ORAU Team 

NIOSH Dose Reconstruction Project

Technical Information Bulletin: Occupational Dose from 

Elevated Ambient Levels of External Radiation 

Document Number: 

ORAUT-OTIB-0007 

Effective Date: 11/12/2003 

Revision No.: Rev 00 

Controlled Copy No.: _________ 

Page 1 of 6 

Subject Expert: Dan Strom 

Approval: Signature on File Date: 11/19/2003

Judson L. Kenoyer, Task 3 Manager 

Concurrence: Signature on File Date: 11/19/2003

 Richard E. Toohey, Project Director 

Approval: Signature on File Date: 11/21/2003

 James W. Neton, OCAS Health Science Administrator 

Supersedes: 

None 

RECORD OF ISSUE/REVISIONS 

ISSUE 

AUTHORIZATION 

DATE 

EFFECTIVE 

DATE 

REV. 

NO. DESCRIPTION 

Draft 09/30/2003 00-A Draft ORAU Technical Information Bulletin to 

establish occupational dose from elevated 

ambient levels of external radiation. Initiated by 

Judson L. Kenoyer and Steve Merwin. 

Draft 11/3/2003 00-B Incorporates resolution of OCAS consolidated 

comments. 

11/12/2003 11/12/2003 00 First approved issue. Initiated by Judson L. 

Kenoyer and Steve Merwin. 
Effective Date: 11/12/2003 Revision No. 00 Document No. ORAUT-OTIB-0007 Page 2 of 6 

Occupational Dose from 

Elevated Ambient Levels of External Radiation 

Daniel J. Strom, John J. Fix, Steven E. Merwin, and Bruce A. Napier 

Introduction 

It is possible that external dosimetry results account for both occupational and environmental 

penetrating radiation exposures if control dosimeters were not exposed to elevated ambient levels of 

external radiation (EALER) due to weapons production operations. EALER may come from 1) passing 

plumes of radioactive gas (the neutron activation product 41Ar predominates), 2) sky shine, and 3) 

ground contamination. 

As discussed below, under many circumstances doses due to EALER may have been recorded by 

personnel dosimeters, and would not need to be added separately in the dose reconstruction. 

Control Dosimeters 

External dosimeters using film or thermoluminescent dosimeters have been used for occupational 

radiation monitoring since the 1940s. To account for background radiation levels, which are not 

traditionally included in occupational radiation dose records, control dosimeters have been used from 

the outset. Good radiation protection practice dictates that, during shipment, a control dosimeter 

accompany each batch of dosimeters issued to workers. Between manufacture (or annealing) and 

issuance, and between retrieval and processing, each shipment of dosimeters is irradiated by natural 

cosmic and terrestrial radiation sources, and potentially inadvertently irradiated by other sources. The 

function of the control dosimeter is to measure all non-occupational radiation exposure to the batch of 

dosimeters. On processing, the reading from the control dosimeter is subtracted from the reading of 

each of the other dosimeters in the batch, yielding a result for each dosimeter that is uniquely due to 

occupational radiation exposure. Note that the subtraction could occur with raw data, such as optical 

density readings for film or glow curves, or with transformed data, such as exposures in R, absorbed 

doses in rads or grays, or dose equivalents in rems or sieverts. 

Were Control Dosimeters Exposed to Elevated Ambient Levels of External Radiation? 

The question arises of where the control dosimeters were stored. From the intended use of control 

dosimeters, it is clear that controls should be subjected to exactly the same non-occupational 

radiation exposure as the issued dosimeters, and differ only in the occupational component. The 

implementation of this intention, that is, procedures for issuance and retrieval of dosimeters, likely 

differed over time within a given facility and certainly differed among various DOE and AWE sites. For 

example, at large facilities like Hanford, the Idaho National Engineering and Environmental 

Laboratory, Los Alamos National Laboratory, and Savannah River, controls may have been kept at a 

central dosimeter location, or distributed with batches of dosimeters to remote identification (ID) 

badge/dosimeter exchange buildings such as guard stations near reactors, reprocessing facilities, or 

manufacturing facilities. During some periods of time, dosimeters were incorporated into ID badges to 

ensure that no one entered without a dosimeter, and these ID badges were picked up at the entrance 

station at the beginning of each shift, and turned in there at the end of each shift. 

If control dosimeters were kept at remote exchange facilities, then they would have recorded elevated 

ambient levels of external radiation (EALER) at those facilities. Such doses from EALER recorded by 

the controls would subsequently have been subtracted from each worker’s dosimeter reading. 

However, if control dosimeters were kept at a distant, central badging facility where ambient radiation 

levels were lower than in the work areas, then each worker’s dosimeter would have recorded not only 
Effective Date: 11/12/2003 Revision No. 00 Document No. ORAUT-OTIB-0007 Page 3 of 6 

his or her occupational exposure, but his or her exposure to elevated ambient radiation levels. In the 

latter case, no adjustment for occupational environmental radiation levels is needed, since they would 

have been included in the worker’s occupational measurements. 

Elevated Ambient Levels of External Radiation (EALER) 

Near operating reactor facilities in the early days, one important component of external environmental 

dose arose from submersion in, or irradiation at a distance from, a plume containing 41Ar (with a 

radiological half-life of 1.83 hours), formed when naturally-occurring 40Ar nuclei absorb neutrons. The 

emissions from 41Ar are primarily a 1.2-MeV (maximum) β particle and a 1.3-MeV γ photon. A wooden 

badge exchange building would likely provide very little shielding or attenuation of the γ emission, and 

if air exchange rates at the control dosimeter storage point were high, even the β component may 

have approached outdoor levels. 

