose coefficients for ingestion that are adjusted to account for the fraction of the 

inhaled material that is assumed to be swallowed. 

 Dose coefficients for inhalation or ingestion that are used in most dose reconstructions 

are 50-year committed doses—i.e., doses delivered over a period of 50 years following an acute 

intake of radionuclides—that are assigned to the year of intake.44 For short-lived radionuclides 

or longer-lived radionuclides with short retention half-times in the body (e.g., 137Cs), 50-year 

committed doses essentially are received within the first year after an intake. For long-lived 

radionuclides with long retention half-times in the body (e.g., plutonium), 50-year committed 

doses to many organs or tissues are protracted over time at a nearly constant rate, and the dose 

received in any year is approximately 1/50th of the 50-year committed dose. 

4.1.5.1 Sources of Uncertainty in Dosimetric and Biokinetic Models. Dosimetric models 

that are used to calculate dose coefficients for inhalation or ingestion give estimates of absorbed 

dose to specific target organs or tissues per decay of radionuclides in specific source organs or 

tissues, which are sites of deposition or transit in the body. Uncertainty in dosimetric models 

arises mainly from uncertainties in the masses of target organs or tissues (e.g., the thyroid), the 

44 An exception occurs when leukemia is the cancer type of concern and a dose reconstruction is 

required. In such cases, doses to red bone marrow that are received in each year following an intake in a 

given year are calculated (DTRA, 2007), because use of 50-year committed doses that are assigned to the 

year of intake could result in underestimates of upper 99% credibility limits of the probability of 

causation of leukemia (Kocher and Apostoaei, 2007) in some cases. Such calculations are rarely required, 

however, because Department of Veterans Affairs (DVA) regulations in 38 CFR 3.309 specify that most 

types of leukemia are presumptive diseases, and service connection usually is granted without regard for a 

participant’s dose. 
70

 

spatial relationships between sites of deposition or transit and other target organs or tissues, and 

calculations of radiation transport between a source and target. These uncertainties are 

unimportant in some cases, such as when a radionuclide emits mainly high-energy photons or is 

distributed relatively uniformly in body tissues (e.g., 137Cs, 14C). However, they can be 

important in other cases, such as in estimating dose to red bone marrow from alpha-emitting 

radionuclides (e.g., plutonium) deposited in the skeleton or dose to walls of the stomach and 

colon from ingested alpha emitters in contents of the GI tract (Eckerman et al., 1999). 

 Biokinetic models describe the behavior of inhaled or ingested radionuclides in the body 

over time after an intake and are used to estimate residence half-times in specific organs or 

tissues. By taking known half-lives of radionuclides into account, biokinetic models essentially 

give estimates of the number of decays of radionuclides in specific source organs or tissues over 

a specified time after intake (e.g., 50 years) per unit activity intake. Uncertainty in biokinetic 

models arises mainly from uncertainties in absorption of radionuclides into blood from the lungs 

or GI tract, the fraction of the absorbed activity that is deposited in specific organs or tissues, and 

the biological half-times for retention at each site of deposition. The biokinetic behavior of 

many radionuclides depends on their chemical form, and that dependence can be an important 

source of uncertainty in biokinetic models when chemical forms of radionuclides are unknown or 

the behavior of known chemical forms has not been studied in humans or animals. Uncertainties 

in biokinetic models can be small (e.g., a factor of about 3 or less) in some cases, such as intakes 

of 137Cs or 131I by any route, but they can be large (e.g., a factor of 10 or more) in other cases, 

such as ingestion of plutonium or other radionuclides for which the uncertainty in absorption into 

blood from the GI tract is large. 

 Another possible source of uncertainty in dose coefficients for inhalation is an 

uncertainty in the distribution of particle sizes of inhaled material. This distribution can affect 

the fraction of inhaled material that is deposited in various regions of the respiratory tract. Dose 

coefficients for inhalation of particles with an AMAD of 1 μm or greater usually are calculated 

by assuming a lognormal distribution of particle sizes with a GSD of 2.5 (ICRP, 1994).45 The 

45 For a given GSD, the 95th and 5th percentiles of a lognormal distribution are a factor of GSD1.645

above and below the geometric mean (median), respectively. 
71

 

GSD of particle-size distributions of inhalable material that was resuspended by nuclear 

detonations at NTS could be substantially different. However, calculations by Huston (1995) 

suggest that any such differences are unimportant. In cases of inhalation of respirable particles 

with an AMAD of about 10 μm or less, which are deposited to a significant extent in the 

bronchial and pulmonary regions, those calculations indicate that an increase in the GSD of the 

particle-size distribution from 2 to 4 would change the uncertainty in a dose coefficient for the 

lung by less than a factor of 2. When larger, nonrespirable particles, which are deposited almost 

entirely in the nose, throat, and mouth, are inhaled, the deposition fraction and subsequent 

transfer to the GI tract are independent of particle size, as noted in Section 4.1.3.2.7. On the 

basis of these calculations, we assume that uncertainties in dose coefficients for inhalation that 

arise from an uncertainty in the distribution of particle sizes of inhaled material are negligible 

compared with uncertainties in dosimetric and biokinetic models.46

4.1.5.2 Overview of Approach to Evaluating Uncertainty in Dose Coefficients. A 

rigorous analysis of uncertainty in dose coefficients for inhalation or ingestion of radionuclides 

in fallout would be a difficult undertaking. Such an analysis would require a consideration of 

uncertainties in dose coefficients for essentially all organs or tissues, including organs or tissues 

(e.g., the prostate) at minor sites of deposition, which often are of concern in dose 

reconstructions when cancers at those sites are nonpresumptive diseases, and for many 

radionuclides.47 However, uncertainties appear to be well characterized for only a few 

combinations of radionuclide and organ or tissue, and those organs or tissues usually are not of 

concern in dose reconstructions when cancers at those sites are presumptive diseases. 

46 We also note that 10 μm is a reasonable dividing line between monodisperse particles (particles 

of the same diameter) that are respirable and deposit to a significant extent in the deep lung and particles 

that are nonrespirable (ICRP, 1994). These considerations, along with the importance of subjective 

judgment in estimating uncertainties in resuspension factors and the inhalable and respirable fractions of 

resuspended radionuclides, provide some justification for the lack of rigor in using the term “diameter” to 

describe particle sizes in this report (see also Section 4.1.3.2.2). When the objective of our analysis is to 

derive effective resuspension factors to the nearest power of 10 only, such rigor is not necessary. 

47 Although cancers in many organs or tissues are presumptive diseases, as specified in DVA 

regulations in 38 CFR 3.309, and a dose reconstruction usually is not required in adjudicating claims for 

compensation, a dose reconstruction is required when an individual’s participation in the atmospheric 

nuclear-weapons testing program is not adequately established or a claim is intended to apply to a time 

period prior to the time when an individual’s cancer was declared to be a presumptive disease. 
72

 

 Another confounding factor in evaluating uncertainties in dose coefficients is that 

biokinetic models recommended by ICRP may be based on studies of chemical and physical 

forms of radionuclides that differ substantially from chemical and physical forms in fallout. For 

example, data in humans (LeRoy et al., 1966) indicate that the GI-tract absorption fraction of 

strontium and cesium in fallout particles is less than ICRP’s recommended values, and animal 

studies also indicate that GI-tract absorption of many (but not all) radionuclides in fallout 

particles is unusually low.48 However, there also are data which indicate that an appreciable 

fraction of cerium in fallout is more soluble than oxide forms (NCRP, 1978) and, thus, that 

absorption in the GI tract and lung may be higher than recommended by ICRP. Doses to walls 

of the GI tract from ingestion of plutonium in larger fallout particles also could be overestimated 

substantially when ICRP’s dosimetric model for the GI tract (ICRP, 1979) does not take into 

account that plutonium should be distributed in the volume of insoluble fallout particles and, 

thus, that much of the emitted alpha energy should be absorbed in the particles. 

 In principle, it is desirable to develop estimates of uncertainty in dose coefficients for 

inhalation or ingestion that apply to specific radionuclides, or groups of radionuclides, and to 

specific organs or tissues, or groups of organs or tissues, for which uncertainties are expected to 

be similar, because studies discussed in the following section indicate that uncertainties can vary 

greatly depending on the radionuclide and organ or tissue of concern. However, even if 

available information on uncertainties in dose coefficients were adequate to pursue such an 

approach, we believe that it would be impractical to use several different estimates of uncertainty 

in dose coefficients in this analysis, or in dose reconstructions for military participants. The 

number of substantially different mixtures of radionuclides to which participants could have been 

exposed is potentially large when exposure to resuspended fallout at many times after 

detonations, ranging from hours to years, could have occurred, and it is not clear how a 

presumably small number of discrete estimates of uncertainty should be applied to what is 

essentially a continuum of mixtures of radionuclides. An assumption of different uncertainties in 

dose coefficients for different combinations of radionuclides and organs or tissues of concern 

could result in estimates of effective resuspension factors in the thermal-pulse and blast-wave 

48 R.W. Leggett, Oak Ridge National Laboratory, personal communication. 
73

regions to be used in dose reconstructions that depend on the organ or tissue and the times since 

previous depositions of fallout when exposure occurred. Such an approach would be 

incompatible with the approach currently used in dose reconstructions in other resuspension 

scenarios, in which a single adjustment factor, which is intended to account for uncertainty, is 

applied to point estimates of inhalation dose to obtain credible upper bounds in all cases (DTRA, 

2007; Case et al., 2008). Use of uncertainties in dose coefficients that depend on the particular 

mixture of radionuclides and the organ or tissue of concern probably can be justified only if dose 

reconstructions were performed by taking into account uncertainties in all parameters (i.e., by 

using a fully probabilistic uncertainty analysis). 

 On the basis of considerations discussed above, we believe that the only practical 

approach for purposes of this analysis is to develop estimates of uncertainty in dose coefficients 

for inhalation or ingestion (i.e., inhalation of larger, nonrespirable particles) that are intended to 

apply to all organs or tissues of possible concern. As in assessing the effects of fractionation of 

radionuclides in fallout (see Section 4.1.2.4), plutonium is considered separately from fission and 

activation products on the grounds that there are sources of uncertainty in internal dosimetry 

models that are more important for alpha-emitting radionuclides than for fission and activation 

products. The aim is to develop estimates of uncertainty in dose coefficients for fission and 

activation products or plutonium that do not underestimate the uncertainty for any organ or 

tissue. We estimate these uncertainties on the basis of published assessments of uncertainties in 

dose coefficients discussed in the following section and the use of judgment in evaluating and 

applying the results of those assessments. 

4.1.5.3 Assessments of Uncertainty in Dose Coefficients. Several published assessments 

of uncertainty in dose coefficients for inhalation or ingestion of radionuclides were considered in 

developing probability distributions of dose coefficients for inhalation of fission and activation 

products or plutonium in respirable or nonrespirable form used in this analysis. 

4.1.5.3.1 Assessment by NCRP. An assessment of the reliability of effective dose 

coefficients for several radionuclides in healthy adult males, as calculated using dosimetric and 

biokinetic models that were recommended in ICRP Publication 30 (ICRP, 1979), was performed 
74

 

by NCRP (1998); see also Bouville et al. (1994).49 Results of NCRP’s assessment are 

summarized in Table 4-8. Estimated uncertainties range from a factor of 2 or 3 (e.g., for intakes 

of 90Sr, 131I, and 137Cs) to a factor of 10 (e.g., for ingestion of 144Ce and intakes of 239Pu). 

 We note the following points about NCRP’s estimates of reliability in dose coefficients. 

First, uncertainties in dose coefficients for specific organs or tissues, especially minor sites of 

deposition, could be substantially larger than uncertainties in effective dose coefficients. 

Second, NCRP’s assessment focused on dose coefficients for soluble forms of radionuclides, and 

estimates of reliability may not apply to less soluble forms of some radionuclides that are 

expected to occur in fallout. Finally, NCRP’s estimates of reliability represent subjective 

judgment, rather than results of an analysis of uncertainty in dosimetric and biokinetic models 

due to uncertainties in model parameters, and they were based mainly on judgments about the 

quality of available data on biokinetic behavior.50 Therefore, it is questionable whether NCRP’s 

assessment adequately represents uncertainties in dose coefficients for specific organs or tissues 

from inhalation or ingestion of radionuclides in fallout. 

4.1.5.3.2 Assessment in EPA’s federal guidance. EPA’s Federal Guidance Report 

No. 13 (Eckerman et al., 1999) includes an assessment of uncertainties in risk coefficients for 

inhalation or ingestion of radionuclides in the environment; this assessment has been updated by 

Pawel et al. (2007). EPA’s risk coefficients give estimates of lifetime cancer mortality or 

morbidity (incidence) per unit activity intake of radionuclides in a population of all ages—i.e., 

these are age- and gender-averaged risks. EPA’s assessment of uncertainties in risk coefficients 

considered uncertainties in (1) estimates of the risk per unit absorbed dose in specific organs or 

49 Although the quantity for which reliability was estimated was referred to as an “effective dose 

coefficient,” dose coefficients evaluated by NCRP were effective dose equivalents as defined in ICRP 

Publication 26 (ICRP, 1977), rather than effective doses as defined in ICRP Publication 60 (ICRP, 1991). 

This difference is not important for purposes of our analysis. 

50 The importance of NCRP’s focus on data quality is indicated by the following example (R.W. 

Leggett, Oak Ridge National Laboratory, personal communication). The dose coefficient for inhalation 

of 95Zr was assigned a low reliability by NCRP. However, a sensitivity analysis would show that 

estimates of effective dose equivalent in that case are rather insensitive to gaps in biokinetic data, because 

the effective dose equivalent is dominated by the dose to the lung, an organ in which the dosimetry and 

biokinetic behavior of radionuclides is relatively well characterized. Therefore, the uncertainty in the 

effective dose coefficient for inhalation of 95Zr probably is substantially less than the estimated reliability 

in Table 4-8. A similar conclusion may apply in other cases. 
75

 

tissues, including uncertainties in a tissue-specific dose and dose-rate effectiveness factor 

(DDREF) for photons and electrons51 and the relative biological effectiveness (RBE) of alpha 

particles, and (2) estimates of absorbed dose to specific organs or tissues due to uncertainties in 

dosimetric and biokinetic models currently recommended by ICRP [(1996a; 2002) and 

references therein]. Uncertainties in risk models were judged to be important in all cases. 

 Selected results of EPA’s assessment of uncertainties in risk coefficients are summarized 

in Tables 4-9 and 4-10. Uncertainties were divided into five categories that are defined by ratios 

of upper bounds (upper 95% credibility limits) of risk coefficients to lower bounds (lower 5% 

credibility limits). Uncertainty factors in Table 4-10 can be compared, for example, with the 

corresponding uncertainty factors from NCRP’s assessment in Table 4-8. Given the importance 

of uncertainty in the risk model in all cases, EPA’s estimates of uncertainty in dose coefficients 

would be less than the estimates of uncertainty in risk coefficients. 

 The following points about EPA’s estimates of uncertainty in risk coefficients should be 

noted. First, risk coefficients are determined primarily by doses and risks at major sites of 

deposition in the body, and uncertainties at minor sites of deposition, especially uncertainties in 

doses per unit activity intake of radionuclides, could be larger. Second, to the extent that risk 

coefficients are dominated by the risks due to intakes by younger age groups in a population of 

all ages, uncertainties in risk coefficients that would apply to intakes by adults could be 

overestimated in many cases, because risks per unit absorbed dose and the biokinetic behavior of 

radionuclides often are better understood in adults than in younger age groups. Third, EPA’s 

judgments about uncertainties in risks per unit absorbed dose in specific organs or tissues were 

based on results of an expert elicitation (Little et al., 1997), rather than an analysis of available 

data, such as an analysis performed by EPA (1994; 1999). EPA thus assumed that an 

inconsistency in estimates of risk by different experts is a valid measure of uncertainty. This 

approach may inflate the importance of uncertainties in risks per unit absorbed dose in some 

organs or tissues relative to uncertainties in doses per unit activity intake of radionuclides (Pawel 

et al., 2007). Finally, EPA’s analysis applies to chemical forms of radionuclides that are 

51 A DDREF takes into account that the risk per unit absorbed dose of low-LET radiations may be 

lower at low doses or low dose rates than at higher acute doses in Japanese atomic-bomb survivors. In 

radiation protection, for example, a DDREF of 2 usually is assumed (ICRP, 1991; NCRP, 1993). 
76

 

expected to be the most important in releases from nuclear facilities or natural sources, and 

assumed biokinetic models may not always apply to chemical forms in fallout. The last point 

could be especially important in considering uncertainties in EPA’s risk coefficients for 

ingestion, because ingested radionuclides were assumed to occur in tap water or foods and 

chemical forms in those sources often should be more soluble than chemical forms in fallout. 

4.1.5.3.3 Assessment in NRC-CEC expert elicitation. In a study conducted for the U.S. 

Nuclear Regulatory Commission (NRC) and Commission of the European Communities (CEC), 

a group of experts was asked to estimate median values and 90% credibility intervals of 

committed dose coefficients for selected radionuclides and organs or tissues (Goossens et al., 

1998); see also Harrison et al. (1998). A summary of results of the expert elicitation is given in 

Table 4-11. Estimated dose coefficients are absorbed doses per unit activity intake. 

 In all cases, results in Table 4-11 indicate that the difference between the experts’ 

aggregated median estimate of a dose coefficient and the point value currently recommended by 

ICRP is negligible compared with the experts’ aggregated estimate of uncertainty. In many 

cases, the experts’ estimated uncertainty (ratio of the 95th to the 5th percentile) is much larger 

than the uncertainty in the corresponding effective dose coefficient in Table 4-8 or risk 

coefficient in Table 4-10.52 Large uncertainties in Table 4-11 may be due, at least in part, to 

differences in assumptions by each expert about absorption of radionuclides in the lungs and GI 

tract, and its uncertainty, that could arise from uncertainty in their chemical form. Effects of 

changes in chemical form were not considered in analyses summarized in Tables 4-8 and 4-10. 

