X-Ray Screening Glossary

A

ACC3 (Air Cargo or Mail Carrier operating into the Union from a Third Country Airport)

EU designation that an airline needs for each non-EU airport from which it carries cargo or mail into the EU. It requires an EU aviation security validation of the carrier's cargo operations. See air cargo screening.

ACSTL (Air Cargo Screening Technology List)

TSA list of the equipment (X-ray, explosives detection and trace detection systems) that regulated parties may use to screen air cargo under their security programmes.

AIT (Advanced Imaging Technology)

TSA's term for whole-body scanners that detect metallic and non-metallic items under clothing. Current US units use millimetre-wave technology with automated target recognition. See body scanners.

Atomic number (Z)

The number of protons in an atom's nucleus. Because X-ray absorption at low energies depends strongly on atomic number, dual-energy systems can estimate the effective atomic number of a material and colour it accordingly.

ATR (Automated Threat Recognition / Automated Target Recognition)

Software that analyses screening data and flags possible threats. In body scanners it marks anomaly locations on a generic avatar instead of showing an image of the person; in baggage systems it highlights suspect regions for the operator.

B

Backscatter X-ray

Imaging that detects X-rays scattered back toward the source rather than transmitted through the object. Sensitive to low-Z organic material near the surface; used for vehicle inspection and some personnel screening. See backscatter X-ray.

C

CCSP (Certified Cargo Screening Program)

TSA program (49 CFR Part 1549) under which shippers, forwarders and third-party facilities are certified to screen air cargo before tendering it to passenger airlines, with chain-of-custody controls.

Compton scattering

Interaction in which an X-ray photon collides with a loosely bound electron, loses part of its energy and changes direction. It is the main interaction in light materials at typical screening energies and the basis of backscatter imaging.

Computed tomography (CT)

Imaging that combines many projections taken from different angles into a 3D volume. Used in checked-baggage EDS, checkpoint CT scanners and industrial inspection. See CT scanners.

D

Dual-energy X-ray

Technique that measures attenuation at two energy ranges (often using stacked low- and high-energy detectors) to estimate effective atomic number, so materials can be displayed as organic (orange), mixed or light inorganic (green) and metallic (blue). See X-ray image colours.

E

ECAC (European Civil Aviation Conference)

Intergovernmental organisation of European states. Its Common Evaluation Process (CEP) tests security equipment such as EDS, cabin-baggage EDS, liquid explosives detection, ETD and security scanners against agreed standards.

EDS (Explosives Detection System)

Equipment that automatically detects explosives in baggage or cargo, typically using CT. In the US, EDS for checked baggage are certified by TSA; in Europe, hold-baggage EDS are evaluated against ECAC standards (Standard 3 being the current highest). See checked baggage EDS.

EDSCB (Explosives Detection Systems for Cabin Baggage)

ECAC/EU equipment category for cabin-baggage screening systems, mostly CT, with graded standards such as C1–C3 (higher standards allow more items, such as laptops and liquids, to stay in bags).

ETD (Explosives Trace Detection)

Detection of microscopic explosive residues collected on a swab, usually analysed by ion mobility spectrometry or mass spectrometry. Used for alarm resolution, random screening and cargo. See ETD.

F

False alarm rate (FAR)

Proportion of harmless items that a system or operator flags as suspicious. There is always a trade-off between detection probability and false alarm rate; required values are set by certification programmes and are not public.

I

ICAO (International Civil Aviation Organization)

UN specialised agency for civil aviation. Annex 17 to the Chicago Convention sets international standards for aviation security that member states implement nationally.

IMS (Ion mobility spectrometry)

Analytical technique used in most ETD devices: sample vapour is ionised and the ions' drift time through a gas under an electric field identifies the substance. It is the principle on which most ETD machines work.

L

LINAC (Linear accelerator)

Device that accelerates electrons onto a target to produce high-energy X-rays, typically several MeV in cargo scanners. Used to penetrate loaded containers and vehicles. See container scanners.

M

Millimetre-wave scanner

Body scanner using non-ionising radio waves (around 24–30 GHz in TSA's units) that reflect off the skin and objects under clothing. Replaced backscatter X-ray body scanners at US airports in 2013.

N

NDT (Non-destructive testing)

Inspection of materials and components without damaging them. Radiographic testing (RT) is one NDT method. See industrial NDT.

NII (Non-intrusive inspection)

Inspection of cargo, containers or vehicles without opening them, using X-ray or gamma-ray imaging, radiation detection and similar technologies. See cargo screening.

P

Photoelectric effect

Interaction in which an X-ray photon is completely absorbed by an inner-shell electron. Its probability rises steeply with atomic number and falls with energy, which is why it dominates material discrimination at low energies.

Probability of detection (Pd)

Probability that a system or operator detects a threat item when present. Certification tests measure it against defined threat sets; the required values are not public.

Q

QATT (Qualified Anti-Terrorism Technology)

Designation under the US DHS SAFETY Act that gives liability protection to sellers of qualifying anti-terrorism technologies. It is not an approval for use in TSA screening.

R

Radiographic testing (RT)

NDT method using X-rays or gamma rays to image internal structure, for example welds and castings, on film, imaging plates or digital detectors.

Regulated agent

In EU and ICAO terminology, a company (typically a forwarder or handler) approved by the authority to apply security controls to cargo, including screening. Works alongside known consignors in the secure supply chain.

S

Steel penetration

Thickness of steel behind which a test object can still be seen on an X-ray image. A standard image-quality measure for baggage systems (tens of millimetres) and cargo scanners (hundreds of millimetres).

T

TIP (Threat Image Projection)

Software that inserts images of threat items into real X-ray images of bags during live screening, to keep operators alert, measure their performance and target training. See Threat Image Projection.

TSA (Transportation Security Administration)

US agency created by the Aviation and Transportation Security Act of 2001, responsible for security in civil aviation and other transport modes. It screens passengers and baggage and regulates airports, airlines and air cargo.

Z

Z_eff (Effective atomic number)

Single number representing the X-ray absorption behaviour of a compound or mixture. Organic materials have low Z_eff (roughly 6–8), aluminium about 13, and iron 26. Dual-energy systems estimate it to assign display colours.