1. Clearance Protocol for Lead at Accelerator Facilities1
Clearance Protocol for Lead at Accelerator Facilities
James Liu, Maranda Cimeno, Ted Liang, Ludovic Nicolas and Henry Tran
Radiation Protection Department
SLAC National Accelerator Laboratory, CA, USA
ARIA2017, Lund, Sweden, May 22-24, 2017

2. Outline Progress of clearance of common metals at SLAC2
Outline
Progress of clearance of common metals at SLAC
Development of lead clearance protocol:
Induced activity characteristics from FLUKA calculations:
Dominated by Tl-204 (a hard-to-measure, pure-beta-emitting radionuclide)
Development of clearance measurement method:
Clearance criteria: measurements are indistinguishable from background (IFB)
Have to Use a large-area GM survey meter
Detection threshold (DT) is lower than ANSI N Screening Level (1 Bq/g for Tl-204)
Conclusions

3. US Regulations and Standards for Clearance3
US Regulations and Standards for Clearance
DOE Order “Radiation Protection of the Public and the Environment”, 2011 (chg 3, 2013): dose criterion of 10 Sv/y
ANSI N13.12 “Surface and Volume Radioactivity Standards for Clearance” (2013): Dose-risk-dependent Screening Level (SL in Bq/g)
Radionuclide Group in ANSI N13.12
SL (Bq/g)
Group 1: High-energy gamma, radium, thorium, transuranics, and mobile beta-gamma emitters
(e.g., 22Na, 46Sc, 54Mn, 56Co, 60Co, 65Zn, 152Eu, 182Ta, 207Bi)
0.1
Group 2: Uranium and selected beta-gamma emitters
(e.g., 57Co, 58Co, 59Fe, 113Sn, 185Os, 204Tl, 206Bi) 1
Group 3: General beta-gamma emitters (e.g., 7Be, 202Tl) 10
Group 4: Low-energy beta-gamma Emitters (e.g., 3H, 45Ca, 63Ni)
100
Group 5: Low-energy beta emitters (e.g., 55Fe)
1000

4. SLAC Clearance Protocol for Common Metals
SLAC RPD-010 “SLAC Material Release Program Manual” 2011
Metal
Induced Radionuclides
Half-life
Aluminum
22Na (proxy)
2.6 y
Carbon Steel (Fe, C)
Cast Iron (Fe, C, Si, Mn)
54Mn (proxy)
312 d
55Fe (5.9 keV X-ray)
2.73 y
57Co
272 d
Copper
60Co (proxy)
5.26 y
Radionuclides with long half-lives are of interest
Hard-to-measure radionuclides (55Fe), which emit only low-energy X rays or beta rays
Proxy radionuclides (22Na, 54Mn, 60Co), which emit high-energy and high-intensity gamma rays
ANSI N13.12 SL:
55Fe: 1000 Bq/g
22Na, 54Mn, 60Co: 0.1 Bq/g
From FLUKA calculations, SLAC technical bases show that:
Evaluation: ∑i (Ai / SLi)  1
Measurements with IFB criterion: ∑i (DTi / SLi)  1

5. SLAC, JLAB, ORNL, SNL, ORNL, and US DOE5
DOE-STD-6004 (2016): 7 Chapters
SLAC, JLAB, ORNL, SNL, ORNL, and US DOE
Purpose and Scope
Introduction
Material Clearance Protocols
Documentation and Reporting Requirements
DOE Independent Verification, Stakeholder Communication
References
Common Acronyms and Definitions

6. DOE-STD-6004 (2016): 5 Appendices
Rationale for Endorsement of ANSI N SLs as DOE Pre-Approved Authorized Limits
Process Knowledge for Volumetric Activation in Accelerator Facilities
Technical Basis for Volumetric Activation at Electron Accelerator Facilities
Technical Basis for Volumetric Activation at Proton Accelerator Facilities
Technical Basis for Measurement Methods of Volumetric Radioactivity and Determination of Detection Capabilities
Appendices C and D: “proxy” radionuclides in materials are identified for effective measurements in the field

