ORAU Team

Dose Reconstruction Project for NIOSH

Assignment of Missed Neutron Doses Based on Dosimeter 

Records

Document Number:

ORAUT-OTIB-0023

Effective Date: 03/07/2005

Revision No.: 00

Controlled Copy No.: ______

Page 1 of 4

Subject Expert: Steven E. Merwin

Document Owner

Approval: Signature on File Date: 03/02/2005

Edward F. Maher, Task 5 Manager

Concurrence: Signature on File Date: 03/05/2005

Richard E. Toohey, Project Director

Approval: Signature on File Date: 03/07/2005

James W. Neton, Associate Director for Science

Supersedes:

None
Effective Date: 03/07/2005 Revision No. 00 Document No. ORAUT-OTIB-0023 Page 2 of 4

RECORD OF ISSUE/REVISIONS

ISSUE 

AUTHORIZATION 

DATE

EFFECTIVE 

DATE

REV. 

NO. DESCRIPTION

Draft 12/01/2004 00-A New technical information bulletin to provide 

information to allow ORAU Team dose 

reconstructors to determine when it is appropriate 

to assign neutron doses to workers at DOE sites 

using the LOD/2 method. Initiated by Steven E. 

Merwin.

Draft 12/16/2004 00-B Incorporates NIOSH review comments. Initiated 

by Steven E. Merwin.

Draft 02/25/2005 00-C Incorporates additional NIOSH review comments. 

Initiated by Steven E. Merwin.

03/07/2005 03/07/2005 00 First approved issue. Initiated by Steven E. 

Merwin.
Effective Date: 03/07/2005 Revision No. 00 Document No. ORAUT-OTIB-0023 Page 3 of 4

1.0

The purpose of this Technical Information Bulletin (TIB) is to provide information to allow ORAU Team 

dose reconstructors to determine when it is appropriate to assign neutron doses to workers at DOE 

sites using the LOD/2 method.

PURPOSE

2.0

According to OCAS-IG-001, missed doses are to be assigned using the “Limit of Detection (LOD)/2 

method,” which was originally proposed by the National Research Council in their evaluation of film 

badge dosimetry for compensation of atomic veterans. The method involves the assignment of a 

dose equal to the LOD divided by 2 for each dosimetry measurement that is recorded as zero, below 

the limit of detection, or below a reported threshold. According to the IG, this method is 

recommended “since this scheme has been used in other compensation programs and has been 

shown to result in a slight positive bias.” 

BACKGROUND

Workers who were unmonitored for external radiation exposure are not assigned missed dose using 

the LOD/2 method; rather, they are assigned either external on-site ambient doses, if they were nonradiological workers and would not have been exposed to workplace radiation sources; or 

unmonitored doses (using co-worker studies or some other approach) if a potential for exposure 

existed.

The assignment of missed neutron doses is somewhat more complex. In the early years at most 

DOE sites, neutron doses were not measured reliably, so missed neutron doses are assigned based 

on neutron-gamma ratios, co-worker studies, or some other approach. As stated in the IG, “An 

exception to the [LOD/2] method is needed for unreasonably high neutron exposures. Therefore, 

when the neutron missed dose central estimate (nLOD/2) would exceed 75% of the photon dose 

(dosimeter dose + missed dose), the exposure should be treated as unmonitored exposure and 

radiation survey data combined with stay times (frequency of exposure) should be used to estimate 

the missed dose.”

3.0

The guidance in this TIB applies to cases in which the neutron monitoring devices in use at the site 

produced results that were considered the dose of record. It does not apply to periods during which 

the monitoring was unreliable and some method other than the monitoring data (e.g., neutron-gamma 

ratios) is normally used to assign neutron dose based on information in the site TBD or other reliable 

source.

APPLICATIONS AND LIMITATIONS

4.0

1. NIOSH (National Institute for Occupational Safety and Health), External Dose Reconstruction 

Implementation Guideline, Rev. 0, OCAS-IG-001, Office of Compensation Analysis and Support, 

Cincinnati, Ohio, 2002.

REFERENCES

5.0

As described in OCAS-IG-001, the LOD/2 method results in a positive bias for photon exposures. By 

definition, this bias is extreme if there was no potential for photon exposure (e.g., a worker downtown 

in an administrative building who did not visit the site). By and large, however, workers who were 

issued dosimeter badges at DOE sites had a potential for photon exposure, and photon radiation 

ANALYSIS 
Effective Date: 03/07/2005 Revision No. 00 Document No. ORAUT-OTIB-0023 Page 4 of 4

sources were generally omnipresent at the sites so the issuance of dosimeter badges is considered 

an indicator of the potential for exposure. Thus, even though the LOD/2 method for assigning missed 

dose is claimant favorable in general, and highly claimant favorable for employees with limited or no 

potential for exposure (i.e., employees with all or mostly zeroes in the records), this approach has 

been prescribed in the IG upon analysis of alternative approaches. 

Regarding neutron exposures, however, at some DOE sites and during certain eras, neutron 

dosimeters were included in the site dosimetry badges as a matter of administrative practice rather 

than as an indicator of a potential for neutron exposure. Thus, some employees have a string of 

zeroes in the neutron column in their monitoring records even though there may have been little or no 

exposure potential based on their work locations. Additionally, at a few DOE sites zeroes may be 

included in the records as an administrative practice even though monitoring did not occur. 

Therefore, not only are there instances in which the LOD/2 method results in unreasonably high 

neutron doses, as acknowledged in the IG, but also instances in which the method is not applicable 

because it could result in the assignment of neutron doses even though there was no potential for 

neutron exposure.

6.0

Workers who were monitored for neutrons using reliable dosimeters should generally be assigned 

missed doses in accordance with OCAS-IG-001 (i.e., using the LOD/2) method for any null results. 

As described in the IG, however, an exception to the method is needed for unreasonably high neutron 

doses.

GUIDANCE

Missed neutron doses do not need to be assigned if both

1. The neutron missed dose central estimate (nLOD/2) would exceed 75% of the photon dose 

(dosimeter dose + missed dose).

of the following conditions are met:

2. Based on the employee’s work location(s) and relevant information in the site TBD or other 

documentation (e.g., neutron source term information, neutron survey results, and the potential for 

neutron exposures), the dose reconstructor determines that the employee’s neutron dose was 

zero or incidental relative to the external dose assigned.

If both of the above conditions are met, dose reconstructors should include appropriate explanatory 

language in the dose reconstruction (DR) report. This should include a discussion in the DR report of 

the available information regarding work locations and the rationale for the conclusion that neutron 

doses could not have exceeded incidental levels.