TO: Advisory Board on Radiation and Worker Health, Work Group on Mound Plant 

FROM: Robert Anigstein, Ron Buchanan, Joe Fitzgerald, and John Mauro, SC&A 

SUBJECT: Comments on NIOSH Evaluation of NTA Neutron Film Fading at Mound 

DATE: January 20, 2011 

The recent NIOSH (2010) report is a response to our earlier report (Anigstein and Olsher 2010) 

and to observations made by SC&A staff members at the July 27, 2010, meeting of Work Group 

on the Mound Plant. SC&A has a number of comments on the NIOSH report that we would like 

to communicate to the Work Group, which are discussed below. 

First, SC&A would like to clarify a statement in the first paragraph on page 2 of NIOSH (2010) 

in which NIOSH quotes from SC&A’s comments during the July 27–28, 2010, Mound work 

group meeting: As a result, the fading values used by NIOSH in the site profile are: 33% in the 

first week after exposure and 56% in the subsequent week may not be favorable to the claimant. 

SC&A made this statement on the basis that the workplace neutron energy spectrum could have 

been moderated compared to the bare calibration sources and therefore contained lower energy 

neutrons, increasing the fading factors compared to those derived from unmoderated calibration 

sources. 

The site profile (Proctor and Alguitifan 2004) discusses the history of neutron dosimetry, using 

NTA film, at Mound during the period 1949–1976. The profile mentions the corrections for 

fading—33% in 1 week and 56% in 2 weeks—that were applied by the Mound dosimetry section 

to all films processed on or after July 15, 1968. (A correction of 56% was also applied to 4-week 

films.) Starting January 13, 1969, calibration films “were exposed progressively over a four 

week period to match the time different groups wore their film badges. This compensated for an 

image fading problem.” (Meyer 1994) However, the site profile does not direct dose 

reconstructors to apply a fading correction to NTA film badge records. Faust et al. (2009, 

Table 4-3) list a fading correction of 9% per week to be applied to MESH neutron data prior to 

1969. We are not sure if the statement by NIOSH (2010) quoted above was meant to imply that 

the fading values of 33% in 1 week and 56% in 2 weeks were applied by NIOSH in 

reconstructing neutron doses from NTA film records; such an assertion is not supported by the 

available documentation, nor in NIOSH’s recent responses. 

NIOSH (2010) highlighted a typographical error in Anigstein and Olsher (2010, p. 9). Our 

report stated that the predicted fading of NTA film after 2 weeks is 87%. The correct value is 

57%, which is obtained from our Equation 6, and is consistent with the 56% reported by 

Mound.1

 

NIOSH (2010) discussed a note by Kahle et al. (1969) that described experiments performed at 

Mound to study the dependence on fading of NTA films on neutron energies. Kahle et al. 

summarized two Mound reports on the fading of NTA films as a function of time after exposure. 

The first report, a study of fading following exposure to a 238PuF4 source, was the basis of the 

fading rate of 34% per week discussed by Anigstein and Olsher (2010). 

 

 1

 We informed the Work Group of this error in an e-mail dated December 29, 2010. 

Comments on NTA Neutron Film Fading at Mound 1 SC&A – January 20, 2011 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82. 
Comments on NTA Neutron Film Fading at Mound 2 SC&A – January 20, 2011 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.

The second was a Monsanto draft report (Arnett 1994) that claimed that a PuO2 source 

moderated with 8 inches of polyethylene had an average neutron energy of 0.9 MeV.2

 This may 

or may not be correct. What is important is the average energy of the neutrons that are actually 

recorded by the NTA film. 

Eight inches of polyethylene has about the same hydrogen cross-sectional density (atoms/cm2

) as 

10 inches of water. We can therefore compare the average energies yielded by our MCNPX 

calculations for a PuO2 source inside a 10-inch water sphere with those from a bare PuF4 source. 

These results are shown in Table 1. 

Table 1. Average Energies of Two Neutron Sources, as Recorded by NTA Film 

Eave > Eo (MeV) E0 (MeV) 

Bare PuF4 PuO2: 10" H2O

0.5 1.40 2.11 

0.6 1.44 2.29 

0.7 1.50 2.46 

Lehman 1.49 2.54 

The table lists the average energies of neutrons above three threshold energies—0.5, 0.6, and 

0.7 MeV—as well as the average energy of the neutron spectrum weighted by the energydependent efficiency of the neutrons in producing tracks on the NTA film, based on Lehman 

(1961) and described by Anigstein and Olsher (2010). As can be seen, regardless of which 

assumption one makes about how the neutrons are registered, the average energies of the 

attenuated 238PuO2 source that are measured by the NTA film are significantly higher than the 

energies of the bare 238PuF4 source, and much higher than the 0.9 MeV cited by Arnett (1994).3 

MCNP calculations for the neutron spectra of both sources were performed at the simulated 

location of the film badge worn by a worker 60 cm from the source. 