 Uncertainties in Table 4-11 take into account differences in median dose coefficients that 

were estimated by each expert as well as each expert’s ratio of the 95th to the 5th percentile. 

Thus, an uncertainty can be greatly influenced by the median and 90% credibility interval that 

was estimated by a single expert when that expert’s estimates differ greatly from all the others. 

To investigate this effect, we examined estimates by each expert in all cases where the 

uncertainty in Table 4-11 is a factor of 400 or greater. Medians and 90% credibility intervals of 

dose coefficients that were estimated by each expert in those cases are given in Table 4-12. If 

52 Ratios of the 95th to the 5th percentile of probability distributions can be compared with ratios of 

the 95th to the 50th percentile by taking the square root of the former or by squaring the latter. 
77

the case of the dose to bone surfaces from inhalation of 144Ce is excluded on the grounds that the 

uncertainties in Tables 4-11 and 4-12 are inconsistent, a single set of estimates by one expert that 

differed greatly from all the other experts’ estimates is seen in most cases. The existence of an 

outlier is especially evident when the uncertainty in Table 4-11 exceeds a factor of 1,000. 

 We believe that there are important flaws in the NRC-CEC expert elicitation that cast 

doubt on the value of the results in providing reasonable estimates of uncertainty in dose 

coefficients. For example, the method used to aggregate the results provided by each expert to 

obtain the uncertainties in Table 4-11 (Goossens et al., 1998, Vol. 1) incorporates a questionable 

assumption that probably resulted in artificially high estimates of uncertainty. Specifically, each 

expert’s 95th and 5th percentiles of a dose coefficient were assumed to define upper and lower 

bounds of a uniform or log-uniform probability distribution; a uniform distribution was assumed 

when the uncertainty was relatively small, and a log-uniform distribution was assumed when the 

uncertainty was relatively large. An important consequence of those assumptions is that 

intermediate values in a probability distribution were not given greater weight than one or both 

of the bounding values. This is a particularly important concern when a log-uniform distribution 

is assumed, because the largest probability is assigned to the lowest value in an assumed range 

and the probability decreases monotonically with increasing value across the range. By 

weighting bounding values of each expert’s distribution in those ways, which we believe is 

unreasonable, a larger uncertainty in aggregated results is obtained than would be obtained by 

assuming probability distributions in which intermediate values are given greater weight than 

values near the extremes (e.g., lognormal distributions). 

 We also have concerns about the design and execution of the expert elicitation. An 

examination of the responses provided by each participant (Goossens et al., 1998, Vol. 2) 

indicated to us that the number of questions posed in the elicitation was overwhelming to some 

participants, that many participants were not experts on some topics they were asked to address, 

and that the level of effort and study in responding to the elicitation varied considerably among 

the participants. Thus, the large uncertainties that were generated in many cases by combining 

median values and uncertainties that were provided by each participant probably are not a 
78

reasonable representation of uncertainties in current information about the dosimetry and 

biokinetics of inhaled or ingested radionuclides. 

4.1.5.3.4 Assessments by ICRP. An ICRP task group has undertaken several assessments 

of uncertainties in dose coefficients for inhalation or ingestion of radionuclides by members of 

the public (Leggett, 2001, 2003; Harrison et al., 2001); see also Leggett et al. (1998). 

 Of particular interest to our analysis is an assessment of uncertainty in the GI-tract 

absorption fraction (f1) for various radionuclides in adults and the effect of that uncertainty on 

uncertainty in the committed effective dose from ingestion (Harrison et al., 2001). Results of 

that assessment are summarized in Table 4-13. The uncertainty in f1, which is expressed as the 

ratio of the 95th to the 5th percentile of a subjective probability distribution, is as high as a factor 

of 10 for 60Co and 239Pu, 20 for 106Ru, and 100 for 95Zr and 125Sb. However, data in animals 

suggest that the uncertainty in f1 for plutonium in oxide form could be much greater than a factor 

of 10 (Harrison et al., 2001). Only for longer-lived radionuclides is the uncertainty in the 

committed effective dose from ingestion due to the uncertainty in f1 usually about the same as the 

uncertainty in f1 itself. For most shorter-lived radionuclides (i.e., 60Co, 95Zr, 106Ru, and 125Sb), a 

large uncertainty in f1 has only a small effect on uncertainty in the committed effective dose, 

because the effective dose is dominated by calculated doses to walls of the stomach and colon 

during passage through the GI tract and the effective dose thus is insensitive to variations in f1. 

However, for all radionuclides, an uncertainty in f1 usually would lead to a comparable 

uncertainty in doses to specific organs or tissues following absorption in the GI tract. 

4.1.5.3.5 Other assessments. Several other assessments of uncertainty in dose 

coefficients for inhalation or ingestion of radionuclides are discussed below. 

Assessment of doses from off-site fallout at NTS. In an assessment of doses to the public 

from exposure to fallout from weapons tests at NTS, Ng et al. (1990) estimated uncertainties in 

inhalation and ingestion dose coefficients for a large number of radionuclides. For inhalation of 

radionuclides that were assumed to be attached to particles with an AMAD of 1 μm, an 

uncertainty represented by a GSD of 1.8 was assigned to most combinations of radionuclide, 

organ, and age group, although a GSD as high as 2.0 was assigned in some cases; in a lognormal 

distribution, a GSD of 1.8 corresponds to a ratio of the 95th to the 50th percentile of 2.6. For 
79

ingestion, a GSD of 1.3−1.8 was estimated for isotopes of strontium, iodine, and cesium, and a 

default GSD of 1.8 was assigned to all other radionuclides. However, estimated uncertainties in 

dose coefficients for isotopes of strontium apparently did not take into account an uncertainty in 

the dosimetric model for beta particles emitted by strontium and any decay products in the 

skeleton (Eckerman et al., 1999), and the assigned uncertainty in dose coefficients for most 

radionuclides, for which radionuclide-specific data were lacking, is a default value that was 

based on assumed uncertainties in dose coefficients for isotopes of strontium, iodine, and cesium. 

Therefore, we believe that many uncertainties in dose coefficients estimated by Ng et al. (1990) 

are too small. 

Assessment of uncertainty in ICRP’s respiratory-tract model. Bolch et al. (2001; 2003) 

and Farfán et al. (2003) performed a detailed analysis of uncertainties in ICRP’s current model of 

the respiratory tract (ICRP, 1994) in cases of inhalation of insoluble plutonium and uranium 

oxides that are attached to monodisperse, unit-density spheres of diameter 0.001–50 μm; see also 

Huston (1995). At all diameters, the median dose to the lung, which was calculated as a 

weighted sum of the doses to different tissues,53 differed from a point estimate that was 

calculated using ICRP’s recommended parameter values by less than a factor of 2. Uncertainties 

in lung doses, which were expressed as ratios of the 95th to the 5th percentile of probability 

distributions, ranged from nearly a factor of 10 at particle diameters less 2 μm to as high as a 

factor of about 700 at diameters greater than 10 μm; the corresponding uncertainty factors (ratios 

of the 95th to the 50th percentile) range from about 3 to more than 25. 

The largest uncertainties apply to nonrespirable particles for which the dose to the lung is 

very low compared with the dose from inhalation of respirable particles. For 239PuO2 attached to 

monodisperse particles of diameter less than 10 μm, uncertainties in doses to the bronchial (BB) 

and bronchiolar (bb) regions and the thoracic lymph nodes (LNth) were considerably larger than 

the uncertainty in the dose to the lung, ranging from a factor of about 20 to about 700; the 

corresponding uncertainty factors ranged from more than 4 to more than 25. At particle sizes 

 53 Doses to the lung were calculated from doses to the bronchial (BB), bronchiolar (bb), and 

alveolar-interstitial (AI) regions and the dose to lymphatic tissues (LN) that drain those regions by 

assigning a weight of 0.001 to the dose to lymphatic tissues and a weight of 0.333 to each of the doses to 

the other three regions (ICRP, 1994). 
80

between 1 and 10 μm, however, the uncertainty in the dose to all tissues except basal cells of the 

BB region decreased as the GSD of the distribution of particle sizes increased from 1 

(monodisperse particles) to 4 (Huston, 1995). At a particle size of 10 μm, for example, the 

uncertainty factor for the dose to the lung decreased from about 10 for monodisperse particles to 

less than 2 for a distribution of particle sizes with a GSD of 2.0. Doses to the BB region were 

nearly independent of the assumed GSD of the distribution of particle sizes. 

The analyses summarized above indicate that uncertainties in doses to the lung from 

inhalation of insoluble plutonium oxide in a distribution of particle sizes are not large. 

Assessments of uncertainty for selected fission and activation products. Apostoaei et al. 

(1999) estimated uncertainties in organ-specific dose coefficients for ingestion of 60Co and 106Ru. 

GSDs of 3.2 for 60Co and 3.0 for 106Ru were obtained. Those estimates correspond to 

uncertainty factors (ratios of the 95th to the 50th percentile) of about 7 and 6, respectively. 

Uncertainties in organ-specific dose coefficients for ingestion of 131I, 137Cs, and 90Sr also were 

estimated, as discussed below. 

 Apostoaei and Miller (2004) performed a detailed analysis of uncertainties in dose 

coefficients for ingestion of 131I, 137Cs, and 90Sr. For 90Sr, estimated uncertainties are represented 

by a GSD of 2.6 for bone surfaces, 2.4 for red bone marrow, and 1.8 or less for most other 

organs. For 131I, the uncertainty in the dose coefficient for the thyroid is represented by a GSD 

of 1.7, and the uncertainty in the dose coefficient for 137Cs and any organ in males is represented 

by a GSD of 1.24. The estimated uncertainties for 131I and 137Cs thus are similar to other 

estimates in Tables 4-8 and 4-11 and earlier estimates by Dunning and Schwarz (1981) and 

Matthies et al. (1981).54 However, comparisons with estimated uncertainties in risk coefficients 

in Table 4-10 are difficult when the importance of uncertainties in cancer risks per unit absorbed 

dose to those results is unknown to us. The estimated uncertainties for 90Sr are somewhat larger 

than the estimate in Table 4-8 when the dominant importance of doses to bone surfaces and red 

bone marrow in determining the effective dose is taken into account; the ratio of the 95th to the 

50th percentile of the probability distribution of the effective dose coefficient obtained from the 

 54 The comparison with estimated uncertainties in Table 4-8 takes into account that the effective 

dose from 131I is determined by the equivalent dose to the thyroid, and that the effective dose from 137Cs is 

about the same as the equivalent dose to any organ or tissue (ICRP, 2002). 
81

results of Apostoaei and Miller (2004) is about 5. However, estimated uncertainties for 90Sr are 

much smaller than those in Table 4-11—i.e., ratios of the 95th to the 5th percentile of the 

probability distributions of dose coefficients for the colon, red bone marrow, and bone surfaces 

are about 7, 18, and 23, respectively, compared with ratios of 600, 240, and 390 in Table 4-11. 

The much larger uncertainties that were obtained in the NRC-CEC expert elicitation were due 

primarily to differences in the median estimates of dose coefficients by different experts, because 

ratios of the 95th to the 5th percentile estimated by each expert (Goossens et al., 1998, Vol. 2; 

Appendix C) were much less than uncertainties in Table 4-11 that represent the combined 

estimates of all experts. As discussed in Section 4.1.5.3.3, differences in the median estimates of 

dose coefficients by different experts may be due, at least in part, to different assumptions about 

absorption in the GI tract, and it is doubtful that the expert elicitation provides reasonable 

estimates of uncertainty in many cases. 

Assessment of uncertainties in dose coefficients for plutonium. In an assessment of 

cancer risks from inhalation of plutonium and their uncertainties, Grogan et al. (2000; 2001) 

estimated uncertainties in organ-specific absorbed dose coefficients for inhalation of insoluble 

plutonium oxide. Organs and tissues that were considered in that analysis include the lung, liver, 

bone, and red bone marrow. The AMAD of inhaled particles was assumed to be 1, 5, or 10 μm, 

and the GSD of all particle-size distributions was assumed to be 2.5. Estimated uncertainties in 

absorbed dose coefficients, as represented by GSDs, for inhalation of plutonium oxide at the 

three particle sizes are summarized as follows: 

• AMAD of 1 μm – GSD of 1.9 for the lung and 3.0 for the liver, bone, and red bone 

marrow; the corresponding uncertainty factors (ratios of the 95th to the 50th percentile) are 

2.9 and 6.1, respectively; 

• AMAD of 5 μm – GSD of 2.7 for the lung and 3.5 for the liver, bone, and red bone 

marrow; the corresponding uncertainty factors are 5.1 and 7.9, respectively; 

• AMAD of 10 μm – GSD of 4.3 for the lung and 4.5 for the liver, bone, and red bone 

marrow; the corresponding uncertainty factors are 11 and 12, respectively. 
82

4.1.5.4 Present Assessment of Uncertainties in Dose Coefficients. In this analysis, 

uncertainties in dose coefficients for inhalation of fission and activation products in respirable or 

nonrespirable form are assessed separately from uncertainties in dose coefficients for plutonium. 

This separation is appropriate when uncertainties in dosimetric models can be more important for 

alpha-emitting radionuclides than for beta/gamma emitters (Eckerman et al., 1999; Pawel et al., 

2007). As discussed in Section 4.1.5.2, an approach that is both practical and consistent with 

current methods of dose reconstruction for military participants is to develop two estimates of 

uncertainty that apply to all organs or tissues, one estimate for inhalation of any mixture of 

fission and activation products in respirable or nonrespirable form and the other for inhalation of 

plutonium in either form. 

 Uncertainties in dose coefficients for inhalation of radionuclides in respirable or 

nonrespirable form are estimated in the following way. We first estimate uncertainties in dose 

coefficients that are calculated using dosimetric and biokinetic models currently recommended 

by ICRP. We then consider an uncertain bias factor, which is intended to take into account that 

dose coefficients calculated by ICRP may overestimate values that apply to chemical and 

physical forms of radionuclides in fallout, especially in cases of inhalation of large, 

nonrespirable particles (see Section 4.1.5.2). When such a bias factor is assumed to apply, an 

uncertainty in dose coefficients is estimated by combining an assumed uncertainty in ICRP’s 

dose coefficients with an uncertain bias factor. 

 Our assessment of uncertainties in dose coefficients incorporates two assumptions 

implicitly. First, in accordance with policy and procedures of the NTPR Program (DTRA, 2007; 

Case et al., 2008), we assume that internal doses to military participants will be estimated using 

dose coefficients for adult members of the public currently recommended by ICRP [(1996a; 

2002) and references therein], rather than dose coefficients based largely on earlier 

recommendations (ICRP, 1979), which were used in dose reconstructions until recently, and we 

further assume that dose coefficients for radionuclides in oxide form will be used, as has 

generally been the case in dose reconstructions (Egbert et al., 1985; Raine et al., 2007). 

 Second, if ingestion dose coefficients are used to estimate doses from inhalation of large, 

nonrespirable particles, we assume that values currently recommended by ICRP would be 
83

reduced by a factor of about 4 to account for assumptions in the current respiratory-tract model 

that about half of all large particles that are inhaled are deposited in the nose, throat, and mouth, 

and that about half of the deposited material is transferred to the GI tract by swallowing (ICRP, 

1994). As noted in Section 3.1, dose reconstructions that were performed until recently assumed 

that nearly all large inhaled particles are transferred to the GI tract (ICRP, 1979). 

4.1.5.4.1 Uncertainty in ICRP’s dose coefficients for fission and activation products. 

Many fission and activation products are potentially important in inhalation exposures of military 

participants, and the important radionuclides and their relative activities vary with time after a 

detonation (Egbert et al., 1985; Raine et al., 2007). However, as indicated by studies discussed 

in Section 4.1.5.3, uncertainties in dose coefficients for inhalation or ingestion of fission and 

activation products appear to be reasonably well characterized for only a few combinations of 

radionuclide and organ or tissue, including 131I (thyroid), 90Sr (bone surfaces, red bone marrow, 

and various soft tissues), and 137Cs (all organs and tissues). 

 Development of a probability distribution to represent uncertainties in dose coefficients 

for inhalation of fission and activation products in respirable or nonrespirable form for purposes 

of this analysis is not straightforward, given that (1) uncertainties are radionuclide-specific and, 

for a given radionuclide, organ-specific, and (2) radionuclides that contribute significantly to 

dose depend on the organ or tissue of concern and the time after a detonation when exposure to 

fallout from that detonation occurred. For example, if exposure occurred a few years after a 

detonation and inhalation of nonrespirable particles is assumed, important fission products 

include 90Sr, which mainly irradiates bone surfaces and red bone marrow, 106Ru and 144Ce, which 

mainly irradiate the lower GI tract, and 137Cs, which irradiates all organs and tissues nearly 

uniformly. In addition, uncertainties in dose coefficients for inhalation or ingestion have not 

been studied for some potentially important fission and activation products, and uncertainties in 

dose coefficients at minor sites of deposition in the body could be large even for well-studied 

radionuclides, due to uncertainties in deposition fractions at those sites. 

