Comparison of NIOSH and SC&A External Exposure Assessments at GSI 

Robert Anigstein 

S. Cohen & Associates
 

February 21, 2013
 

1
PERIODS OF SITE OPERATIONS,
 

DIVIDED ACCORDING TO LIMITING EXPOSURE SCENARIOS
 

•	 January 1, 1953: Start of covered operations under EEOICPA 

o Two 500-mCi 226Ra sources used for radiography, in addition to 24-MeV betatron (“Old Betatron”) 

60	 226 •	 May 21, 1962: GSI acquires two Co sources (260 and 280 mCi) to replace Ra 

•	 January 1, 1963: Assumed date St. Louis Testing Laboratories (SLTL) began radiography at GSI site, 

60	 192 using 10-Ci Co and 50-Ci Ir sources 

•	 October 1, 1963: Assumed date “New Betatron” began operation at Commonwealth foundry in Granite 

City; Old Betatron upgraded to 25 MeV 

•	 June 30, 1966: End date of last MCW purchase order—beginning of residual period 

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SOURCES OF EXTERNAL RADIATION EXPOSURE AT GSI 

(Entire period of AEC operations, unless otherwise noted) 

• Exposure to direct penetrating radiation (photons) from betatron operations 

o Stray radiation during betatron operation 

o Delayed radiation from activated metals 

• Exposure to sealed radiography sources 

o 226 Ra—2 sources, 500 mCi ea: 1953–May 21, 1962 

o 60 Co—260 & 280 mCi (initial activities): May 21, 1962–June 30, 1966 

o 60 Co—10 Ci, employed by SLTL: from January 1, 1963 

o 192 Ir—50 Ci, occasionally employed by SLTL: from January 1, 1963 

• Exposure of skin to non-penetrating (beta) radiation 

o Natural uranium and photoactivated uranium isotopes 

o Activated steel 

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BOUNDING ANNUAL EXPOSURES TO PENETRATING (PHOTON) RADIATION
 

Years SC&A—applied to all employees NIOSH 

Bounding scenario Dose/exposure Source Radiographers Others 

1953–1954 

1955–5/21/62 

5/22/62–12/31/62 

1/1/63–9/30/63 

9/30/63–6/30/66 

Radiographer—Ra-226 

15 rem 

12 rem 

Betatron operator 1.35 rem* 

SLTL Co-60 source 2.669 R 

Layout man 9.2 R 

Ra-226 

Co-60—GSI 

Co-60—SLTL 

Betatron 

3.573 R 

1.17 R 

2.671 R 

4.483 R 

2.087 R 

1.348 R 

* Note change of units from previous reports 

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BOUNDING SCENARIOS FOR NEUTRON AND BETA EXPOSURES
 

Apply to All Employees 

Year 

Neutron dose (rem/y) â dose to skin—betatron operator (rads/y) 

SC&A NIOSH Hands & forearms Other skin 

Betatron operator Layout man SC&A NIOSH SC&A NIOSH 

1953-1957 

1958 

1959-1960 

1961 

1962 

1963 

1964 

1965 

1966a 

0.48 

0.148 

0.48 

0.48 

0.48 

0.48 

0.47 

0.46 

0.46 

0.23 0.072 

33.4 25.9 6.27 2.27 

32.1 25.9 6.22 2.27 

30.9 25.9 6.18 2.27 

34.2 29.5 6.30 2.47 

27.2 21.8 6.04 2.04 

13.9 7.0 5.56 1.23 

10.7 3.5 5.45 1.03 

10.2 3.0 5.43 1.00 

4.8 2.4 2.71 0.97 b b 

a Doses prorated to first 6 months, except as noted 

b Doses should be prorated to first 6 months 

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DETAILED DISCUSSION OF BOUNDING SCENARIOS
 

Radiographer Using 226 Ra: 1953-May 21, 1962 

•	 “During this period [1953–1962] the exposure limits published by the A.E.C. at the applicable time were 

followed. They were never exceeded and averaged under 25%.” (GSI AEC license application) 

•	 AEC Form 4: Occupational External Exposure History of GSI worker 

o	 18 quarters (July 1, 1957–December 31, 1961) 

o	 9.1 rem total, 2.02 rem/y 

o	 Worker performed radiography on weekends 

• 	 1–2 shifts, 80%–90% of the time 

• 	 40–90 shifts/y: 22–50 mrem/shift 

o	 Extrapolate dose to full-time radiographer, 65 h/wk: 9–20 rem/y 

o	 Worker testified he wore film badge while performing radiography 

•	 MCNPX and exposure rate analysis, based on worker's account of radiographic practices: ~10 R/y 

(~11 rem/y) 

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Betatron Operator 

•	 Maximum dose of 26 mrem/week, due to hypothetical 30 keV radiation from behind, film badge partially 

shielded by operator's body 

Exposure to SLTL Sources 

•	 Maximum exposure duration: 

o	 180 h longest shot 

o	 10 shots during 6-month period 

o	 Maximum fraction of time: 180 h × 10 shots × 6 mo ÷ 12 mo/y = 3,600 h/y ÷ 8760 h/y = 41% 

•	 Exposure rate at exclusion area boundary: 2 mR/h 

o	 Maximum exposure of worker at boundary: 2 mR/h × 3250 h/y × 0.41 = 2.67 R/y 

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Layout Man—1963–1966
 

New Betatron Building (A.E.C. license application)
 

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MCNPX Model of Exposure Geometry of Layout Man
 

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