Draft

Advisory Board on Radiation and Worker Health

National Institute for Occupational Safety and Health

SC&A’s Review of NIOSH’s White Paper, “Neutron Dose 

Assignment for K-25 and Portsmouth Gaseous Diffusion 

Plants” 

Contract No. 75D30119C04183

Document No. SCA-TR-2019-SP002, Revision 0

Prepared by

Ron Buchanan, PhD, CHP

SC&A, Inc.

2200 Wilson Boulevard, Suite 300

Arlington, VA 22201-3324

September 16, 2019

DISCLAIMER

This is a working document provided by the Centers for Disease Control and Prevention (CDC) 

technical support contractor, SC&A for use in discussions with the National Institute for 

Occupational Safety and Health (NIOSH) and the Advisory Board on Radiation and Worker 

Health (ABRWH), including its Working Groups or Subcommittees. Documents produced by 

SC&A, such as memorandum, white paper, draft or working documents are not final NIOSH or 

ABRWH products or positions, unless specifically marked as such. This document prepared by 

SC&A represents its preliminary evaluation on technical issues.

NOTICE: This document has been reviewed to identify and redact any information that is

protected by the Privacy Act 5 U.S.C. § 552a and has been cleared for distribution.
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SC&A, Inc. Technical Support for the Advisory Board on Radiation and Worker Health’s Review 

of NIOSH Dose Reconstruction Program

Document Title SC&A’s Review of NIOSH’s White Paper, “Neutron Dose Assignment for 

K-25 and Portsmouth Gaseous Diffusion Plants”

Document Number SCA-TR-2019-SP002

Revision Number 0 (Draft)

Supersedes N/A

Effective Date September 16, 2019

Task Manager Ron Buchanan, PhD, CHP [signature on file]

Project Manager John Stiver, MS, CHP [signature on file]

Document Reviewer(s) John Stiver, MS, CHP [signature on file]

Record of Revisions

Revision Number Effective Date Description of Revision

0 (Draft) 9/16/2019 Initial Issue
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Table of Contents

Abbreviations and Acronyms........................................................................................... 4

1 Introduction and Background ................................................................................... 5

2 Outline of White Paper............................................................................................. 5

2.1 Development of approach .................................................................................. 5

2.2 Data available for Paducah, Portsmouth, K-25, and Y-12.................................. 5

2.3 Quantile regression analyses............................................................................. 6

2.4 Conclusions........................................................................................................ 6

2.5 Appendix A......................................................................................................... 6

3 SC&A’s Evaluation of the White Paper .................................................................... 6

3.1 Selection of available data to use for estimating N:P ratios ............................... 6

3.2 Analyses of dosimetry data ................................................................................ 6

3.3 SC&A’s evaluation of NIOSH’s recommendations ............................................. 7

4 Summary and Conclusions ...................................................................................... 8

5 Reference ................................................................................................................ 9
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Abbreviations and Acronyms

ABRWH Advisory Board on Radiation and Worker Health

GDP gaseous diffusion plant

HEU highly enriched uranium

IREP Interactive RadioEpidemiological Program

LOD limit of detection

MeV mega-electron volt

N:P neutron-to-photon

NIOSH National Institute for Occupational Safety and Health

NTA nuclear track emulsion, type A (film)

QRA quantile regression analyses

TLD thermoluminescent dosimeter

Y-12 National Security Complex
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1 Introduction and Background

The National Institute for Occupational Safety and Health (NISOH) issued on May 6, 2019, the 

white paper, “Neutron Dose Assignment for K-25 and Portsmouth Gaseous Diffusion Plants”

(NIOSH, 2019; hereafter referred to as the “white paper”). The purpose of the white paper was to 

determine a reasonable neutron-to-photon (N:P) ratio that can be used to assign dose for gaseous 

diffusion plant (GDP) energy employees during periods when neutron dose data were not 

reliable, not available, or not recorded. For K-25, this time period was prior to 1992. For 

Portsmouth, this time period was prior to 1995. SC&A was tasked on June 27, 2019, with

reviewing the white paper.

2 Outline of White Paper

2.1 Development of approach

The white paper presents the potential data that could be used to develop N:P values. These are 

outlined on page 3 of the white paper as follows:

• Uranium hexafluoride cylinder yard survey (Paducah) 

• Highly enriched uranium (HEU) storage cylinder dose rates (Portsmouth) 

• HEU storage vault/storage cylinder measurements (Portsmouth) 

• Area monitoring: neutron and photon dose measurements (Portsmouth) 

• Personnel monitoring: neutron and photon dose measurements (Portsmouth) 

• Neutron dose rate survey results (K-25) 

• Neutron and photon dose rate modeling for cylinder yards (K-25) 

• Neutron and photon survey data area and area monitoring results (K-25) 

• Personnel monitoring: neutron and photon dose measurements (K-25) 

• Static dosimetry measurements (National Security Complex (Y-12 Plant))

• Neutron and photon survey data (Y-12 Plant) 

• Personnel monitoring: neutron and photon measurements (Y-12 Plant) 

2.2 Data available for Paducah, Portsmouth, K-25, and Y-12

A summary and a brief analysis of the available neutron and photon dose measurements from 

various GDPs are presented in the white paper, pages 3 through 10.