 Our estimate of uncertainty in ICRP’s dose coefficients for inhalation of fission and 

activation products in respirable or nonrespirable form is based on assessments of uncertainties 

in dose coefficients discussed in Section 4.1.5.3, except little credence is given to the large 
84

uncertainties that were obtained in the NRC-CEC expert elicitation (see Section 4.1.5.3.3 and 

Table 4-11). Additional considerations are needed when exposure to mixtures of fission and 

activation products occurs, as was the case in exposures of military participants. For example, 

unless there are strong correlations among dose coefficients for important radionuclides (i.e., all 

dose coefficients that apply to an individual’s organ or tissue of concern would be larger or 

smaller than values calculated by ICRP, rather than randomly distributed about ICRP’s 

calculated values), the uncertainty in a dose coefficient for mixtures of radionuclides (i.e., ratio 

of the 95th to the 50th percentile) should be no larger than the largest uncertainty that applies to 

any radionuclide in a mixture when exposures generally should involve some radionuclides for 

which the uncertainty is relatively small. On the other hand, some correlation among dose 

coefficients for different radionuclides is expected and, therefore, adding doses from different 

radionuclides should not always reduce the overall uncertainty by a large amount. For example: 

(1) dose coefficients for isotopes of strontium and barium, which are bone-seeking alkaline-earth 

elements (Group IIA), probably are correlated to a significant extent, but dose coefficients for 

isotopes of cesium (alkaline metal, Group IA) and cerium (lanthanide series) should have little 

correlation; (2) dose coefficients for source organs should be negatively correlated with organ 

mass (i.e., a lower organ mass results in a higher dose from all deposited radionuclides, and vice 

versa, if deposition fractions do not depend on organ mass); and (3) some correlation in GI tract 

absorption of different radionuclides is expected when there should be a tendency for all 

insoluble oxide forms of radionuclides to be more strongly or more weakly absorbed in an 

individual than is assumed by ICRP and ingestion of large, insoluble fallout particles could result 

in very low absorption of all refractory radionuclides that are dispersed in the volume of such 

particles, compared with ICRP’s assumptions. 

 By considering available information on uncertainties in dose coefficients for inhalation 

and ingestion and the complicating factors that arise in applying that information to mixtures of 

radionuclides, it is our judgment that a reasonable estimate of uncertainty in dose coefficients for 

inhalation of mixtures of fission and activation products in respirable or nonrespirable form 

currently recommended by ICRP is a factor of 10. We represent this uncertainty by a lognormal 

probability distribution with a 90% credibility interval between 0.1 and 10. 
85

 

 The choice of an uncertainty factor of 10 is supported by the following rationale. 

Although uncertainties in dose coefficients for certain radionuclides at minor sites of deposition 

in the body could be more than a factor of 10, such large uncertainties should be compensated to 

a significant extent by (1) the presence of several fission and activation products in all exposures 

to resuspended fallout at NTS, (2) the lower uncertainties in dose coefficients at minor sites of 

deposition for at least some important radionuclides, and (3) a lack of correlation in dose 

coefficients for at least some important radionuclides. When exposure to fallout that was 

deposited a few years previously occurred, fewer fission and activation products would be of 

concern, and these compensating factors could be less significant. However, we do not expect 

that exposures in the thermal-pulse and blast-wave regions at NTS only involved fallout that was 

deposited a few years previously, without the presence of significant quantities of more recent 

fallout that contained many fission and activation products. 

 The uncertainty in dose coefficients for mixtures of fission and activation products could 

be substantially less than a factor of 10, especially when exposure to a large number of those 

radionuclides occurred. A smaller uncertainty might apply, for example, when uncertainties in 

dose coefficients for important radionuclides are less than a factor of 10 or are uncorrelated. 

However, we believe that it is difficult to justify a lower uncertainty factor that would apply to 

all possible mixtures of fission and activation products and all organs or tissues of concern. In 

addition, it is important that this uncertainty not be underestimated when effective resuspension 

factors derived in this report are to be used in dose reconstructions for military participants and 

estimated doses should be at least upper 95% credibility limits of possible doses. 

4.1.5.4.2 Uncertainty in ICRP’s dose coefficients for plutonium. As noted in 

Section 4.1.2.4, measurements at NTS after the period of weapons testing indicated that 

plutonium was the most important alpha-emitting radionuclide in fallout, and that other alpha 

emitters, such as 241Am and 238Pu, were relatively unimportant (McArthur, 1991).55 An 

55 If other alpha-emitting radionuclides were important, dose coefficients for all such 

radionuclides are expected to be highly correlated, due mainly to their similar biokinetic behavior [ICRP 

(1996a; 2002) and references therein]. Therefore, in contrast to the case of mixtures of fission and 

activation products, it would not be appropriate to consider that dose coefficients for different alpha 

emitters are uncorrelated in assessing uncertainties in dose coefficients for mixtures of such radionuclides. 
86

evaluation of uncertainties in organ-specific dose coefficients for inhalation of plutonium in 

respirable or nonrespirable form requires a consideration of uncertainties in dosimetric and 

biokinetic models. 

An uncertainty in the biological effectiveness of alpha particles relative to photons and 

electrons also contributes to uncertainties in equivalent doses to specific organs or tissues per 

unit activity intake of plutonium. However, given that probability distributions of radiation 

effectiveness factors (REFs) that were developed by Kocher et al. (2002; 2005) to represent the 

biological effectiveness of alpha particles in inducing cancer in humans are incorporated in the 

computer code that is used to evaluate causation of cancers in military participants when a dose 

reconstruction is required (Land et al., 2003; Kocher et al., 2008), an uncertainty in the biological 

effectiveness of alpha particles is not taken into account in this analysis. Taking uncertainties in 

REFs into account would result in a double counting of this source of uncertainty. 

 We assume that uncertainties in dose coefficients for inhalation or ingestion of plutonium 

due to uncertainties in dosimetric and biokinetic models should be substantially larger than 

uncertainties in dose coefficients for mixtures of beta/gamma-emitting fission and activation 

products. This assumption is based mainly on two considerations: (1) the greater importance of 

uncertainties in dosimetric models for alpha-emitting radionuclides in some organs or tissues 

(e.g., the skeleton and GI tract) compared with uncertainties in dosimetric models for 

beta/gamma emitters and (2) the larger uncertainty in absorption of plutonium in the GI tract 

compared with uncertainties in GI-tract absorption for many fission and activation products 

(Eckerman et al., 1999; Harrison et al., 2001; Pawel et al., 2007). Estimated uncertainties in 

dose or risk coefficients for plutonium that were obtained in studies summarized in Tables 4-8 

and 4-10 are among the highest for any radionuclide. 

 For purposes of this analysis, it is our judgment that a reasonable estimate of uncertainty 

in dose coefficients for inhalation of plutonium in respirable or nonrespirable form currently 

recommended by ICRP is a factor of 30. We represent this uncertainty by a lognormal 

probability distribution with a 90% credibility interval between 0.033 and 30. 

 The choice of an uncertainty factor of 30 is based mainly on three considerations. First, 

data in animals discussed by Harrison et al. (2001) and noted in Table 4-13 suggest that the 
87

uncertainty in the GI-tract absorption fraction for plutonium in oxide form (i.e., the ratio of the 

95th to the 50th percentile) could be a factor of about 10. Data in Table 4-13 indicate that an 

uncertainty factor of 10 also applies to a few other radionuclides for which the GI-tract 

absorption fraction is poorly known. Second, given that data in humans on accumulation of 

plutonium at minor sites of deposition (i.e., sites other than the lung, skeleton, liver, and gonads) 

are not extensive and show considerable variability (ICRP, 1993), we believe that the uncertainty 

in the deposition fraction at minor sites could be as high as a factor of 10. By combining these 

two uncertainties, which should be uncorrelated, an uncertainty factor of about 27 is obtained. 

Third, we assume that uncertainties in dosimetric modeling of plutonium contribute to the overall 

uncertainty, even in estimating dose in soft tissues. An uncertainty in dosimetric modeling in 

soft tissues occurs, for example, when the particular location of deposited plutonium with respect 

to radiosensitive cells in which cancer would be induced is uncertain. This uncertainty can be 

important due to the very short ranges of alpha particles in tissue. 

 An estimated uncertainty of about a factor of 8–12 in the risk coefficient for ingestion of 

plutonium in EPA’s Federal guidance (see Tables 4-9 and 4-10) is much lower than the 

uncertainty factor of 30 used in this analysis. Similarly, the analyses by Bolch et al. (2001; 

2003), Farfán et al. (2003), and Grogan et al. (2000; 2001) discussed in Section 4.1.5.3.5 indicate 

that uncertainties in dose coefficients for inhalation of plutonium in respirable form could be less 

in some organs or tissues than uncertainties in dose coefficients for ingestion (i.e., inhalation of 

plutonium in nonrespirable form). However, such differences are not taken into account in this 

analysis when other assessments focused on dose coefficients at major sites of deposition but we 

are concerned with dose coefficients at minor sites as well. We also note that assessments of 

uncertainty in dose coefficients for ingestion of plutonium focused on more soluble chemical 

forms, rather than insoluble oxide forms of interest in exposures to fallout. However, we believe 

that the dependence of uncertainties in dose coefficients on chemical form should be 

substantially less than the dependence of dose coefficients themselves. That is, uncertainties in 

dose coefficients for plutonium oxide should be similar to uncertainties in dose coefficients for 

other chemical forms, even though dose coefficients for the two forms may differ substantially. 
88

4.1.5.4.3 Bias in ICRP’s dose coefficients. Uncertainties in dose coefficients for 

inhalation of radionuclides in respirable or nonrespirable form that were developed in the 

previous two sections are intended to apply to dose coefficients for adult members of the public 

and for radionuclides in oxide form currently recommended by ICRP [(1996a; 2002) and 

references therein]. However, as noted in Section 4.1.5.2, ICRP’s dose coefficients may tend to 

overestimate values that apply to radionuclides in fallout at NTS, due primarily to the 

preponderance of large particles in fallout at locations close to ground zero and their low 

solubility. The possibility that use of ICRP’s dose coefficients results in substantial 

overestimates of internal doses to military participants was noted in a previous review of 

methods of dose reconstruction (NRC, 1985). 

 We assume that a possible bias in ICRP’s dose coefficients is important for inhalation of 

larger, nonrespirable particles (i.e., ingestion) but is not important for inhalation of smaller, 

respirable particles. The latter assumption is based on data which indicate that the solubility of 

smaller fallout particles is substantially higher than the solubility of larger particles (Larson et 

al., 1966; LeRoy et al., 1966) and the consideration that absorption of beta and alpha radiation in 

fallout particles of diameter less than 10 μm should not be important. Biases in ICRP’s dose 

coefficients for ingestion are considered below. 

Bias in dose coefficients for ingestion of fission and activation products. We are aware 

of two sources of data on a possible bias in ICRP’s dose coefficients for ingestion of fission and 

activation products in fallout. Glasstone and Dolan (1977; Paragraph 12.169) noted, without 

attribution, that about 10% of ingested strontium and barium oxide in early fallout is absorbed 

into blood. Compared with ICRP’s current assumptions that 30% of strontium oxide and 10% of 

barium oxide is absorbed in the GI tract (ICRP, 1996a; 2002), the estimate of 10% noted by 

Glasstone and Dolan suggests that ICRP’s dose coefficients for radioisotopes of those elements 

could be too high by a factor of about 2 when they are applied to nonrespirable fallout 

particles.56 A bias of a factor of 2 should be a minimum value for mixtures of fission and 

activation products when it is considered that (1) strontium and barium oxide are considerably

 56 This conclusion takes into account that the total activities of shorter-lived isotopes of strontium 

and barium in fresh fallout are about the same (Trabalka and Kocher, 2007). 
89

d 

(e.g., cerium). 

 

more soluble than oxide forms of many other elements (ICRP, 1996a; 2002) and (2) strontium 

and barium tend to be volatile elements that are preferentially deposited on the surface of fallout

particles (Freiling et al., 1965; Hicks, 1982) and, thus, should be more available to be dissolve

than refractory elements 

 The second source of data is a study on human subjects who ingested fallout particles of 

different sizes that were collected at 5 days after a detonation at NTS (LeRoy et al., 1966). At 

particle sizes less than about 180 μm, which are of greatest interest in evaluating a possible bias 

in ICRP’s dose coefficients for inhalation of nonrespirable particles, the fraction of the total 

activity of photon-emitting radionuclides that was absorbed in the GI tract ranged from about 

0.01 to 0.09, and the average absorption fraction was about 0.05.57 In comparison, on the basis 

of estimates of the relative activities of fission and activation products in fallout at 2 days after a 

detonation (Trabalka and Kocher, 2007), we estimate that the average absorption fraction would 

have been between 0.1 and 0.2 if GI-tract absorption fractions for oxide forms recommended by 

ICRP (1996a; 2002) applied to ingestion of radionuclides in fallout particles, depending on 

assumptions about the extent to which isotopes of iodine were retained on fallout particles prior 

to ingestion by study subjects. This comparison indicates that ICRP’s dose coefficients for 

ingestion could be too high by a factor of about 2−4 when they are applied to mixtures of many 

fission and activation products in nonrespirable fallout particles. 

 On the basis of the limited data and analysis described above, we assume that the bias in 

ICRP’s dose coefficients for ingestion of fission and activation products when they are applied to 

inhalation of fallout particles in nonrespirable form should not exceed a factor of 4. Since the 

data also indicate that the bias could be very small if particles were sufficiently small to be 

inhalable, we represent the uncertainty in the bias in ICRP’s dose coefficients for ingestion by a 

uniform distribution between 0.25 and 1.0. Thus, we assume that, on average, ICRP’s dose 

coefficients for ingestion of fission and activation products overestimate values that apply to 

inhalation of nonrespirable fallout particles by less than a factor of 2. 

57 In developing these estimates, we ignored results for two subjects in which the activity 

absorbed in the GI tract was too low to be detected above a background count rate (LeRoy et al., 1966). 
90

Bias in ingestion dose coefficients for plutonium. We are unaware of any published 

studies on absorption of plutonium in the GI tract following ingestion of fallout particles. 

However, we believe it is reasonable to assume that the bias in ICRP’s dose coefficients for 

ingestion of plutonium in oxide form when they are applied to inhalation of nonrespirable fallout 

particles should be larger than the assumed bias in ICRP’s dose coefficients for inhalation of 

fission and activation products in nonrespirable form given above. Our reasoning is that 

plutonium, which is highly refractory (Freiling et al., 1965; Hicks, 1982), should be distributed 

in the volume of insoluble fallout particles to a greater extent than mixtures of fission and 

activation products, which include refractory and volatile radionuclides. 

 In the absence of data, an assumption about the bias in ICRP’s dose coefficients for 

ingestion of plutonium is based on judgment. In addition to assuming that the bias should be 

larger than the assumed bias for mixtures of fission and activation products, we assume that the 

uncertainty in the bias for plutonium should be larger. On the basis of these considerations, we 

assume that the bias in ICRP’s ingestion dose coefficients for plutonium could range from 0.1 to 

1.0, and we represent this assumption by a log-uniform probability distribution with a minimum 

at (ln 0.1) = −2.3 and maximum at (ln 1.0) = 0. The median of this distribution is 0.32, the mean 

is 0.39, and the 90% credibility interval ranges from 0.11 to 0.89. Thus, we assume that, on 

average, ICRP’s dose coefficients for ingestion of plutonium oxide overestimate values that 

apply to inhalation of fallout particles in nonrespirable form by less than a factor of 3. 

4.1.5.5 Summary of Uncertainties in Dose Coefficients. Assumed uncertainties in the 

different factors that contribute to estimated uncertainties in dose coefficients for inhalation of 

fission and activation products or plutonium in respirable or nonrespirable form in resuspended 

fallout are summarized in Table 4-14. Representations of uncertainty in dose coefficients for 

inhalation of fission and activation products or plutonium in respirable or nonrespirable form 

used in this analysis are obtained by combining the probability distributions of the different 

parameters. The following medians and 90% credibility intervals of probability distributions to 

represent uncertainties in dose coefficients are obtained: 
91

• Inhalation of fission and activation products in respirable form – Median at 1.0 and 90% 

credibility interval between 0.1 and 10; 

• Inhalation of fission and activation products in nonrespirable form – Median at 0.6 and 

90% credibility interval between 0.054 and 6.4; 

• Inhalation of plutonium in respirable form – Median at 1.0 and 90% credibility interval 

between 0.033 and 30. 

• Inhalation of plutonium in nonrespirable form – Median at 0.3 and 90% credibility 

interval between 0.0087 and 12. 

These probability distributions represent the assumed uncertainties in dose coefficients that apply 

in the resuspension scenarios of concern at NTS relative to dose coefficients for adult members 

of the public currently recommended by ICRP. For example, for inhalation of plutonium in 

nonrespirable form, an upper 95% credibility limit of the dose coefficient to any organ or tissue 

is assumed to exceed ICRP’s dose coefficient by a factor of 12. 

 For inhalation of radionuclides in nonrespirable form, assumed uncertainties in 

dosimetric and biokinetic models currently recommended by ICRP contribute 93% of the total 

uncertainty for fission and activation products and 91% of the total uncertainty for plutonium. 

Thus, this source of uncertainty is much more important that the assumed uncertainties in the 

bias in ICRP’s dose coefficients when they are applied to inhalation of radionuclides in 

nonrespirable form. 

 The probability distributions of dose coefficients for inhalation of all radionuclides in 

respirable form summarized above are assumed to be lognormal. The probability distributions of 

dose coefficients for inhalation of radionuclides in nonrespirable form also are well represented 

by lognormal distributions with the indicated 90% credibility intervals. This is an expected 

result when the parameter with the largest uncertainty is assumed to be lognormally distributed. 

GSDs of lognormal probability distributions of dose coefficients with the indicated 90% 

credibility intervals for radionuclides in nonrespirable form are about 4.3 for fission and 

activation products and 9.0 for plutonium. 
92

4.1.6 Summary of Uncertainties in Estimates of Inhalation Dose

 Sections 4.1.1−4.1.5 present the assumed probability distributions of parameters in the 

model that is used in dose reconstructions to estimate doses from inhalation of resuspended 

radionuclides [see Section 3.1, eq. (5)] when that model is applied to resuspension of fallout in 

the thermal-pulse or blast-wave region of nuclear detonations at NTS. Except for the uncertainty 

in the breathing rate (see Section 4.1.4), assumed uncertainties in the different factors that 

contribute to uncertainties in estimated doses from inhalation of radionuclides in respirable or 

nonrespirable form are summarized in Tables 4-1, 4-7, and 4-14. 

