ORAU TEAM

Dose Reconstruction

Project for NIOSH

Oak Ridge Associated Universities I Dade Moeller & Associates I MJW Corporation

Page 1 of 87

Document Title:

Site Profile for Ames Laboratory

Document Number: ORAUT-TKBS-0055

Revision: 00 PC-1

Effective Date: 08/20/2008

Type of Document TBD

Supersedes: Revision 00

Subject Expert(s): Jerome B. Martin, Dillard B. Shipler, Donald E. Bihl, Eva E. Hickey, and Bruce A. Napier

Site Expert(s): N/A

Approval: Signature on File Approval Date: 08/12/2008

Karen S. Kent, Document Owner

Concurrence: Signature on File Concurrence Date: 08/13/2008

John M. Byrne, Task 3 Manager

Concurrence:

 Signature on File Concurrence Date: 08/12/2008

Edward F. Maher, Task 5 Manager

Concurrence: Signature on File Concurrence Date: 08/19/2008

Kate Kimpan, Project Director

Approval: Signature on File Approval Date: 08/20/2008

James W. Neton, Associate Director for Science

 New Total Rewrite Revision Page Change

FOR DOCUMENTS MARKED AS A TOTAL REWRITE, REVISION, OR PAGE CHANGE, REPLACE THE PRIOR 

REVISION AND DISCARD / DESTROY ALL COPIES OF THE PRIOR REVISION. 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 2 of 87

PUBLICATION RECORD 

EFFECTIVE 

DATE

REVISION 

NUMBER DESCRIPTION

06/22/2007 00 Approved new Site Profile for Ames Laboratory. Incorporates formal 

internal and NIOSH review comments. Adds Glossary and 

Attributions and Annotations section. There is no change to the 

assigned dose and no PER is required. Training required: As 

determined by the Task Manager. Initiated by Jerome B. Martin.

Approval:

Signature on File 06/11/2007

Jerome B. Martin, Document Owner

Signature on File 06/08/2007

John M. Byrne, Task 3 Manager

Signature on File 06/08/2007

Edward F. Maher, Task 5 Manager

Signature on File 06/12/2007

Kate Kimpan, Project Director

Brant A. Ulsh Signature on File for 06/22/2007

James W. Neton, Associate Director for Science

08/20/2008 00 PC-1 Approved page change revision made to include SEC-00075 on 

pages 10 and 11 in Section 1.3 where Sections 1.3.1, 1.3.2 and 

Table 1-2 were added. NIOSH required language was revised on 

pages 9 and 10 in Section 1.1. Added reference on page 74.

Incorporates formal internal review comments. As a result of formal 

internal review, editorial changes were made on the following pages: 

8 in Acronym and Abbreviations Section; 11 (Table 1-2), 25 (Table 4-

1), 30 (Table 4-2), 32 (Table 4-6), 34 (Table 5-1), 36 (Table 5-2 and 

5-3), 48 (Table 5-6), 51 (Table 6-1), in Sections 1.3, 4.2, 4.4, 4.7, 5.0, 

5.1, 5.4, and 6.2. SEC changes occurred on pages 11 (Table 1-1), 

32, 33, 37-39 (Table 5-4), 40, 41, 46 (Table 5-5), 49 (Table 5-7), 50, 

57, 60, 61 (Table 6-4), 63 (Figure 6-2) in Sections 1.3, 4.7, 5.0, 5.1, 

5.2, 5.3, 5.5, 6.1, and 6.3. Incorporates formal NIOSH review 

comments on page 2 (Publication Record), 30 (Table 4-2), 41, 48 

(Table 5-6), and 74 in Sections 4.4, 5.2, 5.4, and Reference Section. 

References were updated on pages 10, 11, 19, 29, 30, 32, 33, 37, 

40, 41, 46, 47, 50-52, 57-62, 64, 65, 70, 74-76 in Sections 1.3, 2.3, 

4.4, 4.7, 5.0, 5.1, 5.2, 5.4, 6.1, 6.2, 6.3, 6.4, 7.0, and Reference 

Section. No sections were deleted. Training required: As 

determined by the Task Manager. Initiated by Karen S. Kent.
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 3 of 87

TABLE OF CONTENTS 

SECTION TITLE PAGE

Acronyms and Abbreviations ............................................................................................................... 7

1.0 Introduction .............................................................................................................................. 9

1.1 Purpose ........................................................................................................................ 9

1.2 Scope ......................................................................................................................... 10

1.3 Special Exposure Cohort ............................................................................................ 10

1.3.1 January 1, 1942 to December 31, 1954 .......................................................... 10

1.3.2 January 1, 1955 to December 31, 1970 .......................................................... 11

2.0 Site Description ...................................................................................................................... 11

2.1 Facilities ..................................................................................................................... 12

2.1.1 Physical Chemistry Annex 1 ............................................................................ 13

2.1.2 Chemistry Building (Gilman Hall) .................................................................... 13

2.1.3 Physics Building (Physics Hall) ....................................................................... 14

2.1.4 Physical Chemistry Annex 2 ............................................................................ 14

2.1.5 Metallurgy Building (Wilhelm Hall) ................................................................... 15

2.1.6 Research Building (Spedding Hall) .................................................................. 15

2.1.7 Office and Laboratory Building ........................................................................ 15

2.1.8 Synchrotron Building (Spangler Geotechnical Laboratory) .............................. 16

2.1.9 Metals Development Building .......................................................................... 16

2.1.10 Ames Laboratory Research Reactor (Applied Science Complex) .................... 16

2.2 Operations .................................................................................................................. 17

2.2.1 Uranium Metal Operations .............................................................................. 17

2.2.2 Thorium Metal Operations ............................................................................... 17

2.2.3 Other Operations ............................................................................................ 18

2.3 Source Terms and Personnel Monitoring .................................................................... 19

3.0 Occupational Medical Dose .................................................................................................... 20

3.1 Organ Dose Calculations ............................................................................................ 21

4.0 Occupational Environmental Dose - Introduction .................................................................... 23

4.1 Uranium/Thorium Production Period, 1942 to 1953 .................................................... 23

4.2 SyNchrotron Operations Period, 1949 to 1971 ........................................................... 25

4.3 Ames Laboratory Research Reactor Operations Period, 1965 to 1977 ....................... 26

4.4 Ames Laboratory Research and Development Activities, 1942 to Present .................. 27

4.5 Significant Environmental Event ................................................................................. 30

4.6 Environmental Contamination, 1953 to Present .......................................................... 31

4.7 Summary of Environmental External Doses and Intakes ............................................ 32

5.0 Occupational Internal Dose .................................................................................................... 32

5.1 Uranium Exposure ...................................................................................................... 33

5.1.1 Estimating Internal Doses from Uranium Metal ............................................... 33

5.1.1.1 Uranium Inhalation ........................................................................... 33

5.1.1.2 Uranium Ingestion ............................................................................ 35

5.1.1.3 Resuspension During Periods with No Uranium 

Operations ........................................................................................ 36

5.1.1.4 Uranium Excretion Plots for Use with Bioassay Data ........................ 36

5.2 Thorium Exposure from Thorium Contamination After 1954 ....................................... 37
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5.3 Tritium Exposure ........................................................................................................ 41

5.3.1 Tritium Exposure for Monitored Workers, 1965 to 1981 .................................. 41

5.3.2 Tritium Dose to Workers, 1982 to Present ....................................................... 44

5.3.3 Tritium Dose to Unmonitored Workers, 1965 to 1981 ...................................... 45

5.4 Fission Product Intakes .............................................................................................. 46

5.4.1 Fission Product Intakes from Early Fuel Research .......................................... 46

5.4.2 Fission Product Intakes from Research Reactor Operations and 

Decontamination and Decommissioning ......................................................... 48

5.5 Summary of Internal Dose Recommendations ............................................................ 49

6.0 Occupational External Dose ................................................................................................... 50

6.1 Introduction ................................................................................................................. 50

6.2 External Radiation Dosimeters and Records .............................................................. 50

6.2.1 Historical Administrative Practices .................................................................. 50

6.2.2 Dosimetry Technology .................................................................................... 53

6.2.2.1 Beta/Photon Dosimeters ................................................................... 54

6.2.2.2 Neutron Dosimeters .......................................................................... 54

6.2.3 Dosimeter Calibration Procedures................................................................... 55

6.2.3.1 Beta/Photon Dosimeters ................................................................... 55

6.2.3.2 Neutron Dosimeters .......................................................................... 55

6.2.4 Workplace Radiation Fields............................................................................. 56

6.2.4.1 Beta Radiation .................................................................................. 56

6.2.4.2 Photon Radiation .............................................................................. 56

6.2.4.3 Neutron Radiation ............................................................................. 57

6.2.5 Dosimeter Response to Radiation Fields ........................................................ 57

6.2.5.1 Beta/Photon Film Dosimeter Response ............................................ 57

6.2.5.2 Beta/Photon TLD Response ............................................................. 57

6.2.5.3 Neutron Dosimeter Response ........................................................... 57

6.2.5.4 Neutron Dose Weighting Factor ........................................................ 58

6.3 Recommendations for Ames laboratory Worker External Dose 

Reconstruction ........................................................................................................... 59

6.3.1 Unmonitored External Dose ............................................................................ 59

6.3.2 Missed External Dose for Monitored Workers ................................................. 60

6.3.3 Uncertainty in Photon Doses ........................................................................... 62

6.3.4 Skin Dose ....................................................................................................... 63

6.3.5 Extremity Dose ................................................................................................ 64

6.3.6 Radiation Dose Fraction .................................................................................. 64

6.4 Organ Dose ................................................................................................................ 64

7.0 Attributions and Annotations .................................................................................................. 64

References ........................................................................................................................................ 71

Glossary ............................................................................................................................................ 80
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 5 of 87

LIST OF TABLES 

TABLE TITLE PAGE

1-1 Feasibility findings for SEC-00038 ......................................................................................... 11

1-2 Feasibility findings for SEC-00075 ......................................................................................... 11

2-1 Timeline of AEC activities at Ames Laboratory, 1942 to 1954 ................................................ 18

3-1 Chest X-ray frequencies ......................................................................................................... 20

3-2 Chest X-ray doses delivered to Ames Laboratory staff members ........................................... 21

3-3 Organ doses from PA chest X-rays, 1942 to 1956 ................................................................. 21

3-4 Organ doses from PA chest X-rays, 1957 to 1977 ................................................................. 22

3-5 Organ doses from PA chest X-rays, 1978 to 1996 ................................................................. 22

3-6 Organ doses from PA chest X-rays, 1997 to present .............................................................. 23

4-1 Survey of fence-line gamma dose rates around the synchrotron facility with the 

beam directed west ................................................................................................................ 25

4-2 Annual environmental fission product intakes from the hot laboratory in the 

Chemistry Building ................................................................................................................. 30

4-3 Environmental dose measurements at the four Ames facilities ............................................... 31

4-4 Gamma analysis of soil samples ............................................................................................ 31

4-5 Summary of 24 soil samples for beta and alpha activity ......................................................... 32

4-6 Summary of environmental external doses ............................................................................ 32

4-7 Summary of environmental intakes ........................................................................................ 32

5-1 Uranium intakes from inhalation ............................................................................................. 34

5-2 Uranium intakes from ingestion .............................................................................................. 36

5-3 Resuspension during periods with no uranium operations ...................................................... 36

5-4 Air concentrations and daily intakes of 232Th at Wilhelm Hall after 1954 ................................. 38

5-5 Results of tritium coworker analysis ....................................................................................... 46

5-6 Default annual fission product intakes for Researchers from hot laboratory in the 

Chemistry Building ................................................................................................................. 48

5-7 Default intakes for Ames Laboratory ...................................................................................... 49

6-1 Dosimeter type, period of use, exchange frequency, MRD, and MDL .................................... 51

6-2 Neutron dose energies, percentages and associated ICRP correction factors ....................... 58

6-3 Assigned dose for unmonitored workers ................................................................................ 60

6-4 Potential missed dose for monitored workers ......................................................................... 61
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LIST OF FIGURES 

FIGURE TITLE PAGE

2-1 ISU campus map showing locations of Ames Laboratory buildings ........................................ 13

2-2 ISU campus map showing locations of reactor facilities and Synchrotron Building ................. 14

4-1 Wind rose for Des Moines, Iowa, 1950 to 1955 ...................................................................... 24

4-2 Ames Laboratory Research Reactor Site ............................................................................... 27

4-3 Environmental monitoring in the vicinity of the ALRR ............................................................. 28

5-1 Urinary excretion of uranium expected from 365-d chronic intake at 6,061 pCi/d 

inhalation and 124 pCi/d ingestion ......................................................................................... 37

5-2 Urinary excretion of uranium expected from 730-d chronic intake at 6,061 pCi/d 

inhalation and 124 pCi/d ingestion ......................................................................................... 38

5-3 Urinary excretion of uranium expected from 1,826-d chronic intake at 6,061 pCi/d 

inhalation and 124 pCi/d ingestion ......................................................................................... 38

5-4 Bioassay record example 1 .................................................................................................... 45

5-5 Bioassay record example 2 .................................................................................................... 45

5-6 Distribution of worker doses from tritium in 1970 .................................................................... 47

6-1 Comparison of Hp(10) for photons with energy responses for sensitive DuPont 

502 emulsion in two-element film badge and sensitive DuPont 555 emulsion in 

multielement film badge ......................................................................................................... 54

6-2 Flowchart for monitored and unmonitored workers ................................................................. 63
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 7 of 87

ACRONYMS AND ABBREVIATIONS 

AEC U.S. Atomic Energy Commission 

ALRR Ames Laboratory Research Reactor 

AP anterior-posterior 

AWE atomic weapons employer 

BNL Brookhaven National Laboratory 

cGy centigray 

Ci curie 

cm centimeter 

d day

D&D decontamination and decommissioning 

DOE U.S. Department of Energy 

dpm disintegrations per minute 

EEOICPA Energy Employees Occupational Illness Compensation Program Act of 2000 

ESE entrance skin exposure 

ft foot 

g gram 

GSD geometric standard deviation 

Gy gray 

HEPA high-efficiency particulate air 

HFBR High Flux Beam Reactor 

hr hour

HVL half-value layer 

IADPH Iowa State Department of Public Health 

ICRP International Commission on Radiological Protection 

IMBA Integrated Modules for Bioassay Analysis

in. inch 

INL Idaho National Laboratory 

IREP Interactive RadioEpidemiological Program 

ISU Iowa State University 

keV kiloelectron-volt, 1,000 electron-volts 

kg kilogram 

kV kilovolt 

L liter 

m meter 

MDA minimum detectable activity 

MDL minimum detection level 

MeV megaelectron-volt, 1 million electron-volts 

mg milligram
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 8 of 87

mGy milligray 

mi mile 

mL milliliter 

mm millimeter 

mo month 

mR milliroentgen 

mrad millirad 

MRD minimum recordable dose 

mrem millirem 

mrep millirep 

MTR Materials Test Reactor 

MW megawatt 

N/A Not applicable 

NCA Nucleonic Corporation of America 

NCRP National Council on Radiological Protection and Measurements 

NIOSH National Institute for Occupational Safety and Health 

NTA Eastman Kodak nuclear track emulsion, type A 

NVLAP National Voluntary Laboratory Accreditation Program 

PA posterior-anterior 

pCi picocurie 

POC probability of causation 

R&D research and development 

s second 

S/N serial number 

SEC Special Exposure Cohort 

SLAC Stanford Linear Accelerator Center 

SRDB Ref ID Site Research Database Reference Identification (number) 

TASF Technical and Administrative Services Facility 

TBD technical basis document 

TLD thermoluminescent dosimeter 

U.S.C. United States Code 

wk week 

yr year 

β beta 

γ gamma 

μCi microcurie 

μg microgram 

μm micrometer 

§ section or sections 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 9 of 87

1.0 INTRODUCTION

1.1 PURPOSE 

Technical basis documents and site profile documents are not official determinations made by the 

National Institute for Occupational Safety and Health (NIOSH) but are rather general working 

documents that provide historic background information and guidance to assist in the preparation of 

dose reconstructions at particular sites or categories of sites. They will be revised in the event 

additional relevant information is obtained about the affected site(s). These documents may be used 

to assist NIOSH staff in the completion of the individual work required for each dose reconstruction. 

In this document the word “facility” is used as a general term for an area, building, or group of 

buildings that served a specific purpose at a site. It does not necessarily connote an “atomic weapons 

employer facility” or a “Department of Energy [DOE] facility” as defined in the Energy Employees 

Occupational Illness Compensation Program Act [EEOICPA; 42 U.S.C. § 7384l(5) and (12)]. 

EEOICPA defines a DOE facility as “any building, structure, or premise, including the grounds upon 

which such building, structure, or premise is located ... in which operations are, or have been, 

conducted by, or on behalf of, the Department of Energy (except for buildings, structures, premises, 

grounds, or operations ... pertaining to the Naval Nuclear Propulsion Program)” [42 U.S.C. § 

7384l(12)]. Accordingly, except for the exclusion for the Naval Nuclear Propulsion Program noted 

above, any facility that performs or performed DOE operations of any nature whatsoever is a DOE 

facility encompassed by EEOICPA. 

For employees of DOE or its contractors with cancer, the DOE facility definition only determines 

eligibility for a dose reconstruction, which is a prerequisite to a compensation decision (except for 

members of the Special Exposure Cohort). The compensation decision for cancer claimants is based 

on a section of the statute entitled “Exposure in the Performance of Duty.” That provision [42 U.S.C. § 

7384n(b)] says that an individual with cancer “shall be determined to have sustained that cancer in the 

performance of duty for purposes of the compensation program if, and only if, the cancer ... was at 

least as likely as not related to employment at the facility [where the employee worked], as 

determined in accordance with the POC [probability of causation1] guidelines established under 

subsection (c) ...” [42 U.S.C. § 7384n(b)]. Neither the statute nor the probability of causation 

guidelines (nor the dose reconstruction regulation, 42 C.F.R. Pt. 82) define “performance of duty” for 

DOE employees with a covered cancer or restrict the “duty” to nuclear weapons work (NIOSH 2007a). 

The statute also includes a definition of a DOE facility that excludes “buildings, structures, premises, 

grounds, or operations covered by Executive Order No. 12344, dated February 1, 1982 (42 U.S.C. 

7158 note), pertaining to the Naval Nuclear Propulsion Program” [42 U.S.C. § 7384l(12)]. While this 

definition excludes Naval Nuclear Propulsion Facilities from being covered under the Act, the section 

of EEOICPA that deals with the compensation decision for covered employees with cancer [i.e., 42 

U.S.C. § 7384n(b), entitled “Exposure in the Performance of Duty”] does not contain such an 

exclusion. Therefore, the statute requires NIOSH to include all occupationally-derived radiation 

exposures at covered facilities in its dose reconstructions for employees at DOE facilities, including 

radiation exposures related to the Naval Nuclear Propulsion Program. As a result, all internal and 

external occupational radiation exposures are considered valid for inclusion in a dose reconstruction. 

No efforts are made to determine the eligibility of any fraction of total measured exposure for inclusion 

in dose reconstruction. NIOSH, however, does not consider the following exposures to be 

occupationally derived (NIOSH 2007a): 

 

1

 The U.S. Department of Labor (DOL) is ultimately responsible under the EEOICPA for determining the POC. 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 10 of 87

 Background radiation, including radiation from naturally occurring radon present in 

conventional structures 

 Radiation from X-rays received in the diagnosis of injuries or illnesses or for therapeutic 

reasons 

1.2 SCOPE 

This site profile provides information about U.S. Atomic Energy Commission (AEC) and DOE 

operations at Ames Laboratory that pertains to radiation exposures for monitored or unmonitored 

workers. Section 2 provides a description of the site and operations that pertain to possible radiation 

exposures and discusses radiation source terms. Section 3 provides guidance for the determination 

of occupational medical dose. Section 4 provides guidance for the determination of dose to workers 

outside radiological facilities due to releases of radioactive materials to the environment. Section 5 

provides guidance for the determination of intakes of radionuclides inside facilities. Section 6 

provides guidance for the determination of external doses from measured doses or for periods for 

which records of measured doses are missing. 

Attributions and annotations, indicated by bracketed callouts and used to identify the source, 

justification, or clarification of the associated information, are presented in Section 7.0. 

1.3 SPECIAL EXPOSURE COHORT 

The Secretary of Health and Human Services has designated two classes of employees at Ames 

Laboratory for addition to the Special Exposure Cohort (SEC) as authorized under the EEOICPA. 

1.3.1 January 1, 1942 to December 31, 1954

This includes DOE employees or DOE contractor or subcontractor employees who worked at the 

Ames Laboratory in one or more of the following facilities/locations: Chemistry Annex 1 (also known 

as the old women‟s gymnasium and Little Ankeny), Chemistry Annex 2, Chemistry Building (now 

Gilman Hall), Research Building, or the Metallurgical Building (now Harley Wilhelm Hall), from 

January 1, 1942, through December 31, 1954, for a number of workdays that total at least 250 

workdays, or in combination with workdays within the parameters (excluding aggregate workday 

requirements) established for one or more classes of employees in the SEC, and who are monitored 

or should have been monitored. 

NIOSH evaluated the feasibility for completing dose reconstructions for employees at Ames 

Laboratory from January 1, 1942, through December 31, 1954. NIOSH found that the monitoring 

records, process descriptions, and source term data available are not sufficient to perform complete 

dose reconstructions for the SEC (SEC-00038) class of employees (NIOSH 2006). Table 1-1 

summarizes the results of the feasibility findings for each exposure source for the period from January 

1, 1942, through December 31, 1954. 
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Table 1-1. Feasibility findings for SEC-00038, January 1, 1942 to December 31, 

1954. (NIOSH 2006, Table 7-1). 

Source of exposure

Dose reconstruction 

is feasible

Dose reconstruction 

is NOT feasible

Internal dose: X

Uranium X

Thorium/plutonium X

Thoron X

External dose: X

Uranium beta/gamma X

Thorium/plutonium beta/gamma X (except 1953 and 1954)

Neutron X

Occupational medical X-ray X

1.3.2 January 1, 1955 to December 31, 1970

This includes sheet metal workers, physical plant maintenance and associated support staff (includes 

all maintenance shop personnel of Ames Laboratory), and supervisory staff who were monitored, or 

should have been monitored for potential internal radiation exposures associated with the 

maintenance and renovation activities of the thorium production areas in Wilhelm Hall (a.k.a. the 

Metallurgy Building or “Old” Metallurgy Building) at the Ames Laboratory, for the time period from 

January 1, 1955 through December 31, 1970 and who were employed for a number of work days 

aggregating at least 250 work days, either solely under this employment or in combination with work 

days within the parameters (excluding aggregate work day parameters) established for other classes 

of employees included in the SEC. 

NIOSH evaluated the feasibility for completing dose reconstructions for employees at Ames 

Laboratory from January 1, 1955, through December 31, 1970. NIOSH found that the monitoring 

records, process descriptions, and source term data available are not sufficient to perform complete 

dose reconstructions for the SEC (SEC-00075) class of employees (NIOSH 2007c). Table 1-2 

summarizes the results of the feasibility findings for each exposure source for the period from January 

1, 1955, through December 31, 1970. 

Table 1-2. Feasibility findings for SEC-00075, January 1, 1955 to December 31, 

1970. (NIOSH 2007c, Table 7-1). 

Source of exposure

Dose reconstruction 

is feasible

Dose reconstruction 

is NOT feasible

Internal X

Th-232 and progeny X

Ambient Environmental X

External X

 Gamma X

Beta X

Neutron N/A

Ambient Environmental X

 Occupational Medical X-ray X

2.0 SITE DESCRIPTION

The Ames Laboratory site consists of a number of buildings at Iowa State University (ISU) in Ames, 

Iowa. The precursor to the Ames Laboratory was the Ames Project, which was established in 1942 in 

a contract between the Metallurgical Laboratory at the University of Chicago and Iowa State College 
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(Spedding 1947). Ames Laboratory was established by the AEC in May 1947 (Karsjen 2003). The 

Ames Project/Laboratory played a key role in the production of strategic nuclear materials for the 

Manhattan Project and the AEC. 

Early in 1942, at the beginning of the Manhattan Project, the most pressing problem was the 

preparation of large amounts of pure uranium metal (Ames 1960). Faculty members in the Chemistry 

Department at Iowa State College, with expertise in rare earth metallurgy, were called on to develop a 

method to purify uranium and reduce its cost of production (Ames 1960). By November 1942, 

successful methods had been developed and approximately one-third of the uranium used in the 

Chicago pile was supplied by the Ames Project (Karsjen 2003). The Ames Project was asked to turn 

its process over to industry and, in the meantime, to produce as much pure uranium as possible 

(Ames 1960). Between mid-1942 and August 1945, more than 1,000 tons of pure uranium metal 

were supplied to the Manhattan Project (Ames 1960). 

Once the potential need for thorium metal was recognized, the Ames Project began to develop 

methods for purifying thorium in 1943 (Ames 1960). By late 1944, a large-scale process for thorium 

metal production was developed; between 1950 and April 1953, when thorium production was turned 

over to industry, more than 65 tons of pure thorium metal and thorium compounds were produced by 

the Ames Laboratory (Ames 1960). 