• Paducah – Page 3. Surveys around cylinder storage resulted in N:P ratios ranging from 

0.14 to 0.42, with an approximate average of 0.2.

• Portsmouth – Pages 3–6. Thermoluminescent dosimeter (TLD) data for 1992–2013 from 

161 records indicate an N:P ratio of 0.369.

• K-25 – Pages 7–9. TLD data for 1989–2012 from 369 records indicate an N:P ratio of 

0.420.
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• Y-12 – Page 10. Dosimetry film data for 1955–1959 from 89 records were included in the 

quantile regression analyses (QRA) of the N:P data. SC&A’s analysis of the 89 records 

indicated an N:P ratio of approximately 0.828. 

2.3 Quantile regression analyses

In addition to the derivation of average N:P ratio values, the white paper provides QRA of the 

Portsmouth, K-25, and Y-12 dosimetry data on pages 10 through 15. The results are summarized 

in table 6, page 18, of the white paper. 

2.4 Conclusions

The white paper used the personnel dosimetry measurements (as opposed to using area survey or 

cylinder storage survey dose data) to derive the recommended assignment of neutron dose for 

unmonitored workers at the GDPs. NIOSH used the QRA method to derive the recommended 

neutron dose equations, as listed in table 6, page 18, of the white paper, and reproduced below: 

50th neutron = 0.195 [photon (rem)] + 0.002 (rem) 

95th neutron = 0.846 [photon (rem)] + 0.002 (rem) 

2.5 Appendix A

Appendix A of the white paper provides a brief description of the application of QRA and the 

Monte Carlo simulation method to be used when assigning neutron dose in the Interactive 

RadioEpidemiological Program (IREP).

3 SC&A’s Evaluation of the White Paper

The following is a summary of SC&A’s evaluation of the white paper.

3.1 Selection of available data to use for estimating N:P ratios

SC&A concurs with NIOSH’s use of personnel dosimetry measurements (as opposed to using 

area survey or cylinder storage survey dose data) to derive the N:P ratio values to assign neutron 

dose for unmonitored workers at the GDPs. Dosimetry data are much more relevant in 

determining N:P ratios than area surveys or cylinder storage survey measurements because 

dosimetry data more realistically reflect workers’ exposure as a function of time and location. 

3.2 Analyses of dosimetry data

SC&A analyzed the Portsmouth, K-25, and Y-12 dosimetry dose data and derived an average 

N:P ratio of 0.412 for Portsmouth, 0.420 for K-25, and 0.828 for Y-12; which are similar to the

N:P ratios stated in the white paper (i.e., NIOSH derived an N:P ratio of 0.369 for Portsmouth 

and 0.420 for K-25). SC&A also analyzed the overall dosimetry data from Portsmouth, K-25, 

and Y-12 (giving equal weight to each N:P ratio value) and derived an average N:P ratio of 

0.474, a 50th percentile ratio of 0.251, and a 95th percentile ratio of 0.901. These values are

summarized in table 1 of this report. SC&A does not consider the N:P values are known to the 

third significate figure (as would be indicated by the numbers listed) but provides them for 

comparison and obtaining averages. 
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Table 1. Summary of N:P ratios

Analysis Portsmouth K-25 Y-12 Weighted 

average

50th 

%

95th 

%

QRA

50th %

QRA

95th %

SCA 0.412 0.420 0.828 0.474 0.251 0.901 NA NA

White paper 0.367 0.420 (0.828) (a) 0.465 NA NA 0.195 0.846

(a) SC&A-derived from NIOSH’s dosimetry data for Y-12.

The N:P ratio values were derived from TLD data for Portsmouth and K-25 and from film 

dosimetry data for Y-12. Neutron dose measurements using nuclear track emulsion, type A 

(NTA) film is sometimes questionable, considering it has a 0.5 mega-electron volt (MeV) 

neutron energy threshold, unless it is calibrated to account for the neutron energy spectra less 

than 0.5 MeV, or unless most of the neutron dose equivalent is greater than 0.5 MeV. Therefore,

the NTA film data from Y-12 could have been questionable. However, its results were similar to 

the TLD results, were slightly claimant favorable, and did not constitute a majority of the total 

data. Therefore, including it did not appear to be an issue in this situation. 

3.3 SC&A’s evaluation of NIOSH’s recommendations

SC&A concurs with NIOSH’s analyses of the available neutron and photon dosimetry data up 

through page 9 of the white paper (to include the Y-12 data with an average N:P ratio of 0.828), 

with the following observation: 

Observation 1: apparent inconsistency in use of limit of detection

The white paper lists the following concerning the application of the lower limit of detection 

(LOD) in the use of dosimetry data: 

• Portsmouth – Page 5 of the white paper states, “result that exceeded the neutron limits of 

detection (LOD) of 10 mrem,” and page 6 states, “neutron dose values greater than the 

LOD of 10 mrem.” 

