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4/18/2012
1
Introducing Improved Detection Systems and Techniques into Non Destructive Assay (NDA) Programs
Graham V. Walford1,2), Debbie B. Browning2), John E. Patterson2), Laurence F. Miller1),
Sean J. Branney3), David W. Roberts3), Raymond K. Maynard3), John N. Dewes3), John E. Gunning4)
1. University of Tennessee 2. Strata-G, LLC 3. Savannah River National Laboratory4. Oak Ridge National Laboratory
Savannah River National Laboratory
David W Roberts
Sean Branney
Raymond K Maynard
John H. Dewes
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Graham V. Walford Laurence F. Miller
University of Tennessee
Jeffery A. Chapman John E. Gunning
Oak Ridge National Laboratory
NDA Targets
• NDA technologies are directed towards assessment of Special Nuclear Materials (SNM).
• SNM comprises quantification of Pu and U bearing compounds in various forms and enrichments
• The SNM is often in difficult to locate geometries within machines or other objects.
• Variability in deposit type, condition and geometric disposition are major contributors to total measurement uncertainty.
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Standards
• US DOE 414.1D
• DOE/PPPO/03‐235&D1 ‐ Quality System for Non Destructive Assay Characterization (QSNDA)
• Responding QA document of Contractor
• This Drives Subsequent Gamma and Neutron NDA
Measurement Guidance and Control
• Laboratory and Field characterization follows guidelines and controls developed over a number of years
• Detection is typically through gamma and neutron emission using techniques that have become refined.
• These techniques can be both controlling (absolutely essential) but can be restrictive in the implementation of newer detector systems or techniques.
• Controls also exist because of recognition of both the radiation based and the chemical based chemical hazards involved with SNM compounds
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Understanding the Problem
• Technical: – Better measurement – newer or optimal detection use –– minimized uncertainty –– Less risk –– optimal throughput
• Commercial: – Competitive playing field – Recognize vendor investment – Facility investment and risk
Understanding the problem ‐ The User:
• The NDA technicians and engineers must follow rigorous procedure and control to make known measurements in difficult conditions. For example in one facility:
• Detector Acceptance
• Detector Calibration
• Data and flow control
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Understanding the Problem ‐ The Manufacturer:
• Detector Makers:– Portability– Detector focus at the equipment– Restrictive application/market– Flexibility?
• Therefore:– Introducing new geometries can be difficult particularly with modeling considerations to understand
– We can build in flexibility in mind set and small changes into the controls that maintain integrity but allow other detector approaches to be examined
Two Example Detector Systems to Examine
• HMS‐4 Measurement Software/System
• HPGe Detectors
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Use of HPGe Detector :• Canberra ISOCS and Ortec IsoCart examples
• HPGe crystals are limited by the laws of physics and competitors largely make similar devices – they might argue that
• They are expensive
• Differences may fall between software and applications development
• Differences can be made in use of collimation. So look at use of parallel plate geometry. It does not solve all problems and like everything else is application specific
• This could be complex with MCNP. Using also “Peak Analysis” based upon Generalized Geometry Holdup becomes “doable” without complex collimator modeling
• Parallel plates can be MCNP modeled just takes time – set optimal geometries based upon applications
NDA Data Flow – Primary HPGe Detector Operations(For Detectors for ISOCS and “Peak Analysis”)
Confirmationof Calibration
Re Verification of Calibration
Newor
Repair
Laboratory
Field
Maintenance and
Check
Detector Acceptance
Test
To Repair by Vendor
To Repair by Vendor
Calibration(“Peak
Analysis”)
Background Checks
ISOCS
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Quality Assurance Measurements Being Made with 1.94% Enriched Source
Outline Diagram Showing Measurement of ISOCS Detector Spatial Performance with 10.892 gm U235 Source
Ge Detector