In addition to the early uranium and thorium metal production operations, personnel at Ames 

Laboratory handled a number of other radionuclides, and operated an 80-MeV synchrotron, a 5-MW 

research reactor, and several radiation-generating machines. Each of these radiation sources is 

described in the following sections. 

2.1 FACILITIES 

The original buildings at Iowa State College that were used for the Ames Project included the Physical 

Chemistry Annex 1, the Chemistry Building (now Gillman Hall), and the Physics Building (now Physics 

Hall) (Ames 1967). In 1944, a new building, called Physical Chemistry Annex 2, was constructed to 

house operations to recover uranium from scrap material (Spedding 1947). 

In November 1945, the buildings used by the Ames Project were designated as the Institute for 

Atomic Research (Ames 1962). Four additional buildings were constructed: the Metallurgy Building 

(now Wilhelm Hall), the Research Building (now Spedding Hall), the Office and Laboratory Building 

that connected the Chemistry and Physics Buildings, and the Synchrotron Building (now the Spangler 

Geotechnical Laboratory) (Ames 1962). The Metals Development Building was added in 1960 (Ames 

1960). In May 1947, the AEC established a major research facility at Ames, known as Ames 

Laboratory (Ames 1962), which operated as an integral part of the Institute for Atomic Research. 

Construction of a 5-MW heavy-water-moderated research reactor began in 1962, and operations 

began in 1965. The Technical and Administrative Services Facility (TASF) was added later to 

connect the Research Building (Spedding Hall) and the Chemistry Building (Gilman Hall); the TASF 

includes only offices. The locations of Ames Laboratory buildings on the ISU campus are shown in 

Figure 2-1. The locations of the Reactor facilities (now known as the Applied Science Complex) and 

the Synchrotron Building are shown in Figure 2-2. 

To avoid confusion between the historical building names and the current names, as shown in Figures 

2-1 and 2-2, both names are used in the following sections with the historical name first and the 

current name in parentheses, where applicable. 
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Figure 2-1. ISU campus map showing locations of Ames Laboratory buildings. The former sites of 

Physical Chemistry Annex 1 and Annex 2 are also shown. Source: ISU (2006). 

2.1.1 Physical Chemistry Annex 1

The production of uranium metal was conducted in the Physical Chemistry Annex 1 building, which 

was an old wooden structure east of the Dairy Industries building and west of Wallace Road (Karsjen 

2003). Uranium operations began there in mid-1942 and ended on August 5, 1945, when the uranium 

purification process was transferred to industry. More than 1,000 tons of pure uranium and more than 

300 tons of uranium scrap were produced during this period (Karsjen 2003). In 1943, an open porch 

area was enclosed (to control dusty operations) and additions were constructed to accommodate 

increases in uranium production (Payne 1992). Beginning in 1943, the building was also used to 

produce thorium metal until the processing equipment was transferred to the new Metallurgy Building 

in 1949 or 1950 (Ames 1960). The Physical Chemistry Annex 1 building was torn down in 1953 

(Karsjen 2003). The building site was decontaminated, surveyed in May 1976, and designated 

acceptable for future construction (Voss 1979). 

2.1.2 Chemistry Building (Gilman Hall)

The initial Ames Project work was conducted in the Chemistry Building in early 1942. The process for 

purifying uranium metal and the methods and equipment to increase production were developed in 

the Chemistry Building (Spedding 1947). Uranium production operations were moved to the Physical 

Chemistry Annex 1 in mid-1942, while other uranium research continued in the Chemistry Building, 

including determination of uranium properties, studies of uranium corrosion, development of protective 

coatings for uranium, and development of uranium alloys and compounds (Spedding 1947). Other 
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research in the Chemistry Building involved development of pure thorium metal, thorium alloys and 

compounds, yttrium metal, cerium metal, and beryllium metal (Ames 1962). Analytical work centered 

on plutonium chemistry and the radiochemistry of the separation of fission products from uranium and 

plutonium, which was conducted in the “hot laboratory” between 1942 and 1951 (Ames 1960). The 

Chemistry Building was decontaminated and surveyed in May 1976 (Voss 1979).

Figure 2-2. ISU campus map showing locations of reactor facilities and 

Synchrotron Building. Source: ISU (2006). 

2.1.3 Physics Building (Physics Hall)

Research and development (R&D) to support other work at Ames Laboratory was conducted in the 

Physics Building. Analytical equipment was developed, including three beta-ray spectrometers, a 

bent crystal X-ray spectrometer, a kevatron, X-ray and neutron diffraction spectrometers, scintillation 

and conduction crystal spectrometers, X-ray and electron diffraction machines, and an electron 

microscope (Ames 1951, 1962). Nuclear fission was studied to identify the individual fission 

fragments, the energies involved, and the ionized state of the emitted particles (Ames 1951). 

Research was conducted to determine the stopping power and shielding properties of various solid 

materials (Ames 1951). Personnel of the Physics Department operated the 80-MeV synchrotron, 

which is described below (Ames 1962). 

2.1.4 Physical Chemistry Annex 2

The Physical Chemistry Annex 2 Building was a brick fireproof structure built east of Wallace Road in 

early 1944 to house the recovery of uranium from scrap uranium metal turnings collected from other 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 15 of 87

Manhattan Project sites (Spedding 1947). Operations in this building through December 1945 

produced more than 300 tons of recovered uranium metal (Spedding 1947). Operations ended in 

1953 when the building was converted to a plumbing shop; it was razed in 1972 (Ames 1985). The 

area where the building stood was covered with concrete and served as a parking lot and loading 

zone. The area was surveyed in May 1979 (Voss 1979). Part of the General Services Building now 

covers part of the former building site (see Figure 2-1). 

2.1.5 Metallurgy Building (Wilhelm Hall)

The Metallurgy Building, constructed by the AEC, was completed in October 1949 (Ames 1951). The 

building houses research directed toward the development of special metals and alloys used in 

nuclear energy projects (Ames 1962). Zircaloy was initially developed at Ames Laboratory as part of 

a basic study of the zirconium-tin alloy phase diagram (Ames 1962). The subject of reactor coolants 

was studied, as were the heat-transfer properties of various metals and alloys (Ames 1951). 

Equipment available for research, development, and production in metallurgy included many types of 

furnaces; high-vacuum systems; pyrometric devices; fabricating and testing machines; metallographs; 

X-ray diffractometers; and ultrasonic, spectrographic, dilatometric, and other instruments for 

examination and study of metals and alloys (Ames 1962). A glovebox line in the Metallurgy Building 

was used to study the behavior of plutonium in molten metal systems (Ames 1962). 

Thorium production and research activities were moved from Physical Chemistry Annex 1 to the 

Metallurgy Building in 1949 and work on thorium continued until 1953 (Hokel et al. 1998). Poor 

contamination control practices and poor ventilation contributed to contamination of the building 

(Hokel et al. 1998). However, contamination levels have been reduced by mitigation, 

decontamination, remodeling, and renovation projects (Hokel et al. 1998). Contamination still exists in 

many interspatial areas of the building and in some relatively inaccessible areas (Hokel et al. 1998). 

2.1.6 Research Building (Spedding Hall)

The Research Building was constructed by the AEC and occupied in early 1951 (Ames 1951). Many 

metals, including the rare earths, were investigated for mechanical, chemical, electrical, and other 

properties, and were studied by experimental techniques that probed the inner structures and forces 

of the materials (Ames 1962). Research facilities in the building included a 150-kV accelerator that 

produced 14-MeV neutrons; a glovebox line for radiochemistry experiments; a hot canyon and hot cell 

with steel shielding, lead glass windows, and manipulators for work with highly radioactive materials; 

and an electron microprobe analyzer (Ames 1967). The hot canyon was two stories high with the 

lower level in the basement adjacent to the hot cell. Research activities included electron beam 

welding; the study of electronic structure of metals; and the separation, preparation, and 

measurement of properties of the rare earth metals (Ames 1967). The initial research on liquid metal 

coolants was done at Ames Laboratory in an engineering sodium test loop utilized in corrosion, fluidflow, and heat transfer studies with liquid sodium (Ames 1967). 

2.1.7 Office and Laboratory Building

The Office and Laboratory Building connects the Chemistry and Physics Buildings and provides 

administrative offices of the Ames Laboratory, the special research laboratories used jointly by 

chemists and physicists, and a large physical sciences reading room (Ames 1951). 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 16 of 87

2.1.8 Synchrotron Building (Spangler Geotechnical Laboratory)

The Synchrotron Building was constructed in 1949 on a 200-acre tract northwest of the campus that 

was set aside for special use by the Institute for Atomic Research (Ames 1962). The synchrotron 

room housed two electron accelerators that could project electrons up to 80 MeV onto a target, which 

produced high-energy gamma rays that interacted with nuclei to release neutrons, protons, and alpha 

particles (Ames 1967). The accelerators were operated from a Control Room where there was a 

safety gate that prohibited access to the synchrotron room when the beam was on (Ames 1967). In 

many cases, the products of these reactions were radioactive, and were used in research in nuclear 

physics and radiochemistry (Ames 1967). In addition, the synchrotron was used to probe nuclear 

structure and to provide radioisotopes for nuclear spectroscopy (Ames 1962). Operations at the 

Synchrotron Building ended in June 1971; the equipment was decommissioned in the early 1990s. 

2.1.9 Metals Development Building

Ames Laboratory facilities were expanded in 1960 to include the Metals Development Building (Ames 

1960). Its missions were to conduct process development research on larger-than-laboratory scale 

and to evaluate commercial feasibility of the processes developed (Ames 1960). One major process 

was the production of very pure metals, and the production of small quantities of these metals to be 

used elsewhere as standards (Ames 1960). The building contained a complete pilot plant with 

facilities for each step of the metal production process from ore treatment to metal fabrication or 

analysis (Ames 1960). Equipment in the building included electron microscopes, an electron 

microprobe, metallography apparatus, liquid-liquid extraction apparatus, extrusion presses for 

producing rods and tubes, and rolling machines for making sheet metal (Ames 1967). 

2.1.10 Ames Laboratory Research Reactor (Applied Science Complex) 

Construction of a 5-MW, heavy-water-moderated research reactor began in 1961; the reactor was first 

operated in February 1965 (Ames 1967; Voigt 1981). The reactor and its support facilities were about 

1.5 mi northwest of the ISU campus on a 200-acre site used by the Institute for Atomic Research 

(Ames 1967). The reactor fuel was 93% enriched 235U contained in 24 fuel assemblies in a hexagonal 

arrangement in a core 30 in. across and 25 in. high (Voigt 1981). The reactor shielding was an 

irregular decahedral prism shape with a thermal column on one face and nine faces with beam tubes 

from which radiation beams (primarily neutrons) could be extracted and directed to experimental 

areas surrounding the reactor (Ames 1967; Voigt 1981). Numerous other tubes and thimbles 

provided access to the reactor core for irradiation experiments. Research activities included radiation 

damage studies, the determination of the crystalline structure of solids, the determination of 

mechanical properties of reactor materials, and analysis of the decay products of nuclear fission 

(Ames 1967). The experimental equipment featured an online isotope separator that received fission 

products directly from the operating reactor, separated them by weight, and analyzed them by isotope 

(Ames 1967). Other research equipment included a neutron diffractometer used to determine the 

physical properties of solids and a hot cell for handling spent reactor fuel (Ames 1967). Operation of 

the reactor resulted in airborne tritium concentrations in occupied spaces of the building (Voigt 1981). 

A routine tritium bioassay program was part of the radiation safety program at the reactor (Voss 

1971). Operation of the reactor ended in December 1977 and decontamination and decommissioning 

(D&D) of the facilities was completed in 1981 (Voigt 1981). At the time operations ended, the heavywater coolant contained approximately 1.7 Ci of tritium per liter (Voigt 1981). 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 17 of 87

2.2 OPERATIONS 

Two major operations at Ames Laboratory resulted in radiation exposure to the staff – the production 

of large quantities of pure uranium (1942 to 1945) and thorium metal (1943 to 1953). A number of 

smaller operations contributed to staff exposure to radiation. 

2.2.1 Uranium Metal Operations

The initial Ames process for production of uranium metal was based on the chemical reduction of 

uranium tetrafluoride by calcium metal. Finely ground uranium tetrafluoride was mixed with 

granulated calcium metal and the mixture was poured into a refractory-lined container. A fuse wire 

buried in the charge was electrically heated to initiate the reaction, which continued until both uranium 

metal and calcium fluoride were in the molten state. The more dense uranium collected at the bottom 

of the container, where it was allowed to cool to room temperature, after which it was removed for 

casting. The uranium metal was cast by placing it in a graphite crucible, heating it in a vacuum, and 

allowing the liquid metal to flow into a graphite mold for specific shapes (Spedding 1947). Although 

more complex, the uranium production process was improved by replacing the calcium reagent with 

magnesium metal (Spedding 1947). 

Most of the uranium metal production operations were conducted in the Physical Chemistry Annex 1 

Building, which had poor contamination control and poor ventilation (Friedell 1942). Workers in this 

building were likely to have received intakes of uranium between 1942 and 1945 and thorium between 

1943 and 1950 as well as external exposures to beta and gamma radiation. These exposures are 

estimated in Sections 5 and 6. Effluents from the building were not monitored and local 

environmental contamination by uranium compounds was likely. Uranium and thorium contamination 

of the ground surface around Annex 1 required removal and offsite disposal of the contaminated soil 

(Payne 1992). No other records could be found that addressed the disposal of contaminated waste or 

the control and monitoring of air and liquid effluents. 

A substantial amount of uranium scrap material was produced, which was processed in the Physical 

Chemistry Annex 2 Building from early 1944 to December 1945 (Spedding 1947). Radiation 

exposures to workers in this building during this period were similar to the uranium exposures in 

Annex 1, and these exposures are estimated in Sections 5 and 6. Local environmental contamination 

around Annex 2 was assumed to be similar to that around Annex 1, and this is addressed in Section 

4.1. 

2.2.2 Thorium Metal Operations

The uranium metal production method was adjusted between August 1943 and August 1944 to 

produce thorium metal (Spedding 1947). Thorium tetrafluoride was mixed with calcium metal with a 

zinc chloride booster to produce a thorium-zinc alloy with a 96% yield of thorium metal. The alloy was 

heated under vacuum in a graphite crucible to distill off the zinc. Casting of thorium metal was difficult 

because of its high melting point and its reactive properties. Beryllium oxide crucibles had to be used; 

melting the thorium in a crucible the size and shape of the desired ingot proved to be a more reliable 

method of casting, although it often did not separate well from the slag and oxide. Castings were 

improved in late 1946 by pouring molten thorium into graphite molds (Spedding 1947). Production of 

thorium metal and thorium compounds continued until April 1953, when thorium production operations 

were turned over to industry (Ames 1960). 

The purified feed material for the thorium production operation was prepared by dissolving thorium 

nitrate in nitric and oxalic acids, precipitating the thorium oxalate, drying the precipitate in trays, 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 18 of 87

hydrofluorinating the precipitate to thorium tetrafluoride, and crushing the thorium tetrafluoride to a 

fine powder (Spedding 1947). This process was used throughout thorium production operations. 

Thorium production operations, which were conducted in the Physical Chemistry Annex 1 Building 

after uranium operations ended in 1945, continued until 1949 or 1950, when the operation and 

equipment was moved to the new Metallurgy Building (Wilhelm Hall) (Ames 1960). Workers in Annex 

1 were likely to have intakes of thorium and external exposures to beta and gamma radiation. These 

exposures are estimated in Sections 5 and 6. Effluents from the building were not monitored and 

local environmental contamination by thorium compounds was likely. Thorium production operations 

in the Metallurgy Building improved with better ventilation, but personnel exposures and 

environmental contamination continued to be unquantified until 1953 because of a lack of monitoring 

and inadequate records. 

The molding and machining of beryllium oxide crucibles raised a concern about toxic dust (Spedding 

1947), which causes the serious lung disease berylliosis (Van Bemmel 1957). Ames Laboratory staff 

members were required to have physical examinations and chest X-rays every 6 mo (Van Bemmel 

1957). The subject of chest X-rays is addressed in more detail in Section 3. 

A summary of AEC activities at Ames Laboratory during the period from 1942 to 1954 is presented in 

Table 2-1. 

Table 2-1. Timeline of AEC activities at Ames Laboratory, 1942 to 1954. 

Operation Datesa Building Activity

Uranium metal production Feb 1942–Aug 1942 Chemistry (Gilman Hall) Process development

Uranium metal production Aug 1942–Dec 1942 Chemistry Production

Uranium metal production Sept 1942–Aug 1945 Annex 1 Production

Uranium scrap recovery Late 1943–Early 1944 Chemistry Process development

Uranium scrap recovery Early 1944–Dec 1945 Annex 2 Production

Uranium metal casting Sept 1942–Aug 1945 Annex 1 Production

Thorium metal production Aug 1943–Jun 1946 Annex 1 Process development

Thorium metal production Jun 1946–late 1949 Annex 1 Production

Thorium metal production Early 1950–Apr 1953 Metallurgy (Wilhelm Hall) Production

Studies of plutonium properties Jun 1943–Dec 1947 Chemistry & Metallurgy Research

Plutonium/fission product 

separations

Summer 1943–Dec 1954 Chemistry & Research 

(Spedding Hall)

Research and hot cell 

work

Thorium metal casting Jun 1946–late 1949 Annex 1 Production

Thorium metal casting Early 1950–Apr 1953 Metallurgy Production

Studies of uranium and thorium 

properties

Early 1942–Dec 1954 Chemistry Research

Development of analytical 

procedures

Early 1943–Dec 1954 Chemistry Research

Annex 1 demolition 1953 Annex 1 Demolition

a. Exact start–end dates vary depending on the reference. Listed dates are the most common or consensus. 

2.2.3 Other Operations

Methods for routine analysis of fission products were developed at Ames Laboratory. These activities 

resulted in the discovery of the previously unidentified isotopes 33P, 144Pm, 125Sb, and five isotopes of 

ruthenium and rhodium. Research on the parent-daughter relationship of 90Sr/90Y was conducted 

(Spedding 1947). Pioneering research in applications of alpha and beta spectroscopy and mass 

spectroscopy to identify specific radionuclides was part of the development of laboratory methods. A 

process for separating 233U from thorium was developed at Ames Laboratory (Spedding 1947). 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 19 of 87

2.3 SOURCE TERMS AND PERSONNEL MONITORING 

Ames Laboratory staff members were exposed to a number of radiation sources, including medical 

X-rays, environmental effluents, radioactive intakes, and external radiation dose. Routine chest 

X-rays are discussed in the previous section and are addressed in more detail in Section 3. 

Environmental effluents from the early Ames Laboratory buildings were unmonitored and 

uncontrolled. Radioactive effluents near these buildings could have exposed workers to unmonitored 

occupational environmental doses. An accidental release of thorium waste materials to the sanitary 

sewer system occurred in 1951 (Voss 1979). This release could have contributed to the occupational 

environmental dose received by Ames Laboratory workers who were involved in the incident response 

and is addressed in Section 4. 

Uranium and thorium metal production involved several dusty operations that resulted in work-area 

contamination and potential worker inhalation and ingestion (Spedding 1947). The principal sources 

of surface contamination and airborne dust were the processes of grinding uranium fluoride into a fine 

powder, transferring the uranium fluoride powder from the grinder, and then mixing and loading the 

powder charge into the reduction crucibles. Because the uranium had been separated from radium 

and its decay products, 222Rn was not a potential inhalation concern (Spedding 1947). The principal 

sources of thorium surface contamination and airborne dust were the processes of preparing and 

drying the fine powder and mixing and loading the powder charge into the reduction crucibles 

(Spedding 1947). 

There were frequent small explosions and fires associated with the uranium and thorium production 

operations (Payne 1992). Payne (1992) cited as many as six small fires in a single day; these fires 

contributed to work-area contamination and potential airborne radioactive material exposures. No 

records were found to indicate that air sampling or contamination control was associated with these 

fires. 

Personnel protection for potential dusty operations included the use of Laboratory-provided clothing 

and gloves, as well as restrictions on eating and smoking in areas where radioactive materials were 

handled. Although respiratory protection measures, such as gas masks and dust masks, were 

provided, their use was not enforced at Ames Laboratory before about 1952. Showers were 

recommended for workers at the end of each day, but records indicated that not all workers complied 

with this recommendation (Klevin 1952; Payne 1992). 

Many other radioactive materials were handled in the Ames Laboratory buildings before routine 

monitoring for radiation exposures began in about 1952. Because the bioassay program was minimal 

and records are sparse, intakes that might have occurred before 1953 were estimated. When reactor 

operations started in 1965, a routine tritium bioassay program was started, and tritium intakes can be 

reliably estimated. Occupational internal dose is addressed in Section 5. 

The uranium and thorium metal production operations resulted in beta and gamma radiation 

exposures to workers. Beta radiation was the dominant external source of radiation associated with 

unshielded sources of uranium, such as the uranium metals production, uranium scrap recovery, and 

uranium machining processes (NIOSH 2006). The significance of beta emissions from thorium 

depends on the state of equilibrium with the 232Th parent, which is a factor of the time elapsed since 

the thorium process feed material was separated (NIOSH 2006). Photon exposure rates as high as 

22 mR/hr were reported for a thorium storage area, suggesting that this raw material for the thorium 

production process was not newly separated (Klevin 1952). 
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Only two film badge results were identified for 1944 with results in units of “average roentgens/8 hour 

day during week” (Tybout 1944). Before 1952, only pencil dosimeters were used in Ames Laboratory 

facilities and the records are sparse. The use of film badges began in late 1952; records from 1953 

and 1954, along with workplace measurements, are used to estimate earlier radiation doses. 

Records of external radiation exposures received from 1955 to the present are used in Section 6 to 

evaluate occupational external dose. 

3.0 OCCUPATIONAL MEDICAL DOSE

Occupational medical examinations were conducted for the staff of the Ames Project (later the Ames 

Laboratory) as prescribed by the Medical Services of the Manhattan Project (Van Horn 1943; Wirth 

1946). Preemployment examinations included a chest X-ray and urine analysis. Annual physical 

examinations also included a chest X-ray, and annual chest X-ray films dated back to 1946 were 

examined to verify an annual frequency. When work with beryllium oxide crucibles began in 1944, 

there was concern about beryllium dust and the potential for berylliosis (Spedding 1947). It is 

possible that more frequent chest X-rays were required for beryllium workers, but this could not be 

verified because no films or records from before 1946 were found [1]. X-ray film records from the 

early and mid-1950s indicated that some (possibly beryllium) workers did receive chest X-rays on a 

quarterly frequency; other workers had chest X-rays on an annual or semiannual frequency. In 1957, 

the frequency of chest X-rays was changed to twice per year for all Ames Laboratory staff members 

(Van Bemmel 1957). X-ray film records indicated that the frequency of chest X-rays was changed to 

annual in 1960 and biannual in 1982. The general frequencies of chest X-rays during various periods 

are summarized in Table 3-1. Although the projection for most chest X-rays was posterior-anterior 

(PA), some lateral (LAT) projections were also taken. The actual dates and projections of chest Xrays for workers were reported by Ames Laboratory in response to data requests for each claim. 

Table 3-1. Chest X-ray frequencies. 

Period Beryllium workersa Other workers

1942–1943 Annual

1944–1949 Quarterly Annual

1950–1956 Quarterly Semiannual

1957–1960 Semiannual Semiannual

1960–1981 Annual Annual

1982–present Biannual Biannual

a. If a claim mentions beryllium at any time between 1944 and 

1953, the claimant should be considered a beryllium worker. 

X-ray examinations of Ames Laboratory staff members were conducted at the Iowa State Student 

Health Center/College Hospital. The radiation dose delivered by the medical X-ray machine was 

determined in February 1957 (Voss 1957a). The measurements indicated the exposure dose per 

X-ray film ranged from 40 to 65 mrem, depending on the body thickness of the worker (Voss 1957a). 

All X-ray films examined in the archives at Ames Laboratory were 14-in. by 17-in. films; there was no 

evidence of any X-rays being taken with photofluorographic X-ray equipment. 

In 1978, a Picker Model 851 (Serial Number 1101) X-ray machine was installed at the Iowa State 

Student Health Center. The Iowa State Department of Public Health (IADPH) conducted surveys 

(CRCPD 2005; HHS 1995) of this unit on February 2, 1988 (IADPH 1988) and April 20, 1995 (IADPH 

1995). A Continental Model 6626.235 (Serial Number 971941) X-ray machine was installed on May 

12, 1997; it was surveyed by IADPH on September 17, 1997 (IADPH 1997). The occupational 

medical dose for each chest X-ray delivered to Ames Laboratory staff members is estimated and 

summarized in Table 3-2 for specific periods. 
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Table 3-2. Chest X-ray doses delivered to Ames Laboratory staff members. 

