AIRBORNE PARTICLE RESUSPENSION AND 

INHALATION RADIOLOGICAL DOSE ESTIMATION 

FOLLOWING VOLCANIC EVENTS 

Prepared for 

U.S. Nuclear Regulatory Commission 

Contract NRC–02–07–006

Prepared by 

R. Benke 

D. Hooper

Center for Nuclear Waste Regulatory Analyses 

San Antonio, Texas

September 2011
ii 

ABSTRACT 

This report presents concepts and factors that influence airborne radionuclide contamination in 

the biosphere and the calculation of inhalation radiological doses so that analysts can consider 

these concepts and factors to develop independent models or evaluate models developed by 

others for volcanic disruption consequences of a geologic repository for high-level radioactive 

waste and spent nuclear fuel. For extrusive volcanism in long-term performance assessments, 

the inhalation of resuspended radionuclides in ash is expected to dominate over other potential 

exposure pathways. Concepts and factors are presented for the resuspension of particles on 

the ground into air, inhalation of airborne particles, and inhalation dose estimation. The 

discussion on airborne concentration of resuspended radionuclides focuses on ash deposit 

characteristics, waste concentration in resuspended particles, and aerosol characteristics. For 

airborne particle inhalation, highlights are provided for the chemical form of inhaled material, 

airborne particle size, reference values for human and physiological aspects, and age 

dependences as they pertain to standard inhalation dosimetric models. General formulations 

for inhalation intake of radionuclides and conversion of radionuclide intakes to radiological dose 

are presented along with a discussion of additional case-specific factors that could be 

considered further.
iii 

TABLE OF CONTENTS 

ABSTRACT ................................................................................................................................... ii 

ACKNOWLEDGMENTS .............................................................................................................. iv 

1 INTRODUCTION ................................................................................................................ 1-1

2 RESUSPENSION OF PARTICLES ON THE GROUND SURFACE INTO AIR .................. 2-1

2.1 Relationship to Deposit Characteristics ..................................................................... 2-1

2.2 Waste Concentration in Resuspended Particles ....................................................... 2-2

2.3 Aerosol Characteristics .............................................................................................. 2-2

3 INHALATION OF AIRBORNE PARTICLES ........................................................................ 3-1

4 DOSE ESTIMATION ........................................................................................................... 4-1

4.1 Intake of Radionuclides ............................................................................................. 4-1

4.2 Conversion of Radionuclide Intake to Dose .............................................................. 4-2

5 SUMMARY .......................................................................................................................... 5-1

6 REFERENCES ................................................................................................................... 6-1
iv 

ACKNOWLEDGMENTS 

This report was prepared to document work performed by the Center for Nuclear Waste 

Regulatory Analyses (CNWRA®) for the U.S. Nuclear Regulatory Commission (NRC) under 

Contract No. NRC–02–007–006. The studies and analyses reported here were performed on 

behalf of the NRC Office of Nuclear Material Safety and Safeguards, Division of High-Level 

Waste Repository Safety. The report is an independent product of the CNWRA and does not 

necessarily reflect the views or regulatory position of NRC. 

The authors thank Lane Howard for technical review and Osvaldo Pensado for programmatic 

review. The authors also thank Arturo Ramos for support in report preparation and 

Lauren Mulverhill for editorial review. Other staff are acknowledged in Benke, et al. (2009) for 

their contributions to the publication of field measurements and laboratory analyses. 

QUALITY OF DATA, ANALYSES, AND CODE DEVELOPMENT 

DATA: All CNWRA-generated original data contained in this report meet the quality assurance 

requirements described in the Geosciences and Engineering Division Quality Assurance 

Manual. Sources for other data should be consulted for determining the level of quality for 

those data.

ANALYSES AND CODES: No scientific and engineering software was used in the analyses 

contained in this report. 

