Memo – RFP: Np-237 Dose 1 SC&A – May 29, 2015 

NOTICE: This memo 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.

MEMO 

DATE: May 29, 2015

TO: Rocky Flats Plant Work Group 

FROM: Joe Fitzgerald, SC&A

SUBJECT: SC&A Review of NIOSH White Paper: “Evaluation of the Potential for Internal 

Dose from Np-237 at the Rocky Flats Plant after 1983,” Rev. 1, January 8, 2015

SC&A received the subject paper, as Rev. 0, dated December 30, 2014, and as Rev. 1, dated 

January 8, 2015. SC&A was also an addressee on, or was forwarded, on two sets of petitioner 

comments: a January 5, 2015, email from a petitioner representative expressing concerns over 

operational dates cited for Np operations in the 1980s and the application of one of the key 

references cited; and emails forwarded by the same petitioner representative during the March 

17, 2015, Work Group meeting pertaining to specific technical concerns about neptunium 

monitoring. SC&A participated in some of the early data capture reviews at the Environmental 

Management Consolidated Business Center and Department of Energy (DOE) Legacy 

Management (EMCBC-LM) facility in Denver, Colorado, as well as in most of the interviews 

conducted with former Rocky Flats Plant (RFP) workers who had some involvement or 

knowledge of neptunium operations. 

INTRODUCTION 

As noted in its white paper, the Special Evaluation Cohort Petition (SEC) Evaluation Report 

(ER) for Petition SEC-00192 proposed the following class of workers to be added to the SEC: 

All employees of the Department of Energy, its predecessor agencies, and their 

contractors and subcontractors who worked at the Rocky Flats Plant in Golden, 

Colorado, from April 1, 1952, through December 31, 1983, for a number of work 

days aggregating at least 250 work days, occurring either solely under this 

employment or in combination with work days within the parameters established 

for one or more other classes of employees included in the Special Exposure 

Cohort. (NIOSH 2013; SRDB 132777).

As noted by NIOSH, this recommendation was derived, in part, “from NIOSH’s conclusion that 

neptunium processing at the Rocky Flats Plant (RFP) took place at least until 1983, and that 

available monitoring data are insufficient for estimating potential internal exposures to 

neptunium (Np)” (NIOSH 2015). Since that ER, both NIOSH and SC&A have reviewed 

additional records and interviewed additional former workers and established that evidence 

existed for additional operations, as well as inventory, involving neptunium beyond 1983. 

NIOSH’s subject white paper examines this information and discusses it in terms of Np 

operations, inventories, monitoring data, and potential exposure to Np-237 after the 1983 cutoff 

date for the current SEC period. 
Memo – RFP: Np-237 Dose 2 SC&A – May 29, 2015 

NOTICE: This memo 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’S EVALUATION

Neptunium operations at RFP were examined and contrasted between the period of 1962 through 

1983, and for the period after 1983. Generally, Np operations at RFP in the earlier years 

consisted of the production of high-purity Np metal, as well as neptunium-plutonium alloys, both 

for use in weapons research and testing. Special projects included high-purity neptunium oxide 

produced for Oak Ridge National Laboratory for its isotope pool, Np metal foils for Savannah 

River Plant, and neptunium metal disks for use in the liquid-metal fast-breeder reactor program. 

After 1983, document reviews and interviews have uncovered only one Np operation, an 

approximate 1-year campaign1in the mid-1980s that processed plutonium scrap containing 

residual amounts of Np in order to recover neptunium and purify plutonium (resulting in 

purification of 58,282 grams of Pu). Key attributes of this operation, Plutonium-Neptunium 

Separation and Residue recovery, were (1) the processing of the Pu/Np scrap in a “closed” 

separation system involving a glovebox containing a “wet” section (for aqueous processes) and 

a “dry” section (for calcining precipitates and weighing powders) separated by an air lock, with 

tanks containing feed material (plutonium and neptunium nitrate solution) being piped directly 

into the gloveboxes, and (2) lack of any “pure” plutonium or neptunium source term (both metals 

were produced with impurities of the other, i.e., “purified” plutonium contained 0.0069% 

neptunium and “purified” neptunium was co-generated with plutonium at a Pu:Np mass ratio of 

6.4) (NIOSH 2015). 