Period X-ray machine Half-value layer Entrance kerma

1942–1956 Unknown 2.5 mm Ala0.2 cGya

1957–1977 Unknown 2.5 mm Ala0.065 cGyb

1978–1996 Picker 3.0 mm Alc0.020 cGye

1997–present Continental 3.5 mm Ald0.016 cGyf

a. Default value from ORAUT (2005a). 

b. Based on measurements found in Voss survey, February 1957 (Voss 1957a). 

c. Based on measurements found in 1988 IADPH survey (IADPH 1988). 

d. Based on measurements found in 1997 IADPH survey (IADPH 1997). 

e. Based on 75th percentile of entrance skin exposures (ESEs) collected nationwide 

in nonhospital facilities in 1986 (Spelic 2006). 

f. Based on 75th percentile of ESEs collected nationwide in all facility types in 1994 

(Spelic 2006). 

3.1 ORGAN DOSE CALCULATIONS 

Guidance in ORAUT (2005a) was used to determine organ doses. For conventional chest X-rays, 

that document recommends a default entrance kerma of 0.2 rem for pre-1970 examinations (ORAUT 

2005a, Table 3-4). In addition, ORAUT (2005a, Table 6-5) provides factors for converting kerma to 

organ dose for pre-1970 X-ray machines that might have had limited collimation. Because nothing is 

known about the type of X-ray machines used before 1978, it is favorable to the claimant to assume 

limited collimation. It is also assumed that the projection is PA. The dose conversion factors and 

organ doses from ORAUT (2005a) are listed in Tables 3-3 through 3-6 for 1942 to 1956, 1957 to 

1977, 1978 to 1996, and 1997 to the present, respectively. 

Table 3-3. Organ doses from PA chest X-rays, 1942 to 1956. 

Organ

PA dose conversion factor 

(mGy per Gy air kerma) 

HVL 2.5 mm Al

Organ dose 

(rem)a

Thyroid 174 3.48E-2

Eye/brain 32 6.40E-3

Ovaries N/Ab2.50E-2

Liver/gall bladder/spleen 451 9.02E-2

Urinary bladder N/Ab2.50E-2

Colon/rectum N/Ab2.50E-2

Testes N/Ab5.00E-3

Lungs 451 9.02E-2

Thymus 451 9.02E-2

Esophagus 451 9.02E-2

Stomach 451 9.02E-2

Bone surfaces 451 9.02E-2

Breast 49 9.80E-3

Uterus N/Ab2.50E-2

Bone marrow 92 1.84E-2

Skinc N/A 2.70E-1

a. From ORAUT (2005a, Table 6-5, pre-1970). 

b. N/A = not applicable. Organ dose based on measured values from Webster 

and Merrill (1957). 

c. Included backscatter factor of 1.35 from NCRP Report 102 (NCRP 1989, 

Table B-8). 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 22 of 87

Table 3-4. Organ doses from PA chest X-rays, 1957 to 1977. 

Organ

PA dose conversion factor 

(mGy per Gy air kerma) 

HVL 2.5 mm Al

Organ dose 

(rem)

Thyroid 174 1.13E-2

Eye/brain 32 2.08E-3

Ovaries N/Aa2.50E-2

Liver/gall bladder/spleen 451 2.93E-2

Urinary bladder N/Aa2.50E-2

Colon/rectum N/Aa2.50E-2

Testes N/Aa5.00E-3

Lungs 451 2.93E-2

Thymus 451 2.93E-2

Esophagus 451 2.93E-2

Stomach 451 2.93E-2

Bone surfaces 451 2.93E-2

Breast 49 3.19E-3

Uterus N/Aa2.50E-2

Bone marrow 92 5.98E-3

Skinb N/A 8.78E-2

a. N/A = not applicable. Organ dose based on measured values from Webster 

and Merrill (1957). 

b. Included backscatter factor of 1.35 from NCRP Report 102 (NCRP 1989, 

Table B-8). 

Table 3-5. Organ doses from PA chest X-rays, 1978 to 1996. 

Organ

PA dose conversion factor 

(mGy per Gy air kerma) 

HVL 3.0 mm Al

Organ dose 

(rem)

Thyroid 46 9.20E-4

Eye/brain 46 9.20E-4

Ovaries 1.8 3.60E-5

Liver/gall bladder/spleen 535 1.07E-2

Urinary bladder 1.8 3.60E-5

Colon/rectum 1.8 3.60E-5

Testes 0.01 2.00E-7

Lungs 535 1.07E-2

Thymus 535 1.07E-2

Esophagus 535 1.07E-2

Stomach 535 1.07E-2

Bone surfaces 535 1.07E-2

Breast 69 1.38E-3

Uterus 2.3 4.60E-5

Bone marrow 117 2.34E-3

Skina N/A 2.80E-2

a. Included backscatter factor of 1.4 from NCRP Report 102 (NCRP 1989, 

Table B-8). 

 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 23 of 87

Table 3-6. Organ doses from PA chest X-rays, 1997 to present. 

Organ

PA dose conversion factor 

(mGy per Gy air kerma) 

HVL 3.5 mm Al

Organ dose 

(rem)

Thyroid 62 9.92E-4

Eye/brain 62 9.92E-4

Ovaries 3.2 5.12E-5

Liver/gall bladder/spleen 610 9.76E-3

Urinary bladder 3.2 5.12E-5

Colon/rectum 3.2 5.12E-5

Testes 0.01 1.60E-7

Lungs 610 9.76E-3

Thymus 610 9.76E-3

Esophagus 610 9.76E-3

Stomach 610 9.76E-3

Bone surfaces 610 9.76E-3

Breast 91 1.46E-3

Uterus 3.0 4.80E-5

Bone marrow 146 2.34E-3

Skina N/A 2.24E-2

a. Included backscatter factor of 1.4 from NCRP Report 102 (NCRP 1989, 

Table B-8). 

4.0 OCCUPATIONAL ENVIRONMENTAL DOSE - INTRODUCTION

The occupational environmental dose refers to the dose received by workers on the site but outside 

facilities (e.g., buildings). These doses can be internal and/or external depending on the 

characteristics of the individual radionuclides. Radionuclides used at Ames Laboratory during various 

periods included uranium, plutonium, thorium, and small amounts of other radionuclides used in the 

R&D program (Spedding 1947). Tritium, argon, and krypton were released at the Ames Laboratory 

Research Reactor (ALRR) (Voigt 1973). While most radionuclides when inhaled would give a dose to 

particular organs in the body, tritium gas would give a dose to the whole body (Voigt 1973). These 

radionuclides are addressed in the following sections. 

Occupational environmental dose was not measured (direct radiation dosimeters) until 1953, when 

workers were badged (Martin 2006a, 2006b), and it was not calculated from environmental media 

concentrations until 1962 (Voss 1963a). Sources of potential environmental exposures (releases to 

the environment) were not measured until 1962 (Voss 1963a). 

Different activities were carried out during distinct periods of the Ames Laboratory history. 

Occupational environmental doses are, therefore, addressed below for each of these periods and 

their activities. A significant release of radioactive materials to the environment from Ames Laboratory 

facilities is addressed in Section 4.5. 

4.1 URANIUM/THORIUM PRODUCTION PERIOD, 1942 TO 1953 

Uranium production occurred in the Physical Chemistry Annex 1 Building (see Figure 2-1) from mid1942 through August 5, 1945 (Karsjen 2003). Uranium scrap recovery occurred in the Physical 

Chemistry Annex 2 Building (see Figure 2-1) from early 1944 through December 1945, and some 

operations continued until 1954. Thorium production occurred first in the Physical Chemistry Annex 1 

Building from 1944 through 1949 when the operation moved to the new Metallurgical Building, now 

Wilhelm Hall (see Figure 2-1). The operation in the Metallurgical Building continued until April 1953. 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 24 of 87

Like Annex 1 and Annex 2, there was no onsite or offsite designation for this facility. Workers, 

students, and college personnel moved freely by and around the building. No measurements were 

made of the particulate or gaseous effluents from the buildings or of the radiation levels outside the 

buildings (Voss 1963b). 

Workers conducted their work inside the facilities and there were no specific work assignments 

outside the facilities; that is, input materials arrived at the facilities and were processed, and products 

were shipped from the facilities. Workers did not move between the facilities on campus and there 

was no transportation of materials among the facilities on campus (Ames 1962). 

There were room and hood ventilation stacks on the facilities but no filters on either (Skoog 1952, 

Section e; Spedding 1952). Concentrations of uranium dust were measured in the operation rooms 

(Voss 1978). To estimate a bounding dose outside the facilities, it was assumed that losses of 0.1% 

of the uranium or thorium as dust in a facility were emitted continuously and dispersed from ground 

level in accordance with local and regional meteorological conditions (see Figure 4-1) (Voss 1981) 

and a standard Gaussian atmospheric dispersion computer model (Napier et al. 2004). When 

resuspension is included, the daily intake rate of uranium (to be modeled as 234U, type M or S) was 5 

pCi. This intake applies outside the Physical Chemistry Annex 1 for July 1942 through August 1945 

and outside the Physical Chemistry Annex 2 for 1944 through 1954. In addition, daily intakes of 232Th, 

228Th, and 228Ra at 0.07 pCi each apply to the Physical Chemistry Annex 1 for June 1946 through 

1949 and to the Metallurgy Building for 1950 through April 1953. These are upper bound intakes so 

the distribution is constant (Napier 2006). 

Figure 4-1. Wind rose for Des Moines, Iowa, 1950 to 1955. Source: Voss (1981). 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 25 of 87

4.2 SYNCHROTRON OPERATIONS PERIOD, 1949 TO 1971 

Synchrotron operations occurred in what is now called the Spangler Geotechnical Laboratory from 

1949 through June 1971 (see Figure 2-2). Unlike the uranium and thorium facilities, this facility was 

fenced, providing a defined exclusion area outside the building. Dosimeters were not provided to 

anyone at the facility until late 1952 (Martin 2006c). There were small research amounts of 

radioactive materials that were generated during operations and negligible particulate or gaseous 

effluents were released from the building [2]. No routine measurements of direct gamma or neutron 

radiation were made outside the buildings, but a detailed survey of the facility, including fence-line 

gamma dose rates, was made on May 16, 1961, during a special synchrotron operation (Ames 1961). 

The results of that survey are listed in Table 4-1 (Ames 1961). 

Table 4-1. Survey of fence-line gamma dose rates around the 

synchrotron facility with the beam directed west (Ames 1961, p.7). 

Location Dose rate, mrem/hraLocation Dose rate, mrem/ha

1 0.75–1 14 1.8

2 3.5 15 1.8

3 7 16 1.8

4 6 17 1.6

5 5.5 18 1.5

6 7 19 1.5

7 4.75 20 1.75

8 3.5 21 1.6

9 2.6 22 1.6

10 1.5 23 1.5

11 2 24 0.75–1

12 2 25 4.5

13 1.8

a. Background reading in the beam direction (see locations 3-6) before 

turning on the beam was 0.5-1.0 mrem/hr. 

The fence line gamma dose rates measured in the radiation survey (Ames 1961) were worst case and 

were produced with the maximum beam current on a target and direction that would produce 

maximum dose rates at the fence [3]. This condition was most unusual in relation to typical research 

studies because it produced radiation levels in the normally occupied parts of the Synchrotron 

Building that were clearly hazardous to staff (tens of mR/hr) (Ames 1961). Dosimeter results for 

Synchrotron staff verified that the machine was not operated in this condition for significant periods 

(during the May 16, 1961, survey or at any other time) (Martin 2006c).

The Synchrotron was operated part time by Physics Department faculty and graduate students. The 

typical research schedule would have been weekdays and evenings plus occasional weekends, which 

was estimated at a maximum of 3,000 hr/yr. Much of this time would have been occupied with 

experiment set-up, maintenance, system start-up, etc., so the maximum operating time would have 

been about 2,000 hr/yr [4]. Most of this operating time would have been dedicated to various material 

property studies that involved electron beams, beam currents, and targets that produced gamma 

fields outside the building that were at least a factor of 10 (and more likely a factor of 100) less than 

the survey dose rates given in Ames (1961) [5]. 

A topographical map that was part of the 1961 radiation survey (Ames 1961) indicates that the 

Synchrotron Building was surrounded by hills that would have protected nearby buildings from a direct 

beam. Therefore, the primary source of environmental exposures from this facility would have been 

skyshine from the synchrotron. The Waste Chemical Handling Facility (see Figure 2-2) was not built 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 26 of 87

until 1980, so the area was not affected by synchrotron operations between 1949 and 1971. The 

ALRR (now the Applied Science Complex) is about 750 ft from the nearest part of the Synchrotron 

Building, and construction or operations at the two facilities overlapped, at a maximum, from 1962 to 

1971. Skyshine from both heavy particles and photons decreases at rates equal to or greater than 

the reciprocal of the square of the distance (1/r

2

) from accelerator facilities (NCRP 2003). If it is 

conservatively assumed that all of the radiation field measured in the 1961 survey was from skyshine, 

the dose rate at the ALRR would have been less than 0.13 mrem/hr during the worst-case operation 

and less than 0.013 mrem/hr during routine operations. On the main campus of the University, the 

dose rate would have decreased to less than about 0.00025 mrem/hr during routine operations. 

It is favorable to claimants to use the environmental external dose from synchrotron operations at the 

ALRR for full-time exposure (2,000 hr/yr) for all locations at 25 mrem/yr for the period from 1949 to 

1971.

4.3 AMES LABORATORY RESEARCH REACTOR OPERATIONS PERIOD, 1965 TO 1977

The ALRR started operations in February 1965 and continued through December 1977 (Ames 1967; 

Voigt 1981). The facility is surrounded by a fence about 700 ft from the reactor building, which 

designates what is on and off the site (see Figures 2-2 and 4-2). From review of dosimetry records, it 

seems evident that all employees working inside the ALRR fence were provided dosimeters. 

However, not all dosimetry records are identified with names. Therefore, not all workers at the ALRR 

have recorded doses. In addition, environmental doses from gaseous effluents released from the 

operating reactor were not monitored. However, environmental doses to the public from airborne 

releases were calculated and reported (Voss 1975, 1976, 1977). The only air monitoring station in the 

vicinity of the reactor was on the roof of the reactor building, as shown in Figure 4-3. 

Environmental Monitoring at Ames Laboratory: Calendar Year 1974 was the first annual report to 

provide gamma spectroscopy of environmental media samples (Voss 1975); subsequent annual 

reports (Voss 1976, 1977) provided similar results. The average release estimates from these reports 

were used to estimate the environmental dose to off-site workers from gaseous releases from reactor 

operations. From the effluent data, it was shown that the contribution to radioactivity in air from ALRR 

operations consisted principally of 41Ar and tritium (Voss 1975, 1976, 1977). An atmospheric 

dispersion model, which used annual average meteorological data for Ames and an exposure model 

(Napier et al 2004, Napier 2006b), was used to determine external dose rates from the 41Ar and 

inhalation intake estimates for the tritium. 

At the fence line location with the highest dose from gaseous effluents, the average annual dose to a 

person at this location for the entire year (8,760 hr) was estimated to be 4.2 mrem from 41Ar during the 

years of reactor operation. An off-site worker who worked full time at this location would not have 

been exposed for more than 2,080 hr/yr, which would result in a submersion dose of about 1 mrem/yr. 

At the fence line location with the highest concentration of tritium effluents, the average annual intake 

of tritium to a person at this location for the entire year (8,760 hr) was estimated to be about 2.9 μCi/yr 

during the years of reactor operation. An off-site worker who worked full time at this location would 

not have been exposed for more than 2,080 hr/yr, which would result in an intake of tritium of about 

0.7 μCi/yr or 2,700 pCi/d. 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 27 of 87

Figure 4-2. Ames Laboratory Research Reactor Site. Source: Voss (1974). 

4.4 AMES LABORATORY RESEARCH AND DEVELOPMENT ACTIVITIES, 1942 TO 

PRESENT 

R&D activities have been carried out at Ames Laboratory from 1942 to the present. It was the R&D 

capabilities of Iowa State College that attracted the attention of the Manhattan Engineer District in 

1942 (Ames 1960). Buildings owned by the government (AEC, the Energy Research and 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 28 of 87

Development Administration, and now DOE) in addition to the uranium/thorium, synchrotron, and 

research reactor buildings discussed above, are on the main campus of ISU (see Figure 2-1). 

Figure 4-3. Environmental monitoring in the vicinity of the ALRR. Source: Voss (1975).

The Ames Laboratory facilities consist of (Ames 1989): 

 Metals Development Building 

 Spedding Hall (formerly the Research Building) 

 Wilhelm Hall (formerly the Metallurgy Building) 

 TASF 

Facilities owned by ISU but leased to the Government include (Ames 1989): 

 Gillman Hall (formerly the Chemistry Building) 

 Zaffarano Physics Addition 

 Office and Laboratory Building 
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As can be seen in Figure 2-1, these R&D facilities are an integral part of the ISU campus and are, 

therefore, open to the staff, students, and public traffic [6]. There were no restrictions on the 

movement of this traffic outside the facilities. In addition, there was no monitoring of radiation 

exposure or contamination of the personnel or environmental areas around and among these 

facilities. There was little, if any, exposure of these personnel in that the quantities of radioactive 

materials involved in the R&D work were small and little, if any, were released to the environment 

among the facilities (Skoog 1952, p.4). 

There was insufficient information about releases from the R&D facilities to determine intakes directly. 

Principal sources would have been uranium, thorium, and fission products from the hot canyon/hot 

cell in the Research Building. Because of the smaller amounts of radioactive materials in the R&D 

facilities in comparison to the production facilities, the releases from the R&D facilities were assumed 

to be one one-hundredth of the releases from the production facilities [7]. That assumption resulted in 

daily environmental intakes of 5 × 10-2 and 7 × 10-4 pCi/d for uranium and thorium, respectively. A 

review of environmental intakes at other somewhat related sites (Argonne National Laboratory–East, 

Brookhaven National Laboratory, and Lawrence Berkeley National Laboratory) was made. Neither 

Argonne nor Brookhaven listed any environmental intakes of uranium or 232Th (ORAUT 2006a, 

2006e). The Berkeley Laboratory listed environmental intakes of unspecified gross alpha and gross 

beta emitters. From 1939 through 1999, the gross alpha intakes ranged from 6.6 × 10-3 to 2.7 × 10-1

pCi/d, and the gross beta intakes ranged from 1.5 x 10-1 to 63 pCi/d (ORAUT 2007b). The highest 

gross alpha intake occurred in 1996 and appears to be an anomaly; the second highest gross alpha 

intake was 5.9 × 10-2 pCi/d. So the proposed uranium intake is comparable to the second highest 

gross alpha intake from the Berkeley Laboratory, and therefore appears to be a reasonable upper 

bound. For environmental intakes for workers exposed around the R&D facilities, a daily intake of 5 × 

10-2 pCi of 234U and 7 × 10-4 pCi each of 232Th, 228Ra, and 228Th was assumed [8]. Because the nature 

of the research materials is not known, absorption types F, M, or S for the uranium and M or S for the 

thorium/radium isotopes were assumed [9].

A hot laboratory was operated in the Chemistry Building but replaced in 1951 by a “hot canyon/hot 

cell” in the Research Building. In the 1940s, the hot laboratory was used to study extraction of 

plutonium from irradiated uranium by means of ion exchange columns. A final report on plutonium 

R&D was published in July 1946 (Spedding 1947), at which time plutonium R&D and the staff who 

conducted it were transferred to Los Alamos (Payne 1992). “A hot laboratory, capable of handling 5 

curies through the adsorption process, was designed and built. The method proved successful in a 

number of runs. The uranium and plutonium were separated from one another and from the fission 

products using 1 kg samples of uranium, from the pile, which had an activity of 5 curies” (Spedding 

1947). Releases were estimated from this operation by making the following assumptions (see Bihl 

2006 for details of the calculation): 

 A total annual throughput of the lab of 50 Ci/yr 

 An airborne fraction of 0.002, for boiling liquids 

 Filtration efficiency for average particle sizes of 99.5% (high-efficiency particulates air filters 

(HEPAs) were just being developed during this period) 

These assumptions produce a total release of fission products of 5 × 108 pCi/yr. 

Using the least dispersive approach recommended by the NCRP in Publication 123 (NCRP 1996), the 

ground-level annual average air concentration would have been 13.2 pCi/m3. Using the inhalation 

rate of 2,400 m3/yr and converting to a daily intake, results in 87 pCi/d. 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 30 of 87

Using the recommended fission product ratios for 180-d cooled fuel from Fission and Activation 

Product Assignment for Internal Dose-Related Gross Beta and Gross Gamma Analyses (ORAUT 

2007d), 87 pCi/d intake of fission products is assigned to specific radionuclides as listed in Table 4-2. 

Table 4-2. Annual environmental 

fission product intakes from the hot 

laboratory in the Chemistry Building 

(1943 – 1981). 

Radionuclide

Relative 

fraction

Intake, 

pCi/d

Ce-141 0.0221 1.92

Ce-144 0.2191 19.1

Cs-134 0.0054 0.470

Cs-137 0.0208 1.81

Eu-155 0.0014 0.122

Fe-55 0.0172 1.50

Nb-95 0.2492 21.7

Pm-147 0.0546 4.75

Ru-103 0.0321 2.79

Ru-106 0.0844 7.34

Sr-89 0.0558 4.85

Sr-90 0.0157 1.37

Y-91 0.0911 7.93

Zr-95 0.1311 11.4

Because maximizing assumptions were used for most of the parameters in this analysis, the 

distribution is an upper bound (constant). The absorption type for each radionuclide that is most 

favorable to claimants, as listed in International Commission on Radiological Protection (ICRP) 

Publication 68 (ICRP 1995), should be used with the exception that only type F should be used for 

strontium. The date of first use of the hot laboratory was not found. Because it received fuel from the 

Chicago Pile, the earliest reasonable use would have been 1943 [10]. It was replaced by a hot cell 

with improved ventilation and filtration in the Research Building in 1951, which in turn was removed 

from service and decontaminated in 1982. Releases from the hot cell are not documented but 

certainly would have been smaller than those estimated above for the hot laboratory. It is favorable to 

claimants to apply the Table 4-2 intakes for each year from 1943 through 1981 [11]. 

4.5 SIGNIFICANT ENVIRONMENTAL EVENT 

The only significant environmental event in the history of the Ames Laboratory was the release to the 

environment from operations that occurred from July 1951 through August 1952 (AEC 1956). Metallic 

thorium was being produced from thorium nitrate tetrahydrate. During an early stage of the process, a 

filtrate with traces of thorium in the form of thorium nitrate and oxalate was released to the sewer that 

connected to the City of Ames sewer system. At the time disposal to the sewer was decided upon, it 

was believed that this waste had a very low level of radioactivity. However, due to a change in feed 

material supplied to the Laboratory, considerable quantities of mesothorium (228Ra) were being 

discharged in the filtrate. Mesothorium is one of the progeny of thorium decay; it decays by emitting 

gamma rays and beta and alpha particles. All sewage was processed in a complete-treatment 

sewage plant, which resulted in liquid effluent and dry sludge that was used for fertilizer. The liquid 

effluent contained negligible quantities of mesothorium. The dry product was spread on lawns at the 

sewer plant, airport, municipal parkway, and a cemetery. A thorough study of the incident disclosed 

that there was little hazard to the public or the employees of the sewer plant (AEC 1956). Table 4-3 is 

a summary of environmental dose measurements at the four facilities in Ames, Iowa: 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 31 of 87

Table 4-3. Environmental dose measurements at the four 

Ames facilities (mrem/y). Source: Voss 1979. 

Lawn site Maximuma Average

Sewer plant 780 400

Cemetery 440 350

Airport 530 350

Parkway 530 350

a. Background in central Iowa is about 300 mrem/yr. 

An aerial survey showed doses to be lower than those measured on the ground. Occupancy factors 

would reduce the doses in Table 4-3 by a large fraction, making them below the current public dose 

limit of 100 mrem/yr (10 C.F.R. pt. 20 2006).

All the locations in Table 4-3 are outside the ISU campus and all are accessible by the public except 

portions of the sewer plant. Most Ames Laboratory workers were not exposed to the radioactive 

materials released during this event and were not involved in responding to the event. However, the 

Ames Laboratory health physics staff responded to the release event and were exposed to the 

released radioactive materials while making radiation measurements and collecting environmental 

samples for analysis. It is reasonable to assume that radiation exposures to the health physics staff 

were monitored and offsite doses were included in their recorded occupational doses. Thus, no 

additional dose is recommended for occupational environmental dose for any workers. 

4.6 ENVIRONMENTAL CONTAMINATION, 1953 TO PRESENT 

Gamma spectral analysis of samples of environmental media was not initiated until November 1974 

(Voss 1974). By that time, uranium and thorium production and scrap recovery had ceased, and the 

Annex 1 Building had been demolished in 1953 (Karsjen 2003). Annex 2 operations had ceased in 

1953, and the building was razed in 1972 (Ames 1985). The synchrotron operations had ceased in 

1971, and the building was decommissioned in 1990 [12]. ALRR operations ceased in 1977 and D&D 

was completed in 1981 (Voigt 1981). Only R&D activities continued after 1981. 

Soil samples collected at five locations around the campus in 1974 showed only 137Cs in very low 

concentrations, as shown in Table 4-4. 

Table 4-4. Gamma analysis of soil samples (Voss 1975). 

Site Sample weight (g) Cs-137 (pCi/g)a

1S 336 0.839

2S 332 1.100

4S 500 1.100

6S 341 0.991

7S 426 0.286

Background 336 0.294

a. Gamma detection limit for Cs-137 in soil samples was 0.01 pCi/g. 

