Applications of Commercial LINACS in Cargo Screening Dr ... · PDF fileAir Cargo Screening...
Transcript of Applications of Commercial LINACS in Cargo Screening Dr ... · PDF fileAir Cargo Screening...
Applications of Commercial
LINACS in Cargo Screening
Dr. Imran Tahir
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Rapiscan Cargo Scanners with Low Energy LINACS
Airport Cargo Portal Gantry
Mobile Rail
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A10
A10
Air Cargo Screening
1MeV LINAC
120mm steel penetration
1mm wire resolution
2mmx2mm spatial resolution
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Gantry/Portal G10, G45, G60
G10,G45,G60/HP
1MeV, 4.5MeV or 6MeV LINAC
Max Speed: 8kph
steel penetration:
120mm, 275mm, 340mm-400mm
1mm Wire resolution
4mmx4mm spatial resolution
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Mobile/Trailer M10, M45, M60
M10,M45,M60/HP
1MeV, 4.5MeV or 6MeV LINAC
Max Speed: 8kph
steel penetration:
120mm, 275mm, 310mm/330mm
1mm Wire resolution
4mmx4mm spatial resolution
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Rail Scanner R60, R90
R60/R90
6MeV, 9MeV LINAC
Max Speed: 60kph
Steel Penetration: 310mm, 340mm
2mm wire resolution, 5mmx5mm spatial resolution
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Detector Architecture
Scintillator + Photodiode
8 vertical channels Photodiodes beneath the scintillator
Hamamatsu 16 element Si photodiode
Array S11212 Series
(Images from device datasheet)
Scintillator Architecture
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Scintillator Arrangement vs. Object Speed
5kph
Single column array
15kph
Three column array
60kph
12 column array
LINAC’s secondary collimation is adjusted to fit the scintillator array width
Normally 128 of such arrays are arranged vertically in the detector boom
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LINAC and Detector Array Setup
30o
30o LINAC
Secondary Collimator
X-Ray
Fan Beam
Detector
Boom
Pulse Generator
Safety
Interlocks
X-Ray ON/OFF
Pulse width
& Energy
Object
Detection
Object
Speed
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X-Ray Scan Sequence Control
• Scanning is fully automated using PLCs and DSPs.
• LINAC is fired when a valid object is detected at the scan line.
Laser profilers for slow speed objects and Intelligent Infrared for
high speed objects is used to determine the validity of an object for
X-Ray.
• Line scan cameras and Optical Container Code Recognition along
with Axle Profile is used to distinguish between a rail cargo and
locomotives with drivers.
• Speed of the object is precisely measured and the LINAC pulse
rate is changed accordingly.
• If an object stops in the middle of a scan, LINAC is turned off
immediately.
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X-Ray Data Acquisition
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Image Preprocessing
Offset Correction
Using Dark data
Gain Correction by
Averaging w.r.t.
Uniform X-ray
exposure
Linear to Log
Transformation
Bad Pixel
Elimination
RAW Image
Processed RAW Image
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Image Processing
Exposure
Recognition Edge
Restoration
Noise
Reduction
Grayscale
Rendition
Contrast
Enhancement
Material
Separation
Processed RAW Image
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LINAC Interlaced Mode
Mi60 Varian Datasheet
LINAC is pulsed with High and Low energy alternatively Interlaced Mode) to achieve material discrimination.
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Material Separation
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Cargo Imaging Low Speed (5kph)
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Cargo Imaging Medium Speed (10-30kph)
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Cargo Imaging High Speed (60kph)
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LINAC Performance
• Dose Stability
Standard deviation on dose should ideally be 1 to 2%. 3% is the
max. threshold (Pulse to pulse, as well as scan to scan).
• Focal Point consistency
Should not move more than a pixel width (2mm nominal)
• X-Ray Beam symmetry
should not exceed 5% at +/-7.5 degrees off the beam centre axis
• Turn on time
Within 10 pulses
• Energy switching rate
Low: 50 - 400 PPS, High: 50-300Hz,
• No missing pulses
• Dose rate outside the shielding
2.5x10-6 with respect to the primary beam (Ultra Low), <20uSv/hr on
package surface
• Environmental robustness
Temperature conditions -40C to +60C
Must be able to cope with mild vibrations during operation
Must be fully sealed to work in outdoor environment such as mobile
applications
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System Level Safety
• The LINAC must turn off immediately soon as a human is detected in the
scan area
• Laser Imaging and Infrared curtains used at the entry of the scan area
making sure it is only cargo vehicles or containers that trigger the LINAC
• Line-scan cameras and automatic container code recognition systems are
used to verify that only a valid cargo is scanned
• Barrier interlocks to stop unauthorised movements
• LINAC Housing Interlocks to stop accidental fire during servicing
• Low dose (Non-LINAC) driver cab scan when occupied