 Assumed uncertainties in estimated concentrations of radionuclides in fallout that was 

deposited on the ground surface as those concentrations affect estimates of inhalation dose [i.e., 

the product of a measured photon exposure rate in air, I, and the radionuclide concentrations per 

unit exposure rate, SA/I, in eq. (5)], resuspension factors, the breathing rate, and dose coefficients 

for inhalation of radionuclides in respirable or nonrespirable form are summarized in Table 4-15 

as median values and 90% credibility intervals. Since inhalation doses are estimated as the 

product of the parameters in Table 4-15, this summary permits a qualitative assessment of the 

relative importance of different sources of uncertainty. The assumed uncertainties in dose 

coefficients and resuspension factors clearly are the most important. The importance of the 

different parameters that contribute to those uncertainties is described in Sections 4.1.3.3 

and 4.1.5.5. 

4.2 Calculated Probability Distributions of Inhalation Dose

 Assumed probability distributions of parameters in the model in eq. (5) (see Section 3.1), 

as summarized in Table 4-15, were combined (multiplied) using Latin Hypercube sampling as 

implemented by Crystal Ball® software (Decisioneering, 2001) (see Section 3.2) to generate 

probability distributions to represent estimated uncertainties in the equivalent dose to any organ 

or tissue from inhalation of radionuclides in respirable or nonrespirable form in fallout that was 

resuspended by nuclear detonations at NTS. In the following sections, results of these 
93

calculations are presented separately for fission and activation products and for plutonium. In 

Section 5, these results are compared with point estimates of inhalation dose that would be 

obtained in dose reconstructions for military participants, as described in Section 3.1, to derive 

effective resuspension factors that should be assumed in the thermal-pulse and blast-wave 

regions to ensure that estimated doses are at least upper 95% credibility limits. 

4.2.1 Approach to Combining Parameter Uncertainties

 For each of the eight exposure situations of concern (inhalation of fission and activation 

products or plutonium in respirable or nonrespirable form in the thermal-pulse or blast-wave 

region), probability distributions to represent uncertainty in inhalation doses that are estimated 

using the model in eq. (5) can be obtained by combining (multiplying) the assumed probability 

distributions of each relevant parameter given in Tables 4-1, 4-7, and 4-14 and the assumed 

probability distribution of the breathing rate given in Section 4.1.4. However, a simpler 

approach is to assume that upper and lower bounds of the 90% credibility intervals of each 

parameter in Table 4-15 define 5th and 95th percentiles of lognormal probability distributions. 

Use of lognormal distributions to represent the calculated probability distributions of 

concentrations of radionuclides on the ground surface, resuspension factors, and dose 

coefficients is justified on the grounds that those distributions are well represented by lognormal 

distributions (see Sections 4.1.2.5, 4.1.3.3, and 4.1.5.5). 

 The adequacy of an assumption that upper and lower bounds of the 90% credibility 

intervals of the probability distributions of parameters in Table 4-15 other than the breathing 

rate, which is described by a lognormal distribution, define 5th and 95th percentiles of lognormal 

distributions was checked in two ways. The simplest way was to note that, for each parameter in 

Table 4-15, the geometric mean of the 5th and 95th percentiles, which is the median of a 

lognormal distribution, is close to the median of the probability distribution that was calculated 

using the assumed probability distributions of all relevant parameters. In the worst case, which 

occurs in the probability distribution of the concentrations of fission and activation products in 

nonrespirable form on the ground surface, the calculated median differs from the geometric mean 
94

 

of the 5th and 95th percentiles by less than 10%. If the calculated probability distribution of a 

parameter in Table 4-15 deviated substantially from a lognormal distribution, the median would 

not be close to the geometric mean of the 5th and 95th percentiles. The adequacy of our 

assumption was also checked by fitting each continuous probability distribution that can be 

specified in Crystal Ball® to the calculated probability distributions and testing for goodness of 

fit (Decisioneering, 2001).58 In all cases, a lognormal distribution gave a significantly better fit 

to the calculated probability distribution than any other continuous distribution. 

 On the basis of these considerations, we obtained estimated uncertainties in inhalation 

doses for each exposure situation of concern by representing all parameters in Table 4-15 by 

lognormal probability distributions and combining (multiplying) the probability distributions of 

each parameter. This approach facilitates ease of calculations and transparency of the results. 

This approach also can be justified on the grounds that: (1) assumed probability distributions of 

all parameters that contribute to the results in Table 4-15 represent subjective judgments about 

90% credibility intervals and the shapes of distributions, rather than results of a rigorous 

statistical analysis of relevant data, which are lacking for most parameters; and (2) results of this 

analysis are used to derive effective resuspension factors, which are highly uncertain, to the 

nearest power of 10 only, and more precise estimates are not needed. 

4.2.2 Probability Distributions of Dose from Inhalation of Fission and Activation Products

 In assessing uncertainties in estimated doses from inhalation of mixtures of fission and 

activation products in previously deposited fallout that was resuspended by nuclear detonations 

at NTS, we distinguished between intakes of small, respirable particles and larger, nonrespirable 

particles. This distinction was based on the considerations that (1) the effects of fractionation of 

fission and activation products and its uncertainty on inhalation doses depend on particle size 

(i.e., whether or not resuspended fallout particles were respirable), (2) the nonrespirable fraction 

of inhalable radionuclides in resuspended fallout should have been substantially larger than the 

58 Continuous probability distributions that can be specified in Crystal Ball® include normal, 

triangular, poisson, binomial, lognormal, uniform, exponential, geometric, Weibull, beta, hypergeometric, 

gamma, logistic, pareto, extreme value, negative binomial, log-triangular, and log-uniform. 
95

respirable fraction, and (3) there could be a substantial bias in ICRP’s current dose coefficients 

for inhalation of radionuclides in nonrespirable form that results in overestimates of dose in 

resuspension scenarios of concern, but it is less likely that there is a substantial bias in ICRP’s 

dose coefficients for inhalation of radionuclides in respirable form (see Sections 4.1.2.4.1, 

4.1.3.2, and 4.1.5.4.3; Tables 4-1, 4-7, and 4-14). 

 Estimated uncertainties in doses from inhalation of fission and activation products in 

fallout that was resuspended in the thermal-pulse or blast wave region of nuclear detonations at 

NTS obtained in this analysis are summarized in Table 4-16 as medians and 90% credibility 

intervals of lognormal probability distributions. These distributions are relative to the 

concentrations of fission and activation products in fallout at NTS that are assumed in dose 

reconstructions and relative to dose coefficients for specific organs or tissues from inhalation of 

radionuclides in respirable or nonrespirable form by adult members of the public that are 

currently recommended by ICRP. They are intended to apply to any organ or tissue and any 

mixture of fission and activation products in resuspended fallout (i.e., at any time after a previous 

detonation that resulted in fallout at NTS). 

 Results in Table 4-16 indicate that the probability distributions of dose from inhalation of 

fission and activation products in respirable or nonrespirable form do not differ greatly. The 

uncertainty is slightly larger for respirable particles, because the uncertainty in the respirable 

fraction of inhalable particles (see Table 4-7) is larger than the uncertainty in the bias in ICRP’s 

dose coefficients, which is assumed to apply only to nonrespirable particles (see Table 4-14). 

The contributions to estimated uncertainties in doses from inhalation of fission and activation 

products in respirable or nonrespirable form in the thermal-pulse and blast-wave regions, as well 

as GSDs of the assumed lognormal probability distributions, are as follows: 

 Thermal-pulse region, respirable (nonrespirable) particles [GSD = 16 (14)] – 

 Resuspension factor, 65% (58%) 

 Dose coefficients, 26% (30%) 

 Concentrations on ground surface, 8% (10%) 

 Breathing rate, 2% (2%) 
96

 Blast-wave region, respirable (nonrespirable) particles [GSD = 38 (33)] – 

 Resuspension factor, 80% (76%) 

 Dose coefficients, 15% (17%) 

 Concentrations on ground surface, 5% (6%) 

 Breathing rate, 1% (1%) 

The most important contributors to the estimated uncertainties in inhalation doses are the 

assumed uncertainties in the resuspension factor and dose coefficients; assumed uncertainties in 

the concentrations of fission and activation products in fallout on the ground surface and the 

breathing rate are minor contributors. Thus, parameter uncertainties that are the most important 

in determining uncertainties in doses from inhalation of resuspended fission and activation 

products are the assumed uncertainties in the resuspension factor that applies to all fallout on the 

ground surface and the inhalable fraction of resuspended radionuclides (see Table 4-7) and the 

assumed uncertainty in dose coefficients due to uncertainties in ICRP’s recommended dosimetric 

and biokinetic models (see Table 4-14). 

4.2.3 Probability Distributions of Dose from Inhalation of Plutonium

 The analysis of uncertainty in estimated doses from inhalation of plutonium in previously 

deposited fallout that was resuspended by nuclear detonations at NTS is similar to the analysis 

for mixtures of fission and activation products described in the previous section. The only 

difference is that the effects of fractionation and its uncertainty on doses from inhalation of 

plutonium do not depend on particle size; i.e., those effects are the same for plutonium in 

respirable or nonrespirable form (see Section 4.1.2.4). This difference has little effect on 

comparisons of estimated uncertainties in doses from inhalation of fission and activation 

products and inhalation of plutonium. 

 Estimated uncertainties in doses from inhalation of plutonium in fallout that was 

resuspended in the thermal-pulse or blast-wave region of nuclear detonations at NTS obtained in 

this analysis are summarized in Table 4-17 as medians and 90% credibility intervals of 
97

lognormal probability distributions. These distributions are relative to the concentrations of 

plutonium in fallout at NTS that are assumed in dose reconstructions and relative to dose 

coefficients for specific organs or tissues from inhalation of plutonium in respirable or 

nonrespirable form by adult members of the public that are currently recommended by ICRP. 

They are intended to apply to any organ or tissue. 

 Results in Table 4-17 indicate that the probability distributions of dose from inhalation of 

plutonium in respirable or nonrespirable form do not differ greatly, as is the case in the results 

for fission and activation products; the uncertainty again is slightly larger for respirable particles. 

The contributions to estimated uncertainties in doses from inhalation of plutonium in respirable 

or nonrespirable form in the thermal-pulse and blast-wave regions, as well as GSDs of the 

assumed lognormal probability distributions, are as follows: 

 Thermal-pulse region, respirable (nonrespirable) particles [GSD = 23 (22)] – 

 Resuspension factor, 48% (41%) 

 Dose coefficients, 44% (51%) 

 Concentrations on ground surface, 6% (7%) 

 Breathing rate, 2% (2%) 

 Blast-wave region, respirable (nonrespirable) particles [GSD = 51 (50)] – 

 Resuspension factor, 68% (63%) 

 Dose coefficients, 27% (32%) 

 Concentrations on ground surface, 4% (4%) 

 Breathing rate, 1% (1%) 

As in the analysis for fission and activation products, the most important contributors to the 

estimated uncertainties in inhalation doses are the assumed uncertainties in the resuspension 

factor and dose coefficients; assumed uncertainties in the concentrations of plutonium in fallout 

on the ground surface and the breathing rate are minor contributors. However, for inhalation of 

plutonium in nonrespirable form in the thermal-pulse region, the uncertainty in dose coefficients 

is more important than the uncertainty in the resuspension factor. The greater importance of the 
98

uncertainty in dose coefficients for plutonium compared with the importance of that uncertainty 

for fission and activation products is a result of the assumptions of a larger uncertainty in ICRP’s 

dosimetric and biokinetic models for plutonium and, in the case of inhalation of nonrespirable 

particles, a larger uncertainty in the bias in ICRP’s dose coefficients (see Table 4-14). Thus, as 

in the case of fission and activation products, parameter uncertainties that are the most important 

in determining uncertainties in doses from inhalation of resuspended plutonium are the assumed 

uncertainties in the resuspension factor that applies to all fallout on the ground surface and the 

inhalable fraction of resuspended radionuclides (see Table 4-7) and the assumed uncertainty in 

dose coefficients due to uncertainties in ICRP’s recommended dosimetric and biokinetic models 

(see Table 4-14). 

4.2.4 Comparison of Results for Fission/Activation Products and Plutonium

 A comparison of the results of our analysis of uncertainty in estimated doses from 

inhalation of fission and activation products in Table 4-16 with the corresponding results for 

plutonium in Table 4-17 indicates that estimated uncertainties are larger for plutonium. The 

larger uncertainties for plutonium are due primarily to an assumption of a larger uncertainty in 

ICRP’s dosimetric and biokinetic models for plutonium (a factor of 30, compared with a factor 

of 10 for fission and activation products). Consequently, at the upper 95% credibility limit (95th

percentile), estimated doses from inhalation of plutonium are higher than estimated doses from 

inhalation of fission and activation products. The 95th percentiles differ by a factor of 3 for 

respirable and nonrespirable forms in both regions. 

 The comparison summarized above indicates that the results for plutonium are more 

relevant in deriving point values of effective resuspension factors that should be assumed in dose 

reconstructions to ensure that estimates of inhalation dose due to resuspension of fallout in the 

thermal-pulse or blast-wave region of a nuclear detonation at NTS provide credible upper bounds 

(at least 95% credibility limits) of possible doses. More specifically, the 95th percentiles of the 

probability distributions of doses from inhalation of plutonium in nonrespirable form are the 
99

relevant quantities that should be used in deriving effective resuspension factors that apply in the 

thermal-pulse or blast-wave region. These resuspension factors are derived in Section 5. 

4.2.5 Consideration of Parameter Correlations

 With one exception, the analysis of uncertainties in estimated inhalation doses presented 

in this report and summarized in Tables 4-16 and 4-17 assumes that there are no correlations 

among different parameters that contribute to uncertainties in estimated concentrations of 

radionuclides on the ground surface, resuspension factors, the breathing rate, and dose 

coefficients for inhalation. The one exception, which is described in Section 4.1.3.2, is that the 

respirable and nonrespirable fractions of resuspended radionuclides in inhalable form are 

perfectly correlated by requiring that their sum is unity. 

 In this section, possible parameter correlations and their potential effects on estimated 

uncertainties in inhalation doses and, therefore, the derivation of effective resuspension factors 

are considered. Two possibilities noted previously are a correlation between the degree of 

fractionation of radionuclides in fallout at NTS and the fraction of resuspended radionuclides in 

inhalable form (see Section 4.1.2.4.1, footnote 20) and a correlation between the respirable and 

nonrespirable fractions of radionuclides in inhalable form and the inhalable fraction of 

resuspended radionuclides (see Section 4.1.3.2.6). Another possibility is a correlation between 

the degree of fractionation of radionuclides in fallout and the bias in dose coefficients 

recommended by ICRP—i.e., the greater the degree of fractionation, the more likely it could be 

that ICRP’s dose coefficients overestimate values that apply to radionuclides in fallout. There 

should not be any correlations that involve measured or calculated exposure rates in air from 

radionuclides deposited on the ground surface, the shielding effect of ground roughness, and the 

resuspension factor that applies to all radionuclides on the ground surface. In addition, by 

including a parameter to account for a possible bias in applying ICRP’s dose coefficients to 

inhalation of radionuclides in fallout, uncertainties in ICRP’s dosimetric and biokinetic models 

are considered to be independent of the degree of fractionation and are uncorrelated with any 

other parameter. 
100

 As noted in the previous section, estimated uncertainties in doses from inhalation of 

resuspended plutonium in nonrespirable form that were obtained in this analysis provide the 

limiting cases that should be used in deriving effective resuspension factors in the thermal-pulse 

and blast-wave regions. Therefore, we consider possible parameter correlations and their effects 

for those cases only. 

 The fraction of resuspended plutonium in inhalable form and the bias in ICRP’s dose 

coefficients for inhalation of plutonium in nonrespirable form both should be negatively 

correlated with the degree of fractionation of radionuclides (enhancement of plutonium) in 

fallout at NTS—i.e., the greater the degree of fractionation, the smaller the fraction of 

resuspended plutonium in inhalable form and the smaller the equivalent doses per unit activity 

intake of plutonium relative to ICRP’s dose coefficients—essentially because an increase in the 

degree of fractionation should result in an increase in the fraction of larger particles (see 

Section 4.1.2.4). Increases in the fraction of larger particles should reduce the fraction of 

resuspended plutonium in inhalable form and should weight the particle-size distribution of the 

inhalable fraction more toward larger particles. The latter effect should increase the tendency for 

ICRP’s dose coefficients to overestimate doses from inhalation of plutonium in nonrespirable 

form when fallout particles are expected to be insoluble, plutonium is expected to be distributed 

mainly in the volume of fallout particles, and some of the energy of emitted alpha particles 

would be absorbed in the particles (see Sections 4.1.5.2 and 4.1.5.4.2). If the fraction of 

resuspended plutonium in inhalable form and the bias in ICRP’s dose coefficients for inhalation 

of plutonium are negatively correlated with the degree of fractionation, those two parameters 

would be positively correlated—i.e., the smaller the fraction of resuspended plutonium in 

inhalable form, the greater the reduction in inhalation doses compared with doses calculated 

using ICRP’s dose coefficients. 