A summary of soil samples from 24 locations around the ISU campus in 1974 for alpha and beta 

particle activity is given in Table 4-5.

These analytical results are consistent with the low doses that the laboratory has reported over the 

years and with the position of not monitoring workers in the environs of the Ames Laboratory facilities. 

They are the basis for demonstrating that environmental intakes from contamination other than the 

uranium and thorium intakes already discussed were negligible. 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 32 of 87

Table 4-5. Summary of 24 soil samples for 

beta and alpha activity (pCi/g). (Voss 1975). 

Activity Betaa Alphab

Average 10.56 0.61

High 13.01 0.96

Low 7.66 0.38

Background 11.9 0.76

a. Beta detection limit was 0.25 pCi/g. 

b. Alpha detection limit was 0.10 pCi/g. 

4.7 SUMMARY OF ENVIRONMENTAL EXTERNAL DOSES AND INTAKES 

Tables 4-6 and 4-7 summarize the conclusions of the preceding sections concerning environmental 

external doses and intakes. 

Table 4-6. Summary of environmental external doses (to be applied only to unmonitored workers). 

Location Dates

Dose 

(mrem/yr)a Distribution

Skyshine from Synchrotron Building 1949–June 1971 25 Constant

41Ar from ALRR 1965–1977 1 Constant

All other R&D Buildings (see list in Section 4.4) All Negligible N/A

a. The energy range for all environmental external dose is assumed to be 100% 30-250 keV (NIOSH 2007b).

Table 4-7. Summary of environmental intakes.a 

Dates Radionuclide/absorption

Intake 

(pCi/d)

Distributio

n

July 1942–1953 U (assume U-234); type M or S 5 Constant

1954–present U (assume U-234); type F, M, or S 0.05 Constant

June 1943–April 1953 Th-232, Ra-228, Th-228; all type M 0.07 each Constant

1954–present Th-232, Ra-228, Th-228; type M or S 0.0007 each Constant

1965–1977 Tritium 2,700 Constant

1943–1981 Fission products per Table 4-2 Per Table 4-2 Constant

a. Apply the environmental intakes in this table if no occupational intakes are applied for the same 

radionuclide and the same period in accordance with the instructions in Table 5-7. 

5.0 OCCUPATIONAL INTERNAL DOSE

The radionuclides of interest for internal dose at Ames Laboratory are uranium, thorium, tritium, and 

fission products. Based on the Evaluation Report for Petition SEC-00038 (NIOSH 2006) for the 

period from January 1, 1942, through December 31, 1954, it was determined that internal doses from 

the production and casting of thorium metal for DOE employees or DOE contractor or subcontractor 

employees who worked in Chemistry Annex 1 (also known as the old women‟s gymnasium and Little 

Ankeny), Chemistry Annex 2, Chemistry Building (now Gilman Hall), Research Building, or the 

Metallurgical Building (now Harley Wilhelm Hall) for a number of workdays that total at least 250 

workdays, cannot be reconstructed. Therefore, only doses from thorium contamination left over after 

1954 are addressed here. 

Additionally, based on the Evaluation Report for Petition SEC-00075 (NIOSH 2007c) for the period 

from January 1, 1955, through December 31, 1970, it was determined that internal doses from the 

maintenance and renovation activities of the thorium production areas in Wilhelm Hall (a.k.a. the 

Metallurgy Building or “Old” Metallurgy Building) cannot be reconstructed for sheet metal workers, 

physical plant maintenance and associated support staff (includes all maintenance shop personnel of 

Ames Laboratory) and supervisory staff who were monitored, or should have been monitored, and 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 33 of 87

who were employed for at least 250 workdays. Therefore, internal doses from these activities to this 

class of workers cannot be assessed using the approach described in Section 5.2 below. 

5.1 URANIUM EXPOSURE 

Few data on uranium exposure were found (Ferretti, Price, and Schwartz 1951); however, the SEC 

petition evaluation report determined that doses could be estimated (NIOSH 2006). If uranium 

bioassay data are available for a worker, they should be used. However, because it is unlikely that 

uranium bioassay data will be available, default intakes were determined. Because even workplace 

sampling data was unavailable, this analysis used data from two recent documents: Battelle-TBD6000, Site Profiles for Atomic Weapons Employers (AWE) that Worked Uranium and Thorium Metals, 

and Battelle-TBD-6001, Site Profiles for Atomic Weapons Employers that Refined Uranium and 

Thorium (Battelle 2006a and 2006b) to estimate doses to workers in the Chemistry Building, Physical 

Chemistry Annex 1, and Annex 2 buildings. These two documents are considered representative of 

the potential intakes that workers at Ames Laboratory might have had because the processes were 

often developed at Ames Laboratory and still remained similar to the processes used at the AWE 

sites. The two processes that were used here to estimate doses are Reduction to Metal from BattelleTBD-6001 and Uranium Scrap Recovery and Casting from Battelle-TBD-6000. 

5.1.1 Estimating Internal Doses from Uranium Metal

Historical aspects of the production of uranium metal at Ames Laboratory are discussed in Section 2.0 

of this document. Although there was much historical information on the general methods for 

producing uranium metal (Spedding 1947), there was very little specific information useful for 

determining intakes from uranium. If uranium bioassay data are available for a worker, they should be 

used to estimate the intake. However, it is likely that bioassay data will not be available. In that case, 

the information below has been abstracted from Battelle (2006a) and Battelle (2006b) as methods for 

assigning internal dose to workers. 

The next two sections describe estimated doses for workers from January 1, 1942, through 

December 31, 1954. Additional information is provided to calculate dose to workers from radioactivity 

left over from the sites where uranium had been processed after 1954. Because there were 

numerous studies of various compounds of uranium during this period, all three absorption types (fast, 

moderate, and slow) were possible. 

5.1.1.1 Uranium Inhalation 

From 1942 through August 1945, individuals working in the Physical Chemistry Annex 1 (also known 

as Little Ankeny) can be assigned doses from inhalation of uranium [13]. Similarly, individuals who 

worked in the Chemistry Building during this period and individuals who worked in Physical Chemistry 

Annex 2 from 1944 through December 1945 should be assigned doses from inhalation of uranium 

[14]. Job titles of researchers acknowledged for their work in uranium production (found in Spedding 

1947), include: (1) chemist, (2) associate chemist, (3) junior chemist, (4) research assistant, (5) junior 

research assistant, (6) physicist, (7) analyst, (8) assistant physicist, (9) associate director, and 

(10) director. However, it is not entirely clear how much time these researchers spent in the area 

where the production was being performed. 

Because it is not clear if there were clerical, janitorial, nontechnical personnel, and other types of 

researchers working in these buildings, and it is not known what precautions might have been taken 

for contamination control, it can be assumed that all individuals who worked in the buildings had some 

potential for exposure to uranium. 
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The data in Tables 5-1 and 5-2 was derived from data in Battelle (2006a) and Battelle (2006b). In 

Battelle (2006b), there is a description of the reduction to metal that is similar to the process used at 

Ames Laboratory for production of uranium metal (Spedding 1947). The primary difference appears 

to be that at Ames Laboratory the process used granulated calcium metal and at the AWE sites the 

process used magnesium. Spedding (1947) also describes the process using magnesium, and it 

appears to be similar enough to be representative of the intakes at Ames Laboratory. 

Battelle (2006b) provides data for multiple stages of the production operation and four categories of 

workers. However, review of Ames Laboratory documentation did not reveal any information specific 

enough for determination of who would be responsible for what aspects of the process and for how 

long. Therefore, the value used for determining inhalation intakes was taken from Table 8.29 in 

Battelle (2006b) and is for the Metal Reduction Bomb Preparation for an operator that works a 48-hr 

week. This value was the highest intake rate for the metal reduction process. This number is then 

scaled for the potential for intake (see Table 5-1). 

Battelle (2006a) provides data for a process of scrap recovery that is similar to the scrap recovery 

described in Spedding (1947). Data from Battelle (2006a, Table 7.8) are used in Table 5-1 for Ames 

Laboratory workers who worked in the Physical Chemistry Annex 2 building. The value used from 

Table 7.8 in Battelle 2006a represents the most conservative intake for the scrap recovery operations, 

similar to those performed in Physical Chemistry Annex 2.

For workers involved in research only from January through July 1942 in the Chemistry Building, an 

exposure of one-tenth of that of the workers involved in the production operations was assumed, 

which corresponds to smaller quantities of uranium [15]. There are very few details on the research 

activities that occurred in the Chemistry Building after July 1942; therefore, it was assumed that the 

one-tenth fraction applied to the researchers in the Chemistry Building through 1953. 

Individuals supervising the production processes were assumed to be exposed for one-fourth of the 

time of the production staff [16]. 

For workers not directly associated with uranium metal research or production, an exposure of 

one-tenth of that of the supervisors was assumed (see Table 5-1) [17]. 

Table 5-1. Uranium intakes from inhalation (pCi/d). 

Period

Chemistry 

Building

Physical Chemistry 

Annex 1

Physical Chemistry 

Annex 2

January 1942–June 1942 85a,b N/A N/A

July 1942–August 1945 8.5a,b 853b N/A

January 1944 – December 1945 See above See above 6,061b

September 1945–December 1950 8.5a,b N/A 6,061

January 1951-December 1953 8.5a,b N/A 5,556b

a. No data was available for determination of intakes in the Chemistry Building, therefore it was assumed that research 

activities would have one-tenth of the intake of that of production activities, and the research activities on uranium after 

uranium metal production ended would be one-tenth the intakes of the original research. 

b. Values are for workers assumed to work in research or production full time. For supervisors, assume one-quarter of the 

intake; for all other employees (clerical, janitorial, security, etc), assume one-tenth of the supervisor‟s intake. 

The intakes in Table 5-1 were compared to the few actual bioassay results found for workers in 

approximately the same time period. Chapter 7 in Stone (1951), titled “Uranium Excretion Studies,” 

provided data from a series of uranium bioassay obtained from Ames workers in 1944 and 1945. Of 

special interest were a series of samples taken from the supposedly highest exposed worker at Ames 

and samples taken from the most highly exposed group of workers at Ames (21 samples from 11 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 35 of 87

workers). An intake evaluation was performed on the results for the highest exposed worker 

assuming chronic intake from the start of that person‟s employment at Ames and assuming absorption 

type M uranium (the document indicated that the person was exposed to UF4). The estimated intake 

was 1,200 μg/d or 820 pCi/d assuming natural uranium. This is consistent with the intake estimate in 

Table 5-1 for Annex 1 and quite a bit lower than for Annex 2. The average bioassay result for the 

group of highest exposed workers was 75 μg/L. Assuming chronic intake for 1 yr prior to the 

bioassay, the estimated intakes were 

 Absorption type F: 390 μg/d, 260 pCi/d 

 Absorption type M: 1,670 μg/d, 1,100 pCi/d 

 Absorption type S: 45,400 μg/d, 31,000 pCi/d. 

If the geometric mean of the data is used, the estimated intakes are smaller; if the highest bioassay 

result of the set is used, the estimated intakes are 2.7 times greater. For type M this range is still 

consistent with the intakes in Table 5-1. The type S intake estimates are greater than those in Table 

5-1 but it is unlikely that anyone was actually exposed to just type S for long periods. UF4 and metal 

were the principal forms of uranium in the production facilities. 

Another small set of urinalysis data was found involving 5 or 6 samples from 6 workers during July 13 

to September 4, 1944 (Tybout 1944). The data were hard to read and most results were listed as 

0.00 mg/L. Using the data from the worker with the highest result and the most nonzero results and 

assuming chronic intake for 1 yr of absorption type M uranium, the estimated intake was 850 μg/d 

(580 pCi/d). The estimated intake was slightly less if the intake period started in August 1942. These 

results provide a measure of confidence that the default intakes in Table 5-1 are favorable to 

claimants [18]. 

5.1.1.2 Uranium Ingestion 

As discussed in Battelle (2006b), ingestion intakes are determined using NIOSH (2004) and are 

shown in Table 5-2. To describe this process in brief, the daily ingestion rate from food contamination 

is given by 

 .0 0985AI

, where I is the daily ingestion rate in picocuries per day and A is the average 

air concentration in picocuries per cubic meter. The ingestion rate I must be adjusted for the fact that 

the Integrated Modules for Bioassay Analysis (IMBA) assumes chronic intakes, even during 

weekends, and that the number of hours worked in a year changed over time (Strom 2006). The 

adjustments result in an IMBA chronic intake rate 

I Ah 5

IMBA .3 10373





 where IIMBA is the daily intake 

and A is the median air concentration using the specified units, and h is the number of hours in a 

working year. Making similar adjustments to Neton‟s equations for incidental hand-to-mouth ingestion 

(NIOSH 2004), the chronic IMBA daily intake rate is 

I Ah 5

IMBA .3 10425





 where IIMBA is the daily 

chronic intake rate, A is the median dust concentration, and h is the number of hours in a work year. 

The total ingestion rate is the sum of the food contamination and incidental hand-to-mouth ingestion 

rates and is 

I

I Ah 5MBA .6 10798





 where the variables are the same as previously defined. This 

intake applies to the period from 1942 through August 1945. The same rationale used in Table 5-1 for 

reduced fractions for other workers is applied in Table 5-2. 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 36 of 87

Table 5-2. Uranium intakes from ingestion (pCi/d). 

Period

Chemistry 

Building

Physical Chemistry 

Annex 1

Physical Chemistry 

Annex 2

January 1942–June 1942 0.87a b N/A N/A

July 1942–August 1945 0.08a b 8.7b N/A

January 1944 – December 1945 See above See above 124 b

September 1945–December 1950 0.08a b N/A 124 

January 1951-December 1953 0.08a b N/A 114 b

a. No data was available for determining intakes in the Chemistry Building; therefore, it was assumed that research 

activities would have one-tenth of the intake of that of production activities, and the research activities on uranium after 

uranium metal production ended would be one-tenth the intakes of the original research. 

b. Values are for workers assumed to work in research or production full time. For supervisors, assume 0.25 of the intake; 

for all other employees (clerical, janitorial, security, etc), assume one-tenth of the supervisor‟s intake. 

5.1.1.3 Resuspension During Periods with No Uranium Operations 

As described in Battelle (2006b), there was a potential for internal exposure to resuspended material 

from the AEC work during non-AEC operations soon after the actual operations. To estimate 

exposure from resuspended materials, this analysis assumed that surfaces in the building became 

contaminated by deposition of uranium dust during operations similar to metalworking operations. 

The estimate used here assumes the maximum intake from inhalation for the researchers in uranium 

metal production (Chemistry Building), the metal production operations (Annex 1), and scrap recovery 

(Annex 2). The method used in Battelle (2006b) was applied to the maximum intake described for 

each process. Table 5-3 shows the intake in picocuries per day for each building for the specified 

periods. The annual inhalation intake from resuspension of deposited material for a worker in the 

Chemistry Building, Physical Chemistry Annex 1, and Annex 2 buildings, assuming the worst-case air 

concentrations for a 1-yr working operation, is shown in Table 5-3. These intakes apply to anyone in 

the building regardless of job description. For ingestion, NIOSH (2004) indicates that the ingestion 

rate, in terms of disintegrations per minute for an 8-hr workday, can be estimated by multiplying the air 

concentration in disintegrations per minute per cubic meter by a factor of 0.2. The ingestion intakes 

are also provided in Table 5-3. 

Table 5-3. Resuspension during periods with no uranium operations (pCi/d). 

Period

Chemistry Building

inhalation/ingestion

Physical Chemistry 

Annex 1

inhalation/ingestion

Physical Chemistry 

Annex 2

inhalation/ingestion

September 1945–December 1953 N/A 17.5/1.6 N/A

January 1954–May 1976 1.8/0.16 N/A 124.7/11.2 (only 

through 1972), then 0

a

a. The Physical Chemistry Annex 2 building was razed in 1972. 

5.1.1.4 Uranium Excretion Plots for Use with Bioassay Data 

Figures 5-1, 5-2, and 5-3 are plots for expected urinary excretion assuming chronic intakes at the 

highest intake values (scrap recovery) for both inhalation and ingestion, for chronic intake periods of 

365, 730, and 1,826 d, respectively. If bioassay results are available for a worker, they can be 

compared to the excretion curves in the figures if efficiency techniques are being used; for instance, 

for a noncompensable efficiency case based on the default intakes, the energy employee‟s actual 

bioassay should be less than the applicable curve in the figures [19]. F, M, and S are defined as fast, 

medium, and slow, respectively, in the figures. 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 37 of 87

5.2 THORIUM EXPOSURE FROM THORIUM CONTAMINATION AFTER 1954 

As discussed in Section 1.3, NIOSH determined that it was not feasible to complete dose 

reconstruction for internal dose for thorium, plutonium, and thoron for 1942 through 1954 (NIOSH 

2006) and, therefore, internal dose is not addressed here for those radionuclides during those years. 

Research was conducted using small quantities of plutonium (micrograms) in the 1940s, and it 

involved methods of extraction of plutonium from up to 5 Ci of fission products in irradiated fuel, which 

would not have contained much plutonium (Spedding 1947). There is no indication of research that 

involved sufficient plutonium such that exposure to plutonium after 1954 would have been significant. 

However, one building, Wilhelm Hall at Ames Laboratory, was the location of the main activities with 

thorium and is still in use. As discussed in Section 1.3, it is not feasible to determine internal doses 

for sheet metal workers, physical plant maintenance and associated support staff (includes all 

maintenance shop personnel of Ames Laboratory), and supervisory staff who performed maintenance 

and renovation activities in Wilhelm Hall (Old Metallurgy Building) during the period of January 1, 

1955, through December 31, 1970. This method can be used however, to provide an estimate of 

internal exposures for others who performed work in this building. 

In March of 1952 a study was performed in Wilhelm Hall to identify health and safety issues that were 

occurring during refining and thorium metal production. The results of the study are in a document 

titled Ames Research Laboratory Occupational Exposure to Thorium and Beryllium (Klevin 1952). 

Starting in 1984 and continuing through the early 1990s, surveys were conducted in Wilhelm Hall to 

determine locations of contamination left over from the early production years. This information is 

described in Hokel et al. (1998). The following discussion using data from both Hokel and Klevin 

provides an estimate for intakes by workers in Wilhelm Hall from 1955 to the present. A summary of 

the air concentrations and daily inhalation and ingestion intakes are provided in Table 5-4.

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

10 100 1000 10000

Days Since Start of Chronic Intake

Excretion, pCi/d 

Type F

Type M

Type S

Figure 5-1. Urinary excretion of uranium expected from 365-d 

chronic intake at 6,061 pCi/d inhalation and 124 pCi/d ingestion. 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 38 of 87

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

10 100 1000 10000

Days Since Start of Chronic Intake

Excretion, pCi/d 

Type F

Type M

Type S

Figure 5-2. Urinary excretion of uranium expected from 730-d 

chronic intake at 6,061 pCi/d inhalation and 124 pCi/d ingestion. 

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

10 100 1000 10000

Days Since Start of Chronic Intake

Excretion, pCi/d 

Type F

Type M

Type S

Figure 5-3. Urinary excretion of uranium expected from 1,826-d 

chronic intake at 6,061 pCi/d inhalation and 124 pCi/d ingestion. 

Table 5-4. Air concentrations and daily intakes of 232Th at Wilhelm Hall 

after 1954. 

Year t (yr)

Air 

concentration 

(dpm/m3)

Chronic 

inhalation 

intake (pCi/d)

Chronic 

ingestion intake 

(pCi/d)

1955a0.5 448 1330 40.4

1956a1.5 392 1160 35.3

1957a2.5 343 1020 30.9

1958a3.5 300 887 27.0

1959a4.5 262 776 23.6

1960a5.5 229 679 20.6

1961a6.5 200 594 18.1

1962a7.5 175 519 15.8

1963a8.5 153 454 13.8

1964a9.5 134 397 12.1

1965a10.5 117 347 10.6

1966a11.5 103 304 9.24
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 39 of 87

Year t (yr)

Air 

concentration 

(dpm/m3)

Chronic 

inhalation 

intake (pCi/d)

Chronic 

ingestion intake 

(pCi/d)

1967a12.5 89.7 266 8.08

1968a13.5 78.4 232 7.07

1969a14.5 68.6 203 6.18

1970a15.5 60.0 178 5.40

1971 16.5 52.5 155 4.73

1972 17.5 45.9 136 4.13

1973 18.5 40.1 119 3.61

1974 19.5 35.1 104 3.16

1975 20.5 30.7 90.9 2.76

1976 21.5 26.8 79.5 2.42

1977 22.5 23.5 69.5 2.11

1978 23.5 20.5 60.8 1.85

1979 24.5 18.0 53.2 1.62

1980 25.5 15.7 46.5 1.41

1981 26.5 13.7 40.7 1.24

1982 27.5 12.0 35.6 1.08

1983 28.5 10.5 31.1 0.946

1984 29.5 9.18 27.2 0.827

1985 30.5 8.03 23.8 0.724

1986 31.5 7.02 20.8 0.633

1987 32.5 6.14 18.2 0.553

1988 33.5 5.37 15.9 0.484

1989 34.5 4.70 13.9 0.423

1990 35.5 4.11 12.2 0.370

1991 36.5 3.59 10.6 0.324

1992 37.5 3.14 9.31 0.283

1993 38.5 2.75 8.14 0.248

1994 39.5 2.40 7.12 0.217

1995 40.5 2.10 6.23 0.189

1996 41.5 1.84 5.45 0.166

1997 42.5 1.61 4.76 0.145

1998 43.5 1.41 4.17 0.127

1999 44.5 1.23 3.64 0.111

2000 45.5 1.08 3.19 0.0969

2001 46.5 0.941 2.79 0.0847

2002 47.5 0.823 2.44 0.0741

2003 48.5 0.719 2.13 0.0648

2004 49.5 0.629 1.86 0.0567

2005 50.5 0.550 1.63 0.0496

2006 51.5 0.481 1.43 0.0434

2007 52.5 0.421 1.25 0.0379

2008 53.5 0.368 1.09 0.0332

2009 54.5 0.322 0.953 0.0290

2010 55.5 0.282 0.834 0.0254

a. Dose Reconstructors should not use data from 1955-1970 to determine 

 internal doses for employees who are part of the special exposure cohort 

 class defined in SEC-00075 (NIOSH 2007c).

All of the data in Hokel was reviewed and considered. Much of the data was related to locations that 

were hard to access and considered not to be of an issue for inhalation. There was one set of data 

that had floor surveys made in 1988, but these locations all had fixed activity, indicating that this was 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 40 of 87

from beta radiation (see Appendix 6 of Hokel). For this reason, the recommendation for assessing 

dose from thorium from 1954 through the present was provided. The accessible areas of the building, 

including the rooms, air ducts, hallways, stairwells, transformer rooms, etc., were surveyed starting in 

1984. The data in Hokel et al. (1998) present an overview of the survey results. In 1996, some 

measurements were made using an Alpha Continuous Air Monitor in the subbasement pipe tunnels 

and in large vertical void spaces in the stairwells. All of these results were less than background for 

thorium, thoron, or radon (Hokel et al. 1998). Therefore, the results used for this estimation are from 

a pipe tunnel survey that showed removable contamination on smears ranging from background (3 

dpm) to 1,224 dpm. These numbers are considered high for generally accessible areas and with the 

possibility of the contamination becoming resuspended. Although other survey numbers in the report 

with removable contamination are higher, they are in locations that are inaccessible (in a drain line), 

hard to reach (inside a drawer), or small (edge of a sink), or the contamination was fixed. 

Hokel et al. (1998) stated that the thorium in Wilhelm Hall is in equilibrium. 

For estimating dose to individuals working in Wilhelm Hall from 1955 to the present, an intake 

estimate favorable to claimants would be as follows: 

A removable surface concentration of 2,000 dpm/100 cm2 of thorium in equilibrium with its progeny 

was assumed [20]. This means that the 232Th activity was approximately 200 dpm/100 cm2. Applying 

a resuspension factor of 10-4 [21]: 

Air concentration = (200 dpm/100 cm2)(10-4/m )(100 × 100 cm2/m2) = 2 dpm/m3

The value of 2 dpm/m3 on 11/15/1995, when the survey of the pipe tunnel occurred, represents an 

upper bound. 

To estimate residual air concentrations for other years, a single exponential decay of “available” 

activity over time in a facility was used. This applies to a facility in which the contamination is mostly 

undisturbed, but undergoes some weathering or occasional cleaning, maybe minor moving of 

equipment or work benches followed by cleaning, etc. This method of internal dose estimation does 

not apply to workers in the special exposure cohort class described in SEC-00075 (NIOSH 2007c).

Klevin (1952) did a thorough survey during operations, including breathing-zone task-specific air 

concentrations, time-weighted air concentrations for various workers, and general room air 

concentrations. Because survey information in the building just after cessation of the thorium 

operations was not available, the Klevin data was used to represent air concentrations in 1955 with 

some caveats provided below: 

1. The Klevin air concentrations for specific tasks during production and the time-weighted 

averages are not relevant for Wilhelm Hall after 1954. The general room concentrations would 

probably be a bit high, but reasonably representative when applied to long-term chronic 

intakes for people not actually performing tasks with thorium. These can be assumed to 

represent air concentrations in 1955. 

