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