 In considering a possible correlation between the nonrespirable fraction of resuspended 

plutonium in inhalable form and the inhalable fraction of resuspended plutonium, we assume that 

the more the particle-size distribution of plutonium is weighted toward larger particles, the 

higher the nonrespirable fraction of inhalable plutonium would be. Arguments presented above 

then indicate that such a correlation should result in a positive correlation between the degree of 
101

enhancement of plutonium in fallout at NTS and the nonrespirable fraction of inhalable 

plutonium. However, there is little evidence of a positive correlation between the nonrespirable 

fraction of inhalable plutonium and the inhalable fraction of plutonium in fallout at NTS in the 

limited data discussed in Sections 4.1.3.2.5 and 4.1.3.2.6. 

 To investigate potential effects of the correlations described above, we performed two 

calculations using Crystal Ball® (Decisioneering, 2001). In the first calculation, we combined 

assumed probability distributions of the enhancement of plutonium in fallout at NTS due to 

fractionation (see Table 4-1), the inhalable fraction of resuspended plutonium (see Table 4-7), 

and the bias in ICRP’s dose coefficients for inhalation of plutonium in nonrespirable form (see 

Table 4-14) by assuming a perfect negative correlation between the enhancement due to 

fractionation and the other two parameters (i.e., a correlation coefficient of −1). This assumption 

maximizes the effect of correlations. As noted above, these assumptions imply a perfect positive 

correlation (correlation coefficient of +1) between the inhalable fraction of resuspended 

plutonium and the bias in ICRP’s dose coefficients. In the second calculation, we used the same 

assumptions as in the first calculation and included the nonrespirable fraction of resuspended 

plutonium in inhalable form (see Table 4-7) by assuming that it is perfectly positively correlated 

with the enhancement of plutonium due to fractionation. 

 In each calculation, we compared the 95th percentile of the resulting probability 

distribution with the 95th percentile that was obtained by assuming that all parameters are 

uncorrelated. In both calculations, the 95th percentile increased when the correlations described 

above were included. However, the increase was only about 10%. The slight increase in the 95th

percentile in both calculations indicates that the assumed positive correlation between the 

inhalable fraction of resuspended plutonium and the bias in ICRP’s dose coefficients is more 

important than the assumed negative correlation between the enhancement of plutonium due to 

fractionation and the inhalable fraction of resuspended plutonium. The assumed positive 

correlation between the enhancement of plutonium and the nonrespirable fraction of resuspended 

plutonium in inhalable form in the second calculation had virtually no effect, because the 

uncertainty in the latter parameter is very small (see Section 4.1.3.2.6). The small effects of the 

assumed parameter correlations in these calculations are not surprising when the uncertainty in 
102

one parameter (the inhalable fraction of resuspended plutonium) is much larger than 

uncertainties in all other parameters. 

 When uncertainties in other parameters that are not correlated with the enhancement of 

plutonium in fallout due to fractionation, including the resuspension factor that applies to all 

fallout on the ground surface and ICRP’s dose coefficients, are large (i.e., a factor of 10 or 

more), it is evident from the calculations described above that any parameter correlations that 

might be considered would have a negligible effect on estimated upper 95% credibility limits of 

inhalation doses. Therefore, it is not important to account for possible parameter correlations of 

the kind described above in this analysis. 
103

Figure 4-1. Distribution of activity with particle diameter in fallout sample at distance of 

1.1 miles from ground zero at Shot DIABLO in Operation PLUMBBOB at NTS (Miller, 

1969; Figure 8). Activity distribution of large particles is shown at one-tenth of actual 

particle diameter. 
104

Table 4-1. Summary of assumed uncertainties in estimates of concentrations of 

radionuclides in fallout deposited on ground surface at NTSa

Source of uncertaintyb Probability distribution 

Estimation of photon exposure rates in air 

above ground at times and locations of 

exposure based on measurements at various 

times and locations after each detonationc

Lognormal distribution with median at 1.0 and 

90% credibility interval between 0.33 and 3.0 

Calculation of exposure rates from infinite, 

uniformly contaminated plane source 

Normal distribution with 90% credibility 

interval between 0.8 and 1.2 

Reductions in calculated exposure rates due 

to finite extent of source region 

Reductions and their uncertainty are assumed 

to be negligible 

Shielding effect of ground roughnessd Uniform distribution with minimum at 0.78 

and maximum at 1.4 

Effects of fractionation of radionuclides in 

fallout on estimates of inhalation dosee

 Fission and activation products 

 Inhalation of respirable particles 

 Inhalation of nonrespirable particlesf

 Plutonium – Inhalation of respirable and 

 nonrespirable particles 

Uniform distribution between 0.5 and 1.9 

Uniform distribution between 0.2 and 1.7 

Uniform distribution between 1.0 and 3.3 

a

 Analysis of uncertainties is described in Sections 4.1.1 and 4.1.2. Resulting uncertainties in 

activity concentrations of fission and activation products or plutonium in fallout deposited on ground 

surface are summarized in Section 4.1.2.5 and Table 4-15. 

b

 Unless otherwise noted, uncertainties apply to all radionuclides in fallout. 

c

 Uncertainty is relative to point estimates that are assumed in dose reconstructions for military 

participants. 

d

 Probability distribution modifies shielding effect of ground roughness of 0.7 that is assumed in 

dose reconstructions for military participants (Egbert et al., 1985; Raine et al., 2007). 

e

 Probability distributions assume that fallout at NTS was enhanced in refractory radionuclides 

compared with unfractionated mixtures of refractory and volatile radionuclides. 

f

 When inhalation of nonrespirable particles is assumed, inhalation doses can be estimated using 

dose coefficients for ingestion that are adjusted to account for fraction of inhaled material that is 

swallowed. 
105

Table 4-2. Summary of reported resuspension factors associated with mechanical 

stresses at sites where nuclear weapons were testeda

Location Source material Resuspension stress/ 

measurement conditions 

Resuspension factor 

(m−1) 

Maralinga, 

Australiab

Fallout Road survey at 1−2 d 

Cab of landrover, 5th h 

Cab of landrover, 8th h 

< 1 × 10−8 − > 2 × 10−6

6.4 × 10−5

2.5 × 10−5

Uranium Dust stirred at height of 

0.3 m 

1 × 10−3

Plutonium Vehicle dust at height of 

0.3 m 

Pedestrian dust at height 

of 0.3 m 

3 × 10−7 − 7 × 10−4

1.5 × 10−6 − 3 × 10−4

Nevada Test Sitec Plutonium Extensive vehicular 

traffic 

7 × 10−5

Monte Bello 

Islands, Australiab

Fallout Road survey from back 

of landrover, 

 4th d 

 7th d 

At tailboard, 7th d 

8 × 10−7 − 3 × 10−5

7 × 10−7 − 4 × 10−6

1.6 × 10−5 − 3.1 × 10−5

Emu Field, 

Australiab 

Fallout gamma Walking survey 

Vehicle survey, at 

tailboard 

3 × 10−7

2 × 10−6

a

 Data summarized in Table 12.9 of Sehmel (1984); resuspension factors are presumed to apply at 

height of 1 m above ground, except as noted. Data on resuspension factors associated with wind stresses 

summarized in Table 12.7 of Sehmel (1984) are discussed in Section 4.1.3.1.2. 

b

 Data reported by Stewart (1967). 

c

 Data reported by Langham (1971). 
106

Table 4-3. Percentages of total activities in smallest size fractions of fallout samples 

from tower shots in Operation UPSHOT-KNOTHOLE at NTSa

Particle size (μm) Shot Distance 

(miles)b

Exposure rate 

(mR h–1)

c

0−5 5−44d 44−88 88−125 

NANCY 3.5 22.3 22.7 19.0 

12 1.8 × 102 7.9 0.6 0.5 

19.5 1.5 × 102 2.4 1.2 0.7 

BADGER ~ 3 1.1 × 102 0.3 3.1 2.5 8.8 

16.5 3.2 × 101 0.6 3.8 1.9 0.7 

16.6 1.0 × 103 1.5 0.3 1.9 

16.6 9.0 × 102 2.4 3.4 2.3 1.7 

17.5 7.7 × 102 0.7 1.2 1.4 0.7 

18.5 3.3 × 101 1.1 0.9 4.0 3.9 

SIMON ~ 3 0.01 0.03 0.8 

14.7 5.2 × 102 0.2 2.9 5.0 1.0 

14.7 1.6 × 103 0.3 2.5 4.9 1.9 

16.8 4.2 49.2 34.8 5.7 

17.4 2.5 43.6 14.5 15.5 

a

 Data at distances from ground zero to 20 miles obtained from Tables 3.1, 3.5, and 3.10 of 

Rainey et al. (1954); heights of detonation and yields are described in Section 4.1.3.2.2. Data in bold 

face denote measurements within boundary of NTS. 

b

 Distance from ground zero at which fallout was collected. 

c

 Exposure rate at time after detonation of 12 hours. 

d

 Data apply to 0−44 μm size fraction when value for 0−5 μm size fraction is omitted; in those 

cases, quantities of material in 0−5 μm size fraction were insufficient for separation. 
107

Table 4-4. Percentages of total activities in smallest size fractions of fallout samples 

from tower shots in Operation TEAPOT at NTSa

Particle sizes (μm) Shot Distance 

(miles)b

Activity 

(μCi ft–2)

c

0–5 5–20 20–44 44–88 88–125 

TESLA 12 6.3 × 101 4.2 4.0 0.84 22.9 64.9 

8.6 × 101 4.0 0.88 0.31 6.1 80.1 

3.7 × 102 3.4 1.9 0.09 5.0 70.2 

1.1 × 103 3.0 0.32 0.08 4.9 47.3 

8.4 × 102 2.1 1.2 0.20 4.5 48.8 

2.7 × 103 1.7 0.19 0.12 3.6 5.5 

4.3 × 103 0.27 0.07 0.03 3.1 3.0 

4.8 × 103 1.7 0.58 0.05 1.9 1.8 

2.0 × 103 1.7 2.0 0.12 2.1 1.5 

1.5 × 103 2.4 0.49 0.04 2.9 4.2 

5.7 × 101 2.6 6.9 0.27 17.5 11.2 

9.5 27.5 19.6 0.70 22.0 18.5 

TURK 11.5 8.7 × 102 6.7 4.4 0.14 4.7 6.1 

1.4 × 103 10.4 2.2 0.38 4.2 6.1 

1.9 × 103 9.9 4.7 0.35 4.3 3.7 

1.2 × 103 4.3 0.57 0.68 2.3 17.3 

APPLE I 13 7.1 × 102 0.02 0.88 0.40 4.2 1.0 

1.1 × 103 4.9 6.6 1.2 3.0 0.42 

9.2 × 102 5.3 4.2 0.95 1.4 0.84 

 Table is continued on following page; see end of table for footnotes. 
108

Table 4-4. (continued) 

Particle sizes (μm) Shot Distance 

(miles)b

Activity 

(μCi ft–2)

c

0–5 5–20 20–44 44–88 88–125 

MET 20 1.9 × 101 16.4 8.3 5.6 8.6 6.1 

1.5 × 101 9.6 15.9 15.0 19.7 12.0 

2.3 × 102 15.7 13.0 2.6 1.8 6.2 

6.7 × 102 6.0 9.5 1.6 2.4 1.1 

2.6 × 103 2.8 4.1 0.46 1.5 0.47 

4.4 × 103 2.6 2.1 0.20 1.7 0.66 

5.5 × 103 3.8 0.90 0.29 1.4 0.53 

3.9 × 103 0.0 0.20 0.42 1.1 0.50 

1.8 × 103 4.3 1.9 0.79 2.0 0.01 

3.0 × 103 3.1 0.95 0.62 2.0 1.4 

1.3 × 103 0.79 0.20 0.07 0.05 0.33 

2.6 × 102 4.8 7.0 1.9 4.9 1.4 

8.7 9.3 22.0 4.9 33.3 10.2 

APPLE II 7 1.3 × 103 0.32 0.22 0.02 0.54 0.01 

4.4 × 103 0.52 0.31 0.10 0.48 0.20 

5.9 × 103 0.36 0.12 0.08 0.33 0.18 

1.2 × 103 1.3 1.1 0.10 0.59 0.28 

2.1 × 103 0.08 0.05 0.02 0.09 0.04 

7.6 × 102 0.10 0.10 0.14 0.65 0.36 

7.5 × 101 0.85 0.0 0.0 2.2 0.0 

a

 Data at distances from ground zero to 20 miles obtained from Tables C.1, D.1, E.1, F.1, and G.1 

of Baurmash et al. (1958); heights of detonation and yields are described in Section 4.1.3.2.2. Data at 

Shot APPLE II at location where total activity was 2.5 × 103 μCi ft–2 are omitted because reported activity 

in each size fraction up to 500 μm was identical to corresponding value at location where total activity 

was 4.4 × 103 μCi ft–2 but total activity in all size fractions was less than 100%. Data in bold face denote 

measurements within boundary of NTS. 

b

 Distance from ground zero at which fallout was collected. 

c

 Areal concentration of total activity at time after detonation of 12 hours. 
109

Table 4-5. Percentages of total activities in smallest size fractions of on-site fallout samples 

from tower Shot SHASTA in Operation PLUMBBOB at NTSa

Distance Particle sizes (μm) 

(miles)b

Total 

activityc

0−43 43−74 74−104 104−146 

2.2 398 0.29 0.15 0.10 0.16 

2.5 6.2 1.4 1.1 0.31 0.31 

2.5 23.6 2.1 2.6 1.5 1.1 

2.5 635 0.22 0.18 0.09 0.17 

3.1 1,080 0.09 0.20 0.13 0.24 

4.2 1,870 0.38 0.19 0.09 0.11 

4.7 1,480 0.37 0.20 0.17 0.01 

a

 Data obtained from Table 16 of Miller (1969) apply to magnetic and nonmagnetic particles 

combined; height of detonation and yield are described in Section 4.1.3.2.2. 

b

 Distance from ground zero at which fallout was collected. 

c

 Value multiplied by 1012 gives estimated number of fissions in all particle sizes. 
110

Table 4-6. Percentages of total activities in size fractions of 0−104 μm magnetic particles in

on-site fallout samples from tower Shot SHASTA in Operation PLUMBBOB at NTSa

Distance Particle sizes (μm) 

(miles)b

 

Total 

activityc 

Percent 

magneticd 0–10 10–20 20–43 43–74 74–104 

2.2 398 93 – 0.027 0.16 0.15 0.11 

2.5 635 93 0.002 0.019 0.12 0.18 0.16 

3.1 1,080 99.6 – 0.001 0.041 0.15 0.16 

4.2 1,870 99.5 – 0.086 0.19 0.17 0.13 

4.7 1,480 99.7 0.019 0.084 0.20 0.19 0.13 

a

 Data obtained from Table 17 of Miller (1969); height of detonation and yield are described in 

Section 4.1.3.2.2. 

b

 Distance from ground zero at which fallout was collected. 

c

 Value multiplied by 1012 gives estimated number of fissions in magnetic and nonmagnetic 

particles combined in all particle sizes. 

d

 Percentage of total activity in all particle sizes that was contained in magnetic particles.
111

Table 4-7. Summary of assumed uncertainties in parameters to estimate resuspension factors 

that apply to respirable or nonrespirable radionuclides in inhalable form in thermal-pulse 

and blast-wave regions near nuclear detonations at NTSa

Parameter Probability distribution 

Resuspension factor that applies to all 

previously deposited fallout 

 Thermal-pulse region Lognormal distribution with median at 10−3 m−1 and 

90% credibility interval between 10−4

 and 10−2 m−1

 Blast-wave region Lognormal distribution with median at 10−5 m−1 and 

90% credibility interval between 10−7

 and 10−3 m−1

Inhalable fraction of resuspended 

radionuclidesb

Lognormal distribution with median at 0.01 and 

90% credibility interval between 0.001 and 0.1 

Respirable fraction of resuspended 

radionuclides in inhalable formc

Log-triangular distribution with minimum at 

(ln 0.01) = −4.6, mode at (ln 0.3) = −1.2, and 

maximum at (ln 1.0) = 0d

Nonrespirable fraction of resuspended 

radionuclides in inhalable form 

Calculated from requirement that sum of respirable 

and nonrespirable fractions of resuspended 

radionuclides in inhalable form must be unitye

a

 Thermal-pulse and blast-wave regions are described in Section 2, and analysis of uncertainties 

in resuspension factors is presented in Section 4.1.3. Resulting uncertainties in resuspension factors for 

radionuclides in respirable form or inhalable radionuclides in nonrespirable form in thermal-pulse and 

blast-wave regions are summarized in Section 4.1.3.3 and Table 4-15. 

b

 Inhalable fraction is assumed to be the fraction of the activity of resuspended radionuclides in 

particles of diameter 44 μm or less (see Section 4.1.3.2.4). Larger particles of diameter up to 100 μm also 

would be inhalable, but such particles should not have remained airborne for significant periods of time 

during exposures of military participants in thermal-pulse or blast-wave region. 

c

 Particles of diameter less than 10 μm are assumed to be respirable. 

d

 Lower bound, most probable value (mode), and upper bound of probability distribution are 

assumed to be 0.01, 0.3, and 1.0, respectively; median of distribution is 0.17, mean is 0.22, and 90% 

credibility interval ranges from 0.024 to 0.59. 

e

 Requirement ensures that correlation between respirable and nonrespirable fractions of 

resuspended radionuclides in inhalable form is preserved when those fractions are described by 

probability distributions. Resulting probability distribution has lower bound, most probable value, and 

upper bound at 0, 0.7, and 0.99, respectively; median of distribution is 0.83, mean is 0.78, and 90% 

credibility interval ranges from 0.41 to 0.98.
112

Table 4-8. Estimates by NCRP of reliability of effective dose coefficients for intakes of 

radionuclides relative to values calculated by ICRPa

Radionuclide Route of intakeb Uncertainty factorc

High reliability

 3

H (HTO) 

 14C (CO2) 