2. The general room air concentrations included one room that was 10 times higher than all the 

others and included the lunch room. The highest room was clearly related to operations so 

that datum was excluded as was the lunch room which was assumed not to be contaminated 

(the result was zero). With these results removed, the geometric mean of the distribution was 

7.9 dpm/m3 and the 95th percentile was 479 dpm/m3. 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 41 of 87

Because the 2 dpm/m3 used from the Hokel document represented an upper bound, this value is 

compared with the 479 dpm/m3 value. With 479 as Ao and 2 as A(t) and assuming t is from 1/1/1955 

to 11/15/1995 for a total of 14,929 days, 

A(t) = Aoexp(-λt). λ = 3.7E-4/d or 0.134/yr. 

A(t) was solved for the midpoint of each year from 1995 to present. The air concentration was 

converted to intake using 

intake (pCi/d) = (air conc. dpm/m3)(1 pCi/2.22 dpm)(1.2 m3/hr)(2000 hr/yr)/365d/yr) 

The estimates in Table 5.4 for 232Th assumes an occupancy factor of 1 (100% for a working year). 

This is considered an upper bound (constant) estimate for thorium intakes for individuals who worked 

in accessible areas in Wilhelm Hall from January 1955 to the present. 

The dose reconstructor needs to include equal intakes of 228Ra and 228Th to account for the progeny 

radionuclides [22]. The associated ingestion intakes would be: 

(0.2)(air concentration in dpm/m3) ÷ 2.2 dpm/pCi = X pCi/d each for 232Th, 228Ra, and 228Th. 

The annual ingestion intakes are also shown in Table 5-4.

Workers occasionally entered areas with higher concentrations under Radiation Work Permits to 

perform maintenance or remodeling. However, the spotty contamination in these areas was about 10 

to 100 times greater than the value used in the calculation above [23]. Based on the rarity of 

exposure and the radiation protection measures used (including respiratory protection), the impacts 

from these possible acute intakes would have been adequately accounted for by the chronic intake 

scenario provided in Table 5.4 [24]. However, this assumption is not valid for the class of employees 

described in SEC-00075 (NIOSH 2007c)., 

5.3 TRITIUM EXPOSURE

The ALRR operated from February 1965 through December 1977. The reactor was then 

decommissioned, which was completed in 1981. The ALRR was a 5-MW, heavy-water-moderated 

research reactor. See Section 2.1.10 for more information on the reactor operations. Because of 

operation of the reactor, tritium is the primary radionuclide that must be considered for internal dose. 

No other radionuclides were considered internal dose hazards from the operation of the reactor. A 

routine bioassay program was established in 1965; bioassay data for workers were collected and 

recorded through at least 1981 while the reactor was being decontaminated and decommissioned 

(Voss 1971). 

5.3.1 Tritium Exposure for Monitored Workers, 1965 to 1981

A number of reports addressed tritium dose assessment. Highlights of those reports are given here 

and referenced for further study by the dose reconstructor. 

A document titled Program for Monitoring Personnel for Tritium, Sources of Tritium at the Ames 

Laboratory describes the potential sources of tritium exposure to Laboratory personnel (Voss 1971). 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 42 of 87

In addition to the reactor, Ames Laboratory had a Texas Nuclear Model 9900 Neutron Generator, 

which was a potential source of exposure to tritium. The neutron generator used tritium targets with 

activities ranging from 5 to 10 Ci. The tritium, which was slowly released from the target, was 

documented as a potential airborne contaminant (Voss 1971). Other possible sources of tritium were 

spent targets from the neutron generator, tritium gas in cylinders, and tritiated compounds that would 

have only been present occasionally (Voss 1971). 

The Voss (1971) document is summarized here to help understand the dose records that might be in 

the worker‟s files. It stated that workers and other personnel who were part of the tritium monitoring 

program included: 

1. Reactor operators (monthly samples). 

2. Reactor operators involved in specific operations that were likely to cause tritium exposures 

(sampled during and after the operation). 

3. Other reactor personnel and other personnel assigned to work at the reactor (provide samples 

on a semiannual basis for routine checks on tritium uptake). 

4. Personnel described in (3) who were involved in operations in which the tritium exposure 

conditions existed (sampled during and after the operation). 

5. Other personnel under conditions of potential tritium exposure (monitored on the basis of their 

work with sources of tritium). 

6. All personnel who showed tritium concentration greater than 1,500 dpm/min/mL of urine were 

resampled weekly until the detected activity level is below 1,500 dpm/min/mL of urine. 

7. Samples were taken at the termination of employment of persons assigned to work areas 

where monitoring for tritium is required. 

8. As a check and control, termination samples were taken from other personnel as well (it is not 

clear if it was all personnel or just some personnel). 

The document stated that liquid scintillation counting was used for tritium bioassay analysis (Voss 

1971). 

Assumptions described in the document (Voss 1971) used for radiation dose determination were: 

1. The concentration of tritium was the same in all body water. Urine samples were used as 

representative of all body water in terms of tritium activity levels. The radiation dose was 

considered to be for the whole body. 

2. The radiation dose was due to tritium as tritiated water; other compounds of tritium and other 

organ configurations are not included. Except in unusual circumstances, tritiated water was 

the expected source of exposure. Body water was then the critical organ. 

3. For calculation and derivation consistency, the mass of body water was taken as 43 kg 

(standard man value). 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 43 of 87

4. The effective half-life for dose determination could vary. The actual half-life from the data 

points was used up to a half-life of 15 d. If the half-life could not be determined from the data, 

a value of 12 d was used. The data points that showed a half-life greater than 15 d were 

treated as additional separate exposures. 

5. The quality factor was 1, the effective absorbed energy per disintegration was 0.006 MeV, the 

half-life of tritium was 12.26 yr (4.48 × 103 d). 

Other considerations for assignment of dose that were discussed in the document (Voss 1971) are: 

1. The dose assignment system had two separate conditions of radiation dose delivery to the 

body: (a) The dose delivered by the uptake of tritium from time t = 0 until complete decayremoval (t = ∞). Additional uptakes that occur during the decay-removal of the preceding 

uptakes, and (b) the radiation dose that would be delivered by maintenance of a fixed level of 

tritium in the body. 

2. For anyone with a bioassay sample greater than 1,500 dpm/min/mL in urine, sampling 

continued until the urine sample level was less than 1,500 dpm/min/mL. 

3. For any person on the routine and incident monitoring program, a basic dose assignment was 

made. This basic dose was that associated with the maintenance of a level of 

750 dpm/min/mL of urine, which was equal to 38 mrem/yr whole body based on the 

methodology used at the time. 

4. For single or multiple exposures, the dose assessment was made on the basis of the effective 

half-life applicable to the individual‟s data. The dose contribution from the incident exposure 

that would appear in the basic dose assignment was subtracted from the basic dose 

assignment. 

5. The final reported dose was that due from an incident exposure plus the residual dose from 

the basic dose assignment. In summary, a person on the tritium monitoring program was 

assigned a basic radiation dose of 38 mrem/yr (prorated for a fraction of a year) to which was 

added the adjusted radiation dose contribution from all other exposures received during the 

year. 

A number of other documents discussed tritium dose assessment, but they are all similar to the 

information provided above. A document titled Personnel Monitoring Program provides the Tritium 

Dose Calculation Procedures used at the time (Voss 1974). 

Personnel on the tritium monitoring program should have bioassay and dose records. Tritium 

bioassay records were found for 1965 through 1981, although those for 1965 through 1968 appear to 

be incomplete. 

Figures 5-4 and 5-5 show examples of what a bioassay record in a worker‟s file might look like. The 

data that can be found in this record include: 

1. The year being reported. 

2. The badge number of the individual (Note: It appears that an individual would retain the same 

badge number during employment, but once they terminated, that badge number would be 

reassigned to a new employee.). 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 44 of 87

3. The name of the individual. 

4. Dates during the reporting period for which monitoring for incidents was performed and the 

result was in “DPM.” It is assumed that incidents were operations that were performed and 

sampling was based on potential for intake. 

5. Date that individual was employed. 

6. The individual‟s dose before January 1 of the year for the record. 

7. If the person has terminated, the termination date will be on the record. 

8. The four quarters for the year will be shown. The example in Figure 5-4 is for the first quarter 

and shows dose for quarter 1. For each subsequent quarter, the dose would be added and 

the total for the year calculated. It can be assumed that a “0.00” means the worker was not 

monitored, and not necessarily that there was no dose. 

Documents from the early 1970s (Voss 1971; Ames 1974) indicate that a person on the tritium 

monitoring program would have been assigned a default radiation dose of 38 mrem/yr (or it would 

have been prorated for the time monitored during the year); however, a review of the available dose 

records indicated that the policy to assign a 38-mrem/yr dose to everyone on the tritium program was 

not always followed. 

No information was found that indicated the analysis method or the minimum detectable activity 

(MDA); therefore, it is recommended that 0.1 μCi/L (220 dpm/mL) be used as the MDA. This is a 

reasonable assumption compared to MDAs at other sites during this period and is consistent with the 

way the data were recorded [25]. 

5.3.2 Tritium Dose to Workers, 1982 to Present

An interoffice memorandum (Struss 1987) dated May 8, 1987, addresses radiation dose at the 

Applied Science Center building (inhalation exposure from tritium as tritiated water vapor in air 

resulting from deposition during reactor operations). The memorandum addresses the methodology 

for estimation of dose to an individual in the reactor room assuming 100% occupancy without forced 

ventilation, based on the standard man inhalation rates in BRH (1970). There is also an estimate for 

a maximum dose of 5.8 mrem/yr to an individual in the pump room. In a letter dated May 27, 1987, R. 

G. Struss, Associate Director for Operations, Ames Laboratory, discussed another estimate for 

airborne tritium concentrations that indicated an exposure potential of 8.6 mrem/yr in the reactor pump 

room for a 40-hr workweek (Struss 1987). 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 45 of 87

Figure 5-4. Bioassay record example 1. 

Figure 5-5. Bioassay record example 2. 

The dose reconstructor can consider assigning a dose of 8.6 mrem/yr for personnel working in the 

Applied Science Center building in either the reactor room or the pump room if there are no bioassay 

data available. 

5.3.3 Tritium Dose to Unmonitored Workers, 1965 to 1981

A coworker analysis of worker tritium bioassay was conducted on bioassay samples from 1965 

through 1981 to provide default doses for unmonitored workers. Results of the coworker analysis are 

shown in Table 5-5, columns 2 and 3. If there is an indication that an energy employee worked in the 

ALRR during 1965 through 1981 but was not monitored for tritium, the annual doses listed in 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 46 of 87

Table 5-5, column 4, should be assigned. These doses apply to all organs. Assume a lognormal 

distribution with the geometric standard deviations (GSDs) as shown in Table 5-5, column 5. 

Table 5-5. Results of tritium coworker analysis [26]. 

Year

Coworker results Assigned values

Annual dose

(mrem) GSDa

Annual dose

(mrem) GSDa

1965 0.44 1.6 0 N/A

1966 0.54 1.5 1 3

1967 0.46 1.9 0 N/A

1968 0.23 2.3 0 N/A

1969 1.9 7.9 1.9 7.9

1970 0.88 6.9 1 6.9

1971 1.3 15 1.3 15

1972 1.3 12 1.3 12

1973 1.2 18 1.2 18

1974 1.9 8.1 1.9 8.1

1975 1.3 17 1.3 17

1976 1.0 9.5 1.0 9.5

1977 1.6 25 1.6 25

1978 1.7 11 1.7 11

1979 1.0 7.5 1.0 7.5

1980 1.0 9.8 1.0 9.8

1981 1.1 4.7 1.1 4.7

a. Use a geometric standard deviation of 3.0 if the calculated value is less than 3 in Table 5-5 

The tritium coworker doses were determined using methods described in Analysis of Coworker 

Bioassay Data for Internal Dose Assignment (ORAUT 2005b) and Tritium Calculated and Missed 

Dose Estimates (ORAUT 2004). Each annual dose was the geometric mean of the lognormal 

distribution fitted to the distribution of individual workers„ annual doses. Figure 5-6 shows an example 

distribution and fit for 1970. Annual doses less than 1 mrem are considered insignificant and can be 

ignored when assigning doses; a minimum GSD of 3.0 was assigned if the calculated value was less 

than 3. 

5.4 FISSION PRODUCT INTAKES 

5.4.1 Fission Product Intakes from Early Fuel Research

As described in Section 4.4, a hot laboratory was operated in the Chemistry Building; it was replaced 

in 1951 by a hot canyon/hot cell in the Research Building. In the 1940s, the hot laboratory was used 

to study extraction of plutonium from irradiated uranium by means of ion exchange columns. “A hot 

laboratory, capable of handling 5 curies through the adsorption process, was designed and built. The 

method proved successful in a number of runs. The uranium and plutonium were separated from one 

another and from the fission products using 1 kg samples of uranium from the pile, which had an 

activity of 5 curies” (Spedding 1947). Intakes by workers in the hot laboratory were estimated using 

the approach for calculating intakes described in NUREG-1400, Air Sampling in the Workplace (NRC 

1993). 

The equation from NUREG-1400 is: 

I = Q × 10-6 × R × C × D 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 47 of 87

Figure 5-6. Distribution of worker doses from tritium in 1970. 

where 

I = intake 

Q = source term for one year = assumed to be 50 Ci/yr 

R = release fraction = 0.01 for a liquid (the material comes in as a solid, but would be liquefied 

for research activities) 

C = confinement factor = 0.1 assuming material was handled in some containment 

D = dispersibility factor = 10 for heating or chemical reactions 

I = 50 × 10-6 × 0.01 × 0.1 × 10 = 5 × 10-7 Ci/yr = 5 × 105 pCi/yr 

= 5 × 105 pCi/yr/365d/yr = 1,370 pCi/d 

As described in Section 4.0, using the recommended fission product ratios for 180-d cooled fuel from 

Fission and Activation Product Assignment for Internal Dose-Related Gross Beta and Gross Gamma 

Analyses (ORAUT 2007d), the 1,370 pCi/d intake of fission products is assigned to specific 

radionuclides as listed in Table 5-6. 

Because maximizing assumptions were used for most of the parameters in this analysis, the 

distribution is an upper bound (constant). The absorption type for each radionuclide that is most 

favorable to claimants, as listed in ICRP Publication 68 (ICRP 1995), should be used, with the 

exception that only type F should be used for strontium [27]. The date of first use of the hot laboratory 

was not found. Because it received fuel from the Chicago Pile, the earliest reasonable use would 

have been 1943. The hot laboratory was replaced by a hot cell, with complete separation of the 

source term from workers, in the Research Building in 1951. Intakes from the hot cell would have 

been negligible [28]. 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 48 of 87

Table 5-6. Default annual fission 

product intakes for Researchers from 

hot laboratory in the Chemistry 

Building (1943-1951). 

Radionuclide

Relative 

fraction

Intake 

(pCi/d)

Ce-141 0.0221 30.3

Ce-144 0.2191 300

Cs-134 0.0054 7.4

Cs-137 0.0208 28.5

Eu-155 0.0014 1.9

Fe-55 0.0172 23.6

Nb-95 0.2492 341

Pm-147 0.0546 74.8

Ru-103 0.0321 44

Ru-106 0.0844 115.6

Sr-89 0.0558 76.4

Sr-90 0.0157 21.5

Y-91 0.0911 124.8

Zr-95 0.1311 179.6

5.4.2 Fission Product Intakes from Research Reactor Operations and Decontamination 

and Decommissioning

There was no evidence found during review of any of the Ames Laboratory documents that bioassay 

was performed or considered necessary for radionuclides other than tritium for the ALRR. Review of 

one document, Decommissioning of the Ames Laboratory Research Reactor (Voigt 1981), indicated 

that there was a negligible amount of fission products in the building after shutdown. This indicates 

that there was probably also a negligible amount of fission products released during reactor 

operations; therefore, accounting for internal dose from the reactor operations is not necessary. 

During D&D operations, radiation protection appeared to be acceptable for the time (Ames 1981) and 

external exposure and internal exposure for tritium was tracked. There is no evidence that bioassay 

for other radionuclides was performed. However, during D&D of the reactor, which included 

dismantlement, cutting, grinding, etc., it can be expected that some intakes from activation products 

occurred. 

A reasonable estimate of intakes from D&D of the reactor can be made by using the gross beta air 

concentration limit from 1977 (1 × 10-9 μCi/mL) (DOE 1977) based on the most conservative beta 

emitter (90Sr). 

For workers involved in the actual decontamination or demolition we assumed: 

(1 × 10-9 μCi/mL) (1 × 106pCi/μCi) (1 × 106 mL/m3) = 1,000 pCi/m3

Assuming an occupancy factor of 0.5 (1,000 hr/yr exposure) and a breathing rate of 1.2 m3/hr. 

(1,000 pCi/m3) (1.2 m3/hr) (1,000 hr/yr) ÷ 365 d/yr = 3,300 pCi/d. 

Assign this intake to the D&D workers for the appropriate years between 1978 and 1981. For 

supervisors and others not directly involved in the work, assign one-fourth of the intake. 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 49 of 87

5.5 SUMMARY OF INTERNAL DOSE RECOMMENDATIONS 

Default occupational intakes for workers without the applicable bioassay data are summarized in 

Table 5-7. 

Table 5-7. Default intakes for Ames Laboratory (if no bioassay results are available) [29]. 

Job category 

or task/Building

Dose calculation parameters IREP input parameters

Period Material Mode

Absorption 

type or f1 pCi/d

Distribution 

type

Parameter 

1

Researcher/ChemistryaJan 1942–

July 1942

Natural 

uranium

Chronic 

inhalation

F, M, or S 85 Constant Dose

Researcher/ChemistryaJan 1942–

July 1942

Natural 

uranium 

Chronic 

ingestion

0.02 with F,M; 

0.002 with S

0.87 Constant Dose

All employees/Chemistry Jun 1945–

May 1976 

Natural

uranium

Chronic 

Inhalation

F, M, or S 1.8 Constant Dose

All employees/Chemistry Jun 1945–

May 1976 

Natural

uranium

Chronic 

Ingestion

0.02 with F,M; 

0.002 with S

0.16 Constant Dose

Researcher in hot 

lab/Chemistry Building

1943–1951 Fission 

products

Chronic 

inhalation

Use most 

favorable to the 

claimant, for 

Sr-90 use F

See Table 5-6 Constant Dose

Researcher, production 

technician, anyone involved 

daily with uranium in Annex 1a

Aug 1942–

Aug 1945

Natural 

uranium

Chronic 

inhalation

F, M, or S 853 Constant Dose

Researcher, production 

technician, anyone involved 

daily with uranium in Annex 1a

Aug 1942–

Aug 1945

Natural 

uranium

Chronic 

ingestion

0.02 with F,M; 

0.002 with S 

8.7 Constant Dose

All employees in Annex 1 Sep 1945–

Dec 1953

Natural 

uranium

Chronic

inhalation

F, M, or S 17.5 Constant Dose

All employees in Annex 1 Sept 1945–

Dec 1953

Natural 

uranium

Chronic

ingestion

0.02 with F,M; 

0.002 with S 

1.6 Constant Dose

Researcher, production 

technician, anyone involved 

daily with uranium in Annex 2a

Jan 1944

Dec 1953

Natural 

uranium

Chronic 

inhalation

F, M, or S 6,061 through 

1950, 5,556 from 

1951 to 1953

Constant Dose

Researcher, production 

technician, anyone involved 

daily with uranium in Annex 2a

Jan 1944 –

Dec 1953

Natural 

uranium

Chronic 

ingestion

0.02 with F,M; 

0.002 with S

124 through 

1950; 114 from 

1951 to 1953

Constant Dose

All employees in Annex 2 Jan 1954–

1972

Natural 

uranium

Chronic

inhalation

F, M, or S 124.7 Constant Dose

All employees in Annex 2 Jan 1954–

1972

Natural 

uranium

Chronic

ingestion

0.02 with F,M; 

0.002 with S

11.2 Constant Dose

Anyone routinely in Wilhelm 

Hall (Metallurgy Building)

1955–

present

Th-232 Chronic 

inhalation

M or S See Table 5-4 Constant Dose

Anyone routinely in Wilhelm 

Hall

1955–

present

Th-232 Chronic 

ingestion

5E-4 with M; 

2E-4 with S

See Table 5-4 Constant Dose

Anyone routinely in Wilhelm 

Hall

1955–

present

Ra-228 Chronic 

inhalation

M See Table 5-4 Constant Dose

Anyone routinely in Wilhelm 

Hall

1955–

present

Ra-228 Chronic 

ingestion

0.2 See Table 5-4 Constant Dose

Anyone routinely in Wilhelm 

Hall

1955–

present

Th-228 Chronic 

inhalation

M or S See Table 5-4 Constant Dose

Anyone routinely in Wilhelm 

Hall

1955–

present

Th-228 Chronic 

ingestion

5E-4 with M; 

2E-4 with S

See Table 5-4 Constant Dose

Reactor workers and D&D 

workers

1965–1981 Tritium Total of all 

modes

N/A N/A Lognormal,

see Table 5-5

for GSD

Dose; see 

Table 5-5

Workers involved with D&D of 

reactor, including former reactor 

workers

1978–1981 Co-60 or 

Zn-65

Chronic 

inhalation

Type S 3,300 Constant Dose

Workers involved with D&D of 

reactor, including former reactor 

workers

1978–1981 Co-60 or 

Zn-65

Chronic 

ingestion

Type S 660 Constant Dose

Anyone routinely in Applied 

Science Center

1982–

present

Tritium Total of all 

modes

N/A N/A Constant 8.6 mrem/yr

a. Values are for workers assumed to work in research or production full time. For supervisors, assume 0.25 of the intake; for all other 

employees (clerical, janitorial, security, etc) assume one-tenth of the supervisor‟s intake (0.025 of the intake in the table). 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 50 of 87

6.0 OCCUPATIONAL EXTERNAL DOSE

Workers at Ames Laboratory received external radiation doses between 1942 and 1952 that were 

largely unmonitored [30]. Pocket chambers were available that might have been used to monitor 

external doses, but very few records could be found [31]. External exposures since 1953 have been 

monitored with film badges and thermoluminescent dosimeters (TLDs) and the records are essentially 

complete. However, there were extensive periods (1965 through 1981) when individual names were 

not recorded with dosimeter numbers and many records cannot be clearly associated with individual 

workers [32]. For cases in which the individual‟s name is clearly associated with dosimetry records 

and the records are essentially complete, these individuals are considered monitored workers. For all 

other cases in which the records are unidentified or partially complete, the individuals are considered 

unmonitored workers for the missing or incomplete periods. External doses received since 1982 have 

been reliably recorded for each individual. Details of the external dosimetry program are addressed in 

this section. 

6.1 INTRODUCTION 

Ames Laboratory responses to U.S. Department of Labor requests for claimant records were limited 

to raw data from dosimetry files. Not all of these files had been summarized for annual total doses for 

individuals and the files for some individuals were incomplete as noted above. To assist dose 

reconstructors in determining annual doses for claimants, the raw data were entered into Excel®

spreadsheets and summarized to give annual totals for identified individuals; the spreadsheet data 

was analyzed to give 50th- and 95th-percentile values that could be applied to unidentified 

(unmonitored) individuals (Martin 2006c). 

Dose reconstructors should have access to dosimetry records from Ames Laboratory for each 

claimant, but the records might be incomplete and difficult to use. The spreadsheets assembled by 

Martin (2006c) should be used if there is any doubt about completeness. 

As described in Section 1.3, some portions of external dose (e.g. neutron, and thorium/plutonium 

beta/gamma dose, except for 1953 and 1954), cannot be adequately estimated for certain workers 

from January 1, 1942, through December 31, 1954 (NIOSH 2006). 

6.2 EXTERNAL RADIATION DOSIMETERS AND RECORDS 

An AEC survey conducted at Ames Laboratory from March 18 to 21, 1952, found the personnel 

monitoring program to be less than adequate. A number of recommendations were made in the 

survey report to promote improvements in radiation protection, including film badge service and 

regular radiation monitoring (Hokel et al. 1998). Before this time, only pocket chambers (pencil 

dosimeters) were used to monitor radiation exposure, and records were incomplete (Voss 1949). 

Regular film badge service was started in February 1953; beta/gamma film badges were exchanged 

on a biweekly frequency with the results tabulated monthly and summarized annually (Voss 1954). 

Dosimetry services evolved and improved over the following 50 yr; the characteristics of the 

dosimeters used are summarized in Table 6-1.

6.2.1 Historical Administrative Practices

Some of the early administrative practices at Ames Laboratory related to dosimetry recordkeeping 

were unusual and inconsistent with current practice. The recordkeeping practices that correspond to 

each step in the evolution of dosimetry services (Table 6-1) are addressed in this section. 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 51 of 87

Pocket chambers (pencil dosimeters) were used at Ames Laboratory at various times, possibly as 

early as 1942, through 1952 when film badge service was begun. However, the records of pocket 

chamber results that were found apply only to a brief period in February 1949 and only for a few 

individuals (Voss 1949). Thus, it is only possible to estimate any external doses before 1953. The 

Table 6-1. Dosimeter type, period of use, exchange frequency, MRD, and MDL. 