Lead Shielding Rings
Detector Axis
Source
Source‐Detector Solid Angle
Source‐Detector Distances Measured from This Location
2.0”
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Paddle Check Source Holder
Plan View
Slot for Paddle Source
Detector End Cap
Polyethylene Holder
Hole bored to allow source
direct detector view
Holder Cross
sectionSide View
Source Paddle
Detector and shield assembly
meltdown
Figure 5.4a: Variation of ISOCS response to a Point U235 (185.8 keV) Source Moved Perpendicular to the Source detector Axis at 12.0", 24.0" and 36.0" Distances
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 20 40 60 80 100 120 140
Distance Moved (cm)
Co
un
t R
ate
No
rma
lize
d a
t 1
2.0
"
12.0"
24.0"
36.0"
Source
12,12,12
24,24,2436,36,36
Detector
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Figure 5.4b: Normalized Spatial Resolution for a Point Source Moved at 12.0" 24" and 36" source detector Axix for a Point Source U235 Source (185keV)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 20 40 60 80 100 120 140
Distance From Source-Detector Axis (cm)
No
rmal
ize
d C
ou
nt
Ra
te
12.0" 24.0" 36.0" Location of SRM and CRM Source at 12,12,12 location and 24,24,24, location. 36,36,36 location also shown for interest
Understanding Variance in Detection Efficiency
Axial varianceSmall Source: ε proportional to 1/d2
dRadial Variance
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Functional Diagram of an HPGe ISOCS Detector System
Non uniform attenuating body not necessarily radioactive
Non uniform distributed source
CrystalColl
Scan detector
Rotate drum if necessary
Diagram Showing Crate Measurement Geometry for ISOCS
3.0 ft
4.0 ft
7.0 ft
4.0 ft
Note: Red Locations Denote Location of WRM 3 Successive Locations For Measurement
Crate Top View Crate Side View
ISOCS
T7T8
T4
T6
T3
T5
T2T1
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Functional Diagram of an HPGe ISOCS Detector System With Data Control and Analysis
Detector Location
Power, Signal Processing, MCA
Inspector 2000Fieldof View
Shield Dewar
Laptop/PC
Quality Assurance/
Control S505
Administration
GENIE 2000Spectra
Creation
Reporting Auto
Alarm
Geometry Composer
“Peak Analysis”
MGAULACEReporting,
Data StorageResult
Bracketing the Field Measurement
Background and Source
Check
Collection of Object/Item
Spectra
Background and Source
Check
Blind Test Source Check
“Noise” Analysis
S505 Software
Procedure FBP-GVW-003
Use
NDA TrackerProgram
Procedure FBP-GVW-006
Data control
ADMIN Data CollectionProgram
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Figure 2a: NDA Summary Data Flow – Function and Decision
QC Review (scientist)
Data/Result to End
Customer
Customer Request
Energy Spectrum Series Created
Label(s) Created
Peer Review (2nd NDA Engineer)
Customer Driven
Energy Spectrum Series Created
Label(s) Created
NDA Group
Created
(Items, areas, etc.,)
(Calibrations, tests, etc.,)
NDA Request
Field/lab Operations Supervisor/Data Review
1st NDA Engineer
Initial Data Analysis
Work is Done
Signature Signature ResultSignature
Signature
NDA Manager
Supervisory Review
Administrative Aide
Scan Data to
File
Pass
Order
Fail
Data/Result to NDA
Note: Signature is also a pass/fail barrier
NDA Data Flow – Function and Decision
1st NDA Engineer
Initial Data Analysis
Administrative Aide
Scan Data to
File
NDA Manager
Supervisory Review
QC Review (scientist)
Result
Signature
Data/Result to Customer or
NDA
Customer Request
Energy Spectrum Series Created
Label(s) Created
Order
Signature Fail PassSignature
Peer Review (2nd NDA Engineer)
Customer Driven
Energy Spectrum Series Created
Label(s) Created
NDA Group Driven
(Items, areas, etc.,)
(Calibrations, tests, etc.,)
NDA Request
Fail
Work is Done
Order
Field/lab Operations Supervisor
Data Review
Fail
Fail
Comply
Comply
Order
Order Pass
Signature
Fail Fail
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Hold Up Measurement System HMS4
• A software system where the software can reside in a laptop
• Often gets confused with an existing detector assembly
• Conventional detectors are 1” diameter and 0.5 thick – can use others –people do not because
• From the NDA point of view – physical weight – low count rate how to deal with low enrichment – clumsiness
• From the manufacturer – offers clear detector difference –package. So there fore worth working through the calibration procedure for HMS4 Generalized Geometry Holdup.