The implication of the first attribute of this particular operation is that no routine exposure 

potential would have existed for workers performing the extractions at the glovebox. Workplace 

monitoring for this operation included continuous air monitoring (CAM), contamination surveys, 

and routine bioassay (urinalyses and body counts) typical of a plutonium-handling environment 

for all workers involved. From interviews and reviews of incident reports, only one incident, 

involving a leaking tank, occurred and no worker exposure took place. 

The implication of the second attribute is likewise important, in that the continuing presence of 

plutonium with neptunium product provides a means for radiological monitoring of this 

operation, given the much greater specific activity attributable to Pu as compared with Np, 

making any uptake of the Pu/Np mixture detectable via bioassay results (all personnel were 

provided routine bioassays during this operation). The predominance of plutonium relative to 

neptunium was confirmed in a review of RFP neptunium-containing waste shipped to Idaho 

National Engineering and Environmental Laboratory for disposal (mean mass ratios of 

 

1

 The precise duration of this campaign and its start date were questioned by a petitioner representative 

given former worker recollections that operations “began around January 1985,” and “ended in 1987” (SRDB 

130877, 130921) or were terminated in 1988 (SRDB 33009), respectively, or that the campaign had a duration of 

“approximately one year” (SRDB 129512). Clearly, there is an inconsistency between interviewee recollections 

(i.e., 1- or 2-year duration?), but this may be explainable by differing definitions of when the campaign was 

officially over (one interviewee, in SRDB 130921, noted some management pressure to “denote if the recovery 

project was complete” by finishing up a final report that was issued 2 years after actual startup and months after 

actual cessation of operations). However, this imprecision would not be a problem for dose reconstruction if routine 

bioassay data were available for all workers involved and that Pu dose data bounded any Np dose contribution. 
Memo – RFP: Np-237 Dose 3 SC&A – May 29, 2015 

NOTICE: This memo 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.

Pu-239/Np-237 ranged from 105 to 6,450 in drums assayed, and mean mass concentrations 

ranged from 109 to 5,820) (SRDB 104511). 

Beyond the one post-1983 Np operation identified, NIOSH observes that neptunium was present 

at RFP from 1962 to 2003, with quantities ranging from 29 grams to 1,319 grams (SRDB 

33009). While the one post-1983 Np program was reportedly terminated by 1988, neptunium 

remained in inventory and as residual contamination in gloveboxes, ductwork, and other process 

equipment. In its review of an interview with a former RFP engineer (SRDB 138666), NIOSH 

concluded that for post-1983 handling of this contaminated equipment [e.g., during 

decontamination and decommissioning (D&D) and site closure activities], it does not “dispute 

the potential for personnel Np exposures,” but “contends that the exposure would be dominated 

by the Pu (nothing involved purified or pure Np), and nothing provided up to this point disputes 

that contention” (SRDB 138666). 

In summary, NIOSH concludes that there is “no evidence that Np-237 intakes occurred at RFP 

after December 31, 1983...,” and if intakes did occur after 1983 from the single Np operation 

that was identified, “the resulting organ doses would be adequately accounted for by the 

available Pu bioassay data” (NIOSH 2015). 

SC&A ANALYSIS 

SC&A’s analysis focused on the following lines of inquiry (for the post-1983 time period), with 

the related SC&A findings, as follows. 

1. Was there only the single Np operation identified by NIOSH in place at RFP after December 

31, 1983? 

SC&A participated in onsite data captures at the EMCBC-LM office in Denver in 2012 and 

in a series of interviews conducted in 2012–2014. Available records were searched for any 

reference to neptunium, and former workers were identified for their knowledge of Np 

operations or source terms at RFP. SC&A reviewed the NIOSH white paper from the 

standpoint of sources cited in support of the one post-1983 operation that was identified, and 

proceeded to run extensive keyword searches for any other references for neptunium 

operations, source terms, or contamination at RFP in the post-1983 period. In addition to the 

references cited by NIOSH, additional references, including former worker interviews, were 

found in the SRDB, with three interviews of particular relevance: SRDB 130921, SRDB 

138666, and SRDB 131225. 