Dosimeter type, 

provider Period

Exchange 

frequencya

MRD (mrem)b MDL (mrem)c

Skin β/γ deep Neutron Skin Deep Neutron

Pocket Chambers, Ames 

Laboratory

1942–1952e Daily 5 5

β/γ film, Ames 

Laboratory in-house 

system

Feb 1953–May 1953 Biweekly 10 40 40

June 1953–Dec 1953 25 40 40

Jan 1954–Feb 1957 25 25 40 40

Mar 1957–Dec 1961 10 10 40 40

β/γ/NTA film, 

Brookhaven National 

Laboratory (BNL)

Apr 1954–June 1957 Biweekly 15 15 10 40 40 (d)

β/γ/NTA film, NCA July 1957–June 1963 Biweekly 10 10 10 40 40 (d)

β/γ/NTA film, Atomic Film 

Badge Corporation

July 1963–Mar 1965 Monthly 10 10 10 40 40 (d)

Pocket Chambers, Ames 

Laboratory

Apr 1965–June 1965 Daily 5 5

β/γ/NTA film, Health 

Physics Services 

July 1965–Oct 1979 Monthly 10 5 28 40 40 (d)

β/γ film, Health Physics 

Services

Nov 1979–Sept 1981 Monthly 10 5 40 40

β/γ TLDs, Landauer June 1980–Dec 1981 Monthly & 

Quarterly

40 10 30 30

β/γ TLDs, Landauer Jan 1982–Dec 1994 Quarterly 40 10 30 30

β/γ TLDs, Siemens Jan 1995–June 1996 Quarterly 10 10 30 30

β/γ TLDs, ICN Dosimetry 

Service

July 1996–Sept 1998 Quarterly 10 10 30 30

β/γ TLDs, Landauer Oct 1998–Dec 2004 Quarterly 40 10 30 30

β/γ TLDs, Global 

Dosimetry

Jan 2005–present Quarterly 10 10 30 30

a. The exchange frequency was established from dosimetry reports. 

b. MRD = minimum recordable dose; based on minimum doses recorded on dosimetry reports. 

c. Estimated minimum detection level (MDL) typical of film dosimeter capabilities (Wilson 1960, 1987; NIOSH 1993; NRC 1989; Wilson et 

al. 1990). 

d. For years of NTA film use, between 1954 and 1979, the adjusted neutron dose is calculated using correction factor of 2. 

e. Exposures from January 1, 1942, through December 31, 1952 cannot be reconstructed for workers who are included in SEC-00038 

(NIOSH 2006). 

maximum plausible external dose from uranium to Ames Laboratory workers during the period from 

1942 through 1952 can be estimated using ORAUT (2005c). However, these external doses cannot 

be reconstructed for workers who are included in SEC-00038. An upper bound of the total external 

exposures cannot be made for the SEC-00038 workers, because external doses from beta and 

gamma radiation, resulting from exposure to thorium and its daughters or plutonium cannot be 

reconstructed, due to a lack of information on the percentage of thorium daughter in-growth (up to 

1954, when thorium operations ceased) (NIOSH 2006). 

An in-house film badge system was established at Ames Laboratory in the fall of 1952 in response to 

recommendations from the AEC. Weekly film badges were provided to a few individuals who worked 

at the synchrotron from September 1952 through March 1953, but records are incomplete (Voss 

1954). Regular film badge service began in February 1953 for the Ames Laboratory staff. Beta/ 

gamma film badges were exchanged every 2 wk (biweekly) and results were summarized monthly. 

However, between late September 1953 and early January 1954, there were three 4-wk and one 3-wk 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 52 of 87

exchange periods (Voss 1954). The in-house film badge system again had variable exchange 

periods during 1954, 1957, 1958, 1959, and 1961. There was a 4-wk exchange period in January, a 

3-wk period in February, and a 4-wk period in December 1954; otherwise, the exchange periods were 

2 wk each (Voss 1955). The exchange frequency during 1955 and 1956 was every 2 wk, with no 

exceptions (Voss 1956, 1957b). There was a 4-wk exchange period in May and June 1957; all other 

exchange periods in 1957 were 2 wk (Voss 1958). There was a 3-wk exchange period in December 

1958 and January 1959; all other exchanges periods in 1958 and 1959 were 2 wk (Voss 1959, 1960). 

The exchange frequency during 1960 was every 2 wk without exception (Voss 1961). During 1961, 

there were nine 3-wk exchange periods and 12 2-wk periods (Voss 1962). 

Initially, the MRD was 10 mR, and no distinction was made between beta and gamma doses 

(recorded non-zero doses were assumed to be gamma doses). As of June 1953, the MRD was 

reported as 25 mR. In 1954, the MRD was specified as 25 mrep and 25 mR for beta and gamma, 

respectively. In March 1957, the MRD decreased to 10 mR for both beta and gamma doses; this 

MRD was unchanged through 1961 (Voss 1957c, 1958, 1959, 1960, 1961, 1962). 

Between October 24 and November 21, 1953, unusually high beta dose readings (about 700 mR) 

were “caused by the film being left unprotected near X-ray radiation” (Voss 1954). Corrections that 

are favorable to claimants for this exposure that was not received by personnel are recommended in 

Martin (2006c). 

In the fourth quarter of 1953 and continuing through 1961, beta and gamma doses were reported 

separately, but were added to give a total dose (Voss 1954). Between 1954 and 1961, neutron doses 

were added to the beta and gamma doses to give a total dose (Voss 1954, 1955, 1956, 1957b, 

1957c, 1958, 1959, 1960, 1961, 1962). 

In the annual summaries for 1953 through 1956 (and for January and February 1957), an assumed 

dose of 25-mR gamma was assigned for each month in which the dosimeter reading was zero or less 

than the MRD (Voss 1954, 1955, 1956, 1957b, 1957c). From March 1957 through 1961, when the 

dosimeter readings were zero or less than the MRD, an assumed dose of 10-mR gamma was 

assigned for each dosimeter exchange period (Voss 1958, 1959, 1960, 1961, 1962). This practice of 

assigning doses equal to the MRD is roughly equivalent to the standard method for correction of 

missed dose for monitored workers (NIOSH 2007b). Therefore, no additional correction to the 

gamma dose is required for monitored workers for the period from 1953 through 1961. 

Beginning in April 1954 and continuing through June 1957, a beta/gamma/neutron film badge service 

was provided by BNL for the synchrotron staff (Voss 1955). The film badges were exchanged every 2 

wk and results were included in the annual dose summaries. The MRD was 15 mrep and 15 mR for 

beta and gamma, respectively. Neutron dose was reported as the number of recoil proton tracks in 

the open window, and the number of tracks was multiplied by 10 to give the neutron dose in millirem 

(Voss 1955, 1962). 

Between July 1957 and June 1963, beta/gamma/neutron film badge service was provided by the 

Nucleonic Corporation of America (NCA) for the synchrotron staff (Voss 1958). The film badges were 

exchanged every 2 wk and results were included in the annual dose summaries. The MRDs were 

10 mrad and 10 mrem for beta and gamma, respectively. Neutron dose was reported as the number 

of recoil proton tracks in the open window, and the number of tracks was multiplied by 10 to give the 

neutron dose in millirem (Voss 1958). 

All the data discussed above for the period from 1953 through 1961 was compiled on a spreadsheet 

and the inconsistencies were corrected or minimized (Martin 2006c). For example, when beta, 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 53 of 87

gamma, and neutron doses were reported separately but added together for a total dose, the 

separated beta, gamma, and neutron doses were entered in the spreadsheet to facilitate analysis. In 

all cases when data were questionable, assumptions were made that would be favorable to claimants 

[33]. 

Dosimetry record keeping from January 1962 through June 1963 was less than adequate. The only 

records found for 1962 were some calibration data from April 1962 and the annual summary data for 

1962 (Voss 1963b). It was assumed that the in-house film badge system continued through 

December 1962 with film badges exchanged on a biweekly frequency; however, no records could be 

found to confirm this assumption. Monthly film badge service was provided for all Ames Laboratory 

personnel with the potential for radiation exposure by the Atomic Film Badge Corporation from July 

1963 through March 1965. No records were found for the first half of 1963. The annual summary for 

1963 reflects results from July through December 1963 only; therefore, all Ames Laboratory workers 

are assumed to have been unmonitored for the first half of 1963 (Voss 1964). The annual summary 

for 1964 accurately reflected the sum of the monthly dosimeter readings during 1964 (Voss 1965). 

Dosimetry records for January through March 1965 appeared to be reliable; however, the Atomic Film 

Badge Corporation defaulted on its contract and went out of business in April 1965 (Mattmueller 

1965). Ames Laboratory staff members were monitored with pocket chambers on a daily basis and 

records were compiled in-house from April through June 1965 (Voss 1966). Film badge service was 

provided by Health Physics Services from July 1965 through September 1981. The monthly service 

included beta, gamma, and neutron film badges for the reactor and synchrotron staff members and 

beta/gamma film badges for the remaining Ames Laboratory staff (Voss 1966). The MRDs were 10 

mrad for beta, 5 mR for gamma, and 28 mrem for neutrons (Voss 1966). 

TLD services for beta and gamma dosimetry were provided by Landauer from June 1980 through 

June 1995. Similar TLD services have been provided in subsequent years by Siemens, ICN 

Dosimetry Service, and Landauer. The MRD for TLD services was 10 mrem for beta and gamma, 

except Landauer specified an MRD of 40 mrem for hard beta (greater than 1.5 MeV) (Landauer 1981; 

Siemens 1996; ICN 1997). Dosimetry records compiled since 1981 are considered complete and 

reliable. Records for monitored workers include an identification number, name, Social Security 

Number, and recorded doses for the current period, calendar quarter, and calendar year. The TLD 

services used by Ames Laboratory have been accredited by the National Voluntary Laboratory 

Accreditation Program (NVLAP) since 1985 (Landauer 1985). 

6.2.2 Dosimetry Technology

Ames Laboratory used film badge dosimeters from 1952 through 1981; TLDs have been used since 

1980. The initial beta/gamma film badge system was operated in-house from 1952 to 1962. The film 

was Kodak type K and the developer was Kodak D-19. However, no records could be found that 

described the film holder, although it seems likely that one of several commercially available film 

holders would have been procured, and that such a holder would have had standard design features 

as described in AEC (1955). 

The initial neutron dosimetry service used at Ames Laboratory, which began in 1954 and included 

beta and gamma dosimetry, was provided by BNL. The film badge holder was the basic Oak Ridge 

multielement dosimeter; the neutron film was nuclear emulsion type A (NTA) (ORAUT 2006d). Similar 

film badge holders and film were provided by NCA, Atomic Film Badge Corporation, and Health 

Physics Services for the periods listed in Table 6-1.
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 54 of 87

With the termination of operations at the synchrotron in 1971 and the removal of fuel from the ALRR 

in October 1979, neutron dosimetry services were no longer needed after 1979 [34]. From 1980 to 

the present, beta/gamma TLD service has been provided by Landauer, Siemens, ICN Dosimetry, and 

Landauer for the periods listed in Table 6-1. These services have been accredited by NVLAP since 

1985 (Landauer 1985). 

6.2.2.1 Beta/Photon Dosimeters 

Figure 6-1 shows the response of a film badge to photon radiation of different energies; it also shows 

the Hp(10) response. The figure shows two responses for film badges: one for a sensitive DuPont 

502 emulsion in a two-element badge (Pardue, Goldstein, and Wollan 1944) and one for a sensitive 

DuPont 555 emulsion in the multielement badge (Thornton, Davis, and Gupton 1961). The response 

of the sensitive Eastman Type 2 film in a multielement film badge is similar to that of the sensitive 

DuPont 555 emulsion. The film badges show an over-response at photon energies around 100 keV, 

due primarily to relatively (compared to tissue) high atomic numbers [silver (47) and bromine (35)] in 

the film emulsions. The two-element film badges under-respond to lower energy photons; the 

multielement film badge typically over-responds to photons between 50 and 150 keV. 

10-210-110 |0

Photon Energy (MeV)

0.1

1

10 Relative Response

Hp(10)

Two-Element Film Badge

Multi-Element Film Badge

Figure 6-1. Comparison of Hp(10) for photons with energy 

responses for sensitive DuPont 502 emulsion in two-element film 

badge (Pardue, Goldstein, and Wollan 1944) and sensitive DuPont 

555 emulsion in multi-element film badge (Thornton, Davis, and 

Gupton 1961). 

6.2.2.2 Neutron Dosimeters 

NTA film was used by the dosimetry services provided to Ames Laboratory from 1954 through 1979. 

In general, the response of the NTA film decreases with decreasing neutron energies greater than a 

minimum threshold energy estimated to be between 500 and 800 keV (IAEA 1990; ORAUT 2006d). 

An unknown fraction of the total neutron dose was received from neutrons with energies less than 

about 800 keV. 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 55 of 87

6.2.3 Dosimeter Calibration Procedures

Calibration procedures for beta/photon dosimeters were followed consistently from 1953 to 1981, with 

the exception of 1962 and the first half of 1963 [35]. The suppliers of neutron dosimeters were 

generally relied on for neutron calibrations. 

6.2.3.1 Beta/Photon Dosimeters 

A set of calibration control film badges was exposed and processed with each biweekly set of films 

used in the Ames Laboratory in-house film badge system from 1953 through 1961 (Ames 1974). The 

beta calibration was accomplished by the exposure of films for varying times to a milled uranium plate 

to produce beta doses between 10 and 1,000 mR (sic) (Voss 1955). The gamma calibration was 

done by the exposure of films to doses of gamma radiation from a 10-mg 226Ra source that ranged 

between 10 and 1,000 mR (Voss 1955). The interpretation of film density into exposure units was 

made from curves drawn for the calibration films (Ames 1974). 

Between January 1962 and June 1963, there was evidence of calibrations done only during April 

1962 (Voss 1963b). From June 1963 to March 1965, when the Atomic Film Badge Corporation 

provided film badge services, monthly gamma calibrations were done by the exposure of films to 

doses of gamma radiation from a 10-mg 226Ra source that ranged from 100 to 10,000 mR (Voss 1964, 

1965). There was no evidence of beta or neutron calibrations during this period. 

From July 1965 through September 1981, when film badge services were provided by Health Physics 

Services, a set of calibration control film badges were exposed to beta and gamma sources with each 

biweekly set of personnel film badges (Voss 1966, 1971, 1974, 1978, 1979, 1981). The calibration 

procedures were the same as those used during the period from 1953 to 1961. 

Between 1980 and 1984, when TLD services were provided by Landauer, there is no evidence of any 

dosimeter calibrations by Ames Laboratory. After 1985, NVLAP accreditation was relied on for 

dosimeter calibrations. 

6.2.3.2 Neutron Dosimeters 

From April 1954 through June 1957, when film badge services were provided by BNL, a set of four 

calibration badges was included in each monthly set of films (Voss 1955, 1956, 1957b). The 

calibration badges were exposed to known doses of beta, gamma, and neutron radiation. The beta 

exposures were to a milled uranium plate, the gamma exposures were to a 10-mg 226Ra source, but 

records of the source of neutron exposures were not found (Voss 1955, 1956, 1957b). 

From July 1957 to June 1963, when NCA provided film badge services, a set of area monitor film 

badges was included with each month‟s set of personnel dosimeters (Voss 1958, 1959, 1960, 1961, 

1962, 1963b, 1964). The monthly readings on area monitor film badges were used to check on the 

validity of personnel dosimeter readings, but actual calibrations were not performed by Ames 

Laboratory. NCA calibrated its NTA film badges by exposing films for 40 hr to a fast neutron flux of 

18 n/cm2/s (2.6 × 106 n/cm2/40 hr), which produced approximately 10 recoil proton tracks in 25 fields 

or an exposure equivalent to 100 mrem (NCA 1961). From June 1963 to March 1965, when the 

Atomic Film Badge Corporation provided film badge services, there was no evidence of neutron 

calibrations. 

Between July 1965 and September 1981, when Health Physics Services provided film badge 

services, a set of calibration control film badges were exposed to beta and gamma sources with each 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 56 of 87

biweekly set of films (Ames 1974). However, no evidence could be found that neutron exposures 

were included in this calibration procedure. 

6.2.4 Workplace Radiation Fields

Workplace radiation fields at Ames Laboratory rose from the production of uranium and thorium metal, 

the operation of the synchrotron and ALRR, and research activities in laboratories. With very few 

exceptions, the following sections show that, for external dose reconstruction purposes, all beta 

radiation fields were greater than 15 keV, all photon radiation fields were between 30 and 250 keV, 

and all neutron fields were between 0.1 and 2 MeV [36]. Assuming that 100% of the radiation fields 

are within these ranges is a simplifying conservative assumption that is generally favorable to the 

claimant. 

6.2.4.1 Beta Radiation 

The major sources of beta radiation at Ames Laboratory between 1942 and 1954 were the large 

quantities of uranium and thorium metal produced. The uranium handled is assumed to have been in 

equilibrium with its 234Th (24.1-d half-life) and 234mPa decay products (DOE 2000, p.2-17). From an 

external dose standpoint, the most significant beta radiation emitted from uranium metal is that from 

234mPa, with a maximum energy of 2.29 MeV (Shleien, Slaback, and Birky 1998). The beta dose rate 

(with 7 mg/cm2 filtration) is 233 and 179 mrad/hr at the surface of a uranium slab and UF4, 

respectively (BRH 1970). Thorium, if recently separated from its 228Ra and subsequent decay 

products, would have very little beta emission. However, if ThF4 was stored for several years before 

being processed to thorium metal, beta radiation from 228Ra and 228Ac would be measurable (Shleien, 

Slaback, and Birky 1998). 

A large number of beta-emitting radioisotopes were handled in research work at Ames Laboratory 

throughout its history [37]. However, the activity of these sources was relatively small; the sources 

had a much smaller potential for beta radiation exposure to workers in comparison to the beta dose 

from uranium metal. With the exception of tritium, the energy of all beta sources was assumed to be 

greater than 15 keV; beta doses would have been readily measured in the open-window portion of the 

film badges used at Ames Laboratory. Tritium exposures that occurred at the ALRR were monitored 

by means of urine bioassay, which is addressed in Section 5.0 of this site profile. 

6.2.4.2 Photon Radiation 

Brehmsstrahlung radiation doses from uranium metal ingots were calculated by Anderson and Hertel 

(2005). Contact photon dose rates of a few milliroentgen per hour were calculated for typical plates, 

billets, and cylindrical ingots of the type produced at Ames Laboratory. Another source of photon 

radiation in the early years was from stored thorium in the form of ThF4. A gamma dose rate of 

22 mR/hr in a thorium storage area was reported by Klevin (1952). Exposures to photon radiation 

were possible in the experimental areas at the synchrotron and ALRR, and near the many gammaemitting radioisotopes that were handled in research work. A hot laboratory was located in the 

Chemistry Building and a hot canyon/hot cell was located in the Research Building for work with the 

more intense gamma sources. Photon sources had energies in the 30- to 250-keV and greater-than250-keV ranges. X-ray diffraction machines could have operated at energies less than 30 kV, and 

measured exposures probably would have been reported as beta dose. Limited data do not permit an 

accurate estimate of the fraction of photon exposures expected in these energy ranges. Assuming 

that 100% of the photons were in the 30- to 250-keV range is a simplifying conservative assumption 

that is generally favorable to claimants [38]. Photon radiation in the workplace could have been 

readily measured at Ames Laboratory with available dosimeter technology since 1953. 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 57 of 87

6.2.4.3 Neutron Radiation 

The work involving plutonium and the research associated with thorium and uranium in the 

laboratories had the highest potential for exposure to neutrons. Neutron doses cannot be 

reconstructed for the SEC-00038 class of employees from 1942 through 1954 (NIOSH 2006). 

The primary sources of neutrons at Ames Laboratory were the synchrotron, which operated from 1949 

through 1971, and the ALRR, which operated from 1965 through 1977. In both facilities, fast, 

intermediate, and thermal neutrons would have been present in the workplace [39]. Unfortunately, no 

records could be found that characterized the neutron spectrum in either facility, and there were no 

records of neutron surveys around experimental areas or penetrations in the shielding. The only 

documented evidence of neutrons in the workplace is the many non-zero fast neutron doses 

measured with NTA film worn by personnel at each facility (Martin 2006c). Assuming that 100% of 

the neutrons were in the 0.1- to 2-MeV energy range is a simplifying conservative assumption that is 

generally favorable to claimants. 

6.2.5 Dosimeter Response to Radiation Fields

The personnel dosimeters used at Ames Laboratory were properly selected for the radiation fields 

encountered in the workplace. The response of each of the dosimeters used is described in the 

following sections. 

6.2.5.1 Beta/Photon Film Dosimeter Response 

Ames Laboratory used film badges for beta and photon dosimetry from 1952 to 1981. An in-house 

film badge system was used from 1952 to 1962 and film badges were provided by four commercial 

services from 1954 to 1981 [40]. The dosimeters provided an open window with little filtration, a lower 

energy window that allowed beta particles and lower energy photons to enter a film area with a plastic 

filter, and a film area with a metal (usually aluminum) filter (Ames 1974). The open window enabled 

measurement of beta particles and lower energy photons. The plastic filter enabled measurement of 

intermediate energy photons, and the metal filter enabled measurement of higher energy photons (1-

cm depth). 

The beta/photon dosimeters were calibrated regularly by methods consistent with accepted practice, 

but there was no evidence of any formal dosimeter response testing by an independent entity. The 

recorded beta and gamma doses appear to be consistent with that expected from the source terms 

and personnel monitoring described in Section 2.4. The recorded beta and gamma doses can be 

considered reliable for dose reconstruction purposes [41]. 

6.2.5.2 Beta/Photon TLD Response 

Ames Laboratory has used TLDs for beta and photon dosimetry since 1980. The TLDs, their 

analyses, and recordkeeping have been provided by reliable commercial services. The dosimetry 

services have been accredited by NVLAP since 1985 (Landauer 1985). 

6.2.5.3 Neutron Dosimeter Response 

The neutron doses received by synchrotron staff members measured by NTA film appeared to be 

consistent with similar accelerator operations at other sites. The neutron doses received by ALRR 

personnel were generally higher that those experienced at other sites (e.g., the High Flux Beam 

Reactor at BNL) (ORAUT 2006e). The higher neutron doses at ALRR might have been due to less 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 58 of 87

than adequate management of neutron shielding in the experimental areas [42]. Fast, intermediate, 

and thermal neutrons were present in both Ames Laboratory facilities, but no records were found that 

characterized the neutron energy spectrum at either facility. Thus, there is an unknown fraction of the 

total neutron dose (due to neutrons with energies below about 800 keV) that was not measured by 

NTA film. 

To correct the measured neutron doses for the unmeasured fraction of neutrons with energies below 

800 keV, data from similar facilities were examined. The 200-MeV electron synchrotron at the 

Stanford Linear Accelerator Center (SLAC) was determined to be similar to the 80-MeV synchrotron 

at Ames Laboratory in relation to neutron exposures (ORAUT 2007c). The Materials Test Reactor 

(MTR) at the Idaho National Laboratory (INL) was determined to be similar to the ALRR with respect 

to neutron exposures (ORAUT 2007a). Neutron dosimeters with NTA film were used at both facilities 

and neutron spectral data are available for estimation of the correction factor for missed neutron dose. 

Accelerator operations at SLAC started in 1966; a multielement dosimeter was used until 1971 for 

beta/gamma and neutron (NTA film) dosimetry. ORAUT (2006f) concluded that all SLAC neutron 

doses measured with NTA film should be multiplied by 1.53 ± 0.14 to account for the unmeasured 

neutrons with energies below 800 keV. The SLAC and Ames Laboratory synchrotrons were similar 

but their neutron spectra were not identical [43]. To allow for differences in the neutron spectra and 

other variables, a neutron dose correction factor of 2 is recommended for the Ames Laboratory 

synchrotron workers [44]. 

The MTR at INL, which operated from 1952 to 1970, was similar to the ALRR in that it was fueled with 

enriched uranium and it had a power level of 30 MW (ORAUT 2007a). The MTR was water-cooled 

and light-water-moderated, whereas the ALRR was heavy-water-moderated. Both reactors had ports 

where fast neutron beams could be extracted from the core and directed to accessible experimental 

areas. Both were used to study reactor fuels and structural materials. Neutron doses at both reactors 

were monitored with multielement dosimeters including NTA film. The neutron spectrum in 

experimental areas at the MTR was measured with Bonner spheres in 1961 (Hankins 1961). The 

data from these measurements was reanalyzed in ORAUT (2006e). Measurements made at 22 

locations at the MTR were analyzed in relation to the response of NTA film. It was determined, on 

average for the 22 locations, that 52% of the total neutron dose would have been detected by NTA 

film and 48% would have been below the 800-keV threshold and undetected (ORAUT 2006g). 

Because the MTR and the ALRR had very similar neutron spectra, a neutron dose correction factor of 

2 is recommended for the ALRR workers. 