• The inspiration is the curve shown for current detector and then larger ones with Directional Radiation Monitor System
HMS4 Weight ≈ 12 lbs
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Shielded NaI(Tl) Detector Utilized for the HMS4
PMT Divider Chain
Photomultiplier tube (PMT)
NaI(Tl) Scintillator gamma ray detector
Lead shield and collimator
Note: NaI(Tl) Crystal 0.5” thickness, 1.0” diameter,
1.0”
Thin 241Am reference source
1.0”
Approximate field of view of
detector(FOV)
Pulse output
High voltage bias for PMT
235U
Natural
Depleted
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186 keV
241Am
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Sourcematerial
Collimator
Source Motion
Adjustable Distance
NaI(Tl) Scintillator and
Photomultiplier
Linear Slide
Experimental Configuration Used to Measure System Spatial Resolution. This same configuration is used with both Ge and NaI(Tl) detectors and for
spectroscopic measurement as well as Gross Counting Mode
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0
1000
2000
3000
4000
5000
6000
7000
8000
-40 -30 -20 -10 0 10 20 30 40
Co
un
ts P
er 3
00 S
ec
Distance, cm
Comparison of Spatial Resolutions for HMS4 and Walford Detector With 10.894 gm U235 "Point" source
HMS4 From Crystal Front Face to Source at 40 cm
Walford at 40 cm from collimator front face to source
Walford at 6.0 feet from collimator front face to source
HMS 4 at 40 cm
Walford at 40 cm
Walford at 6.0 feet
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Natural U
Depleted U
186 keV
1001 keV
235U Measured with NaI(Tl), LaBr3 and CZT
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Differing Enrichment 235U Sources Measured with CZT
Parallel Plate Geometry:
(Built with Alternating Pb and EPS Layers)
Sensor Element
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The Concept:Machined Expanded Polystyrene PlatesLead Foil Sheets
Lead Foils can be installed with graded foils to mitigate Pb X‐ray Generation
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0
0.1
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0.4
0.5
0.6
0.7
0.8
0.9
1
0 45 90 135 180 225 270 315 360
Angle of Rotation
Nor
mal
ized
Res
pon
se
235U (186 keV)238U (1001 keV)
235U (186 keV) response for 5.0 and 10 mm thick side shielding
238U (1001 keV) response with 10 mm side shielding
238U (1001 keV) response with 5.0 mm side shielding
Source-Detector Distance 1.0 Meter, Collimator 1.0 cm spacers, 0.5 mm plates, 10 cm by 15 cm
Creating a “Line” Field of View
FOVDetector Collimator
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Spatial Resolution and Field of View - Collimated
Source Location
Detector
Background(eliminated)
Collimator
Sweep
Old uncollimated FOV
New FOV
The Gamma Ray Directional Detector Approach
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Some Detector Field of View Options
0
1000
2000
3000
4000
5000
6000
7000
8000
-40 -30 -20 -10 0 10 20 30 40
Co
un
ts P
er 3
00 S
ec
Distance, cm
Comparison of Spatial Resolutions for HMS4 and Walford Detector With 10.894 gm U235 "Point" source
HMS4 From Crystal Front Face to Source at 40 cm
Walford at 40 cm from collimator front face to source
Walford at 6.0 feet from collimator front face to source
HMS 4 at 40 cm
Walford at 40 cm
Walford at 6.0 feet
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Comparison of Spatial Resolutions for HMS4 and Walford Detector With 10.894 gm U235 "Point" source
0
5000
10000
15000
20000
25000
30000
35000
-40 -30 -20 -10 0 10 20 30 40
Distance, cm
Co
un
ts P
er 3
00 S
ec
HMS4 From Crystal Front Face to Source at 40 cm
Walford at 40 cm from collimator front face to source
Walford at 6.0 feet from collimator front face to source
HMS 4 at 40 cm
Walford at 40 cm
Walford at 6.0 feet
0
500
1000
1500
2000
2500
3000
0 20 40 60 80 100 120 140 160
Counts/200 sec
Distance (cm)
Rad Hunter With Narrow Collimator B Measuring 137Cs as Measured across and perpendicular to plates
Along Collimator
Across Collimator
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Better Way to Plot Data to Show Field of View?
XY
X
Y
Detector Response
HMS-4 Spatial Profile at
40 cm
35 cm
35 cm
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3.0” NaI(Tl) Spatial Profile at
40 cm With Composite Collimator
35 cm
35 cm
4.0” NaI(Tl) (Radhunter) Spatial
Profile at 40 cm With
Composite Collimator
35 cm
35 cm
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Series1
Series5
Series9
Series13
Series17
Series21
Series25
0100200300400500600700800900
1000110012001300140015001600170018001900200021002200230024002500260027002800290030003100320033003400
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
Peak Counts/200 sec
Distance 5 cm increments
Rad Hunter and Wide Collimator Spatial performance for 137Cs
3300‐3400
3200‐3300
3100‐3200
3000‐3100
2900‐3000
2800‐2900
2700‐2800
2600‐2700
2500‐2600
2400‐2500
2300‐2400
2200‐2300
2100‐2200
2000‐2100
1900‐2000
1800‐1900
1700‐1800
1600‐1700
1500‐1600
1400‐1500
1300‐1400
1200‐1300
1100‐1200
1000‐1100
900‐1000
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“Focused Plate Geometry:
(Can be plate or rectangular Pb and EPS Layers)
Sensor Element
Center of “Focal” Point
of Field of View
Steel Wall
Holdup
Fabrication of Cylindrical Collimator
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HPGe Detector
• Reduces Scatter Fraction in Energy Spectrum when observing large bodies
• Reduces continuum under lower energy peaks
• Engineering Procedures to allow such additions enables newer detector innovations
HPGe Measuring 152Eu with and without collimator
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0
5000
10000
15000
20000
0 50 100 150 200 250 300
Cou
nts
Energy keV
20.11% Enriched U Source
185.72 keV
NaI(Tl)
HPGe Detector
HPGe and NaI(Tl) measuring 20% Enriched Source using parallel Plate Collimator
Summary
• Define the procedures to include “or equivalent”
• Identify where a specific and significant improvement can be made
• Enable a control experiment to demonstrate the observable difference
• Understand the cost and time to step from demonstration to approved procedure
• Speak in terms of cost/benefit/throughput to the whole process
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Thank You
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