In the first interview (SRDB 130921) with a former worker knowledgeable about RFP 

materials accountability, considerable “fluctuation” was noted in terms of different “material 

descriptions” for neptunium. While the individual could not be definitive about these 

differences in descriptions without a firsthand review of the accountability records in 

question, there arose a question regarding a small inventory of neptunium-finished items 

reported in 1988: 
Memo – RFP: Np-237 Dose 4 SC&A – May 29, 2015 

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

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 Alloyed finish machined items product – 8 g 

 Assembled items product – 7 g [dating back, unchanged, to June 1985]

 (SRDB 130921) 

The interviewee indicated that this was “inventory left over from previous projects and work 

performed by the Labs (Los Alamos National Laboratories) and that [the RFP group] 

supported special project works for the Labs” (SRDB 130921). It was further indicated by 

the interviewee that any neptunium left over from such projects would remain in storage at 

RFP. 

In the second interview (SRDB 138666), a former engineer at RFP during the years in 

question noted that “[neptunium] processing equipment was abandoned in place, and that 

neptunium (including neptunium residues) was in the plant until site closure.” The worker 

further observed that “equipment that processed Np was left in place and not stripped out” 

and that it “was stored in some shape or form on the site until site closure and that RFP was 

still shipping Np-contaminated materials up to site closure.” It was further noted that “when 

D&D workers cut out the property [equipment] and removed it, they became exposed to the 

Np.” Other detailed information was provided by the interviewee and others highlighting 

what they believed were instances of worker exposure to neptunium during D&D and waste 

management, both before and after 1983. 

NIOSH provided its response at the end of the interview summary. These included: 

 While NIOSH does not dispute the information provided in this response, the 

individual provided no dates or specific references to incidents/accidents that 

could be traced or verified.

 NIOSH is looking for information in the post-1983 (post-SEC period). Any 

discussions of operations that occurred in the pre-1984 period, is not relevant 

to the current evaluation/assessment. While NIOSH does not dispute the 

potential for personnel Np exposures in the post-1983 period, NIOSH 

contends that the exposure would be dominated by the Pu (nothing involved 

purified or pure Np), and nothing provided up to this point disputes that 

contention.

 NIOSH will continue to make contact with the additional individuals identified 

by [redacted names] and also continue to follow-up on Np issues. At this 

point, however, NIOSH does not have information or data to dispute its postSEC (post-1983) findings regarding personnel Np exposures.

(SRDB 138666) 

SC&A participated in this interview and has reviewed this referenced summary. SC&A, 

likewise, has not identified any information that would point to potential worker exposure 

after 1983 involving pure or purified neptunium, albeit such neptunium was in storage or 

being shipped by RFP during that time. (From interviews, pure Np metal forms were kept in 

inventory at RFP and listed in the Nuclear Materials Management and Safeguards System
Memo – RFP: Np-237 Dose 5 SC&A – May 29, 2015 

NOTICE: This memo 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.

(NMMSS) database; however, no evidence of any intakes was identified with such material). 

While contaminated areas and equipment were frequented by RFP workers during cleanup 

and site closure, and there was a likelihood of exposure to neptunium contamination during 

these activities, this contamination would have been dominated by the plutonium also 

present, and monitored by either routine or event-driven bioassay.

In the third interview (SRDB 131225), a former technician performing facility holdup 

measurements in the 1990s found traces of neptunium in about 10% of Building 771 

gloveboxes at levels relatively small compared to the plutonium present. The interviewee 

believed that this was neptunium was likely separated and part of recovery streams, and that 

there was no evidence of contamination spread. SC&A notes that all interviewees agree that 

neptunium remained at RFP beyond 1983 and into final cleanup, and that contaminated 

equipment (e.g., gloveboxes and ductwork) with trace amounts of Np would have undergone 

D&D. However, none of the interviewees identified any other operations involving Np and 

no one cited processing of pure or purified Np that would have had exposure potential. 

2. Was there any exposure potential associated with this one Np operation or from any other Np 

source terms at RFP? 

In an interview with the [redacted] Engineer for the 1985–1987 Plutonium-Neptunium 

Separation and Residue recovery at RFP (SRDB 138682), it was stated that all the processing 

was done in gloveboxes and tanks, with the only materials transported out of the gloveboxes 

being the products. Tanks containing feed materials were located outside of the gloveboxes 

and these materials were piped directly into the gloveboxes. Recovered plutonium was piped 

as a nitrate directly to Production Operations. Recovered neptunium nitrate was put into 

“pencil tanks,” and converted to an oxide and canned and bagged out of the glovebox. The 

operating area was monitored by alpha air counters (CAMs) and radiological control 

technicians (RCTs) were positioned in the area. One incident was cited, a minor leak from a 

feed tank containing plutonium nitrate; this was cleaned up without any reported exposure 

(SRDB 138682). All workers in Building 771, where this separation work took place, were 

on routine bioassay for plutonium.