Reference 

Benke, R.R., D.M. Hooper, J.S. Durham, D.R. Bannon, K.L. Compton, M. Necsoiu, and 

R.N. McGinnis, Jr. “Measurement of Airborne Particle Concentrations Near the Sunset Crater 

Volcano, Arizona.” Health Physics. Vol. 96, No. 2. pp. 97–117. 2009. 
1-1 

1 INTRODUCTION 

Long-term assessments of geologic disposal of high-level radioactive waste and spent 

nuclear fuel are predicated on preventing or minimizing the release of radioactive material 

(i.e., radionuclides) into the biosphere. Because the intended timeframes for repositories to 

contain waste and protect individuals from exposure are very long (e.g., 10,000 years or longer), 

the occurrence of unlikely events with small annual recurrence rates becomes more likely as the 

period of interest or performance increases. For example, an event with a recurrence rate of 

10−7

 yr−1 has a very small probability (0.00001) of occurring within 100 years. For a 

100,000-year period of interest, the probability of at least one event occurring is 0.01. As a 

result, long-term performance assessments consider disruptive events to avoid underestimating 

the aggregated risk from disposal. 

The purpose of this knowledge capture report is to describe, in a single document, the concepts 

and factors that influence a radiological dose calculation for the inhalation of resuspended 

particles contaminated with high-level radioactive waste. This report focuses on extrusive 

volcanism, which is an igneous disruptive event. Extrusive volcanism is of primary interest 

because its consequences can be dominated by different processes and, therefore, can require 

different models than those for intrusive igneous events or other scenarios whose 

consequences are linked directly to potential groundwater contamination. Although volcanic 

hazard assessment and event probability determinations also factor into the long-term 

performance assessment, they are not addressed in this report. 

Extrusive volcanism at the disposal site for high-level radioactive waste and spent nuclear fuel, 

hereafter referred to simply as high-level waste, is conditioned on an igneous event. Although 

the igneous event may be unlikely, it could make important contributions to the total system risk 

if a subsurface volcanic conduit directly intersected the potential repository and resulted in the 

atmospheric release of high-level waste incorporated in volcanic ash. In this report, the 

plain-language term ash is used in place of the more precise term tephra. Although ash refers 

to tephra with particle diameters less than 2 mm [0.08 in], usage of ash in this report does not 

categorically exclude particles with diameters greater than 2 mm [0.08 in]. Depending on 

eruption characteristics and atmospheric conditions, contaminated volcanic ash could be 

deposited in locations where future populations may be exposed as a result of inhalation of 

contaminated resuspended material. In addition to any initial ash deposited at the receptor 

location (an area occupied or inhabited by an individual), the long-term ash transport by wind 

and surficial water drainage, referred to as eolian and fluvial redistribution, respectively, could 

remobilize volcanic ash toward the receptor location and contribute to a persistent exposure to 

contaminated material. 

Respiratory health effects from volcanic ash have been studied. Horwell and Baxter (2006) 

wrote a comprehensive review of published clinical, epidemiological, and toxicological studies. 

Blong (1996) remarked that ashfall covers a wide area and, thus, can affect a large number of 

people relative to other volcanic hazards (e.g., lava flows). These studies consider 

nonradiological health effects. This report, however, addresses radiological dose estimation 

due to high-level radioactive waste contamination in ash from volcanic events that may disrupt a 

potential geologic repository. Nonradiological health effects are not covered in this report. 

Although airborne particle concentrations can reach maximums during heavy ashfall events, 

eruptions are often short-lived (e.g., with active ashfall episodes representing a small fraction of 

time compared to 1 year). Ash deposits, on the other hand, can remain in the local environment 

for extended periods of time, where they can be resuspended and remobilized by natural 

processes or human activities, and contribute to long-term exposure. For extrusive volcanism, 
1-2 

long-term performance assessments are likely to be more sensitive to long-term exposure and 

conditions rather than short-term eruption conditions. Separate considerations of short-term 

exposures can determine if such aspects warrant inclusion in the performance assessment 

model. For the previously described reasons, this report focuses on extrusive volcanic event 

consequences by addressing the resuspension of particles on the ground into air, inhalation of 

airborne particles, and inhalation dose estimation.
2-1 

2 RESUSPENSION OF PARTICLES ON THE GROUND SURFACE 

INTO AIR 

During a volcanic disruption event, high-level waste could be incorporated into ash (or lava) and 

result in radionuclide deposition on the ground surface. Compared to lava flows, the airborne 

transport of contaminated ash is more effective at distributing radionuclides in the biosphere, 

away from the volcanic vent and to locations where individuals can be exposed. Radiological 

doses from a volcanic disruption event are expected to be dominated by radionuclide 

contamination in volcanic ash, and therefore, radionuclide contamination in lava is not 

considered further. As described in the Introduction, the assessment of long-term inhalation 

exposure following a volcanic eruption focuses on the resuspension of ash contaminated with 

high-level waste into air. In addition to the previously mentioned exposure time considerations, 

ashfall episodes include ash (or tephra) particles of various sizes, some of which are too large 

to be inhaled. 