Besides radiation from airborne releases of radioactive materials, other components of EALER could 

arise from 1) scattered radiation from waste trenches, storage facilities, etc., 2) terrestrial 

contamination, and 3) sky shine (radiation scattered to the ground from air over nuclear or highenergy accelerator facilities). However, these components are unlikely to have been the same at 

dosimeter exchange facilities as on the rest of the site, so that control dosimeters stored at remote 

exchange facilities would not have recorded this component. 

Issues 

1. What sites had potential for significant ambient environmental external radiation exposure 

(EALER)? 

Sites with potential for significant EALER include those with 

• operating production reactors, 

• fuel reprocessing, 

• other radiochemical processing facilities, 

• atmospheric nuclear weapons testing, 

• underground nuclear weapons testing with significant venting of fission gasses, 

• accidental airborne releases of radioactive materials, and 

• certain high-energy accelerators (in the early years). 

Sites meeting these criteria include Hanford (which included Hanford Laboratories, what became 

Pacific Northwest National Laboratory in 1965), Savannah River, Oak Ridge National Laboratory, 

Idaho National Engineering and Environmental Laboratory, the Nevada Test Site, and Los Alamos 

National Laboratory. 

2. How elevated could the doses be? 

As an example, doses from EALER at Hanford could have been as high as a few millirem per day in 

some cases during the 1940s. Till et al. (2002) reported measurements near the Redox Plant at 

Hanford as high as 36 mrad/day, averaging 8.5 mrad/day between April 1952 and November 1954, 

with some outdoor contamination areas reaching 6 mrem/hour (p. 4-6). While control dosimeters 

were not kept in such high dose-rate areas, there is some possibility of elevated readings where 

control dosimeters were stored. 
Effective Date: 11/12/2003 Revision No. 00 Document No. ORAUT-OTIB-0007 Page 4 of 6 

3. What sites had potential for significant EALER that might not have been measured by a 

claimant’s dosimeter? That is, at what sites were control dosimeters exposed to EALER? 

Large sites might have had inhomogeneous EALER and a need for distributing control dosimeters 

with batches intended for particular areas. For example, film badges and TLDs were processed at 

Hanford in the 3701 gatehouse from the beginning of the film badge program in October 1944. In the 

early days, a worker who had clearance for several areas would have a badge in each one of those 

areas, as many as 7 badges issued simultaneously. A worker’s badge would be stored at the area 

badge house. Routine practice at Hanford involved dosimeter exchange buildings at each major 

operating area. Workers obtained their individually assigned dosimeters upon ingress and left the 

dosimeter upon egress. Along with the dosimeters in each one of those locations (known as “badge 

houses”) there would also be control dosimeters placed in the badge house. At some point (history 

unknown as of this revision), Hanford switched to a single dosimeter being issued at a time to an 

individual. 

4. For what years was this possible? 

In general, there will be a point in time, probably no later than 1970, after which there will be no need 

to assess a specific EALER to add to claimants’ dose histories, because 1) levels were so low they 

would not significantly impact probability of causation, and 2) control dosimeters were kept out of 

harm’s way and EALER would not have been subtracted. As environmental monitoring programs 

matured, environmental TLD measurements rule out significant EALER values. 

For any given site, however, the cutoff date may be earlier than 1970. This can only be established for 

a particular site by reviewing site activities, as has been done for Hanford, Savannah River, Oak 

Ridge National Laboratory, and a few other sites. In the processing of developing site-specific 

Technical Basis Documents for this project, an evaluation of practices involving control badge 

placement is being conducted for each site. Although specific timelines will be reported in the sitespecific TBDs once developed, it is clear that by 1980 all sites had adopted procedures that ensured 

that control badges were not stored in elevated background environments. 

Conclusions

External dosimetry results account for both occupational and environmental penetrating radiation 

exposures if control dosimeters were not exposed to elevated environmental radiation due to 

weapons production operations. Elevated ambient levels of external radiation exposure (EALER) may 

come from 1) passing plumes of radioactive gas (neutron activation product 41Ar predominates), 2) 

sky shine, and 3) ground contamination. Not all DOE and AWE sites may have experienced the 

problem of missed EALER. 

Although there are uncertainties about the periods of time during which this may have happened, the 

sites at which it may have happened, and the subgroups of workers for whom it may be significant, 

after 1970 missed EALER will not be significant in most cases. After 1980, missed EALER was 

essentially nonexistent at DOE facilities. 

It is concluded that for the years 1980 and later, environmental (on-site ambient) doses need not be 

considered when evaluating occupational doses because they would have been accounted for by 

personnel dosimeters. For extremely small environmental doses that were received but not reported 

due to dosimeter detection limits or reporting practices (i.e., in cases in which the reported dose is 

zero for a particular badge cycle), the assignment of missed doses according to procedures 

developed for this project ensures that such environmental doses have been accounted for. A 
Effective Date: 11/12/2003 Revision No. 00 Document No. ORAUT-OTIB-0007 Page 5 of 6 

subsequent revision to this document will provide specific dates for each site establishing when it is 

known that control badges were stored in appropriate locations, which will allow for environmental 

doses to not be evaluated for certain sites prior to 1980.
Effective Date: 11/12/2003 Revision No. 00 Document No. ORAUT-OTIB-0007 Page 6 of 6 

References 

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Till JE, PG Voillequé, GG Killough, and SK Rope. 2002. Methods for Estimating Radiation Doses from 

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