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X-Ray Backscatter Radiography by
Selective Detection as a Non-
Destructive Testing Tool
James Baciak
University of Florida
Director, Nuclear Engineering Program
Florida Power & Light Professor
Gainesville, FL 32611
@ProfessorBaciak
Nuclear Engineering Program
Overview Introduction to Backscatter Radiography and
Radiography by Selective Detection (RSD) Why Backscatter?
Backscatter Radiography Basics
Detector Requirements
Summary of Successful Applications Land Mine Detection
Spray-on Foam Insulation
Flaw Detection
Deposit Detection
Rail Cross-Tie Inspection
Nuclear Engineering Program
Acknowledgements
Support by: Georgetown Rail Equipment Company
Nucsafe, Inc.
Boeing
NRC
Lockheed Martin Space Systems Co.
NASA
PaR Systems
University of Florida
Nuclear & Radiological Engineering (1988-2010)
Materials Science and Engineering (2012 - )
Can’t Be Done Without
Students Students
Daniel Shedlock, PhD (Varian)
Olivier Bougeant, MS(EDF)
Nissia Sabri, MS (Areva)
Chris Meng, MS (DoD)
Jessica Salazar, PhD (NYU)
Michael Liesenfelt, PhD (Georgetown Rail)
Shuang Cui (PhD Student)
Travis Barker (MS Student)
Plus Former UF Faculty
Dr. Alan Jacobs
Dr. Edward Dugan
Nuclear Engineering Program
Radiography Systems
I. Introduction to backscatter radiography
Transmission Radiography Backscatter Radiography
Detection of X-ray photons not absorbed in the target object
Detection of X-ray photons scattered in the target object
Target object between the X-ray source and the detector(s)
X-ray source and detector(s) on the same side of the target object
X-ray source
Target objectDetector
X-ray source
DetectorTarget object
• Definition and comparison with transmission radiography
Alternative Techniques of Backscatter Radiography: SABR and CSD-SXI
Nuclear Engineering Program
Radiography by Selective
Detection (RSD)
Shedlock, PhD Thesis, 2007
Nuclear Engineering Program
MCNP Simulation Results
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
AL Layer 4 Layer 3 Layer 2 Layer 1
Flush Collimator, 1.14 cm to Surface From NaI
Flush Collimator, 5.14 cm to Surface From NaI
4 cm Collimator, 5.14 cm to Surface From NaI
Detector
Collimator
Aluminum Substrate
Illumination
Beam
Foam Layer 1
Foam Layer 2
Foam Layer 3
Foam Layer 4
Material 45 kVp 60 kVp 75 kVp
SOFI 660 mm 920 mm 1100 mm
Aluminum 3.3 mm 5.7 mm 8.1 mm
MCNP Estimates of Average MFP of X-rays in SOFI and Aluminum
Detector Response by Region (60 kVp)Shedlock, PhD Thesis, 2007
Nuclear Engineering Program
Radiography by Selective
Detection “New” type of Compton backscatter imaging (CBI)
Detect and analyze single and/or multiple scatter components
Can use an array of collimated and uncollimateddetectors, each with a unique “vision,” allowing to view through several mean free paths of material
Correlate members of this array of detected images to produce images with easily recognized object internal structure and /or defect details
Nuclear Engineering Program
Land Mine and Improvised
Explosive Device Detection Confirmation Area
50 cm x 50 cm
30-60 seconds
Large Field Area 1 m x 10 m
20-40 minutes
Optimum X-ray spectrum of 130-160 kVp
1.5 cm x 1.5 cm pixels
2 million x-rays per pixel at 1 joule per pixel
Minimum of 10 ms pixel dwell time requires 100 W of electric power Final ImageFront
Collimated
Detector
Uncollimated
Detector
Back
Collimated
Detector
Shedlock, SPIE (2004)
Nuclear Engineering Program
Spray on Foam Insulation (SOFI)
Used to prevent the buildup of ice on the external tank of the of the space shuttle
Low density ~0.03 g/cm3
Application process has a tendency to produce voids and delaminations
Nuclear Engineering Program
Shuttle Inspection
PAL Ramps
Bi-POD
Bolt Flange
Area
Shedlock, PhD Thesis, 2007
Nuclear Engineering Program
Example System Built By UF
Nuclear Engineering Program
Flange Ramp Panel
Stiffener
Stringer
Origin of scan images
(corner behind detectors)
Tank Flange
Glue Lines
• 610 x 610 mm
• 25.4 mm to 305 mm thick
• 2 mm pixels, 0.1 s/pixel
Shedlock, PhD Thesis, 2007
Nuclear Engineering Program
Round (left) and Square (right) Aperture
Natural
defect 1
Natural
defect 2
Natural
defect 3
Natural
defect 4
Debris 3
(nylon washer)
Debris 4
(bolt)
Debris 2
(pencil)
Debris 1
(tape)Natural
defect 5
• Count rate ~ 1.3 X great for square aperture
• Signal contrast for natural defect 4:
5.2 % for round aperture and 4.0% for
square apertureShedlock, PhD Thesis, 2007
Nuclear Engineering Program
Current Mode (left) Count Mode (right)