• K-25 – Page 8 of the white paper states, “Results from 369 neutron dosimeters were 

greater than or equal to the LOD,” and page 9 states, “neutron doses greater than or equal

to the LOD of 10 mrem” (emphasis added). However, the next sentence on page 9 states, 

“An analysis of dosimeters with paired photon and neutron doses greater than the LOD 

was performed” (emphasis added). 

The use of the neutron dosimetry data and photon dosimetry data that were equal to the LOD 

values needs to be clarified; i.e., were “equal to” values used in NIOSH’s analysis, or only values 

that were greater than the LOD? A set method should have been consistently applied to the 

dosimetry data used from the three sites.

Observation 2: use of Portsmouth dosimetry values near zero

As previously discussed in this review, dosimetry values equal to, or greater than, the LOD value 

were used to derive N:P ratios. However, when the white paper used the QRA method for the 

Portsmouth dosimetry data, as illustrated in figures 2 and 4 of the white paper, it appears from 

the plots (and from the number of data points (N), i.e., 3,727 on page 13 versus 161 on page 6)
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that recorded data with values as low as near zero might have been used. This is not consistent 

with the use of dosimetry that is equal to or greater than the LOD. 

SC&A calculated neutron doses over the normal personnel exposure range using both the 

standard N:P ratio method and the QRA method; the results are summarized in figure 1 of this 

report.

Figure 1. Neutron dose using N:P ratio and 50th percentile regression analysis

As can be seen from this example, the use of the QRA method results in approximately half the 

neutron dose being assigned compared to using the standard N:P ratio method. 

Observation 3: use of the standard N:P ratios versus the quantile-regression and Monte 

Carlo approach

SC&A concurs with the N:P ratios derived using standard analyses of the dosimetry data for 

Portsmouth, K-25, and Y-12. However, analyzing the QRA method recommended in the 

conclusions (page 16) of the white paper indicates that the resulting neutron doses assigned at the 

50th percentile in IREP for dose reconstruction purposes would be approximately half of that 

assigned by the standard N:P averaged ratio method. The QRA method is not claimant favorable, 

nor consistent with neutron dose assignments at other U.S. Department of Energy sites.

4 Summary and Conclusions

SC&A’s review of the white paper found that NIOSH N:P ratios derived using dosimetry data 

from Portsmouth, K-25, and Y-12 were reasonable and technically verifiable. SC&A had no 

finding in this review. However, S&A did have the following observations: 

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

0.500

0.000 0.200 0.400 0.600 0.800 1.000

Neutron Dsoe (rem)

Photon Dose (rem

Neutron Dose Using N:P and 50th Percentile Regression Analysis

N:P = 0.47 50th Percentile
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• Observation 1: apparent inconsistency in use of limit of detection – The white paper

lists the following concerning the application of the lower LOD in the use of dosimetry 

data: 

– Portsmouth – Page 5 of the white paper states, “result that exceeded the neutron 

limits of detection (LOD) of 10 mrem,” and page 6 states, “neutron dose values 

greater than the LOD of 10 mrem.” 

– K-25 – Page 8 of the white paper states, “Results from 369 neutron dosimeters 

were greater than or equal to the LOD,” and page 9 states, “neutron doses greater 

than or equal to the LOD of 10 mrem” (emphasis added). However, the next 

sentence on page 9 states, “An analysis of dosimeters with paired photon and 

neutron doses greater than the LOD was performed” (emphasis added). 

The use of the neutron dosimetry data and photon dosimetry data that were equal to the 

LOD values needs to be clarified; i.e., were “equal to” values used in NIOSH’s analysis, 

or only values that were greater than LOD? A set method should have been consistently 

applied to the dosimetry data used from the three sites.

• Observation 2: use of Portsmouth dosimetry values near zero – As previously 

discussed in this review, dosimetry values equal to, or greater than, the LOD value were 

used to derive N:P ratios. However, when the white paper used the QRA method for the 

Portsmouth dosimetry data, as illustrated in figures 2 and 4 of the white paper, it appears 

from the plots (and from the number of data points (N), i.e., 3,727 on page 13 versus 161 

on page 6) that recorded data with values as low as near zero might have been used. This 

is not consistent with the use of dosimetry that is equal to or greater than the LOD. 

• Observation 3: use of the standard N:P ratios versus the quantile-regression and 

Monte Carlo approach – SC&A concurs with the N:P ratios derived using standard 

analyses of the dosimetry data for Portsmouth, K-25, and Y-12. However, analyzing the 

QRA method recommended in the conclusions (page 16) of the white paper indicates that 

the resulting neutron doses assigned at the 50th percentile in IREP for dose 

reconstruction purposes would be approximately half of that assigned by the standard N:P 

averaged ratio method. The QRA method is not claimant favorable, nor consistent with 

neutron dose assignments at other U.S. Department of Energy sites.

5 Reference

National Institute for Occupational Safety and Health (NIOSH). (2019). Neutron dose 

assignment for K-25 and Portsmouth gaseous diffusion plants [White paper]. Retrieved from

SRDB Ref. ID 176609