Inhalation dose depends on the airborne concentration of radionuclides in the breathing zone 

of exposed individuals. The airborne concentration of resuspended radionuclides depends on 

(i) ash deposit characteristics, (ii) waste concentration in resuspended particles, and (iii) aerosol 

characteristics. Each of these factors is described in this section. 

2.1 Relationship to Deposit Characteristics 

Contaminated ash deposits on the ground surface represent a source for airborne resuspension 

and inhalation dose. Deposit characteristics can influence the high-level waste concentration in 

air. Anspaugh, et al. (2002) described three types of resuspension models—time-dependent 

resuspension factor, resuspension rate, and airborne mass loading—and indicated that the 

mass loading model has been preferred for long times after deposition. Analysts should 

recognize differences associated with radiological contamination events and consider them in 

the model development process. For a volcanic event, the resuspension of contaminated ash is 

of primary interest. In comparison, the airborne radionuclide concentration following the 

deposition of atmospheric fallout from weapons testing is determined from the resuspension of 

soil. Unlike fresh atmospheric fallout deposits, ash deposits can have appreciable mass and 

thickness. The thickness of the ash deposit relative to the resuspendible thickness can be 

important and may be included in performance assessment models. 

Resuspendible thicknesses for soil and sediment tend to be on the order of millimeters 

[approximately tenths of inches] without intentional ground alteration or soil movement or on the 

order of centimeters [about a couple of inches] for localized mechanical surface disturbances 

(Linsley, 1978; Sehmel, 1980). Differences in soil and ash deposits may be pertinent to 

resuspendible thickness considerations (Leslie, et al., 2007, Chapter 15). For ash deposits 

thinner than the resuspendible thickness, the total airborne mass load of resuspended particles 

can be modeled as a mixture of contaminated ash particles and noncontaminated particles from 

underlying soil. For ash deposits thicker than the resuspendible thickness, resuspended 

material can be assumed to be entirely contaminated (i.e., no dilution with noncontaminated soil 

particles). In selecting or evaluating parameter values for resuspensible thicknesses, it is 

important to note that certain resuspendible thicknesses may dilute the airborne concentration 

of radionuclides and reduce estimated doses. Specific effects depend on modeling details, but 

one example for thin ash deposit cases is that greater resuspendible thicknesses could 

increase resuspended contributions from underlying, noncontaminated soil to the total airborne 

particle concentration. 
2-2 

2.2 Waste Concentration in Resuspended Particles 

The concentration of high-level waste in resuspended particles is another factor in the inhalation 

dose calculation. The concentration of high-level waste in resuspended particles can be derived 

from the high-level waste concentration in ash and resuspended ash concentration. In some 

cases, noncontaminated particles or multiple contaminated sources (e.g., with different 

concentrations of high-level waste) could contribute to the total airborne particle concentration. 

Because the mass of ash generated by volcanoes is much greater than the mass of high-level 

waste in geologic repository concepts, mixing of high-level waste in magma and ash is expected 

to result in small mass fractions of high-level waste in ash (Codell, 2004). Downward migration 

of radionuclides into soil due to natural weathering processes may also factor into model 

calculations for the concentration of radionuclides at the surface that can be resuspended 

into air. 

2.3 Aerosol Characteristics 

Aerosol relates to a collection of airborne particles. In this report, an aerosol comprises ash or 

soil that has been resuspended into the air. Aerosol characteristics can be divided into physical 

characteristics and chemical form. Physical characteristics and chemical form of a 

radionuclide-bearing aerosol both factor into the inhalation dose calculation. Physical 

characteristics of particle size, density, shape, and aerodynamic behavior are addressed in this 

section. Because chemical form is manifested in the inhalation dose coefficient, the chemical 

form of airborne particles is addressed in Section 3. 

