SECURITY SCREENING ACADEMY

Security Screening Basics

Understand the principles before choosing equipment. Ten lessons cover how X-rays are produced, how to read images, radiation safety, metal detection, trace detection, 3D-CT and AI screening. Check your understanding with 5 questions at the end.

01How are X-rays produced?02Transmission and attenuation03Identifying materials with dual energy04Image processing05Numbers that define performance06Radiation safety07Metal detection08Explosive trace detection093D-CT10AI screening✓ Quiz
LESSON 01

How are X-rays produced?

Inside an X-Ray Baggage Scanner is an X-ray tube that produces X-rays. Electrons emitted from a filament are accelerated by a high voltage into a metal target, and as the electrons stop abruptly, X-rays are emitted.

Tube voltage (kV)
The higher it is, the more energetic the X-rays, so they pass through thicker objects.
Tube current (mA)
The larger it is, the more X-rays are produced, making the image brighter and sharper.
Collimator
Focuses X-rays into a thin fan beam that illuminates only where needed.
▶ Try it
▶ Try it
Cathode (filament): emits electronsAnode (rotating target)Electrons accelerated by high voltage (kV) →X-raysCollimator → fan beam {{tread}}
Rapidly accelerated electrons strike the metal target and X-rays are emitted.
LESSON 02

How transmission and attenuation form an image

As X-rays pass through an object, part of them is absorbed and they weaken (attenuation). Detectors measure the intensity of the remaining X-rays, and those differences become the light and dark areas of the image.

Density · thickness
The denser and thicker, the more is absorbed.
Atomic number
The heavier the element, the better it blocks X-rays.
Attenuation increases exponentially with thickness: I = I₀ · e−μx
▶ Try it
X-ray photons →Detector Paper83% reachPlastic50% reachIron16% reach X-ray photons →Detector Paper100% reachPlastic83% reachIron50% reach
The higher the density, thickness and atomic number, the fewer X-rays pass through and the darker the image.
LESSON 03

Identifying materials with dual energy

Even for the same object, the ratio of high- and low-energy X-rays absorbed differs by material. Measuring this ratio with a two-layer detector lets the system estimate the material type and display it in color.

Screeners look at color (material)and shapetogether.
Overlapping areas, such as metal hidden inside organic material or organic material between metals, are distinguished by color.
Low-energy detector layer+High-energy detector layer
↓ Absorption ratio of the two signals → material type (effective atomic number) estimated
OrganicMaterials made of light elements, such as paper, clothing, wood, plastic and liquids
MixedLight metals such as aluminum, and areas where organic and inorganic materials overlap
InorganicMaterials made of heavy elements, such as metals like iron and copper
ImpenetrableObjects so thick or dense that X-rays barely pass through must be opened and checked.
LESSON 04

Image processing that reveals hidden objects

Organic/inorganic stripping, black-and-white, high penetration, inversion and brightness adjustment let screeners review the same image in different ways. Below are conceptual examples showing how each function changes the image.

OS / MS
Removes the organic or inorganic color to make the other stand out.
HP
Raises contrast in high-absorption areas to look behind metal.
NEG · ENH
Uses inversion and edge enhancement to find thin wires and boundaries.
▶ Try it
Normal imageOS · Organic strippingMS · Inorganic strippingB/W · Black & whiteHP · High penetrationENH · Image enhancementNEG · B/W inversion▲ · Brightness up▼ · Brightness down
Conceptual example. The actual screening display may differ.
LESSON 05

Numbers that define performance

Catalog specification tables are read with these numbers. Even for equipment with the same name, these numbers determine actual screening quality and safety.

Tip. National performance certification (aviation security equipment) is the result of an accredited institution testing and confirming criteria such as resolution, penetration and continuous operation.
36 AWGWire resolutionDistinguishes wires down to approx. 0.127mm in diameter. The higher the number, the thinner the wire it shows.
34mmPenetrationThickness of steel behind which objects can still be seen; the higher, the better.
1μSv/h or lessSurface radiation dose rateRadiation intensity measured at the equipment surface; the lower, the safer.
0.2m/sStandard conveyor speedThe speed at which baggage passes through, set to balance throughput and image quality.