6.2.5.4 Neutron Dose Weighting Factor 

At Ames Laboratory, neutron dosimeter measurements were based on fluence-to-dose conversion 

factors and quality factors similar to those from ICRP Publication 21 (ICRP 1973) and National 

Council on Radiological Protection and Measurements Report 38 (NCRP 1971). It is necessary to 

adjust the neutron dose to account for the change in neutron quality factors between historical and 

current scientific guidance, as discussed in NIOSH (2006b). Table 6-2 , which is from ORAUT 

(2006c), shows the correction factor to use. 

Table 6-2. Neutron dose energies, percentages, and associated ICRP (1991) correction factors. 

Process description

Neutron energy

(MeV)

Default dose 

fractiona (%)

ICRP (1991)/NCRP (1971)

correction factor

Neutron exposures associated with synchrotron and 

research reactor activities

0.1-2 MeV 100 1.91

a. The assumption that all neutron energies are between 0.1 and 2 MeV is favorable to the claimant. 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 59 of 87

6.3 RECOMMENDATIONS FOR AMES LABORATORY WORKER EXTERNAL DOSE 

RECONSTRUCTION 

Dose reconstruction for Ames Laboratory workers is based on the foregoing information, which 

requires assessment of additional dose to be added to the measured photon dose from three primary 

causes as follows: 

 Adjustments to measured photon dose for dosimeter uncertainty 

 Adjustments to measured neutron dose using a correction factor to account for neutrons with 

energies less than 800 keV that were not measured by NTA film 

 Multiplication of the adjusted neutron dose by an ICRP (1991) neutron weighting factor 

adjustment of 1.91 for neutron energies between 0.1 and 2 MeV 

6.3.1 Unmonitored External Dose

At Ames Laboratory, the concept of unmonitored worker will have to be expanded to include 

monitored but records not found [45]. Extensive dosimetry records have been found for Ames 

Laboratory workers; however, many of the records for 1965 to 1981 do not identify the person 

receiving the radiation dose. If a worker was monitored but cannot be identified in the dosimetry 

records, that individual must be considered unmonitored and assigned a dose in each year for which 

no clearly identified records exist. 

A coworker data study was used for this site profile to permit dose reconstructors to complete certain 

cases for which external monitoring data were unavailable or incomplete. Coworkers are considered 

to be workers at a site (potentially grouped by work location, job description, or other appropriate 

category) whose measured doses are considered representative of those received by one or more 

workers with no individual monitoring data (ORAUT 2005d).

The general approach to applying coworker data for cases with little or no individual external 

monitoring data is to assign either the 50th- or 95th-percentile doses with the intent that the assigned 

doses represent, but do not underestimate, the doses that would have been assigned had the worker 

been monitored (50th percentile) or if the monitored worker was clearly identified in the dosimetry 

records (95th percentile) (ORAUT 2005d).

Some workers might have never been monitored during their employment at Ames Laboratory. 

Workers with job titles such as security patrolman, craftsman, janitor, secretary, or clerk who did not 

work routinely in radiological areas were probably not monitored. In general, the 50th-percentile dose 

can be used to bound doses for those workers when professional judgment indicates the worker was 

likely to have been exposed to intermittent low levels of external radiation (ORAUT 2005d). 

Some workers with job titles such as scientist, chemist, metallurgist, engineer, technician, or machinist 

were probably monitored, but some or all of their dosimetry records might be missing because of the 

lack of clearly identified dosimetry records between 1965 and 1981. If any part of a worker‟s 

dosimetry record is missing (unidentified), coworker data should be applied in the years for which 

records are missing (ORAUT 2005d). The 95th percentile dose should be assigned to those workers 

who could have been regularly exposed. 

The coworker data study for Ames Laboratory included all available dosimetry records from 1952 

through 1981 (Martin 2006c). All dose results were analyzed, including zeros and blank values, to 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 60 of 87

determine the 50th- and 95th-percentile doses for each year for beta, gamma, and neutron exposures 

(McCartney 2006). The results of the analysis are summarized in Table 6-3. The missed dose 

recommended for monitored workers in Table 6-4 was added to the 50th- and 95th-percentile values 

in Table 6-3. Specifically, one-half of the maximum annual missed doses were added to the reported 

annual doses, except the reported positive doses, in which case the maximum missed dose was 

reduced by the dose corresponding to one badge exchange (because it is not possible that all 

individual badge results were zero if a positive annual dose was reported) (ORAUT 2005d). These 

external doses cannot be applied for the SEC-00038 class of employees (NIOSH 2006), which covers 

the period of January 1, 1942, through December 31, 1954. 

6.3.2 Missed External Dose for Monitored Workers

If external dose data are found in a worker‟s file, dose reconstructors should assign a missed photon 

dose based on the MDL/2 method and the number of exchange periods (NIOSH 2007b) listed in 

Table 6-4 for the dosimetry systems. These missed doses are included in the values in Table 6-3. 

Table 6-3. Assigned dose for unmonitored workers, mrem/year (McCartney 2006). 

Year

Beta Gamma Neutron

Raw data files

SRDB Ref ID No.

50th 

percentile

95th 

percentile

50th

percentile

95th 

percentile

50th 

percentile

95th

percentile

1952 N/Aa N/Aa130 268b163c163c18821, 18822, 18833

1953 520 520 520 590b650c650c18821, 18822, 18833

1954 520 520 520 737b650 650 18834, 18835, 25816

1955 520 520 520 520b650 650 18841

1956 520 520 520 520b650 650 25169, 25171

1957 520 520 520 520b650 650 25214, 25215, 25216

1958 520a520a520 520b650 650 25459, 25460

1959 520a520a520 520b650 650 25461, 25898

1960 520 520 520 520b650 650 25898, 25907

1961 520a520a520 520b650 650 25913

1962 520 520 520 520d650 650d25837

1963 240 240 240 265e650 650 25837, 25914

1964 240 240 240 313e650 650 25837, 25916

1965 240 240 240 408e650 820e25919

1966 240 306e240 565e806f988e25922

1967 240 466e240 745e932f1,128e25923

1968 240 307e240 769e876f1,086e25808

1969 240 395e240 1,182e1,030f1,296e25809

1970 240 240 240 671e680f932e25810

1971 240 240 240 809e722f950e25811

1972 240 240 240 512e652f988e25834

1973 240 240 240 701e650 932e25839

1974 240 240 240 721e650 876e25859

1975 240 240 240 1,298e650 870e25860

1976 240 240 240 497e650 958e25861

1977 240 240 240 752e650 904e26613

1978 240 240 240 722e650 652e26615

1979 240 240 240 819e650 650 26619

1980 240 240 240 1,595e N/Ac N/Ac26624

1981 240a240a240 240 N/Ac N/Ac26626

1982 60a60a85 555 N/Ac N/Ac26628

1983 380 565 105 134 N/Ac N/Ac26631

1984 60 60 60 85 N/Ac N/Ac26632
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 61 of 87

Year

Beta Gamma Neutron

Raw data files

SRDB Ref ID No.

50th 

percentile

95th 

percentile

50th

percentile

95th 

percentile

50th 

percentile

95th

percentile

1985 60 60 60 125 N/Ac N/Ac26642

1986 60 60 60 60 N/Ac N/Ac26645

1987 60 60 60 114 N/Ac N/Ac26647

1988 60 365 72 149 N/Ac N/Ac26653

1989 60 60 60 81 N/Ac N/Ac26657

1990 60 64 60 91 N/Ac N/Ac26659

1991 60 106 60 85 N/Ac N/Ac26664

1992 60 85 60 71 N/Ac N/Ac26666

1993 60 77 60 118 N/Ac N/Ac26668

1994 60 75 62 138 N/Ac N/Ac26672

1995 60 125 60 68 N/Ac N/Ac26679

1996 60 60 60 65 N/Ac N/Ac26681

1997 60 60 60 60 N/Ac N/Ac26683

1998 60 60 205 245 N/Ac N/Ac26685

1999 60 170 60 160 N/Ac N/Ac26750

2000 60 205 60 110 N/Ac N/Ac26799

2001 60a60a60 76 N/Ac N/Ac27038

2002 60 104 60 68 N/Ac N/Ac26808

2003 60 205 201 394 N/Ac N/Ac26809

2004 60a60a63 118 N/Ac N/Ac26810

2005 60 259 60 123 N/Ac N/Ac26811

a. No beta doses were measured or reported in 1952, 1958, 1959, 1961, 1981, 1982, 2001, or 2004. 

b. As discussed in Section 6.2.1, the practice of assigning doses equal to the MRD is roughly equivalent to the standard 

method for correction for missed dose for monitored workers (NIOSH 2007b). Therefore, no additional correction to 

gamma doses is required for monitored workers for the period from 1952 through 1961. However, from 1955 through 

1961, this method resulted in adjusted doses that were less than the missed dose assigned to unmonitored workers 

(50th-percentile value), so the higher missed dose was assigned. 

c. Neutron dosimeters were not provided in 1952 or 1953 and were not needed after 1979. 

d. The dosimeter exchange frequency in 1962 is uncertain; therefore, the missed dose for a biweekly frequency was 

assumed to be favorable to claimants. 

e. The 95th-percentile value was assumed to be received all in one month; missed dose was added for the other 11 

months of the year. 

f. The 50th-percentile value was assumed to be received all in one month; missed dose was added for the other 11 

months of the year. 

Table 6-4. Potential missed dose for monitored workers. 

Dosimeter Period

Exchange

frequencya

MDL (mrem)

Missed annual mean 

dose (mrem)

Skin Deep Neutron Skin Deep Neutron

Film badge-β,γ,n 1952–1956 Biweekly 40b40b50b0

c

0

c

0

c

1957–1962 Biweekly 40b40b50b

Film badge-β,γ,n 1963–1981 Monthly 40 40 50 240 240 300

TLD-β and γ 1981–present Quarterly 30 30 N/Ad60 60

a. Exchange frequencies were established from dosimetry reports. 

b. Estimated MDL typical of film dosimeter capabilities (Wilson 1960, 1987; NIOSH 1993; NRC 1989; Wilson et al 1990). 

c. As discussed in Section 6.2.1, doses equal to the MRD were added to the recorded dose when zero readings occurred. 

Therefore, no additional correction is required for monitored workers for the period from 1952 through 1961. 

d. Neutron dosimeters were not assigned after 1979, due to the removal of fuel from the ALRR in October 1979. 

A flow chart is provided in Figure 6-2 to guide dose reconstructors in the application of all the 

foregoing tables and recommendations. The Monitored Worker side of the figure should be used if 

there are dose of record files for the entire period of employment. If data for any exposure period are 

missing, the Unmonitored Worker side of the figure should be used for the missing period only. If 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 62 of 87

there are no dose of record files for a worker, the Unmonitored Worker side of the figure should be 

used for the entire period of employment. 

6.3.3 Uncertainty in Photon Doses

For the usual analysis of measured film badge doses, MDLs in the literature range from about 30 to 

50 mrem for beta/photon irradiation (Wilson et al. 1990). It is possible to read a photon dose of 

100 mrem to within ±15 mrem if the exposure involved photons with energies between several keV 

and several MeV (Morgan 1961). The estimated standard error in recorded film badge doses from 

photons of any energy is ±30% (ORAUT 2006c). The estimated uncertainty in doses recorded by 

TLDs is ±20% from 1982 through 1984 and ±10% since 1985 with NVLAP accreditation (Landauer 

1985). 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 63 of 87

Figure 6-2. Flowchart for monitored and unmonitored workers. Source: authors 

6.3.4 Skin Dose

In years before 1981, the beta and skin dose records included beta doses only; that is, only 

nonpenetrating beta dose is recorded. In 1981 and subsequent years, the beta and skin dose has 

been calculated as the sum of the whole-body penetrating dose and the nonpenetrating dose 

(Landauer 1985). In cases where no nonpenetrating dose was recorded, the skin dose is assumed to 

Monitored Worker Unmonitored Worker

For 1942 to 1952, use ORAUT 

(2005c) to estimate maximum 

plausible dose

For 1953 to present, tabulate 

beta, photon, and neutron 

doses of record for each year

Multiply beta/photon doses by 

uncertainty correction factora

Add adjustments for missed 

and zero doses after 1961b

Multiply neutron dose of record 

by correction factor of 2c

Adjust neutron dose for ICRP 

(1991) weighting factor by 

multiplying by 1.91d

Tabulate annual assigned doses 

from Table 6-3. See text in 

Section 6.3.1 for explanation and 

guidance.

For 1942 to 1952, use ORAUT 

(2005c) to estimate maximum 

plausible dose

Multiply assigned neutron dose 

by correction factor of 2c

Adjust neutron dose for ICRP 

(1991) weighting factor by 

multiplying by 1.91d

a. Uncertainties and correction factors are ±30% and 1.3 for beta/gamma film badges, ±20% and 1.2 for TLDs before 

1985, and ±10% and 1.1 for TLDs after NVLAP accreditation in 1985, respectively.

b. Adjustments for missed and zero doses have already been made to the dose of record for years before 1962 (see 

Section 6.2.1).

c. Correction factor is 2 for neutron (NTA) film badges (see Section 6.2.5.3).

d. ICRP (1991) neutron weighting factor adjustment for neutron energies from 0.1 to 2 MeV.

Note: Photon and neutron organ dose conversion factors are not included in this flowchart and must be 

applied separately.
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 64 of 87

be equal to the whole-body penetrating dose. Additional guidance on determining skin dose can be 

obtained from Interpretation of Dosimetry Data for Assignment of Shallow Dose (ORAUT 2005e).

6.3.5 Extremity Dose

Assignment to and use of extremity dosimeters by Ames Laboratory workers has been inconsistent. 

In some years, there are no reported extremity dose results; in many years, there are only a few 

results, which suggests a less-than-rigorous extremity dosimetry program given the types and 

quantities of radioactive materials handled. Results are so sparse that it must be concluded that 

extremity doses were essentially unmonitored. 

A standard practice in operational health physics is to use a factor of 10 between whole-body and 

extremity exposures (PNNL 2006). That is, if the measured contact dose rate from a source is 10 

times (or more) the measured dose rate at the location of the whole-body dosimeter, extremity 

dosimeters should be assigned for the work. In the case of missing extremity dose data (or 

unmonitored extremities), the whole-body dose can be multiplied by 10 and the result assigned as a 

conservative extremity dose. If the cancer site involves the hands, forearms, feet, or legs below the 

knees, the conservative calculated extremity dose can be used by dose reconstructors. 

6.3.6 Radiation Dose Fraction

Section 6.2.4 addresses the recommended energy ranges and fractions for Ames Laboratory dose 

according to facilities, processes, or activities as required by the Interactive RadioEpidemiological 

Program. 

6.4 ORGAN DOSE 

Once the Hp(10) adjusted doses have been calculated for each year, the values are used to calculate 

organ doses of interest using the external dose reconstruction implementation guidelines (NIOSH 

2007b). Consistent with Project direction, dose reconstructors should assume anterior-posterior (AP; 

front to back) geometry for the irradiation geometry and for conversion to organ dose. Multiply the 

calculated neutron doses by the conversion factors from ambient dose equivalent to organ dose for 

AP irradiation from NIOSH (2007b). For photons applicable to Ames Laboratory (i.e., film badge era), 

use the conversion factor from exposure to organ dose. 

7.0 ATTRIBUTIONS AND ANNOTATIONS 

Where appropriate in this document, bracketed callouts have been inserted to indicate information, 

conclusions, and recommendations provided to assist in the process of worker dose reconstruction. 

These callouts are listed here with information to identify the source and justification for each 

associated item. Conventional References, which are provided in the next section of this document, 

link data, quotations, and other information to documents available for review on the Project‟s Site 

Research Database. 

[1] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

X-ray films and logbooks were examined to determine the frequency of routine chest X-rays 

received by early Ames Laboratory workers. No films or records prior to 1946 could be found. 

Numerous records for 1946 and later established the frequencies given in Table 3-1.
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 65 of 87

[2] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

This statement is based on personal experience with a 52 in. cyclotron at the University of 

Colorado, where a bioassay program, routine contamination surveys, and effluent monitoring 

were conducted. Bioassay results were always indistinguishable from background. 

Particulate contamination frequently had a very short half-life and detectable levels were 

almost always less than 10 CFR 835, Appendix D values. Airborne effluents also had short 

half-lives and were indistinguishable from background. This information is consistent with the 

Site Profile for SLAC (ORAUT 2007c), which found that the environmental dose from 

accelerator effluents was less than 1 mrem/yr and negligible. 

[3] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

Common practice in accelerator health physics is to conduct a periodic fence line survey of 

maximum radiation dose rates. The purpose of such surveys is to determine the maximum 

off-site impact of accelerator operations and identify any special controls or limitations that 

may be needed for safe operation. In order to produce maximum fence line dose rates, the 

maximum beam energy and beam current were applied to a target selected for maximum 

radiation production. These operating conditions were unusual and could be detrimental to the 

accelerator equipment, thus the maximum dose rate conditions only existed long enough to 

obtain the fence line survey results. Normally, the accelerator was operated at reduced beam 

currents and with targets that produced much lower radiation dose rates both on- and off-site. 

This was verified by examining the dosimetry records of the Synchrotron staff, which showed 

no unusually high exposures during the May 1961 survey or at any other time. 

SRDB Ref ID 25766 states that “background reading in this area (synchrotron) prior to beam 

being turned on was 0.5 to 1.0 mr/hr.” Apparently, the background reading was taken near the 

synchrotron where the radiation level was slightly elevated (due to activation products) above 

the normal natural background level. However, the exact location of the background reading 

cannot be determined. The fence line readings were taken some distance from the 

background reading location and should have not been influenced by the elevated background 

near the accelerator. In any event, the elevated background dose rates were not subtracted 

from the fence line dose rates reported in Table 4-1.

[4] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

Experience at other accelerator facilities indicates that generally about one-third of the total 

staff time is spent on various non-operational activities, such as experiment set-up, equipment 

start-up, maintenance, repairs, etc. Thus, about two-thirds of the total time is available for 

operations. 

[5] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

The radiation conditions during the fence line radiation survey on May 16, 1961, produced 

dose rates at occupiable locations inside the Synchrotron Building that were greater than 1 

mR/hr. Full-time occupancy in such a locations would give an annual dose of greater than 

2,000 mrem. A review of dosimetry records for Synchrotron staff indicated that no one 

received such a dose during 1961 or at any other time. The average annual dose was less 

than 200 mrem. The average annual dose outside the Synchrotron Building would have been 

much lower. 

[6] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

The buildings of Ames Laboratory are located on the main campus of Iowa State University 

and are not physically separated in any way from other university buildings (i.e., no fence or 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 66 of 87

other boundaries). Staff, students, and the public are free to walk around the exterior walls of 

the buildings. 

[7] Shipler, Dillard B. ORAU Team. Principal Health Physicist. February 2007. 

Over 1,000 tons of uranium metal were processed at Ames Laboratory in about 3 years. The 

University‟s chemistry labs were used for R&D on small quantities, rather than production 

quantities. The estimate that the source term in the labs was 1/100th of the amount handled in 

production facilities was made and was shown to be comparable to releases from labs at the 

University of California at Berkeley, thereby supporting the estimate as reasonable. 

[8] Shipler, Dillard B. ORAU Team. Principal Health Physicist. February 2007. 

The source of the intake numbers was explained in the previous attribution. The assumption 

was made that the thorium was in equilibrium with its progeny, which is favorable to claimants. 

The intake-to-organ-dose conversion factors require that 232Th, 228Ra, and 228Th be entered as 

separate intakes. 

[9] Bihl, Donald E. ORAU Team. Principal Health Physicist. February 2007. 

Because the chemical forms and, therefore, the absorption types of the uranium and thorium 

were not known, especially for the R&D activities, all of the default values in ICRP 68 were 

considered possible. 

[10] Bihl, Donald E. ORAU Team. Principal Health Physicist. February 2007. 

The first sustained chain reaction occurred in the Chicago Pile on December 2, 1942. The pile 

was dismantled in the spring of 1943, so the first irradiated fuel would not have reached Ames 

Laboratory until after that, probably not until 1944, but assuming 1943 was considered 

favorable to claimants. 

[11] Bihl, Donald E. ORAU Team. Principal Health Physicist, February 2007. 

The hot cell was engineered to prevent releases into the workplace and would have had better 

filtration in the exhaust system than a general chemistry lab built in the 1940s. The exact 

nature of the “hot lab” used in the 1940s was not discovered in the records. Presumably, it 

would have involved some methods for recognizing and controlling the spread of 

contamination with some filtration on the exhausts, but it was considered unlikely that the 

controls of the hot lab were as good as those for the hot cell. 

[12] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

The decommissioning date of 1990 was determined in a personal communications with 

Michael J. McGuigan, Radiation Safety Officer, at Ames Laboratory, July 2006. 

[13] Hickey, Eva Eckert. ORAU Team. Principal Health Physicist. February 2007.

Review of references and discussions in Sections 2.1 FACILITIES and 2.2 OPERATIONS 

indicated the location of operations with uranium. 

[14] Hickey, Eva Eckert. ORAU Team. Principal Health Physicist. February 2007.

Review of references and discussions in Sections 2.1 FACILITIES and 2.2 OPERATIONS 

indicated the location of operations with uranium. 

[15] Hickey, Eva Eckert. ORAU Team. Principal Health Physicist. February 2007.

Because there was no information regarding the amount of time in any one day that a worker 

would be exposed to material, an assumption had to be made. The assumptions in the 

section on uranium are the same as the assumptions used in Battelle 2006a and 2006b. 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 67 of 87

[16] Hickey, Eva Eckert. ORAU Team. Principal Health Physicist. February 2007.

Because there was no information regarding the amount of time in any one day that a worker 

would be exposed to material, an assumption had to be made. The assumptions in the 

section on uranium are the same as the assumptions used in Battelle 2006a and 2006b. 

[17] Hickey, Eva Eckert. ORAU Team. Principal Health Physicist. February 2007.

Because there was no information regarding the amount of time in any one day that a worker 

would be exposed to material, an assumption had to be made. The assumptions in the 

section on uranium are the same as the assumptions used in Battelle 2006a and 2006b. 

[18] Bihl, Donald E. ORAU Team. Principal Health Physicist. April 2007. 

The calculations in the preceding 3 paragraphs were conducted by Mr. Bihl using IMBA from 

data presented in the referenced documents. Although hard to read, the urinalysis values 

used for the most exposed worker from Tybout (1944) were 0.00, 0.06, 0.00, 0.20, 0.00, and 

0.10 mg/L adjusted to mg/d. The 0.00 values were entered as <0.056 mg/d, assuming that the 

detection level was approximately 0.04 mg/L. 

[19] Bihl, Donald E. ORAU Team. Principal Health Physicist. February 2007. 

As long as the energy employee‟s actual excretion is less than the excretion plotted in the 

figures, the energy employee‟s intake is also less than the default intakes. For a 

noncompensable case, if the true intake is less than the default intake, the default intake can 

be used for efficiency purposes. 

[20] Bihl, Donald E., and Hickey, Eva Eckert. ORAU Team. Principal Health Physicists. February 

2007.

The air sample results were indistinguishable from background, so were not of much help. Of 

the surface survey results in areas somewhat accessible to people, the highest result was 

1224 dpm; however, there was no record of the surface area smeared. Surface activity is 

usually reported in units of activity per 100 cm2, but the authors could not be sure of that. We 

had to "assume" the survey values were for 100 cm2. Because of that uncertainty, we 

arbitrarily raised the 1,224 dpm value to 2,000 dpm/100 cm2to clearly represent an upper 

bound. 

[21] Bihl, Donald E. ORAU Team. Principal Health Physicist. February 2007. 

Indoors resuspension factors range from 10-6 to 10-3. The IAEA (“Monitoring of Radioactive 

Contamination on Surfaces,” Technical Reports Series No. 120, 1970) recommends an indoor 

resuspension factor of 5x 10-5. 10-4 was chosen for this application to represent an upper 

bound for chronic intake from surfaces not immediately accessible and therefore, not often 

disturbed. 

[22] Bihl, Donald E. ORAU Team. Principal Health Physicist. February 2007. 

Hokel et al. (1998) indicated that the thorium was assumed to be in equilibrium with its 

progeny. The intake dose conversion factors account for buildup/decay of 232Th progeny in the 

body after the intake, but the activity of the progeny already in the air at intake have to be 

treated as separate intake radionuclides. Because of their short half-lives, 228Ac is included in 

dose calculations for 228Ra and all the progeny from 228Th are included in the dose calculations 

for 228Th, so only 228Ra and 228Th need to be entered as intakes separate from 232Th. 

[23] Hickey, Eva Eckert. ORAU Team. Principal Health Physicist. February 2007.

Review of Hokel et al. (1998) suggested that there were areas with higher contamination, such 

as crawl spaces and vertical void spaces in rooms that were rarely, if ever, occupied. The 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 68 of 87

statement in Section 5.2 that contamination was 10 to 100 times greater generalizes the 

discussion in Hokel et al 1998 on this subject. 

[24] Hickey, Eva Eckert, ORAU Team. Principal Health Physicist. February 2007. 

In various places in Hokel et al. (1998), there were statements that the areas that were rarely 

accessed that are still contaminated are carefully controlled, and that workers wear protective 

equipment and are monitored by health physics technicians; therefore, the 6 pCi/d chronic 

intake is an upper bound. 

[25] Bihl, Donald E. ORAU Team. Principal Health Physicist. February 2007. 