During inhalation, physical characteristics of airborne particles influence their deposition in 

different regions and compartments of the human respiratory tract. Aerosols can consist of a 

range of particle sizes (polydisperse) or a single particle size (monodisperse). For most 

environmental exposure scenarios including potential exposure to resuspended waste following 

a disruptive event (i.e., the scenario of primary interest to this report), aerosols are polydisperse. 

A lognormal particle size distribution is assigned as standard convention. The two parameters 

that define the lognormal particle size distribution are the median diameter and geometric 

standard deviation. As described in ICRP (2003, Section 4.1.2), the activity median 

aerodynamic diameter (AMAD) is used when particle deposition depends mainly on 

sedimentation and inertial impaction (greater than about 0.5 μm). Half of the radioactivity in an 

aerosol is associated with particles with aerodynamic diameters greater than and less than 

AMAD. Activity median thermodynamic diameter (AMTD) is used when particle deposition 

depends mainly on diffusion (less than about 0.5 μm). Because irregular shapes are 

commonplace for airborne particles, equivalent diameters are used to describe airborne 

particle diameters. The aerodynamic equivalent diameter is the diameter of a unit density 

spherical particle that exhibits the same terminal settling velocity as the irregularly shaped 

particle in air. ICRP (1994, Equation D.5) indicates the following relationship for the 

aerodynamic equivalent diameter 

ܦ ௘௔ൌ ݀௘ට ఘ஼ሺௗ೐ሻ

ఞఘబ஼ሺௗೌ೐ሻ

 (2-1) 

where 

݀௔௘ — aerodynamic equivalent diameter (μm) 
2-3 

݀௘ — diameter of a spherical particle with the same volume as the particle 

 considered, referred to as the equivalent volume diameter (μm) 

ߩ — particle mass density (g cm−3

) 

ߩ — ଴unit density (1 g cm−3

) 

ܥ — slip correction factor, shown as dependent on ݀௘and ݀௔௘ (unitless) 

߯ — particle shape factor (unitless) 

From Eq. (2-1) for a given particle (i.e., equivalent volume diameter, ݀௘), the aerodynamic 

equivalent diameter is proportional to the square root of ߩ

ൗ߯. ICRP (1994, Section B.1.2) states 

that ܥሺ݀௘ሻ and ܥሺ݀௔௘ሻ are approximately one for larger particles. Information regarding 

resuspended particle size can be used to determine if slip correction factors are important in the 

determination of the aerodynamic diameter. For example, the sizes of resuspended airborne 

particles from basaltic deposits, as measured by Benke, et al. (2009) at the Sunset Crater 

Volcano, Arizona, are large enough such that the unity approximation could be applied to the 

quotient ܥሺ݀௘ሻ

ܥሺ݀௔௘ሻ ൘ ൎ1. 

For cases in which the unity approximation is appropriate for the slip correction quotient, the 

relationship between aerodynamic equivalent diameter and equivalent diameter simplifies to 

݀௔௘ ൌ ݀௘ටఘ

ఞ

 (2-2) 

where 

݀௔௘ — aerodynamic equivalent diameter (μm) 

݀௘ — equivalent volume diameter (μm) 

ߩ — particle mass density (g cm−3

) 

߯ — particle shape factor (unitless) 

ICRP (1994, Section 4.2) defines a density of 3 g cm−3

 [187 lb ft−3] and a particle shape factor 

of 1.5 as default values for typical compact, irregularly shaped airborne particles. Typical values 

for the shape factor range from 1 to 2 (ICRP, 1994, Section 4.1.2). Analog deposits can yield 

insights on resuspended particle sizes and aerodynamic diameters. In some cases, 

aerodynamic diameter can be measured directly. In other cases, Eq. (2-1) or (2-2) can be used 

to account for the effect of airborne particle density and particle shape on the aerodynamic 

diameter and particle behavior in the human respiratory tract. These physical characteristics of 

airborne particles determine where ash and radionuclide deposition occurs within the respiratory 

tract following inhalation. The distribution of radionuclide deposition in specific regions or 

compartments serves as input to biokinetic modeling of radionuclide absorption in, transfer 

within, and clearance from the human body. These aspects of the inhalation dose calculation 

are described further in the next two sections.
3-1 

3 INHALATION OF AIRBORNE PARTICLES 

This section focuses on the human and physiological aspects that factor into the calculation of 

radiological doses from inhalation. An inhalation internal dose occurs following the intake of 

airborne radioactive material. Airborne radioactive material can be suspended particulates, 

vapors, or gases, but must be present in the breathing zone of an individual to be inhaled. 