3. Was Np always present in combination with plutonium in this particular operation or any 

other operations or source term identified as having exposure potential? 

The Pu-Np separations work was effective at purifying both plutonium and neptunium, but as 

noted earlier, not to a degree that would have negated the much greater specific activity 

afforded by the presence of plutonium relative to the neptunium present. Other than pure 

metal forms and components, neptunium was always found with plutonium at a relatively 

small mass concentration ratio. There is no evidence or reports that anyone had an internal 

exposure potential from the pure Np metal that was retained in RFP’s inventory during the 

1980s into the early 1990s. SC&A continues to look for any evidence of such exposure. 

4. Were all workers having exposure potential from this one Np operation bioassayed and 

would those results encompass any intake of Np? 
Memo – RFP: Np-237 Dose 6 SC&A – May 29, 2015 

NOTICE: This memo 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.

All workers in Building 771, which encompassed the 1985–1987 Plutonium-Neptunium 

Separation and Residue recovery operation at RFP were bioassayed, with the target 

radionuclide being plutonium. Given that any neptunium would have only been present with 

a predominant plutonium source term (in terms of specific activity), intakes of Np would 

have been picked up as collateral to intakes of plutonium, whose much higher specific 

activity level would have led to assigned organ doses that would clearly bound any 

neptunium contribution. In only one interview (SRDB 122550) was the possibility of 

unmonitored worker exposure raised, in terms of office workers adjacent to a [radioactive] 

material storage area, but this appears to be related to Building 371, not 771 (it is also not 

clear whether these office workers had been bioassayed due to proximity). 

5. Were there any recorded post-1983 incidents that would be indicative of potential 

unmonitored exposure to Np? 

The plutonium nitrate tank leak previously cited was the only recorded incident specific to 

neptunium. This was associated with Tank 1007, was relatively minor (involving a leaking 

valve), and no radiological alarms were triggered (SRDB 138682). No reported worker 

intakes associated with this leak or the subsequent cleanup were identified. 

6. Is it technically sound to rely on plutonium bioassays to account for any Np intakes that may 

have occurred during this timeframe? 

SC&A reviewed the relevant RFP documents in the SRDB, particularly SRDB 137075 that 

addressed the dominance of the specific activity of plutonium as compared with neptunium, 

and compared the results with Radiological Health Handbook (DHEW 1970) information 

and the results of the calculation of some chronic annual doses from existing dose 

reconstruction cases. SC&A found that the resulting neptunium dose is about equal to 

plutonium on the basis of per-dpm intake, but would be 1/100 times less on a per-mass basis 

due to the specific activity, and even less for a 6.4:1 Pu:Np mass ratio. Counting all alpha 

monitored as being plutonium appears to be claimant favorable in this case. 

CONCLUSION 

SC&A conducted an independent evaluation of available documents and accounts by former 

RFP workers, and concurs with NIOSH that only one processing operation in the post-1983 

period involved neptunium, namely the Plutonium-Neptunium Separation and Residue recovery 

operation, which ran from late-1985 to the end of 1987. Other activities at RFP involved 

neptunium contamination, including radioactive waste handling and later D&D, but in all of 

these instances, there is no evidence, to date, that neptunium source terms existed without the 

presence of plutonium. SC&A concurs with NIOSH that the co-presence of neptunium with 

plutonium enables radiological monitoring to account for any neptunium exposure component in 

a claimant-favorable manner. All workers involved with this one post-1983 operation, as well as 

other work activities in Building 771, were routinely bioassayed for plutonium intakes during the 

years in question (as were radiological waste handlers and D&D workers). Pure Np metal forms 
Memo – RFP: Np-237 Dose 7 SC&A – May 29, 2015 

NOTICE: This memo 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.

were stored and transported, but no internal intake (e.g., from surface oxidation) would have 

been likely and none was detected through routine bioassay monitoring. 