MDAs or recording levels varied at the major AEC sites in the 1960s and 1970s from 1 μCi/L 

at Hanford, Savannah River, and Los Alamos, to 0.02 μCi/L at Oak Ridge and Livermore 

National Laboratories, to 0.0002 μCi/L at the Idaho National Engineering Lab. The Hanford 

and Savannah River values were recording levels with actual laboratory MDAs generally being 

lower. Review of the way data were recorded at Ames indicated that 0.1 μCi/L was the likely 

MDA or recording level. 

[26] Bihl, Donald E. ORAU Team. Principal Health Physicist. February 2007. 

The table was created by Mr. Bihl using the lognormal tritium dose plots created by Thomas R. 

La Bone as explained in the text. 

[27] Bihl, Donald E. ORAU Team. Principal Health Physicist. February 2007. 

Strontium is type F except for the titanate form, which is rare. There is no reason to suspect 

Sr titanate was in use at Ames. 

[28] Hickey, Eva Eckert. ORAU Team. Principal Health Physicist. February 2007. 

Hot cells are designed to be inherently safe with no material being released. Since no 

information was found that indicated that there was ever a problem or accident with the hot 

cell, it can be assumed that it functioned as expected. 

[29] Hickey, Eva Eckert. ORAU Team. Principal Health Physicist. February 2007.

Table 5-7 is a summary of the intakes described in this Section. The data is taken from (1) 

Table 5-1 and the discussion in Section 5.1.1.1 on uranium inhalation; (2) Table 5-2 and the 

discussion in Section 5.1.1.2 on uranium ingestion; (3) Table 5-3 and the discussion in Section 

5.1.1.3 on resuspension of uranium during periods of no operation; (4) the discussion in 

Section 5.2 on thorium exposure from left over thorium contamination; (5) doses from tritium 

as discussed in Section 5.3; and (6) Table 5-6 doses from fission product intakes as discussed 

in section 5.4. 

[30] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

The uranium and thorium metal production processes at Ames Laboratory established that 

workers were exposed to external radiation doses between 1942 and 1952. The only records 

of radiation dosimetry measurements during this period are Trybout (1944) and Voss (1949), 

which are very incomplete records. Either the radiation doses were not measured or 

essentially no records were kept. In either case, the workers during this period were 

unmonitored. 

[31] Martin, Jerome B.. ORAU Team. Senior Health Physicist. February 2007. 

Voss (1949) recorded radiation exposures measured by pocket chambers for 15 individuals 

during a 2-week period in February 1949. These were the only pocket chamber dosimeter 

records found for the 1942 to 1952 period. The record suggests that pocket chambers were 
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 69 of 87

available during this period, but either they were not used or if they were used, records of the 

dosimeter readings were not kept. 

[32] Martin, Jerome B.. ORAU Team. Senior Health Physicist. February 2007. 

During the 1965 to 1981 period, the film badge dosimetry records reflect badge numbers only. 

Rosters of names and badge numbers for bioassay records were found and it was possible to 

correlate some badge numbers and individual names. However, there were many badge 

numbers for which a name could not be assigned. 

[33] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

As the spreadsheets were assembled, some adding and subtraction errors in the dosimetry 

records were noted. In all cases, the result that gave the highest dose was assumed and 

recorded in the spreadsheets. 

[34] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

After 1979, neutrons were no longer included in the source term at Ames Laboratory and 

neutron dosimeters were no longer needed. 

[35] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

As stated in Section 6.2.1 Dosimetry, record keeping from January 1962 through June 1963 

was less than adequate. The only records found for 1962 were some calibration data from 

April 1962 and the annual summary data for 1962 (Voss 1963b). It was assumed that the inhouse film badge system continued through December 1962, with film badges exchanged on a 

biweekly frequency; however, no records could be found to confirm this assumption. Monthly 

film badge service was provided for all Ames Laboratory personnel with the potential for 

radiation exposure by the Atomic Film Badge Corporation from July 1963 through March 1965. 

No records were found for the first half of 1963. 

[36] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

With the wide variety of radiation sources used at Ames Laboratory, it is possible that beta, 

photon, and neutron fields with energies outside the assumed ranges existed. However, the 

predominant radiation fields were within the assumed energy ranges and if it is assumed that 

100% of the radiation fields were within these ranges, it is a conservative assumption that is 

generally favorable to claimants. 

[37] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

The early history of research at Ames Laboratory was described by Spedding (1947); later 

history was described in Ames (1985). These documents discussed numerous research 

projects that involved many beta-emitting radioisotopes. The quantities used in research were 

much smaller than the quantities involved in production operations. 

[38] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

The descriptions of research and production operations at Ames Laboratory (Spedding 1947, 

Ames 1985) established the presence of photons in the less than 30 keV, 30-250 keV, and 

greater than 250 keV energy ranges. However, the predominant photon energy range was 

from 30 to 250 keV. If it is assumed that 100% of the photon radiation fields were within this 

range, it is a conservative assumption that is generally favorable to claimants. 

[39] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

Descriptions of the synchrotron (Ames 1967) and the research reactor (Voigt 1981) 

established that neutrons of varying energies were present in these facilities. However, no 
Document No. ORAUT-TKBS-0055 Revision No. 00 PC-1 Effective Date: 08/20/2008 Page 70 of 87

records were found that characterized the neutron spectrum in either facility. If it is assumed 

that 100% of the neutron radiation fields were with the 0.1 to 2 MeV energy range, it is a 

conservative assumption that is generally favorable to claimants. 

[40] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

Commercial film badge service was supplied by Brookhaven National Laboratory from April 

1954 to June 1957, by Nucleonic Corporation of America from July 1957 to June 1963, by 

Atomic Film Badge Corporation from July 1963 to March 1965, and by Health Physics 

Services from June 1965 to September 1981 (see Table 6-1). 

[41] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

The film badge dosimeters used at Ames Laboratory were state-of-the-art commercial 

products that were properly designed and calibrated to give reliable dose results. The TLDs 

used since 1980 were commercial products that were NVLAP accredited and calibrated to give 

reliable dose results. 

[42] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

The neutron doses received by ALRR staff were somewhat higher when compared to similar 

staff at the High Flux Beam Reactor at Brookhaven (ORAUT 2006e). The ALRR records did 

not include any gamma or neutron radiation surveys around the experimental areas, nor was 

there any evidence of neutron spectral measurements. The lack of survey data suggests that 

management of neutron shielding may have been less than adequate. 

[43] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

The maximum beam energy at the Ames Laboratory synchrotron was 80 MeV; the maximum 

beam energy at the SLAC synchrotron was 200 MeV. Both accelerators produced neutrons, 

but the neutron spectrum at SLAC included higher energy neutrons, thus the neutron radiation 

fields were not identical. 

[44] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

The SLAC Site Profile (ORAUT 2007c) used a neutron dose correction factor of 1.53 ± 0.14 to 

account for unmeasured neutrons with energies below 800 keV. Although the neutron spectra 

of the Ames Laboratory and SLAC synchrotrons were not identical, they were similar enough 

to justify the assumption of a neutron dose correction factor of 2 for the Ames Laboratory 

synchrotron. 

[45] Martin, Jerome B. ORAU Team. Senior Health Physicist. February 2007. 

During the 1965 to 1981 period, the film badge dosimetry records reflect badge numbers only. 

Rosters of names and badge numbers for bioassay records were found and it was possible to 

correlate some badge numbers and individual names. However, there were many badge 

numbers for which a name could not be assigned. These records indicate that some workers 

were monitored but they have to be considered unmonitored because the records for specific 

individuals cannot be retrieved.
Document No. ORAUT-TKBS-0055 Revision No. 00 Effective Date: 06/22/2007 Page 71 of 87

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Dosimeter, CH-1553-A-2223, University of Chicago, Metallurgical Laboratory, Chicago, Illinois, 

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Spedding, F. H., 1952, Untitled - Environmental Health Conditions, letter to A. Tammaro (U.S. Atomic 

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Spelic, D. C., 2006, Data from 1984, 1986, and 1994 NEXT Survey of Adult Chest Radiography 

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GLOSSARY 

absorbed dose 

Amount of energy in rads or grays deposited in a substance by ionizing radiation per unit mass 

of the substance. See dose. 

absorption type 

Categories for materials according to their speed of absorption in the body, which replaced the 

earlier inhalation clearance classes. Defined by the International Commission on Radiological 

Protection, the absorption types are F for fast absorption (formerly inhalation class D), M for 

moderate absorption (formerly inhalation class W), and S for slow absorption (formerly 

inhalation class Y). Also called solubility type. 

acute exposure 

Radiation exposure to the body delivered in a short period. See chronic exposure. 

alpha radiation 

Positively charged particle emitted from the nuclei of some radioactive elements. An alpha 

particle consists of two neutrons and two protons (a helium nucleus) and has an electrostatic 

charge of +2. Alpha particles have low penetrating power and a short range (a few 

centimeters in air). Outside the body, the most energetic alpha particle generally fails to 

penetrate the dead layers of cells covering the skin or a sheet of paper. Alpha particles 

emitted by radionuclides inside the body are a more significant health risk. 

background radiation 

Radiation from cosmic sources, naturally occurring radioactive materials including naturally 

occurring radon, and global fallout from the testing of nuclear explosives. Background 

radiation does not include radiation from source, byproduct, or Special Nuclear Materials 

regulated by the U.S. Nuclear Regulatory Commission. The average individual exposure from 

background radiation is about 360 millirem per year. 

becquerel (Bq) 

International System unit of radioactivity equal to 1 disintegration per second; 1 curie equals 

37 billion (3.7 × 1010) becquerels. 

beta radiation 

Charged particle emitted from some radioactive elements with a mass equal to 1/1,837 that of 

a proton. A negatively charged beta particle is identical to an electron. A positively charged 

beta particle is a positron. Most of the direct fission products are (negative) beta emitters. 

Exposure to large amounts of beta radiation from external sources can cause skin burns 

(erythema), and beta emitters can be harmful inside the body. Thin sheets of metal or plastic 

can stop beta particles. 

bioassay 

Determination of kinds, quantities, or concentrations, and in some cases locations of 

radioactive material in a living body, whether by direct measurement (in vivo measurement) or 

by analysis and evaluation of materials excreted or removed from the body (in vitro

measurement). Also called radiobioassay. 
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chronic exposure 

Radiation dose to the body delivered in small amounts over a long period (e.g., days or years). 

For the purposes of input to the Interactive RadioEpidemiological Program, chronic exposure 

is selected under exposure rate for beta and neutron dose. See acute exposure. 

curie (Ci) 

Traditional unit of radioactivity equal to 37 billion (3.7 x 1010) becquerels, which is 

approximately equal to the activity of 1 gram of pure 226Ra. 

depleted uranium (DU) 

Uranium with a percentage of 235U lower than the 0.7% found in natural uranium. As 

examples, spent (used) fuel elements, byproduct tails, residues from uranium isotope 

separation, and some weapons materials contain DU. DU can be blended with highly 

enriched uranium to make reactor fuel or used as a raw material to produce plutonium. 

dose 

In general, the effects of ionizing radiation in terms of the specific amount of energy absorbed 

per unit of mass. Effective and equivalent doses are in units of rem or sievert; other types of 

dose are in units of roentgens, rads, reps, or grays. Various terms narrow the type of dose, 

and some are additive: 

 Absorbed dose is the amount of energy deposited in a substance by ionizing radiation. 

 Collective dose is the sum of the doses to a specific population.

 Committed dose is the dose over time (usually 50 years for workers) to a specific organ 

or tissue from an intake of radioactive material. 

 Cumulative dose is the sum of all doses to the same portion of the body or to the whole 

body over time. 

 Deep dose is the dose at a 1-centimeter depth in tissue (1,000 milligrams per square 

centimeter). 

 Effective dose is the sum of the equivalent doses in the principal tissues and organs of 

the body, each weighted by a tissue weighting factor that accounts for the probabilities 

of fatal and nonfatal cancers according to severity and the average length of life lost 

due to an induced cancer. It indicates the biological effect of the radiation exposure in 

that tissue. 

 Equivalent dose or dose equivalent is the absorbed dose in a tissue or organ multiplied 

by a weighting factor for the particular type of radiation. 

 Organ dose is the dose to a specific organ. 

 Penetrating dose is that from higher energy photon (gamma and X-ray) radiation and 

neutron radiation that penetrates the outer layers of the skin. Nonpenetrating dose is 

that from beta and lower energy photon radiation. 

 Personal dose equivalent is the dose equivalent in soft tissue below a specified point 

on the body at a specified depth. 
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 Shallow dose is the dose at a 0.07-millimeter depth in tissue (7 milligrams per square 

centimeter). 

 Skin dose is the dose to the skin. 

 Whole-body dose is the dose to the entire body excluding the contents of the 

gastrointestinal tract, urinary bladder, and gall bladder. 

deep dose equivalent (DDE, Hd, Hp(10)) 

Dose equivalent in units of rem or sievert for a 1-centimeter depth in tissue (1,000 milligrams 

per square centimeter). See dose. 

depleted uranium (DU) 

Uranium with a percentage of 235U lower than the 0.7% found in natural uranium. As 

examples, spent (used) fuel elements, byproduct tails, residues from uranium isotope 

separation, and some weapons materials contain DU. DU can be blended with highly 

enriched uranium to make reactor fuel or used as a raw material to produce plutonium. 

dose equivalent (H, DE) 

Product of absorbed dose in units of rem or sievert in tissue multiplied by a weighting factor 

and sometimes by other modifying factors to account for the potential for a biological effect 

from the absorbed dose. See dose. 

dosimeter 

Device that measures the quantity of received radiation, usually a holder with radiationabsorbing filters and radiation-sensitive inserts packaged to provide a record of absorbed dose 

received by an individual. See film dosimeter, neutron film dosimeter, and thermoluminescent 

dosimeter. 

dosimetry 

Measurement and calculation of internal and external radiation doses. 

dosimetry system 

System for assessment of received radiation dose. This includes the fabrication, assignment, 

and processing of external dosimeters, and/or the collection and analysis of bioassay samples, 

and the interpretation and documentation of the results. 

enriched uranium (EU) 

Uranium in which processing has increased the proportion of 235U to 238U to above the natural 

level of 0.7%. Reactor-grade uranium is usually about 3.5% 235U; weapons-grade uranium 

contains greater than 90% 235U.

exposure 

In general, the act of being exposed to ionizing radiation. See acute exposure and chronic 

exposure. In this document, exposure does not refer to the radiological physics concept of 

charge liberated per unit mass of air. 

film 

Radiation-sensitive photographic film in a light-tight wrapping. See film dosimeter. 
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film dosimeter 

Package of film for measurement of ionizing radiation exposure for personnel monitoring 

purposes. A film dosimeter can contain two or three films of different sensitivities, and it can 

contain one or more filters that shield parts of the film from certain types of radiation. When 

developed, the film has an image caused by radiation measurable with an optical 

densitometer. Also called film badge. 

fission products 

(1) Radionuclides produced by fission or by the subsequent radioactive decay of 

radionuclides. (2) Fragments other than neutrons that result from the splitting of an atomic 

nucleus. 

gamma radiation 

Electromagnetic radiation (photons) of short wavelength and high energy (10 kiloelectron-volts 

to 9 megaelectron-volts) that originates in atomic nuclei and accompanies many nuclear 

reactions (e.g., fission, radioactive decay, and neutron capture). Gamma rays are very 

penetrating, but dense materials such as lead or uranium or thick structures can stop them. 

Gamma photons are identical to X-ray photons of high energy; the difference is that X-rays do 

not originate in the nucleus. 

gray (Gy) 

International System unit of absorbed radiation dose, which is the amount of energy from any 

type of ionizing radiation deposited in any medium; 1 Gy equals 1 joule per kilogram or 

100 rads. 

ionizing radiation 

Radiation of high enough energy to remove an electron from a struck atom and leave behind a 

positively charged ion. High enough doses of ionizing radiation can cause cellular damage. 

Ionizing particles include alpha particles, beta particles, gamma rays, X-rays, neutrons, 

high-speed electrons, high-speed protons, photoelectrons, Compton electrons, 

positron/negatron pairs from photon radiation, and scattered nuclei from fast neutrons. 

intake 

Radioactive material taken into the body by inhalation, absorption through the skin, injection, 

ingestion, or through wounds. Depending on the radionuclide involved, intakes are in units of 

mass, activity, or potential alpha energy. 

internal dose or exposure 

Dose received from radioactive material in the body. 

internal dose assessment 

Estimation of an intake of radioactive material and the consequent internal radiation dose 

based on measurements in the work environment and/or bioassay. 

in vitro

Of or relating to a process that takes place under artificial conditions or outside a living 

organism (e.g., in the laboratory). From Latin meaning in glass. 

in vivo

Of or relating to a process that takes place in a living organism. From Latin meaning in life. 
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minimum detectable activity or amount (MDA) 

Lowest amount of radioactive activity or substance amount detectable by a specific instrument 

or process. Smallest amount or activity of a radionuclide in a sample or organ that yields a 

result above the detection level with a specific probability of a Type II (false negative) error 

while accepting an specific probability of a Type I (false positive) error. 

minimum detection level (MDL) 

Lowest amount (mass or activity) of a substance detectable by a specific instrument or 

process. Often assumed to be the level at which a dose is detected at the 2-sigma level (i.e., 

95% of the time). Also called minimum detectable limit and minimum detection limit or level. 

missed dose 

Dose to monitored workers that was not measured or recorded due to such factors as a 

missing or damaged dosimeter or a result below the detection limits of the dosimeter. Missed 

dose is especially important in the early years of radiation monitoring, when relatively high 

detection limits were combined with short exchange periods. 

monitoring 

Periodic or continuous determination of the presence or amount of ionizing radiation or 

radioactive contamination in air, surface water, ground water, soil, sediment, equipment 

surfaces, or personnel (for example, bioassay or alpha scans). In relation to personnel, 

monitoring includes internal and external dosimetry including interpretation of the 

measurements. 

natural uranium (U, U-nat, NU) 

Uranium as found in nature, approximately 99.27% 238U, 0.72% 235U, and 0.0054% 234U by 

weight. The specific activity of this mixture is 2.6 × 107 becquerels per kilogram 

(0.7 picocuries per gram). See uranium. 

neutron 

Basic nucleic particle that is electrically neutral with mass slightly greater than that of a proton. 

There are neutrons in the nuclei of every atom heavier than normal hydrogen. 

neutron film dosimeter 

Film dosimeter with a nuclear track emulsion, type A, film packet. 

nuclear track emulsion, Type A (NTA) 

Film sensitive to fast neutrons made by Eastman Kodak. The developed image has tracks 

caused by neutrons that visible under oil immersion with about 1,000-power magnification. 

occupational dose 

Internal and external ionizing radiation dose from exposure during employment. Occupational 

dose does not include that from background radiation or medical diagnostics, research, or 

treatment. 

occupational exposure 

Exposure to radiation and/or to radioactive material from sources of radiation, whether in the 

possession of the DOE site contractor or other person, in a restricted area or in the course of 

employment in which the individual's assigned duties. Occupational exposure does not 

include exposure to background radiation, as a patient from medical practices, from voluntary 

participation in medical research programs, or as a member of the public. 
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occupational medical exposure 

Exposure to radiation or radioactive materials from medical diagnostic procedures during 

physical examinations that are required as a condition of employment. For dose 

reconstruction, occupational medical exposure is a component of occupational exposure. 

personal dose equivalent [Hp(d)] 

Dose equivalent in units of rem or sievert in soft tissue below a specified point on the body at 

an appropriate depth d. The depths selected for personal dosimetry are 0.07 millimeters 

(7 milligrams per square centimeter) and 10 millimeters (1,000 milligrams per square 

centimeter), respectively, for the skin (shallow) and whole-body (deep) doses. These are 

noted as Hp(0.07) and Hp(10), respectively. The International Commission on Radiological 

Measurement and Units recommended Hp(d) in 1993 as dose quantity for radiological 

protection. 

photon 

Basic unit of electromagnetic radiation. Photons are massless “packages” of light energy that 

range from low-energy microwave photons to high-energy gamma rays. Photons have 

energies between 10 and 100 kiloelectron-volts. See photon radiation. 

photon radiation 

Electromagnetic radiation of light energy (photons) from microwaves to gamma rays. Gamma 

rays and X-rays are examples of ionizing photon radiation, which have enough energy to 

penetrate matter, including the body, and deposit energy in that matter. 

probability of causation (POC) 

For dose reconstruction under the Energy Employees Occupational Illness Compensation Act, 

the percent likelihood that a worker incurred a particular cancer from occupational exposure to 

radiation. 

rad 

Traditional unit for expressing absorbed radiation dose, which is the amount of energy from 

any type of ionizing radiation deposited in any medium. A dose of 1 rad is equivalent to the 

absorption of 100 ergs per gram (0.01 joule per kilogram) of absorbing tissue. The rad has 

been replaced by the gray in the International System of Units (100 rads = 1 gray). The word 

derives from radiation absorbed dose. 

radiation 

Subatomic particles and electromagnetic rays (photons) that travel from one point to another, 

some of which can pass through or partly through solid materials including the human body. 

See ionizing radiation. 

radioactivity 

Disintegration of certain elements (e.g., radium, actinium, uranium, and thorium) accompanied 

by the emission of alpha, beta, gamma, and/or neutron radiation from unstable nuclei. 

radiograph 

Photographic image produced on film by gamma rays or X-rays. Some of the rays (photons) 

can pass through parts of an item, while more opaque parts partially or completely absorb 

them and thus cast a shadow on the film. 
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rem 

Traditional unit of radiation dose equivalent that indicates the biological damage caused by 

radiation equivalent to that caused by 1 rad of high-penetration X-rays multiplied by a quality 

factor. The average American receives 360 millirem a year from background radiation. The 

sievert is the International System unit; 1 rem equals 0.01 sievert. The word derives from 

roentgen equivalent in man; rem is also the plural. 

roentgen (R) 

Unit of photon (gamma or X-ray) exposure for which the resultant ionization liberates a positive 

or negative charge equal to 2.58 × 10-4 coulomb per kilogram (or 1 electrostatic unit of 

electricity per cubic centimeter) of dry air at 0°C and standard atmospheric pressure. An 

exposure of 1 R is approximately equivalent to an absorbed dose of 1 rad in soft tissue for 

higher energy photons (generally greater than 100 kiloelectron-volts). 

routine monitoring 

Monitoring carried out at regular intervals during normal operations. See special monitoring. 

shallow absorbed dose (Ds) 

Absorbed dose at a depth of 0.07 centimeters (7 milligrams per square centimeter) in a 

material of specified geometry and composition. 

shallow dose equivalent [SDE, Hs, Hp(0.07)] 

Dose equivalent in units of rem or sievert at a depth of 0.07 millimeters (7 milligrams per 

square centimeter) in tissue equal to the sum of the penetrating and nonpenetrating doses. 

sievert (Sv) 

International System unit for dose equivalent, which indicates the biological damage caused 

by radiation. The unit is the radiation value in gray (equal to 1 joule per kilogram) multiplied by 

a weighting factor for the type of radiation and a weighting factor for the tissue; 1 Sv equals 

100 rem. 

special monitoring 

Monitoring in addition to the routine monitoring program carried out for special purposes such 

as estimating the amount of radionuclide deposited in a person after a known or suspected 

accidental intake or after a known or suspected environmental release. See routine 

monitoring. 

thermoluminescent dosimeter (TLD) 

Device for measuring radiation dose that consists of a holder containing solid chips of material 

that, when heated by radiation, release the stored energy as light. The measurement of this 

light provides a measurement of absorbed dose. 

transuranic (TRU) elements 

Elements with atomic numbers above 92 (uranium). Examples include plutonium and 

americium. All isotopes of the transuranic elements are radioactive, they are naturally either 

rare or nonexistent on Earth, and most are known only as a result of research using nuclear 

reactors and particle accelerators because of extremely short half-lives. 

unmonitored dose 

Potential unrecorded dose that could have resulted because a worker was not monitored. See 

missed dose. 
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uranium (U) 

Heavy, metallic, and radioactive element with atomic number 92. Most natural uranium as 

found in ores is 238U with trace levels of other isotopes. Uranium-235 (0.7% of natural 

uranium) is fissile by itself and used in nuclear weapons as well as reactors. Uranium-238 

(99.3% of natural uranium) is fissionable by fast neutrons and used in nuclear reactors. 

Natural uranium contains a minute amount of 234U. See depleted uranium, enriched uranium, 

and natural uranium. 

whole-body (WB) dose 

Dose to the entire body excluding the contents of the gastrointestinal tract, urinary bladder, 

and gall bladder and commonly defined as the absorbed dose at a tissue depth of 

10 millimeters (1,000 milligrams per square centimeter). Also called penetrating dose. 

See dose. 

X-ray 

(1) See X-ray radiation. (2) See radiograph. 

X-ray radiation 

Penetrating electromagnetic radiation (photons) of short wavelength (0.001 to 10 nanometers) 

and energy less than 250 kiloelectron-volts. X-rays usually come from excitation of the 

electron field around certain nuclei. Once formed, there is no difference between X-rays and 

gamma rays, but gamma photons originate inside the nucleus of an atom.