Inhaled radionuclides are either exhaled or deposited in various regions and subregions 

(or compartments) of the human respiratory tract (e.g., ICRP, 1994; 1979, Part 1, Section 5). 

The compartmental distribution of deposited radionuclides depends on the characteristics of the 

airborne radioactive material. Systemic uptake of radionuclides into blood and body fluids 

results in the biological transfer of radionuclides to individual organs as well as excretion from 

the body. Because radioactive decay within internal organs can continue for several years or 

decades following the original intake of radioactive material, internal dose calculations are 

performed for a commitment period. The accumulated internal dose due to an intake of 

radioactive material (e.g., single intake or annual intake) is typically applied as the receipt of a 

single dose in the year of intake that equals the accumulated dose over the commitment period. 

ICRP (1991, 1979) applies a 50-year commitment period for adults. A 70-year commitment 

period is used for children (ICRP, 2001, Section 2.3). Dose coefficients for intakes are 

published as committed dose quantities. In other words, the summation of accumulated doses 

over the commitment period has already been performed and included in the computation of 

internal dose coefficients. 

For a particular radionuclide, the inhalation dose coefficient depends on the chemical form of 

the inhaled material and its airborne particle size distribution (i.e., AMAD or AMTD, as described 

in Section 2). Different dose coefficient values are specified for lung absorption type 

(ICRP, 2001) or lung inhalation class (U.S. Environmental Protection Agency, 1988), which 

relate to the solubility of inhaled material in lung fluid and clearance rate from the pulmonary 

region of the lung, respectively. Both lung absorption type and inhalation class 

associations are determined from the chemical forms of the compounds [e.g., as stated in 

ICRP (1996, Table 2) and 10 CFR Part 20, Appendix B]. Default airborne particle size 

distributions (e.g., AMAD values) are noted. Dose coefficients are based on reference values 

for human and physiological aspects. In ICRP (2001), differences in these aspects are 

responsible for differences in dose coefficients for workers and members of the public. Dose 

coefficients are also specified for different age groups in ICRP (2001). Because of the many 

factors considered, published dose coefficients can be applied to a wide range of exposure 

situations. When exposure situations differ markedly from reference values or default 

conditions, specific information regarding the actual conditions for retrospective assessments or 

anticipated conditions for prospective assessments should be factored into the dose estimation. 

For example, Benke, et al. (2009) indicated that most of the airborne resuspended mass 

measured during heavy surface-disturbing activity was associated with large particle sizes. 

Similar information can provide a technical basis for selecting inhalation dose coefficients 

corresponding to an AMAD value that is more appropriate for the exposure conditions than the 

one generally recommended in the absence of specific information.
4-1 

4 DOSE ESTIMATION 

Inhalation dose estimation relies on the characterization of the airborne radioactive material and 

human body response to inhaled radionuclides. Details of those aspects have been discussed 

in the prior two sections. A general formulation of the inhalation dose calculation is presented. 

For some applications, a simplified approach may be sufficient. For other applications, greater 

realism and complexity may be needed. For this reason, the general formulation is 

accompanied by a discussion of additional case-specific factors that can be considered further, 

as needed. This section is separated into two subsections. The inhalation intake of 

radionuclides is addressed in Section 4.1. The conversion of radionuclide intakes to radiological 

dose is presented in Section 4.2. 

4.1 Intake of Radionuclides 

Determination of the inhalation intake of radionuclides is an important intermediate quantity in 

the dose calculation. The inhalation intake on radionuclides is computed as 

 Intake ൌ Airborne Radionuclide Concentration ൈ Breathing Rate ൈ Exposure Time (4-1)

Individual radionuclides, multiple sources of contamination, and different physical activity levels 

are not explicitly expressed in Eq. (4-1) but can be accounted for by performing computations 

for separate contributions followed by summation. Intake can be specified as either mass or 

activity for each radionuclide. Specific activity is used to convert radionuclide mass to 

an activity. 