 137Cs 

 90Sr 

 131I 

 140La 

Ingestion 

Inhalation 

Inhalation or ingestion 

Inhalation or ingestion 

Inhalation or ingestion 

Ingestion 

2 

2 

2 

3 

3 

3 

Intermediate reliability

 14C (CO2) 

 55Fe, 95Nb 

 60Co, 144Ce 

 140Ba, 226Ra 

 140La, 210Po 

 210Pb, 230Th 

 234U 

Ingestion 

Inhalation or ingestion 

Inhalation 

Inhalation or ingestion 

Inhalation 

Inhalation 

Inhalation 

5 

5 

5 

5 

5 

5 

5 

Low reliability

 60Co, 210Pb 

 95Zr, 106Ru 

 125Sb 

 144Ce 

 210Po 

 230Th, 234U 

 237Np, 239Pu 

 241Am, 244Cm 

Ingestion 

Inhalation or ingestion 

Inhalation or ingestion 

Ingestion 

Ingestion 

Ingestion 

Inhalation or ingestion 

Inhalation or ingestion 

10 

10 

10 

10 

10 

10 

10 

10 

a

 Estimates of reliability obtained from NCRP (1998; Table 8.2) and Bouville et al. (1994) apply 

to effective dose equivalents per unit activity intake in healthy adult males calculated using dosimetric 

and biokinetic models recommended in ICRP Publication 30 (ICRP, 1979). 

b

 Inhaled material is assumed to be in form of respirable particles with AMAD of 1 μm, except 3H 

(HTO) and 14C (CO2) are assumed to be in vapor and gaseous form, respectively. 

c

 Ratio of upper 95% credibility limit of subjective probability distribution of effective dose 

coefficient to value calculated by ICRP. 
113

Table 4-9. Uncertainty categories in assessment of uncertainties in risk coefficients for 

intakes of radionuclides in the environment in EPA’s current federal guidancea

% radionuclides in each categoryd

Uncertainty 

category Definitionb

Uncertainty 

factorc Inhalation Ingestion 

A Q95/Q5 < 15 ≈ 4 or less 42 26 

B 15 ≤ Q95/Q5 < 35 ≈ 4–6 42 51 

C 35 ≤ Q95/Q5 < 65 ≈ 6–8 10 11 

D 65 ≤ Q95/Q5 < 150 ≈ 8–12 5 8 

E Q95/Q5 ≥ 150 ≈ 12 or greater 1 3 

a

 Uncertainty categories and associated ranges of uncertainty in risk coefficients for radionuclides 

in EPA’s Federal Guidance Report No. 13 (Eckerman et al., 1999) as given by Pawel et al. (2007; 

Table 4). Risk coefficients give cancer risks per unit activity intake by inhalation or ingestion in a 

population of all ages, and uncertainties take into account uncertainties in risk models for specific organs 

or tissues and uncertainties in ICRP’s recommended dosimetric and biokinetic models for inhalation or 

ingestion of radionuclides by members of the public (ICRP, 1996a; 2002).

b

 Q95 and Q5 denote upper 95% and lower 5% credibility limits, respectively, that were judged by 

EPA to define range of credible values (90% credibility interval) of risk coefficient.

c

 Uncertainty factor calculated as (Q95/Q5)

1⁄2 is intended to represent ratio of upper 95% credibility 

limit of risk coefficient to median.

d

 Uncertainty categories for all radionuclides considered in Federal Guidance Report No. 13 are 

given in Tables D-1 and D-2 of Pawel et al. (2007). 
114

Table 4-10. Estimates of uncertainty in risk coefficients for intakes of selected 

radionuclides in the environment in EPA’s current federal guidancea

Route of intake/radionuclide Uncertainty categoryb Dominant cancer sitesc

Inhalationd

 3H (HTO vapor) 

 60Co, Type M 

 90Sr, Type M 

 106Ru, Type M 

 125Sb, Type M 

 131I, Type F 

 137Cs, Type F 

 226Ra, Type M 

 232Th, Type S 

 234U, Type M 

 239Pu, Type M 

A 

B 

B 

C 

B 

C 

A 

C 

C 

C 

C 

No dominant cancer sites 

Lung >> colon 

Lung >> red bone marrow 

Lung >> colon 

Lung >> colon 

Thyroid 

No dominant cancer sites 

Lung 

Lung 

Lung 

Lung ≈ liver > bone 

Ingestione

 3H (HTO) 

 60Co 

 90Sr 

 106Ru 

 125Sb 

 131I 

 137Cs 

 226Ra 

 232Th 

 234U 

 239Pu 

A 

B 

A 

B 

B 

C 

A 

C 

D 

C 

D 

No dominant cancer sites 

Colon 

Red bone marrow >> colon 

Colon 

Colon >> red bone marrow 

Thyroid 

No dominant cancer sites 

Bone ≈ colon 

Bone ≈ colon > liver 

Colon > kidney 

Liver > colon ≈ bone 

a

 Risk coefficients for radionuclides in EPA’s Federal Guidance Report No. 13 (Eckerman et al., 

1999) give cancer risks per unit activity intake of radionuclides in a population of all ages. 

b

 Uncertainty category for each radionuclide and route of intake obtained from Table D-1 or D-2 

of Pawel et al. (2007); uncertainty categories are defined in Table 4-9. Some estimates of uncertainty 

differ from those given previously (Eckerman et al., 1999; Table 2.4). 

c

 Sites that are the most important contributors to uncertainty in risk coefficient (Eckerman et al., 

1999; Table 2.4). Contributions from uncertainties in risk models were judged to be important in all cases 

(Pawel et al., 2007). 

d

 Type F, M, and S denote absorption types fast, medium, and slow, respectively, in model of 

respiratory tract currently recommended by ICRP (1994). 

e

 Radionuclides are assumed to be ingested in tap water and foods. 
115

Table 4-11. Summary of results of NRC-CEC expert elicitation on uncertainties in dose 

coefficients for intakes of radionuclides by adults calculated by ICRPa

Radionuclide Route of intakeb Organ or tissue 50%/ICRPc 95%/5%d

131I Ingestion Thyroid 1 9 

137Cs Ingestion Colon 

Red bone marrow 

1 

1 

4 

4 

Inhalation Lungs 

Red bone marrow 

2(F) 

1(F) 

50 

8 

90Sr Ingestion Colon 

Red bone marrow 

Bone surfaces 

1 

0.6 

0.5 

600 

240 

390 

Inhalation Lungs 

Red bone marrow 

Bone surfaces 

0.7(M) 

1.6(M) 

1.4(M) 

5,300 

35 

28 

144Ce Inhalation Lungs 

Red bone marrow 

Bone surfaces 

0.5(M) 

0.8(M) 

2(M) 

520e

8,500 

6,300e

239Pu Ingestion Colon 

Red bone marrow 

Bone surfaces 

Liver 

1 

1 

0.8 

0.8 

250 

4,300 

20,000 

700e

Inhalation Lungs 

Red bone marrow 

Bone surfaces 

Liver 

2(S) 

3(S) 

3(S) 

3(S) 

400 

1,300 

770 

800 

See following page for footnotes to table. 
116

Footnotes to Table 4-11

a

 Results of expert elicitation summarized by Goossens et al. (1998, Vol. 1; Table 4.1). Dose 

coefficients are 50-year committed absorbed doses per unit activity intake. 

b

 Inhaled material is assumed to be respirable particles with AMAD of 1 μm. 

c

 Ratio of 50th percentile of subjective probability distribution of dose coefficient to represent 

experts’ combined uncertainty to dose coefficient currently recommended by ICRP. Notations F, M, and 

S for inhalation refer to absorption types fast, medium, and slow, respectively, in model of respiratory 

tract currently recommended by ICRP (1994). 

d

 Ratio of 95th to 5th percentile of subjective probability distribution of dose coefficient to 

represent experts’ combined uncertainty. 

e

 Ratio is inconsistent with ratios of 95th to 5th percentiles estimated by each expert, as given in 

Table 4-12, and aggregated results given by Goossens et al. (1998, Vol. 2; Appendix E).
117

Table 4-12. Summary of 90% credibility intervals of dose coefficients for selected 

radionuclides, routes of intake, and organs or tissues in adults estimated by 

experts in NRC-CEC expert elicitationa

90% credibility interval of committed dose coefficient 

(Gy Bq−1)

b Radionuclide, route 

of intake, and organ 

or tissue 

Expert 

5th percentile 50th percentile 95th percentile 

90Sr, ingestion, colon B 

C 

D 

E 

F 

G 

2 × 10−9

1.8 × 10−8

1 × 10−8

5.4 × 10−9

4 × 10−9

9.3 × 10−11

1 × 10−8

5.2 × 10−8

1.5 × 10−8

1.8 × 10−8

1.3 × 10−8

4.4 × 10−10

1 × 10−7

9.4 × 10−8

2.2 × 10−8

2.4 × 10−8

5 × 10−8

2.1 × 10−9

90Sr, inhalation, 

lungs 

B 

C 

D 

F 

G 

1 × 10−10

6.3 × 10−8

1.4 × 10−7

1 × 10−9

3.9 × 10−8

1 × 10−9

1.9 × 10−7

2.1 × 10−7

1 × 10−7

2.3 × 10−7

1 × 10−8

5.7 × 10−7

3.1 × 10−7

3 × 10−7

1.4 × 10−6

144Ce, inhalation, 

lungs 

B 

C 

D 

F 

G 

1 × 10−9

5 × 10−9

9.3 × 10−9

9 × 10−10

7.4 × 10−8

3.5 × 10−9

3 × 10−8

2.8 × 10−8

2 × 10−8

2.2 × 10−7

1 × 10−8

5 × 10−8

8.4 × 10−8

9 × 10−8

6.5 × 10−7

144Ce, inhalation, red 

bone marrow 

B 

C 

D 

E 

F 

G 

8 × 10−10

3 × 10−9

1.6 × 10−8

1.3 × 10−6

4 × 10−10

9.4 × 10−9

2 × 10−9

1.8 × 10−8

4.9 × 10−8

2.6 × 10−6

1 × 10−8

3.2 × 10−8

6 × 10−9

3 × 10−8

1.5 × 10−7

5.2 × 10−6

8 × 10−8

1.1 × 10−7

144Ce, inhalation, 

bone surfaces 

B 

C 

D 

E 

Fc

5 × 10−8

1 × 10−7

6.3 × 10−8

2.2 × 10−6

2 × 10−7

1.9 × 10−7

1.9 × 10−7

4.4 × 10−6

5 × 10−7

4.2 × 10−7

5.7 × 10−7

8.8 × 10−6

 Table is continued on following page; see end of table for footnotes. 
118

Table 4-12. (continued) 

90% credibility interval of committed dose coefficient 

(Gy Bq−1)

b Radionuclide, route 

of intake, and organ 

or tissue 

Expert 

5th percentile 50th percentile 95th percentile 

239Pu, ingestion, red 

bone marrow 

B 

C 

D 

E 

F 

G 

1 × 10−9

7.5 × 10−9

1.3 × 10−9

1.0 × 10−12

2 × 10−9

4 × 10−8

8 × 10−9

3.5 × 10−8

4.0 × 10−9

4.5 × 10−10

2 × 10−8

3.9 × 10−7

2 × 10−7

7 × 10−7

2.0 × 10−8

4.5 × 10−8

6 × 10−8

1.7 × 10−6

239Pu, ingestion, bone 

surfaces 

B 

C 

D 

E 

F 

G 

2 × 10−8

5 × 10−8

2.6 × 10−8

9 × 10−11

6 × 10−8

8 × 10−7

2 × 10−7

4.5 × 10−7

8.0 × 10−8

9 × 10−9

4.2 × 10−7

8.2 × 10−6

3 × 10−6

9 × 10−6

2.4 × 10−7

9 × 10−7

1 × 10−6

3.1 × 10−5

239Pu, ingestion, liver B 

C 

D 

E 

F 

G 

5 × 10−9

1.5 × 10−8

3.4 × 10−9

2.0 × 10−11

1 × 10−8

2 × 10−7

4 × 10−8

7.5 × 10−8

1.7 × 10−8

2.0 × 10−9

8.5 × 10−8

1.7 × 10−6

5 × 10−7

1.5 × 10−6

5 × 10−8

2.0 × 10−7

2 × 10−7

4.7 × 10−6

239Pu, inhalation, 

lungs 

B 

C 

D 

F 

G 

3 × 10−7

3 × 10−6

1.4 × 10−6

3 × 10−6

1.4 × 10−5

3 × 10−6

4.5 × 10−6

4.3 × 10−6

9 × 10−6

6.2 × 10−5

3 × 10−5

1 × 10−5

1.3 × 10−5

2.5 × 10−5

2.8 × 10−4

239Pu, inhalation, red 

bone marrow 

B 

C 

D 

E 

F 

G 

1 × 10−7

2.5 × 10−7

1.5 × 10−7

1.4 × 10−6

8 × 10−8

6.8 × 10−6

1 × 10−6

5 × 10−7

4.6 × 10−7

1.4 × 10−5

4.5 × 10−7

3.8 × 10−5

1 × 10−5

1.5 × 10−6

1.4 × 10−6

5.6 × 10−5

2.5 × 10−6

2.1 × 10−4

 Table is continued on following page; see end of table for footnotes. 
119

Table 4-12. (continued) 

90% credibility interval of committed dose coefficient 

(Gy Bq−1)

b Radionuclide, route 

of intake, and organ 

or tissue 

Expert 

5th percentile 50th percentile 95th percentile 

239Pu, inhalation, 

bone surfaces 

B 

C 

D 

E 

F 

G 

3 × 10−6

5 × 10−6

3.0 × 10−6

1.4 × 10−4

4 × 10−6

1.5 × 10−4

3 × 10−5

1 × 10−5

9.0 × 10−6

2.7 × 10−4

9 × 10−6

7.9 × 10−4

3 × 10−4

4 × 10−5

2.7 × 10−5

4.1 × 10−4

4 × 10−5

4.1 × 10−3

239Pu, inhalation, 

liver 

B 

C 

D 

E 

F 

G 

1 × 10−6

1.5 × 10−6

6.6 × 10−7

3.0 × 10−5

5 × 10−7

4.0 × 10−5

5 × 10−6

2.0 × 10−6

2.0 × 10−6

6.0 × 10−5

2 × 10−6

1.6 × 10−4

3 × 10−5

8 × 10−6

6.0 × 10−6

1.2 × 10−4

1 × 10−5

6.3 × 10−4

a

 Estimates obtained from Goossens et al. (1998, Vol. 2; Appendix C) for cases where uncertainty 

(ratio of 95th to 5th percentile) in Table 4-11 is factor of 400 or greater. 

b

 Values are 50-year committed absorbed doses per unit activity intake; to convert to 

conventional units of rad μCi−1

, multiply entries by 3.7 × 106. 

c

 Expert’s reported 5th percentile of 1.2 × 10−6 is higher than reported 95th percentile of 7 × 10−7

(Goossens et al., 1998, Vol. 2; Appendix C), and correct values cannot be determined. 
120

Table 4-13. Estimates by ICRP task group of uncertainty in GI-tract absorption fraction (f1) 

for radionuclides in adults and effect of uncertainty in f1 on uncertainty in 

committed effective dose from ingestion calculated by ICRPa

Radionuclide Half-life Uncertainty in f1

b

Effect on uncertainty 

in committed 

effective doseb

3

H 12.33 y 1.1 1.0 

60Co 5.27 y 10 2.6 

90Sr 28.8 y 4 3.5 

95Zr 64 d 100 1.1 

106Ru 1.02 y 20 1.4 

125Sb 2.76 y 100 2.4 

131I 8.02 d 1.1 1.1 

137Cs 30.1 y 1.3 1.2 

210Pb 22.3 y 6 6.4 

226Ra 1600 y 6 5.5 

238U 4.47 × 109

 y 5 4.1 

239Pu 2.41 × 104

 y 10c 9.3 

a

 Estimates of uncertainty obtained from Harrison et al. (2001; Tables 1 and 2). 

b

 Ratio of 95th to 5th percentiles of subjective probability distribution. 

c

 Data in animals discussed by Harrison et al. (2001) suggest that uncertainty in f1 for plutonium 

in oxide form could be much greater than factor of 10. 
121

Table 4-14. Summary of assumed uncertainties in estimated dose coefficients 

for inhalation of radionuclides in resuspended fallout at NTSa

Source of uncertaintyb

 Probability distribution 

Fission and Activation Products

 Dosimetric and biokinetic models 

 recommended by ICRP 

Lognormal distribution with median at 1.0 and 

90% credibility interval between 0.1 and 10 

 Bias in dose coefficients recommended 

 by ICRP (inhalation of nonrespirable 

 particles)c

Uniform distribution between 0.25 and 1.0 

Plutoniumd

 Dosimetric and biokinetic models 

 recommended by ICRP 

Lognormal distribution with median at 1.0 and 

90% credibility interval between 0.033 and 30 

 Bias in dose coefficients recommended 

 by ICRP (inhalation of nonrespirable 

 particles)c

Log-uniform distribution between (ln 0.1) = −2.3 

and (ln 1.0) = 0e

a

 Analysis of uncertainties in dose coefficients is described in Section 4.1.5. Resulting 

uncertainties in dose coefficients for inhalation of fission and activation products or plutonium in 

respirable or nonrespirable form are summarized in Section 4.1.5.5 and Table 4-15. 

b

 All uncertainties are relative to dose coefficients for inhalation of radionuclides in respirable or 

nonrespirable oxide form by adult members of the public currently recommended by ICRP [(1996a; 2002) 

and references therein]. 

c

 Bias represents assumed tendency of dose coefficients currently recommended by ICRP to 

overestimate doses from inhalation of larger, nonrespirable fallout particles. ICRP’s dose coefficients for 

inhalation of smaller, respirable particles are assumed to be unbiased. 