With respect to specific technical questions raised during the March 17, 2015, Work Group 

meeting (pertaining to neptunium monitoring at RFP), NIOSH provided responses to each 

concern in a May 13, 2015, email addressed to the Work Group and SC&A. SC&A reviewed 

these responses (attached) and found them satisfactory. 
Memo – RFP: Np-237 Dose 8 SC&A – May 29, 2015 

NOTICE: This memo 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.

REFERENCES 

DHEW 1970. U.S. Dept. of Health, Education, and Welfare, Rockville, Maryland, U.S. 

Government Printing Office, Washington, D.C., January 1970. 

NIOSH 2013. National Institute for Occupational Safety and Health. “SEC Petition Evaluation 

Report, Petition SEC-00192, Rev. 1.” September 30, 2013. SRDB 132777 

NIOSH 2015. National Institute for Occupational Safety and Health. “Evaluation of the 

Potential for Internal Dose from Np-237 at the Rocky Flats Plant after 1983, Rev. 1.” January 8, 

2015.

SRDB 104511: Validation of the Rocky Flats Plant Radionuclide Inventory in the Historic Data 

Task Using SWEPP Assay Data, Volume 1. 

SRDB 33009: Summary of Rocky Flats Plant Waste Buried in the Subsurface Disposal Area: 

Section 10. Special-Order Work. 

SRDB 130877: Documented Communication SEC-00192 with [name redacted] on Neptunium 

handling at Rocky Flats. 

SRDB 129512: Production-Scale Plutonium-Neptunium Separation and Residue Recovery at 

Rocky Flats Plant 

SRDB, 130921: Documented Communication SEC-00192 with [name redacted] on Neptunium 

handling at Rocky Flats. 

SRDB 138682: Documented Communication SEC-00192 re-interview with [name redacted] on 

Neptunium at Rocky Flats. 

SRDB 137075: PDF of Excel Spreadsheet Calculations from [name redacted] SEC-00192 

Rocky Flats Plutonium. 

SRDB 138666: Documented Communication SEC-00192 interview with [name redacted] on 

Neptunium at Rocky Flats. 

SRDB 122550: Documented Communication SEC-00192 interview with [name redacted] on 

Neptunium at Rocky Flats. 

SRDB 131225: Documented Communication SEC-00192 interview with [name redacted] on 

Neptunium at Rocky Flats. 
 

 

 

 

 

 

 

 

ATTACHMENT: NIOSH RESPONSES
 

From: Rutherford, LaVon B. (CDC/NIOSH/DCAS) <[redacted]> 

[ add to contacts ] 

To: Joe Fitzgerald <[redacted]>, 

Phillip Schofield <[redacted]>, 

Bill Field <[redacted]> 

Munn, Wanda I. (CDC/NIOSH/DCAS) <[redacted]>, 

Kotelchuck, David (CDC/NIOSH/DCAS) <[redacted]>, 

Cc: Neton, Jim (CDC/NIOSH/DCAS) <[redacted]>, Hinnefeld, Stuart L. (CDC/NIOSH/DCAS) <[redacted]>, 

Katz, Ted (CDC/NIOSH/OD) <[redacted]> 

Date: Wednesday, May 13, 2015 03:13 pm 

Subject: RFP Neptunium Issues Identified by the Petitioner 

During the last Rocky Flats work group meeting <[redacted]> sent a couple of e-mails from <[redacted]> with 

potential issues associated with the NIOSH Neptunium white paper and general concerns with Neptunium at 

Rocky Flats. I believe the work group members were sent copies of the e-mails, as well. Below I have copied the 

issue from the e-mail and provided a response after the issue. I did not think it would be necessary to revise our 

white paper. If anyone has any questions, feel free to send me an e-mail or we can discuss at the work group 

meeting in July. Thanks, 

LaVon 

Issue 1) 

“I found a document in "Basic Radiation Protection Technology" by Gollnick that says:
 

N237 produces a deep dose of 287 mr/hr per micro centimeter squared at 7mgcm-7
 

whereas Pu-239 Is 0 and Am-41 is 9.3 mr/hr. Based on that they can't use either Am-241 or Pu-239 to evaluate
 

the Np-237 exposure.
 

7 mgcm-7 is the depth that organs start to be affected by gamma radiation. Np-237 can damage more organs
 

internally because its energy reaches further
 

Maybe it is best to talk to a friendly committee member and show them the e-mail and let them research it
 

themselves and ask that that discussion be tabled until this is proven or not.” 