Although the exposed individual may or may not be involved in the generation of airborne 

radioactive material, the activities of the individual during exposure affect the inhalation dose 

calculation. The amount of air breathed is directly proportional to the breathing rate and 

exposure time. Breathing rate also influences the compartmental distribution of deposited 

radionuclides (ICRP, 2003, Table 3.2). ICRP has established reference values for workers 

(ICRP, 1994, Table 6) and members of the general population (ICRP, 2003, Table A4). 

Reference values are widely accepted for prospective dose calculations. When anticipated 

conditions in a prospective dose calculation differ significantly from reference values, reference 

values may be replaced by values that are more representative of anticipated conditions. For 

actual exposures, use of individual values and specific information is advised to improve the 

dose assessment. ICRP (2003, 1994) provides relevant information on differences among 

individuals including the effects of different parameter values on dose assessments. 

When the individual’s local environment is contaminated, the activities of the exposed individual 

can influence the resuspension of and airborne concentration of radionuclides. Accounting for 

the time spent performing different activities and the airborne concentration of radionuclides 

during those activities can provide a more realistic estimate for the inhalation intake of 

radioactive material compared to using a single, conservative value for the airborne 

concentration of radionuclides, breathing rate, and exposure time during the year (or occupancy 

fraction). For example, different levels of surface-disturbing activity can be accounted for 

separately. In addition, different characteristics could be propagated for multiple sources that 

contribute to airborne contamination at the receptor location. This treatment could include 

resuspended radionuclide-bearing particles from ash deposits at the receptor location, from 

fluvially redistributed deposits, and from eolian redistributed deposits (Leslie, et al., 2007, 

Chapter 15). Such modeling flexibility can be beneficial in accounting for realizations without 
4-2 

primary ashfall at the receptor location due to winds that direct the ash plume away from 

the receptor location. In those cases, inhalation dose would arise from redistributed 

deposit contributions. 

4.2 Conversion of Radionuclide Intake to Dose 

The last step of the calculation converts radionuclide intakes into radionuclide doses. 

Contributions from individual radionuclides are summed to yield a total inhalation dose 

 Inhalation Dose ൌ ∑௜ Intake௜ ൈ D௜ (4-2) 

where 

Intake௜ — Inhalation intake of radionuclide i (Bq) 

D௜ — Inhalation dose coefficient for radionuclide i (Sv Bq−1

) 

Inhalation dose coefficients have been tabulated for individual radionuclides in ICRP (2001) and 

U.S. Environmental Protection Agency (1988). Each set of dose coefficients corresponds to a 

specific dosimetric model. Dosimetric models include biokinetic transfer of radionuclides in the 

body, energy deposited in individual organs due to radioactive transformations and radiation 

emitted within the body, radiation weighting factors for converting energy deposited to an 

equivalent dose, and organ weighting factors for computing the effective or whole body 

dose equivalent. 

Dose coefficients in ICRP (2001) are consistent with the dosimetric model and organ weighting 

factors of ICRP (1991) and ICRP (1996), often referred to as ICRP–60 dosimetry and ICRP–72 

dose coefficients. Dose coefficients in U.S. Environmental Protection Agency (1988) are 

consistent with older dosimetric modeling and dose coefficients in ICRP (1979) and adopted in 

the current 10 CFR Part 20. Although recommendations and organ weighting factors have been 

updated by ICRP (2007), a revised set of dose coefficients had not been published at the time 

this report was written.
5-1 

5 SUMMARY 

Concepts and factors that influence the radiological dose calculation were presented for the 

inhalation of resuspended particles contaminated with high-level waste. For extrusive 

volcanism in long-term performance assessments, the inhalation of resuspended radionuclides 

in ash is expected to dominate over other potential exposure pathways. Resuspension of 

particles on the ground into air, inhalation of airborne particles, and inhalation dose estimation 

were described. The discussion on particle resuspension addressed ash deposit 

characteristics, waste concentration in resuspended particles, and aerosol characteristics. The 

airborne particle size distribution, relationship of chemical form of inhaled material to lung 

absorption type or inhalation class, reference values for human and physiological aspects, and 

age dependences were highlighted as they pertain to standard inhalation dosimetric models. 