Consequently, Arnett's findings, that the films exposed to the moderated 238PuO2 source 

experienced less fading than the films exposed to a bare 238PuF4 source, are consistent with the 

observation that fading is greater for NTA films exposed to lower-energy neutrons. Kahle et al. 

(1969), apparently unaware of the mischaracterization of the average energy of the neutrons 

emitted by the moderated 238PuO2 source, ascribed the seemingly anomalous finding—that the 

films exposed to this source exhibited less fading—to the need to consider the detailed neutron 

spectrum, not just the average energy. 

 2

 This review of Arnett’s report was performed in the process of preparing our earlier report (Anigstein and 

Olsher 2010). It was mentioned briefly, but was not included in its entirety because it was not germane to that 

report. Since NIOSH (2010) discussed at length the Kahle et al. (1969) report, we felt it was appropriate to present 

this review at this time. 

3

 Curiously, Arnett cites an average energy of 1.3 MeV for the bare 238PuF4 source, which is not markedly 

different from the 1.49 MeV listed above, the difference being most likely due to ignoring or under-weighting the 

low-energy neutrons in the above analysis. This leads us to believe that the 0.9 MeV value is simply an error. 
Comments on NTA Neutron Film Fading at Mound 3 SC&A – January 20, 2011 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.

NIOSH (2010) agreed to apply the correction factors derived by Anigstein and Olsher (2010, 

Tables 2 and 3) for the “observer” exposed to a neutron source moderated by 8 inches of water to 

NTA film dosimetry data for the various time periods listed. However, for three of these time 

periods, spanning the era from January 25, 1956, through August 8, 1965, NIOSH used the 

factors derived for 210Po-Be sources, and did not note the higher correction factors for 238PuO2

sources and the even higher ones for 238PuF4 during these time periods. According to a time 

chart, “Radioisotopes of Significance Handled at Mound—External Dosimetry” (Meyer 1994, 

Vol. 1 [SRDB Ref ID 3268, p. 9]), 239Pu was present from the beginning of 1956, while 238Pu 

was there from 1959. Since 239Pu has a lower-energy alpha spectrum than 238Pu, the neutron 

spectrum from the (α,n) reaction in compounds of 239Pu is expected to have lower energies than 

the neutron spectrum from sources containing 238Pu. Consequently, absent a specific analysis of 

239Pu, the correction factors derived for 238PuF4 should be applied in the time periods spanning 

January 25, 1956, through August 8, 1965. In cases for which NIOSH is certain that a given 

employee was only exposed to neutrons from 210Po-Be or 238PuO2 sources, the smaller correction 

factors appropriate to these neutron spectra can be employed. 

It is not clear if NIOSH recognized that the correction factors listed by Anigstein and Olsher 

(2010, Tables 2 and 3) need to be multiplied by the factor of 1.33 to account for angular 

dependence, as derived by Kathren et al. (1965) and accepted by Faust et al. (2009). The 

suggested, claimant-favorable correction factors for the various time periods are listed in 

Table 2, below. Corrections for fading of NTA film are not included. 

Table 2. Adjusted Correction Factorsa 

Dates C.F.b C.F. angularc 

August 1949 through September 1951 4.5 6.0 

 October 1951 through December 1954 2.2 2.9 

 January 1955 through January 24, 1956 1 1.3 

 January 25, 1956 through December 1958 2 2.7 

 January 1959 through August 8, 1963 3.7 4.9 

 August 9, 1963 through August 8, 1965 4.7 6.3 

 August 9, 1965 through November 30, 1968 2.2 2.9 

 December 1, 1968 through December 31, 1969 1.7 2.3 

 January 1970 through December 1977 0.9 1.2 

 a Correction for fading not included

 b Correction factors for “observer” exposed to neutron source attenuated by 8 inches of water 

 c Correction factors in column 2, multiplied by 1.33 to account for angular dependence of film response

The major unresolved issue deals with the energy-dependence of track fading in the NTA film. 

Another, potentially more significant, issue is the effect of temperature and humidity on track 

fading. The literature on NTA track fading cites these factors much more often than neutron 

energy dependence. We note that the 33%-per-week fading factor used at Mound is based on a 

single set of films exposed and developed during a single 2-week period. No mention was made 

of the temperature or humidity in the film storage area. The fading rate could be different during 

other periods. 