d

 Uncertainty in biological effectiveness of alpha particles relative to photons and electrons is not 

taken into account (see Section 4.1.5.4.2). 

e

 Lower and upper bound of bias in ICRP’s dose coefficients is assumed to be 0.1 and 1.0, 

respectively.
122

Table 4-15. Summary of assumed uncertainties in parameters to estimate dose from 

inhalation of radionuclides in fallout resuspended by nuclear detonations at NTSa

Parameterb Radionuclides and 

particle sizec

Median value 

(90% credibility interval) 

Fission/activation products 

 Respirable particles 

 Nonrespirable particles 

1.2 (0.32, 4.4) 

0.93 (0.19, 3.5) 

Concentrations of radionuclides 

on ground surfaced

Plutonium 2.2 (0.60, 7.7) 

Resuspension factor (m−1

) All radionuclides 

 Respirable particles, 

 thermal-pulse region 

1 × 10−6

(4 × 10−8, 5 × 10−5) 

 Nonrespirable particles, 

 thermal-pulse region 

8 × 10−6

(3 × 10−7, 2 × 10−4) 

 Respirable particles, 

 blast-wave region 

1 × 10−8

(7 × 10−11, 3 × 10−6) 

 Nonrespirable particles, 

 blast-wave region 

8 × 10−8

(4 × 10−10, 1 × 10−5) 

Breathing rate (m3 h−1) 1.1 (0.6, 2.0) 

Dose coefficientse Fission/activation products 

 Respirable particles 

 Nonrespirable particles 

1.0 (0.1, 10) 

0.6 (0.054, 6.4) 

Plutonium 

 Respirable particles 

 Nonrespirable particles 

1.0 (0.033, 30) 

0.3 (0.0087, 12) 

a

 Model to estimate dose from inhalation of resuspended radionuclides is given in eq. (5) (see 

Section 3.1), and uncertainties in model parameters are described in Sections 4.1.1−4.1.5. 

b

 Uncertainties in parameters that contribute to estimated uncertainties in concentrations of 

radionuclides in fallout deposited on ground surface, resuspension factors, and dose coefficients for 

inhalation are summarized in Tables 4-1, 4-7, and 4-14, respectively. 

c

 If particle size is not indicated, uncertainty applies to respirable and nonrespirable particles. 

d

 Probability distributions to represent uncertainties are relative to point estimates that are 

assumed in dose reconstructions for military participants. 

e

 Probability distributions to represent uncertainties are relative to dose coefficients for inhalation 

of radionuclides in respirable or nonrespirable oxide form by adult members of the public currently 

recommended by ICRP [(1996a; 2002) and references therein]. Uncertainty in biological effectiveness of 

alpha particles relative to photons and electrons is not taken into account (see Section 4.1.5.4.2).
123

Table 4-16. Summary of results of analysis of uncertainties in estimated organ-specific 

equivalent doses from inhalation of mixtures of fission and activation products 

in fallout resuspended by nuclear detonations at NTSa

Probability distribution of inhalation dose 

Regionb Particle sizec

5th percentile 50th percentile 95th percentile 

Thermal-pulse Respirable 2 × 10−8 2 × 10−6 2 × 10−4

Nonrespirable 5 × 10−8 4 × 10−6 3 × 10−4

Blast-wave Respirable 5 × 10−11 2 × 10−8 8 × 10−6

Nonrespirable 1 × 10−10 3 × 10−8 1 × 10−5

a

 Estimated doses are relative to activity concentrations of fission and activation products in 

fallout deposited on ground surface at NTS that are assumed in dose reconstructions for military 

participants and relative to dose coefficients for specific organs or tissues from inhalation of fission and 

activation products in respirable or nonrespirable oxide form by adult members of the public that are 

currently recommended by ICRP [(1996a; 2002) and references therein]; doses are in units of m2

 h−1 and 

give equivalent dose (rem h−1

) per unit concentration on ground surface (Ci m−2) and per unit equivalent 

dose per activity intake (rem Ci−1

). Comparable quantity calculated in dose reconstructions is product of 

assumed resuspension factor and breathing rate. 

b

 Thermal-pulse region is region closest to ground zero where initial pulse of thermal radiation 

produced in nuclear detonations was important in causing resuspension; blast-wave region is region 

beyond thermal-pulse region where resuspension was caused by blast wave (see Section 2). 

c

 Respirable particles are assumed to have diameter of 10 μm or less, and nonrespirable particles 

are assumed to have diameter up to 100 μm. When inhalation of nonrespirable particles is assumed, 

doses can be estimated using dose coefficients for ingestion that are adjusted to account for the fraction of 

inhaled material that is swallowed. 
124

Table 4-17. Summary of results of analysis of uncertainties in estimated organ-specific 

equivalent doses from inhalation of plutonium in fallout resuspended by 

nuclear detonations at NTSa

Probability distribution of inhalation dose 

Regionb Particle sizec

5th percentile 50th percentile 95th percentile 

Thermal-pulse Respirable 2 × 10−8 3 × 10−6 6 × 10−4

Nonrespirable 4 × 10−8 6 × 10−6 1 × 10−3

Blast-wave Respirable 5 × 10−11 3 × 10−8 2 × 10−5

Nonrespirable 8 × 10−11 5 × 10−8 3 × 10−5

a

 Estimated doses are relative to activity concentrations of plutonium in fallout deposited on 

ground surface at NTS that are assumed in dose reconstructions for military participants and relative to 

dose coefficients for specific organs or tissues from inhalation of plutonium in respirable or nonrespirable 

oxide form by adult members of the public that are currently recommended by ICRP [(1996a; 2002) and 

references therein]; doses are in units of m2

 h−1 and give equivalent dose (rem h−1) per unit concentration 

on ground surface (Ci m−2

) and per unit equivalent dose per activity intake (rem Ci−1). Comparable 

quantity calculated in dose reconstructions is product of assumed resuspension factor and breathing rate. 

b

 Thermal-pulse region is region closest to ground zero where initial pulse of thermal radiation 

produced in nuclear detonations was important in causing resuspension; blast-wave region is region 

beyond thermal-pulse region where resuspension was caused by blast wave (see Section 2). 

c

 Respirable particles are assumed to have diameter of 10 μm or less, and nonrespirable particles 

are assumed to have diameter up to 100 μm. When inhalation of nonrespirable particles is assumed, 

doses can be estimated using dose coefficients for ingestion that are adjusted to account for the fraction of 

inhaled material that is swallowed. 
125

5. DERIVATION OF EFFECTIVE RESUSPENSION FACTORS

 The purpose of the analysis in Section 4 is to develop probability distributions to 

represent uncertainties in estimates of doses from inhalation of radionuclides in fallout that was 

resuspended in the thermal-pulse or blast-wave region of nuclear detonations at NTS. By 

comparing upper 95% credibility limits (95th percentiles) of probability distributions of uncertain 

inhalation doses with point estimates that would be obtained on the basis of the model that is 

used to estimate inhalation doses to military participants in other scenarios that involved 

resuspension of radionuclides, effective resuspension factors that should be assumed in 

estimating inhalation doses in the thermal-pulse and blast-wave regions can be derived. 

 In the analysis in Section 4, uncertainties in the concentrations of fission and activation 

products or plutonium in fallout that was deposited on the ground surface and uncertainties in 

dose coefficients for inhalation of radionuclides in respirable or nonrespirable form are estimated 

relative to point values normally assumed in dose reconstructions. Therefore, to derive effective 

resuspension factors that should be assumed in dose reconstructions on the basis of the model in 

eq. (5) (see Section 3.1), upper 95% credibility limits of inhalation doses obtained in our analysis 

are equated to 1.2 × Keff, where 1.2 is the usual breathing rate in m3

 h−1 (Egbert et al., 1985; 

Raine et al., 2007) and Keff is the effective resuspension factor in m−1. This approach takes into 

account that dose reconstructions in other resuspension scenarios incorporate an assumption that 

all resuspended radionuclides were inhalable. 

 To obtain effective resuspension factors that would be sufficiently high to ensure that 

estimated inhalation doses in resuspension scenarios of concern would be at least upper 95% 

credibility limits in all cases, the combination of radionuclides (fission and activation products or 

plutonium) and particle size (respirable or nonrespirable) that results in the highest upper 95% 

credibility limit of an estimated inhalation dose should be used (see Section 4.2.4). Since results 

of our analysis in Tables 4-16 and 4-17 indicate that the limiting case is inhalation of plutonium 

in nonrespirable form, effective resuspension factors in the thermal-pulse and blast-wave 

regions, which are calculated to one significant figure, are estimated as follows: 
126

Thermal-Pulse Region

 (1.2 m3 h−1) × Keff (m−1) = 1 × 10−3 m

2

 h−1, 

 Keff = 8 × 10−4

 m−1 . 

Blast-Wave Region

 (1.2 m3 h−1) × Keff (m−1) = 3 × 10−5 m

2

 h−1, 

 Keff = 3 × 10−5

 m−1 . 

 In dose reconstructions for other resuspension scenarios, assumed resuspension factors 

are given to the nearest power of 10 (Barrett et al., 1986; Phillips et al., 1985) to reflect their 

large uncertainties. By using the same approach in the high-resuspension scenarios of concern to 

this report and rounding up, we obtain the following effective resuspension factors that should be 

assumed in dose reconstructions: 

• Resuspension in thermal-pulse region – Keff = 10–3 m

–1; 

• Resuspension in blast-wave region – Keff = 10–4

 m

–1. 

Again, these are resuspension factors that should be applied to all radionuclides on the ground 

surface in dose reconstructions for scenarios that involved resuspension of previously deposited 

fallout by nuclear detonations at NTS to ensure that inhalation doses that are estimated using 

point values of other parameters normally assumed in dose reconstructions (i.e., concentrations 

of radionuclides on the ground surface, the breathing rate, and dose coefficients for inhalation) 

would be at least upper 95% credibility limits. 

 We note that effective resuspension factors of 10–3 and 10–4

 m

–1 also would be obtained if 

inhalation of respirable, rather than nonrespirable, particles were assumed to be the limiting case. 

This assumption could apply, for example, if exposure in the thermal-pulse or blast-wave region 

did not occur until a sufficiently long time after detonation that larger, nonrespirable fallout 

particles would have fallen to Earth and only smaller, respirable particles remained airborne. In 

such cases, results in Table 4-17 indicate that effective resuspension factors calculated as above 

would be reduced by about one-third compared with values obtained by assuming inhalation of 
127

 

nonrespirable particles. However, when calculated effective resuspension factors are rounded up 

to the nearest power of 10, the same values that should be assumed in dose reconstructions, as 

derived above, are obtained. 

 Current policy and procedures of the NTPR Program specify that upper bounds of 

inhalation doses should be calculated by applying an uncertainty factor of 10 to point estimates 

that are obtained in dose reconstructions (DTRA, 2007; Case et al., 2008). However, this 

uncertainty factor should not be applied in estimating inhalation doses in the high-resuspension 

scenarios in which effective resuspension factors derived in this report should be assumed. 

Effective resuspension factors were selected to ensure that at least upper 95% credibility limits of 

inhalation doses in the thermal-pulse and blast-wave regions would be obtained for all 

radionuclides and organs or tissues. Therefore, no additional adjustment of doses is needed 

when they are calculated using these resuspension factors and point values of the concentrations 

of radionuclides on the ground surface, the breathing rate, and dose coefficients for inhalation 

normally used in dose reconstructions.59

 The derivation of effective resuspension factors in the thermal-pulse and blast-wave 

regions presented in this report is based on an assumption that current methods of dose 

reconstruction for scenarios that involved inhalation of resuspended radionuclides will continue 

to be used. That is, we have assumed that inhalation doses in the high-resuspension scenarios of 

concern to this report will be calculated using point estimates of all parameters in the model in 

eq. (5), and that credible upper bounds (at least upper 95% credibility limits) will be obtained by 

using effective resuspension factors derived in this report. 

59 Regulations on methods of estimating dose in 32 CFR Part 218 and policies and standard 

operating procedures of the NTPR Program (DTRA, 2007; Case et al., 2008) specify that central 

estimates (e.g., mean values) of external or internal doses to participants, as well as upper bounds (at least 

upper 95% credibility limits), should be calculated and reported in all cases. In the high-resuspension 

scenarios of concern to this report, the appropriate central estimate of an inhalation dose is the median. 

Results in Tables 4-16 and 4-17 indicate that the median dose in the thermal-pulse region is about two 

orders of magnitude less than the upper bound that is calculated using an effective resuspension factor, 

and that the median dose in the blast-wave region is between two and three orders of magnitude less than 

the upper bound. The ratio of the upper bound to the median dose is higher for plutonium than for 

mixtures of fission and activation products. Use of the mean dose to represent a central estimate is 

inappropriate in these scenarios, because the mean dose is close to or greater than the upper 95% 

credibility limit when the uncertainty is as large as indicated in Tables 4-16 and 4-17. 
128

 However, if methods of dose reconstruction for all resuspension scenarios were changed 

to incorporate an explicit accounting of uncertainties in all model parameters (i.e., if fully 

probabilistic methods of dose reconstruction were used), effective resuspension factors derived 

in this report would no longer need to be used in calculating credible upper bounds of inhalation 

doses due to resuspension of previously deposited fallout in the thermal-pulse or blast-wave 

regions of nuclear detonations at NTS. Rather, the analyses in this report could provide a basis 

for assumed probability distributions to represent uncertainties in all parameters in the model in 

eq. (5), including resuspension factors that apply to inhalable radionuclides in respirable or 

nonrespirable form. Results of a fully probabilistic uncertainty analysis then could be used to 

select a credible upper bound (95th percentile) of inhalation dose in a given scenario. Methods of 

probabilistic uncertainty analysis are being developed for use in dose reconstructions for military 

participants in the NTPR Program (Case et al., 2009). 
129

6. DISCUSSION OF RESULTS 

 This report has presented an assessment of uncertainties in estimates of inhalation dose 

due to resuspension of previously deposited fallout by nuclear detonations at NTS using 

estimates of relevant parameters and their uncertainties that are intended to be reasonably 

realistic. Result of this uncertainty analysis were used to derive point values of effective 

resuspension factors in the thermal-pulse and blast-wave regions of nuclear detonations that 

should be assumed in dose reconstructions to ensure that estimated inhalation doses to military 

participants in the resuspension scenarios of concern are at least upper 95% credibility limits. 

 The following sections discuss (1) the importance of judgment in deriving effective 

resuspension factors and the credibility of the results and (2) the applicability of the results, 

including the extent of the thermal-pulse and blast-wave regions and the time periods after a 

detonation when effective resuspension factors should be applied in those regions. 

6.1 Importance of Judgment and Credibility of Results 

Discussions in Section 4 have emphasized that the development of probability 

distributions to represent uncertainty in many parameters that are used to estimate inhalation 

doses in the resuspension scenarios of concern to this report is highly judgmental, due to a 

paucity of relevant data. Probability distributions that were developed in this report to represent 

uncertainty in the resuspension factors that apply to all previously deposited fallout in the 

thermal-pulse and blast-wave regions, the inhalable fraction of radionuclides in resuspended 

fallout, the respirable fraction of inhalable radionuclides, dose coefficients recommended by 

ICRP, and bias factors to represent the tendency of ICRP’s dose coefficients to overestimate 

doses from inhalation of radionuclides in nonrespirable form all were based to a significant 

extent on subjective scientific judgment. The only parameter that can be estimated with small 

uncertainty on the basis of relevant data is the breathing rate. However, uncertainties in some 

parameters cannot be large even though they must be estimated on the basis of judgment. For 

example, although the degree of fractionation of radionuclides in fallout from particular 
130

detonations is poorly known, the effects of fractionation on estimated inhalation doses can be 

bounded with relatively small uncertainty on the basis of knowledge of the boiling points of 

chemical elements in weapons debris and the yields of each mass chain in the different fission 

modes of concern (Trabalka and Kocher, 2007). 

 Although subjective scientific judgment was used extensively in our analysis, we believe 

that use of the effective resuspension factors derived in this report should provide credible upper 

bounds (at least upper 95% credibility limits) of inhalation doses in the high-resuspension 

scenarios of concern. Since resuspension factors that are assumed in dose reconstructions are 

given to the nearest power of 10, to reflect their large uncertainties, an increase in the derived 

effective resuspension factors by an order of magnitude (i.e., from 10–3 to 10−2

 m−1 in the 

thermal-pulse region and from 10–4 to 10−3 m−1 in the blast-wave region) should not be required 

to ensure that credible upper bounds of inhalation doses are obtained. This conclusion is based 

on several considerations, which are summarized below. 

• Although data on resuspension factors that apply to all previously deposited fallout that 

could be resuspended by nuclear detonations at NTS are lacking, the assumed upper 

credibility limits of 10–2

 m

–1 and 10–3 m–1 in the thermal-pulse and blast-wave regions, 

respectively, must be close to the maximum possible values, because they represent an 

assumption that nearly all fallout was resuspended by a detonation when estimates of the 

height of the cloud of resuspended material in the two regions, as inferred from 

photographs at several detonations, are taken into account. 

• Although the uncertainty of a factor of 3 that is assumed to apply to estimates of photon 

exposure rates at any location at a fixed time after each detonation is based mainly on 

judgment, we believe it is highly unlikely that this uncertainty could be substantially 

higher (e.g., a factor of 10 or more), especially at locations of higher concentrations of 

fallout and, thus, higher estimates of dose from inhalation of resuspended fallout. 