NIOSH Response: 

 

The cited values pertain to doses from material that’s deposited on the skin. In such a case the gamma radiation 

is of most concern because it can penetrate through the dead layer of skin into organs, as noted in the issue 

above. For radioactive material that’s inside the body, which is what the NIOSH white paper addressed, the 

alpha particles are of much more concern. Material is inhaled or swallowed and makes its way directly to the 

organs, where there’s no protective layer. Many of the gamma rays can make it outside of the body without 

depositing any of their energy, whereas the alpha particles are relatively large and lose all of their energy in a 

very short distance so they do more damage from the inside of an organ than from the outside of the body. Pu239, Am-241 and Np-237 are all alpha emitters. The dose delivered from the same amount of Pu-239 and Np237 differ by organ and type of material but are generally within a factor of 7 of each other. However, Pu-239 

was present at activity levels that were several orders of magnitude greater than Np-237, so the Np-237 doses 

amount to only about 0.1 to 1% of the internal doses from Pu-239. 

Issue 2) 

Memo – RFP: Np-237 Dose 9 SC&A – May 29, 2015
 

NOTICE: This memo 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.
 
Memo – RFP: Np-237 Dose 10 SC&A – May 29, 2015 

NOTICE: This memo 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.

Both U-238 and Np-237 decay into Protactinium - Which isotope did they use? 

 

NIOSH Response: 

The identification/segregation of protactinium (Pa) isotopes is not an issue from our assessment perspective. A 

clarification in the difference between the isotopes of Pa resulting from the decay of U-238 and Np-238 is: 

 U-238 decays into Pa-234, through Th-234 and Pa-234m. All these progeny are in secular 

equilibrium with U-238 after about 7 months, starting with the pure parent. The gamma 

spectrum of aged U-238 has Pa-234m lines at 766 keV and 1001 keV (strong).

 Np-237 decays directly to Pa-233, which also is in secular equilibrium after about 7 

months. The Pa-233 gamma spectrum has several lines below 350 keV; none are above 

416 keV.

 There’s not much way to confuse Pa-234 and Pa-233 in a gamma spectrum.

 

While it is not exactly clear what use the question is talking about, it is not difficult to distinguish the different 

isotopes of Pa in a count. 

 

Issue 3)

 

Line 1 in Building 771 was the Am-241 production line. Am-241 decays into Np-237 by alpha decay at the rate of 

5 percent per 22 years. RF produced 1 Kg of Am-241 per year for close to 40 years so 10% of the 112 Kg of Am241 in 1998 was 11,2 Kgs of Np-237 We had our own source of Np-237 and didn't know it. Did we monitor for 

Np-237 from Line 1? 

 

NIOSH Response:

The calculations in this question use some inaccurate assumptions. The decay rate of a radionuclide is 

exponential rather than linear (e.g., a half-life of 100 years doesn’t equate to 1% decaying per year). In this case, 

1 kg of Am-241 (which is equal to 3428 Ci) would decay to 0.94 kg (3215 Ci) of Am-241 after 40 years. The ingrowth of the decay product is also not linear and, unless stable, it will be decaying as it’s being produced so its 

half-life also factors in. To continue with the example, 3428 Ci (1 kg) of Am-241 would yield 0.043 Ci (0.06 kg) of 

Np-237 after 40 years. So the ratio (both mass and activity) of Am-241 to Np-237 is still quite high, even after 40 

years. 

Issue 4)

Scary thought - the 60 Kev gamma we were told was from Am-241 was really from the Np-237 in the lung 

counter. 

I am backing this up with data as attached files and threw in my own bioassays to show they didn't monitor for 

NP-237. 

 

NIOSH Response:

Np-237 does emit 2 gammas in the 60 keV range but they’re emitted at a very low rate - combined they’re given 

off only once every 252 decays. The 60 keV gamma from Am-241 is emitted once every 3 decays, and given that 

there’s greater than a thousand times more Am-241 (from question 2), the gammas detected in this region by 

the lung counter would be almost entirely Am-241. 

If there were significant quantities of Np-237 in the body, it would be detected at 86 keV, which is emitted about 

once every 8 decays. This energy is within the region seen by the lung counter so it would be difficult to confuse 

Am-241 and Np-237.