• 55 kVp, 1 mm pixel, 0.2 s/pixel
• Large defect - 12.4 mm diameter,
12.4 mm height
• Small defect - 6.35 mm diameter,
6.35 mm height
• Shallow - 50.8 mm deep
• Deep - 203 mm deep (substrate)
• Contrast for the large defects
Current mode - 5.7% (shallow),
3.2% (deep)
Count mode - 4.0% (shallow),
2.0% (deep)Shedlock, PhD Thesis, 2007
Nuclear Engineering Program
Flaw Detection RSD Image of
crack in aluminum aircraft component with 2 mm skin overlay during image acquisition
70 kVp
8 mA
1 mm beam
¼ mm cracks
Courtesy Ed Dugan
Nuclear & Radiological Engineering
Flaw Detection
RSD Image of Space Shuttle reinforced carbon-carbon composite (RCC) tile with test voids
55 kVp
9 mA
1 mm beam
Courtesy Ed Dugan
Nuclear Engineering Program
Flaw Detection
RSD Image of aircraft wing shows corrosion, crushed core, and water
55 kVp
5 mA
2 mm beam
Courtesy Ed Dugan
Nuclear Engineering Program
Boric Acid Residue on RPV Steel
Foil Thermal Insulation
Steel foil thermal
insulation panel
Image showing
boric acid deposit
• Boric acid paste
• 2.5 x 2.5 mm pixels
•100 kVp, 30 mACourtesy Ed Dugan
Nuclear Engineering Program
RSD Scan of Object Through
1.5” of Gypsum Wall
• 100 kVp, 25 mA
• 2.5 x 2.5 mm pixels
Courtesy Ed Dugan
Railroad Tie Inspection
Visual Inspection
Highly Subjective
Labor Intensive
1 - 2 mph
Aurora
• 3D Laser Profiling System
• Machine Vision
• Up to 42 mph
What are both of these methods missing?
Main Project Objective
Develop a prototype system that can
demonstrate the successful imaging of the
internal structure of wood and concrete rail ties
Challenges
Radiation safety for track use
Large scan area, must do this at reasonable speeds
Linear detector arrays
X-ray fan beams
Must sync with GREX AuroraTM
Control is fleeting
Nuclear Engineering Program
X-Ray Fan Beams
For most backscatter radiography applications,
collimated pencil beam is the preferred choice
Precise position imaging
Reduces detector requirements
Relatively slow
Best for laboratory, well controlled imaging
For field measurements, an x-ray fan beam is
preferred Improves speed, but may cost some image resolution
Puts more constraints on the detector
For large areas, fan beams are the best option
Better uniformity in irradiation
Nuclear Engineering Program
Backscatter Scanning Method!!!!!!!!!!!!!!!!!!!!!!!!!!!! !
Detector
X-ray Fan
Beam
X-ray Tube
Salazar, PhD Thesis, 2016
X-Ray Detectors
Detectors from X-Scan
Imaging Corporation (San
Jose, CA)
12” active length
Other lengths readily available
Up to 9000 lines/second
possible, 2000 lines/s nominal
We can travel up to 50+ mph
without losing cm-scale resolution
Nuclear Engineering Program
Fan Beams – Additional
Collimation Necessary
Collimated detector signal
on left, uncollimated on
right
We produce a prototype
system with lead fins,
before moving to tungsten
Nuclear Engineering Program
Bougeant, MS Thesis, 2010
Measuring Position Resolution via
Modulation Transfer Function Most complete description of system spatial
resolution
Describes degradation of contrast with spatial
frequency
Limiting resolution defined at MTF = 10%
Average human eye’s separation power (resolution)
3 commonly used transmission methods
Slit method
Slanted-edge (or knife) method
Bar-pattern (or square-wave) method
Commonly used in the medical imaging
industry for performing QA
Results Good agreement
between 3 curves
Edge (along-scan) is
outlier caused by
differences in how ESF
was sampled
Direction-dependent
MTF
Along-scan MTF higher
than across-scan
Due to fan beam width,
linear motion of system,
and pixel pitch
differences between two
directions
0 0.005 0.01 0.015 0.02 0.025 0.03 0.0350
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Spatial Frequency (line-pairs/mm)
MT
F
Edge (Across-Scan)
Edge (Along-Scan)
Bar (Across-Scan)
Bar (Along-Scan)
Translates to approximately 8-12 mm
resolution.
Salazar, PhD Thesis, 2016
From the Lab to Commercial System
Concluding Remarks RSD works on variety of materials in situations where conventional
radiographic techniques have challenges
Image resolution is highly dependent of application, but we have demonstrated mm-level resolution, with sub-mm resolution possible.
Complex Optimization
Speed vs. Image Quality
Speed vs. Radiation Safety
Designing for Field Conditions
Future Projects
Fan Beam Backscatter Radiography for High-Speed Landmine
Detection
Integrating Backscatter X-Ray, Phenotyping, Modeling, and
Genetics to Increase Carbon Sequestration and Resource Use
Efficiency
Nuclear Engineering Program