Inhalation intake of radionuclides and conversion of radionuclide intakes to radiological dose 

were presented as steps in the inhalation dose calculation. Individual concepts and factors as 

well as their interrelationships were introduced and explained so that they may be considered 

further by analysts in the development of independent models or in the evaluation of models 

developed by others.
6-1 

6 REFERENCES 

Anspaugh, L.R., S.L. Simon, K.I. Gordeev, I.A. Likhtarev, R.M. Maxwell, and S.M. Shinkarev. 

“Movement of Radionuclides in Terrestrial Ecosystems by Physical Processes.” Health Physics.

Vol. 82. pp. 669–679. 2002. 

Benke, R.R., D.M. Hooper, J.S. Durham, D.R. Bannon, K.L. Compton, M. Necsoiu, and 

R.N. McGinnis, Jr. “Measurement of Airborne Particle Concentrations Near the Sunset Crater 

Volcano, Arizona.” Health Physics. Vol. 96, No. 2. pp. 97–117. 2009. 

Blong, B. “Volcanic Hazards Risk Assessment.” Monitoring and Mitigation of Volcanic Hazards. 

R. Scarpa and R.I. Tilling, eds. Berlin, Germany: Springer. pp. 675–698. 1996. 

Codell, R.B. “Alternative Igneous Source Term Model for Tephra Dispersal at the 

Yucca Mountain Repository. Nuclear Technology. Vol. 148, No. 2. pp. 205–212. 2004. 

Horwell, C.J. and P.J. Baxter. “The Respiratory Health Hazards of Volcanic Ash: A Review for 

Volcanic Risk Mitigation.” Bull Volcano. Vol. 69. pp. 1–24. 2006. 

ICRP. “The 2007 Recommendations of the International Commission on Radiological 

Protection.” ICRP Publication 103. New York City, New York: Elsevier Science Inc. 2007. 

_____. “Guide for the Practical Application of the ICRP Human Respiratory Tract Model.” 

ICRP Supporting Guidance 3. New York City, New York: Elsevier Science Inc. 2003. 

_____. “The ICRP Database of Dose Coefficients: Workers and Members of the Public, 

Version 2.01.” International Commission on Radiological Protection. Tarrytown, New York: 

Elsevier Science, Inc. 2001. 

_____. “Age-Dependent Doses to Members of the Public from Intake of Radionuclides: Part 5 

Compilation of Ingestion and Inhalation Dose Coefficients.” ICRP Publication 72. 

Tarrytown, New York: Elsevier Science Inc. 1996. 

_____. “Human Respiratory Tract Model for Radiological Protection.” ICRP Publication 66. 

Tarrytown, New York: Elsevier Science Inc. 1994. 

_____. “1990 Recommendations of the International Commission on Radiological Protection.” 

ICRP Publication 60. Elmsford, New York: Pergamon Press Inc. 1991. 

_____. “Limits for Intakes of Radionuclides by Workers.” Publication 30. Elmsford, New York: 

Pergamon Press Inc. 1979. 

Leslie, B., C. Grossman, and J. Durham. “Total-System Performance Assessment (TPA) 

Version 5.1 Module Descriptions and User Guide.” Revision 1. ML080510329. 

Washington, DC: U.S. Nuclear Regulatory Commission. November 2007. 

Linsley, G.S. “Resuspension of the Transuranium Elements—A Review of Existing Data.” 

NRPB–R75. Didcot, United Kingdom: National Radiological Protection Board. 1978. 

Sehmel, G.A. “Particle Resuspension: A Review.” Environment International. Vol. 4. 

pp. 107–127. 1980. 
6-2 

U.S. Environmental Protection Agency. “Limiting Values of Radionuclide Intake and Air 

Concentration and Dose Conversion Factors for Inhalation, Submersion, and Ingestion.” 

Federal Guidance Report No. 11. EPA–520/1–88–020. Washington, DC: U.S. Environmental 

Protection Agency. 1988.