Example values: based on MSCAN-6040D specifications · KTL test results

LESSON 06

Three principles of radiation safety: time, distance and shielding

X-Ray Baggage Scanners are designed to use X-rays only inside the equipment. Knowing the three basic principles of radiation protection and the equipment’s shielding structure makes safety standards easier to understand.

Units. 1 mSv (millisievert) = 1,000 μSv (microsievert). Equipment surface dose rate is expressed in μSv/h (per hour).
TimeThe shorter the exposure, the lower the dose received.
DistanceThe dose drops sharply with distance from the source.
ShieldingA lead (Pb) tunnel and curtains keep X-rays inside the equipment.
LESSON 07

Finding metal through changes in a magnetic field

Walk-through and Hand-held Metal Detectors create a magnetic field with coils. When metal passes through, an induced current in the metal changes the field, and the detector senses this change and sounds an alarm.

Walk-through units are divided into multiple zones to show the height and direction at which metal passed.
Sensitivity is adjusted to suit the site, reducing alarms from personal items such as keys and coins.
▶ Try it
Walk through Alarm · Zone 4 ◀ AlarmMetal detected at waist height L · R pillar coils → magnetic fieldZone location LEDs Walk through Alarm · Zone 6 ◀ AlarmMetal detected at ankle height L · R pillar coils → magnetic fieldZone location LEDs Walk through L · R pillar coils → magnetic fieldZone location LEDs
LESSON 08

Telling explosive traces apart by ion speed

A sample wiped from a bag or hands with sampling paper is heated and ionized, then the time it takes ions to reach the detector in an electric field is measured. Because ion size and shape differ by substance, arrival times differ (IMS).

Explosives (negative ions) and narcotics (positive ions) can be analyzed together.
Arrival time patterns are compared with a substance library to make a determination.
▶ Try it
Baggage · handle Insert sample Analyzing… ⚠ DetectedExplosive trace · TNT type IMS trace detector Drift tube (electric field): small ions fast, large ions slow TNT Arrival time → library match ① Sampling② Insert · heat③ Ionize · drift④ Result (within 5 s) Baggage · handle Insert sample Analyzing… ✓ SafeNo hazardous substances IMS trace detector Drift tube (electric field): small ions fast, large ions slow Arrival time → library match ① Sampling② Insert · heat③ Ionize · drift④ Result (within 5 s)
Traces wiped with sampling paper are heated · ionized → substance identified by ion arrival time
LESSON 09

3D-CT: imaging from many angles and rebuilding in 3D

In CT, the X-ray generator and detectors rotate around an object to capture transmission images from many angles, and cross-sections and 3D images are reconstructed by computation. The biggest difference from 2D is that overlapping items can be viewed separately.

A rotating gantry scans while turning 360°.
A reconstruction algorithm restores the projection images into 3D.
MIK SCAN is developing a 3D-CT X-Ray Baggage Scanner.
▶ Try it
X-ray generator · detectors rotate together ↻TunnelSlip ring: power · data while rotating
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LESSON 10

AI accuracy depends on what the AI reads

The amount of usable information differs greatly depending on whether AI reads screen-captured images or the raw data produced by the detector.

In numbers. 8-bit holds 28 = 256 levels, and 16-bit holds 216 = 65,536 levels of brightness information.
Screen capture method · 8-bit256 levels
Information is lost by re-reading a screen already converted to color.
Raw data method · 16-bit65,536 levels
AI reads the detector signals (High·Low) directly, seeing both shape and material properties.
See MIK SCAN AI screening technology →
CHECK

Check your understanding with 5 questions

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Equipment principles at a glanceCompare X-ray, walk-through, hand-held, trace detection, Speed Gate and Recheck.Technology Overview →Screening training for operatorsWe support screening training after installation.Service · training →See it in our showroomWe offer demos with actual equipment at our headquarters showroom.Book a demo →