7. SLAC Instruments for Common Metal Clearance Measurements
Ludlum Model 2241 meter with
1”x1” NaI probe (DT ~ 0.03 Bg/g; 30 nSv/h) &
small-area GM pancake probe
Field
Gamma Spectrometer
Portal
Gate
Monitor

8. Excess Metal at SLAC (before clearance)8
Excess Metal at SLAC (before clearance)

9. Excess Metal at SLAC (after clearance)9
Excess Metal at SLAC (after clearance)
3528 tons , $1,479,318 loads
First DOE Lab to release metals
to : 157 tons Al, 271 tons Cu, 3441 tons steel, 493 truck loads, $2.05M

10. How About Clearance for Lead?10
How About Clearance for Lead?
Common shielding material: may become expensive, mixed waste (radioactive and hazardous)
82 tons (10 m3) of lead stored at SLAC
FLUKA shows that Tl-204 (pure beta emitter) dominates and no proxy radionuclides
FLUKA calculation gives sensitivity of small-area GM probe (8 cpm per Bq/g of Tl-204 in lead)
Developed IFB clearance measurement method using a large-area GM probe with a detection threshold (DT) that is quantified to be < ANSI SL of 1 Bq/g

11. Key Radionuclides from Activated Lead for Clearance11
Key Radionuclides from Activated Lead for Clearance
Radionuclide
Half-life
Emission
Yield
Energy (keV)
ANSI N13.12
Group SL
(Bq/g)
Os-185
96.6 d
gamma
78%
646 2 1
Pt-193
50 y
beta
100%
56.6 3 10
Tl-202
12.2 d
91%
440
Tl-204
3.78 y
97%
763
Bi-205
15.3 d
31%
703
Bi-206
6.24 d
99%
803
Bi-207
31.6 y
98%
570
0.1
g,n and g,p and g,np and g,spallation
Reactions leading to induced radionuclides
(p,n)
(,n)
(,p)
(,np)
(,np)

12. Gamma Spectrum for Activated Lead12
Gamma Spectrum for Activated Lead
An experiment: 3 days irradiation and 21 days decay at SLAC FACET
0.3 µSv/h on contact (gammas from Tl-202, Bi-205, Bi-206)
Agreed with FLUKA, which also shows that Tl-204 (pure beta emitter) would dominate after 90 days
Tl-201
Hg-197
Tl-202
g,n and g,p and g,np and g,spallation
Bi-205
Bi-206
Tl-204

13. FLUKA Calculations of Lead Activation13
FLUKA Calculations of Lead Activation
Radionuclides and activities normalized to 1 W for irradiation of 1 and 10 years at decay from 1 day to 1 year
PRESICIO, PHOTONUC, RADDECAY, DCYSCORE, RESNUCLE IRRPROF, DCYTIMES

14. Activity versus Lead Layer14
Activity versus Lead Layer
1 year irradiation
1 day decay
Number after isotope ID is slope (attenuation length of reaction in lead in g/cm2) Tl Bi Pt Tl
Os-185 Bi Bi

15. Radionuclides in Inner 1-cm-thick Lead Layer15
Radionuclides in Inner 1-cm-thick Lead Layer
Dose Risk (Activity / SL) for 1 & 10 year irradiation
Tl-204
Tl-202
Bi-207
Tl-204
Bi-206
Bi-206
Bi-205
Bi-205
Tl-202
Bi-207
Os-185
Os-185
Pt-193
Table for the 7 isotope’s decays, emission, and SLs
Tl-204 (pure beta emitter) has highest activity and dose risk in most cases
No easy-to-detect “proxy” gamma emitter after a few months decay

16. Tl-204 Beta Spectrum from FLUKA16
Tl-204 Beta Spectrum from FLUKA
Tl-204 beta spectrum (Emax of MeV)
FLUKA-generated beta spectrum agrees with ICRP38
Simulation of GM probe sensitivity
FLUKA built-in isotope source BEAM, ISOTOPE, HI-PROPE (Tl-204, Z=81, A=204)
Beta decay RADDECAY
Score transport of beta decays DCYSCORE