Retrospective fading corrections are basically suspect, since the exposure conditions are 
Comments on NTA Neutron Film Fading at Mound 4 SC&A – January 20, 2011 

NOTICE: This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.

unknown. The Mound dosimetry section recognized this problem, and starting in November 

1968, the calibration films were exposed to neutron sources over the same period as the film 

badges were worn by workers. Prior to this time, the calibration films were exposed for periods 

of a few hours and developed the same or the next day, so the fading was not experienced by 

these films. Thus, the accuracy of the NTA film dosimetry at Mound prior to November 1968 is 

degraded. 

A cursory review of the available literature shows a number of studies of fading of the latent 

images on NTA film. These studies utilized a variety of radiation sources; the films were stored 

under various environmental conditions between exposure and development. In principle, it 

should be possible to review these studies and construct a matrix relating fading rates to 

exposure and storage conditions. It may then be possible to develop a claimant-favorable fading 

factor by relating the known exposure conditions at Mound to those reported in the literature and 

performing a curve fit or some other mathematical analysis. 

SC&A finds these correction factors to have the same level of uncertainty as other uncertainties 

and assumptions inherit in the dose reconstruction process; therefore, we conclude that, at this 

point, NTA fading is a site profile and not an SEC issue. At a minimum, we find that to address 

the fading issue, it would be necessary for NIOSH to apply the fading factors that we derived 

from the experiments performed at Mound—34% per week and 57% per 2 weeks—to all NTA 

film readings, unless: 

 They were already corrected by these factors. 

 They were already on a fading-compensation exchange cycle. 

 It can be assured that the exposures only consisted of neutrons from 210Po-Be or 238PuO2

sources. In such cases, a 9% per week fading factor for 210Po-Be or the 16% per week 

fading factor derived by Arnett (1994) for 238PuO2 would be acceptable. 

This is in addition to the MCNP correction factors for low-energy neutrons, and the angular 

correction factor of 1.33. However, not applying the source-specific fading correction factor 

would be considered an SEC issue because lost neutron dose due to fading would not be 

accounted for; therefore, dose reconstruction with sufficient accuracy would not be provided. 
Comments on NTA Neutron Film Fading at Mound 5 SC&A – January 20, 2011 

 This report has been reviewed for Privacy Act information and has been cleared for distribution. 

However, this report is pre-decisional and has not been reviewed by the Advisory Board on Radiation and Worker 

Health for factual accuracy or applicability within the requirements of 42 CFR 82.

NOTICE:

References 

Anigstein, R., and R. H. Olsher. 2010. “Draft White Paper: Sensitivity of NTA Film to Neutron 

Sources at Mound Laboratory” (Rev. 1). Vienna, Virginia: SC&A, Inc. (July 22, 2010) 

Arnett, E. N. 1994, “Latent Image Fading in Personnel Neutron Monitoring Film Exposed to a 

Moderated 238PuO2 Source.” In H. E. Meyer (Ed.) “History of Personnel External Dosimetry 

Program at the Dayton Project and Mound Laboratory -1946 to 1993.” Vol. 2. “From 3/28/66 to 

7/15/69.” Miamisburg, Ohio: EG&G Mound Applied Technologies. [SRDB Ref ID: 3276, p. 106 

et seq] 

Faust, L., R. Morris, and B. Smith. 2009. “ORAUT Neutron Dose Reconstruction at Mound.” 

(December 9, 2009) 

Kahle, J. B., E. N. Arnett, and C. T. Meyer. 1969. “Latent Image Fading in Personnel Monitoring 

Neutron Film.” Health Physics, 17, 735–736. 

Kathren, R. L., C. T. Prevo, and S. Block. 1965. “Angular Dependence of Eastman Type A 

(NTA) Personnel Monitoring Film.” Health Physics 11, 1067-1069. 

Lehman, R. L. 1961. “Energy Response and Physical Properties of NTA Personnel Neutron 

Dosimeter Nuclear Track Film.” UCRL-9513. Berkeley, California: Lawrence Berkeley 

National Laboratory. http://www.escholarship.org/uc/item/8v94979t.pdf

Meyer, H. E. 1994. “History of Personnel External Dosimetry Program at the Dayton Project and 

Mound Laboratory -1946 to 1993” (Vols 1–8). Miamisburg, Ohio: EG&G Mound Applied 

Technologies. 

NIOSH. 2010. “NIOSH Evaluation of NTA Neutron Film Fading at Mound: Response to SC&A 

Issues and Recommendations, December, 2010.” 

Proctor, C. W., Jr. and F. Alguitifan. 2004. “Technical Basis Document for the Mound Site — 

Occupational External Dosimetry,” ORAUT-TKBS-0016-6, Rev. 00. ORAU Team NIOSH Dose 

Reconstruction Project (August 11, 2004).