x-ray backscatter radiography by selective ... - asnt.asnt.org

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

[email protected]

@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


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


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


Radiography by Selective

Detection (RSD)

Shedlock, PhD Thesis, 2007


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


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


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)


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


Shuttle Inspection

PAL Ramps

Bi-POD

Bolt Flange

Area



Example System Built By UF


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



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


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


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


Flaw Detection

RSD Image of aircraft wing shows corrosion, crushed core, and water

55 kVp

5 mA

2 mm beam

Courtesy Ed Dugan


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


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


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


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


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


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


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