17. FLUKA Calculations of GM Probe Sensitivity for Tl-204 in Lead17
FLUKA Calculations of GM Probe Sensitivity for Tl-204 in Lead
Tl-204 inside lead sheet
Tl-204 betas emitted isotopically inside lead
Lead thickness 0.05 cm (range of Tl-204 betas) and radius 5 or 8 cm
GM probe (2.5 cm radius)
Steel wire thickness 0.03 cm
Wire spacing cm
0.5 or 1 cm to lead
15.5 cm2 GM probe
FLUKA scoring “USRBDX”: one-way current passing from lead region to GM gas
Lead to Air
Air to GM Mica Window
Window to Ne-Cl Gas
Steel wire mesh (32x32 wires covering 35% of window area; wire diameter = 475 keV beta range) is critical.

18. Sensitivity of GM Probe (active area 15.5 cm2)18
Sensitivity of GM Probe (active area 15.5 cm2)
GM at 1 cm from thin Pb (5 cm radius)
Region I
Region II
e-/min per Bq/g of Tl-204
Ratio to Source
Source
2661
100%
Lead
Air
145
5.4%
Window
8.1
0.31%
Gas
7.5
0.29%
FLUKA Geometry of Lead and GM Probe
GM Sensitivity
(e-/min per Bq/g of Tl-204)
GM at 0.5 cm from Pb brick (5 cm radius)
8.0
GM at 1 cm from Pb brick (5 cm radius)
7.5
GM at 2.5 cm from Pb brick (5 cm radius)
6.7
GM at 1 cm from Pb brick (8 cm radius)
7.7

19. GM sensitivity calculated19
Benchmark of FLUKA Calculations of Small-Area GM Sensitivity with Three Tc-99 Beta Sources
5 µm
Tc-99 source GM
window
FLUKA-generated
Tc-99 beta spectrum (Emax MeV)
Tc-99
AH-1333
5 cm diameter
TC-99 Source
AH-1334
AH-1333
AH-1336
GM sensitivity calculated
by FLUKA
(e-/min/Bq)
Activity (Bq)
313
381
417
Base/Probe SN
Measured GM Sensitivity (cpm/Bq)
261372/197115
9.7 (7%)
9.9 (7%)
8.9
261297/197100
9.9 (8%)
10.1 (7%)

20. Need to Use Large-Area GM Meters for Lead Clearance Measurements20
Need to Use Large-Area GM Meters for Lead Clearance Measurements
Ludlum Model 44-94
four LND 7311 GM probes
4 x 15.5 = 62 cm² active area
x4 sensitivity, x4 background
x½ detection threshold (DT)
Lead Clearance On-contact Measurements
Ludlum 44-9 GM Probe
15.5 cm2 active area

21. Detection Thresholds of GM Meters21
Detection Thresholds of GM Meters
GM on contact with Lead Brick
Detection Threshold DT
(Bq/g of Tl-204)
44-9
(15.5 cm2) 40 8
1.8
44-94
(4x15.5 cm2)
120 32
0.8
ANSI N13.12 SL of 1 Bq/g
Static, 1-min measurement both sides of lead brick

22. 22
Conclusions
DOE Standard DOE-STD-6004 (2016) was developed for clearance of common metals (e.g., Al, Fe and Cu) in accelerator facilities
Unlike common metals, there are no proxy radionuclides for lead clearance measurements in electron accelerators
Tl-204 (pure beta emitter, Emax = 764 keV, 3.78 yr) dominates activity and risk in lead in most cases
Sensitivity of a small-area (15.5 cm2) GM probe for Tl-204 in lead was calculated with FLUKA to be 8 cpm per Bq/g.
With an average background of 120 cpm, detection threshold of a large-area GM meter (4x15.5 cm2) can be 0.8 Bq/g for Tl-204 inside lead, which is lower than ANSI N13.12 SL of 1 Bq/g.
Lead clearance measurement protocol (e.g., static 1-min measurements with large-area GM probe on contact with a lead brick under maximum background of 180 cpm) is being developed to meet IFB release criterion.