Patterns of fallout at NTS that are inferred from dose-rate contours at 1 hour after 

detonation (Hawthorne, 1979) do not appear to be highly irregular—i.e., there is little 

evidence of localized areas of much higher or lower concentrations than in proximate 
131

areas. The apparent regularity of patterns of fallout provides confidence in the validity of 

interpolations or extrapolations of measurements at a limited number of locations. The 

uncertainty in estimated photon exposure rates that are based on measurement would 

need to be much greater than a factor of 3 to affect effective resuspension factors that 

were derived in this report. However, it seems highly unlikely that this uncertainty could 

be comparable to the most important uncertainties, including uncertainties in 

resuspension factors that apply to all fallout on the ground surface, the inhalable fraction 

of resuspended radionuclides, and dose coefficients for inhalation. 

• On the basis of available data on particle-size distributions of activity in fallout from 

tower shots at NTS, which produced most of the fallout of concern to this report, and the 

consideration that airborne concentrations of dust that can be tolerated while breathing 

are much lower than concentrations that would be calculated on the basis of the assumed 

upper credibility limits of resuspension factors that apply to all material on the ground 

surface, only a small fraction of resuspended radionuclides could have remained in the air 

to be inhaled by participants who were located in the blast-wave region at the time of a 

detonation or who entered the blast-wave or thermal-pulse region shortly thereafter. 

Inhalable fractions of resuspended radionuclides could have been large only if most large 

particles that were dominant in fallout at NTS were transformed into smaller particles 

prior to or during resuspension but there was no such effect on larger soil particles. Such 

a pronounced difference in particle-size distributions of resuspended fallout and native 

soil does not seem plausible. 

• Available data on particle-size distributions of activity in fallout also suggest that our 

assumed 95th percentiles of the inhalable fraction of resuspended radionuclides (0.1) and 

the respirable fraction of resuspended radionuclides in inhalable form (0.59) are higher 

than would be needed to provide at least upper 95% credibility limits of possible values 

in areas where concentrations of fallout and, thus, potential inhalation doses were 

relatively high. 

• Our assumption that, on average, about 20% of all resuspended radionuclides in inhalable 

form were respirable should not be a substantial underestimate when (1) the range of 
132

diameters of respirable particles (0–10 μm) is slightly more than 20% of the assumed 

range of diameters of inhalable particles (0–44 μm) and (2) it is unlikely that respirable 

particles contained most of the activity in inhalable particles. 

• Although information on uncertainties in dose coefficients for inhalation and ingestion of 

radionuclides that are currently recommended by ICRP is limited, especially in regard to 

dose coefficients for organs or tissues at minor sites of deposition, the assumed 

uncertainties would need to greatly underestimate possible differences between ICRP’s 

dose coefficients and values that apply to individual participants to affect the derived 

effective resuspension factors. If assumed uncertainties in other parameters are 

unchanged, an increase in the effective resuspension factors by an order of magnitude 

would be obtained only if the upper 95% credibility limit of a dose coefficient were 

nearly a factor of 100 greater than ICRP’s dose coefficient. Such a large uncertainty 

seems unreasonable, even at minor sites of deposition, when deposition fractions at major 

sites have small uncertainties and only a small fraction of radionuclides that are absorbed 

into blood is deposited at minor sites. 

• Even if it were assumed that there is no bias in ICRP’s dose coefficients for inhalation of 

radionuclides in nonrespirable form, which seems unlikely when refractory radionuclides 

(e.g., plutonium) should tend to be dispersed in the volume of larger, insoluble fallout 

particles, the effect on our results would be small. By assuming no bias, the limiting 

effective resuspension factor in the thermal-pulse region that would be obtained in our 

analysis would increase to slightly above 10–3 m–1, and 10–3 m–1 would still be the 

appropriate value to the nearest power of 10 for use in dose reconstructions. 

An additional consideration is that inhalation doses to organs or tissues at minor sites of 

deposition of radionuclides should be unimportant even when high resuspension factors in the 

thermal-pulse and blast-wave regions and unusually high concentrations of radionuclides in 

previously deposited fallout at NTS are assumed (NCRP, 2003; Appendix E). Doses from 

inhalation of resuspended fallout in the thermal-pulse or blast-wave region that would be 

significant relative to minimum doses that are required to qualify a claimant for compensation 
133

 

for cancer (Kocher and Apostoaei, 2007) are possible only in organs or tissues at major sites of 

deposition (e.g., lung, bone, red bone marrow, liver), and uncertainties in dose coefficients in 

those organs or tissues should be substantially lower than uncertainties assumed in our analysis. 

 Furthermore, when doses from inhalation of long-lived radionuclides with long retention 

times in the body (e.g., plutonium), which deliver doses at essentially a constant rate, are 

important, use of 50-year committed doses per unit activity intake that are assigned to the year of 

intake could result in overestimates of the dose that could have caused a participant’s cancer. 

However, this potential source of bias in estimated doses becomes less important as the time 

since exposure when a cancer is diagnosed increases. Indeed, use of 50-year committed doses 

could result in underestimates of the dose that could have caused a participant’s cancer as the 

time since exposure when cancer is diagnosed increases beyond 50 years.60

 It may seem that the effective resuspension factors of 10−3

 m−1 in the thermal-pulse 

region and 10−4 m−1 in the blast-wave region that were derived in this report are too low when 

they are compared with resuspension factors that are assumed in dose reconstructions for other 

resuspension scenarios. For example, a resuspension factor of 10−5 m−1 is often assumed in 

scenarios that involved walking, marching, trucking, or busing through a fallout field or touring 

of display areas, and resuspension factors as high as 10−3 or 10−2 m−1 have been assumed in 

scenarios that involved helicopter landings and takeoffs or assaults or marches behind armored 

vehicles [Barrett et al. (1986; Table 5); NCRP (2003; Table IV.C.2)], and it is reasonable to 

suppose that resuspension factors in the thermal-pulse and blast wave regions are substantially 

higher than resuspension factors that should be assumed in some of those scenarios, especially 

scenarios that involved resuspension by walking or light vehicular activity. 

 It is important to recognize, however, that assumed resuspension factors in other 

scenarios are intended to substantially exceed expected values (Barrett et al., 1986), and that 

60 The times since exposure when use of 50-year committed doses that are assigned to the year of 

intake could result in underestimates of the dose that could have caused a participant’s cancer depend on 

the minimum latency period for the cancer type of concern, which is about 5−10 years for most solid 

cancers, 4–6 years for thyroid and bone cancer, and 2−3 years for leukemias (Land et al., 2003; Kocher et 

al., 2008). Thus, for example, doses that could have caused most solid cancers could be underestimated 

when a cancer is diagnosed more than about 55–60 years after intakes of long-lived radionuclides with 

long retention times in the body. 
134

dose reconstructions for those scenarios do not consider the possibility that only a fraction of the 

resuspended radioactive material was inhalable or respirable. An accounting of the inhalable and 

respirable fractions could be important to obtaining realistic estimates of inhalation dose in 

scenarios that involved resuspension by vigorous disturbances of surface soil (e.g., helicopter 

landings and takeoffs, assaults or marches behind armored vehicles). Furthermore, the 

assumptions of a resuspension factor of 10−3

 m−1 in the thermal-pulse region and a height of the 

cloud of resuspended material in that region of about 100 m (see Section 4.1.3.1.1) are 

equivalent to assuming that about 10% of all fallout on the ground surface was resuspended, so a 

much higher effective resuspension factor that takes into account the inhalable and respirable 

fractions of resuspended fallout would not be reasonable. Similar considerations apply in the 

blast-wave region, where the height of the cloud of resuspended material was substantially lower 

than in the thermal-pulse region. 

 On the basis of these considerations, we believe that the analysis presented in this report 

provides effective resuspension factors in the thermal-pulse and blast-wave regions of nuclear 

detonations at NTS that would result in estimates of inhalation dose that are credible upper 

bounds (at least upper 95% credibility limits). Thus, the derived effective resuspension factors 

should give participants the benefit of the doubt in estimating inhalation doses, as required by a 

policy of the NTPR Program (DTRA, 2007). 

We also believe that it would not be reasonable to reduce the effective resuspension 

factors that were derived in this report by an order of magnitude and still ensure that estimated 

inhalation doses would be credible upper bounds. Consider, for example, resuspension in the 

blast-wave region. An analysis in Section V.C.3.3 of the NRC (2003) report, in which 

uncertainties in many parameters in the model in eq. (5) (see Section 3.1) were considered, 

suggests that a resuspension factor of 10–5 m

–1 is required to obtain credible upper bounds of 

inhalation doses in scenarios that involved resuspension by walking or light vehicular traffic; this 

is the resuspension factor that is normally assumed in dose reconstructions for these scenarios 

(Barrett et al., 1986; Table 5). Given that the high winds of about 100–200 mph near the inner 

boundary of the blast-wave region (see Section 2.2 and Table 2-1) should be more effective in 

causing resuspension than walking or light vehicular traffic, an assumption that an effective 
135

resuspension factor of 10–5 m

–1 in the blast-wave region would provide credible upper bounds of 

inhalation dose does not seem plausible. Effective resuspension factors that are an order of 

magnitude lower than the values we derived could be obtained only if unreasonably low 

uncertainties in important parameters were assumed. 

6.2 Applicability of Effective Resuspension Factors 

Effective resuspension factors derived in this report are intended to be applied in regions 

near ground zero of nuclear detonations at NTS and for time periods after detonation when 

resuspended radionuclides remained airborne and could have been inhaled by participants. The 

following sections consider how the extent of the thermal-pulse and blast-wave regions and the 

time periods for applying the effective resuspension factors in those regions might be defined. 

6.2.1 Extent of Thermal-Pulse and Blast-Wave Regions 

The extent of the thermal-pulse and blast-wave regions is discussed in Section 2. On the 

basis of a statement by Glasstone and Dolan (1977), dose reconstructions should assume that the 

thermal-pulse region extended to a distance from ground zero where the peak overpressure 

associated with the blast wave was 6 psi. This distance, which should be no more than about 

1.4 miles, can be estimated at any shot using Figure 2-2 and scaling of the burst height and 

distance from ground zero by the cube root of the yield in kt (see Section 2.1). 

The extent of the blast-wave region is difficult to define when the maximum wind speed 

that was associated with a blast wave decreased with distance from ground zero and the wind 

speed that caused unusually high resuspension when the wind persisted for a short time (no more 

than a few seconds) is largely unknown. Section 2.2 discussed an assumption that the blast-wave 

region extended to a distance where the maximum wind speed was about 40–70 mph and the 

corresponding peak overpressure was about 1–2 psi. On the basis of the following argument, we 

believe it is reasonable to assume that the blast-wave region extended to a distance where the 
136

peak overpressure was 2 psi in the absence of information on the extent of the dust cloud at 

specific shots, and that resuspension by the blast wave was not important at greater distances. 

The effective resuspension factor of 10–4 m–1 in the blast-wave region that was derived in 

Section 5 is intended to be an average value that applies to the range of maximum wind speeds 

that caused significant resuspension in that region. On the basis of the conclusion that an 

effective resuspension factor of 10–3 m

–1 should be assumed in the thermal-pulse region to obtain 

credible upper bounds of inhalation doses and the consideration that resuspension in the inner 

portion of the blast-wave region, where the maximum wind speed was the highest, was 

substantially less than in the thermal-pulse region, as indicated by the photograph in Figure 2-1 

and discussed in Section 4.1.3.1.2, we believe that an effective resuspension factor of 10–5 m

–1

would be sufficient to provide credible upper bounds of inhalation doses at the greatest distances 

from ground zero where the blast wave was a significant cause of resuspension. As noted in 

Section 6.1, a resuspension factor of 10–5 m

–1 normally is assumed in estimating inhalation doses 

in scenarios that involved resuspension by walking, marching, trucking, or busing through a 

fallout field or touring of display areas. Therefore, by assuming that an effective resuspension 

factor of 10–4 m

–1 would not need to be applied beyond the 2-psi line, a resuspension factor of 

10–5 m

–1 would be assumed at all locations beyond that line where exposure to previously 

deposited fallout could have occurred. In effect, at distances beyond the 2-psi line, resuspension 

by the blast wave is assumed to be indistinguishable from resuspension due to activities of 

participants. As a consequence of the assumed extent of the blast-wave region, there is assumed 

to be a transition from an effective resuspension factor of 10–3 m

–1 in the thermal-pulse region, 

where resuspension was the highest, to a value of 10–4

 m

–1 between the outer boundary of the 

thermal-pulse region and the distance where the peak overpressure associated with the blast 

wave was 2 psi, to a value of 10–5 m

–1 beyond the 2-psi line where activities of participants, 

rather than the blast wave, are assumed to be the most important cause of resuspension. 

If the maximum extent of the blast-wave region is assumed to be defined by the 2-psi 

line, this region probably extended to a distance from ground zero of about 2.5 miles or less (see 

Section 2.2). However, given the difficulty in defining the maximum extent, we believe that any 
137

reports of unusually high dust loadings at times shortly after a detonation should be taken into 

account in defining the extent of the blast-wave region at specific detonations. 

6.2.2 Time Periods for Applying Effective Resuspension Factors

The time period after a detonation during which the effective resuspension factors in the 

thermal-pulse and blast-wave regions that were derived in this report should be applied generally 

depends on the particle size of resuspended material and the maximum height of the cloud of 

resuspended fallout. The appropriate time period also could depend on the speed and direction 

of the winds close to the ground surface at times after a detonation when participants were 

located in or near the thermal-pulse or blast-wave region, because surface winds would tend to 

disperse resuspended material. In the following discussion, however, the effect of surface winds, 

which often were very low at times of detonations at NTS (Hawthorne, 1979), is ignored. 

In the thermal-pulse region, we estimated that the maximum height of a cloud of 

resuspended fallout might be about 100 m or more (see Section 4.1.3.1.1). In Section 5, we 

showed that an effective resuspension factor of 10–3 m

–1 should be assumed in this region even if 

only respirable particles of diameter 10 μm or less remained airborne at times of exposure. If an 

average diameter of respirable particles of 5 μm is assumed, the average settling velocity of a 

fallout particle of density 2.7 g cm–3, as calculated using Stokes Law and assuming a dynamic 

shape factor of 1.3, would be about 0.16 cm s–1 (Hinds, 1982). Therefore, on average, the time 

required for redeposition of resuspended fallout particles in respirable form from a height of 

100 m would be about 17 hours. The afterwind noted in Section 1, which was caused by the 

rising fireball, presumably increased the time period over which some resuspended fallout in the 

thermal-pulse region remained airborne. Given that the height of a cloud of resuspended fallout 

in the thermal-pulse region may have been greater than 100 m, fall times of respirable particles 

from the top of the cloud may have been longer than 17 hours; the fall time would increase in 

proportion to an increase in cloud height. Therefore, to ensure that credible upper bounds of 

inhalation doses would be obtained, we believe it is reasonable to assume that an effective 

resuspension factor of 10–3 m

–1 should be used to estimate inhalation doses to participants who 
138

entered the thermal-pulse region within a day after a detonation. Again, this recommendation 

assumes that winds were not important in dispersing resuspended radionuclides over that period. 

As indicated in Figure 2-1, the height of a cloud of resuspended fallout in the blast-wave 

region was substantially less than in the thermal-pulse region. Therefore, the time period during 

which resuspended fallout in respirable form remained airborne in the blast-wave region also 

was substantially less. 

On the basis of Figure 2-1 and other photographs of nuclear detonations (AFLML, 1951), 

it appears that that the height of the cloud of resuspended fallout in the blast-wave region was no 

more than a few tens of meters (see Section 4.1.3.1.2). If a maximum height of 30 m is assumed, 

we estimate that respirable fallout particles with an assumed average diameter 5 μm and average 

settling velocity of 0.16 cm s–1, as estimated above, remained airborne for about 5 hours at most. 

Since the height of the cloud in most of the blast-wave region presumably was less than 30 m 

and the concentrations of resuspended radionuclides presumably were less at the top of a cloud 

in this region than near the ground surface, an assumption that exposure to resuspended fallout 

could have occurred up to 5 hours after a detonation should represent a reasonable bounding 

condition. We believe that this assumption is appropriate to ensure that estimated inhalation 

doses in the blast-wave region are credible upper bounds if winds were not important in 

dispersing resuspended radionuclides over that period. We also reiterate that a resuspension 

factor of 10–5 m

–1 would be applied in the blast-wave region at times beyond 5 hours to account 

for resuspension by such participant activities as marching, trucking, or busing (Barrett et al., 

1986; Table 5). 
139

7. SUMMARY OF RESULTS

This report has presented an analysis to derive effective resuspension factors that should 

be assumed in exposure scenarios that involved resuspension of previously deposited fallout by 

nuclear detonations at NTS to ensure that point estimates of inhalation dose that are obtained in 

dose reconstructions for military participants would be credible upper bounds (at least upper 

95% credibility limits). Effective resuspension factors that should be applied in two regions near 

ground zero of a detonation were derived: the thermal-pulse region closest to ground zero, where 

the initial thermal pulse was important in causing resuspension, and the blast-wave region farther 

from ground zero, where resuspension was caused only by the blast wave. The results of this 

analysis are summarized as follows: 

Thermal-Pulse Region

• An effective resuspension factor of 10–3 m

–1 should be assumed; 

• The thermal-pulse region should be assumed to extend to a distance from ground 

zero where the peak overpressure associated with the blast wave was 6 psi; 

• The effective resuspension factor should be applied to exposures of participants in 

the thermal-pulse region that occurred within a day after a detonation, unless it is 

known that resuspended fallout was dispersed by winds within that time. 

Blast-Wave Region

• An effective resuspension factor of 10–4 m

–1 should be assumed; 

• The blast-wave region should be assumed to extend from the thermal-pulse region 

to a distance from ground zero where the peak overpressure associated with the 

blast wave was 2 psi, unless there were reports of high levels of resuspended dust 

at greater distances at times shortly after a detonation; 

• The effective resuspension factor should be applied to exposures of participants in 

the blast-wave region that occurred within 5 hours after a detonation, unless it is 

known that resuspended fallout was dispersed by winds within that time. 
140

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