Technical Glossary

A

ACSTL (Air Cargo Screening Technology List)

TSA-maintained catalog of certified explosive detection systems and screening equipment approved for air cargo security operations. Equipment must meet stringent detection probability and false alarm rate standards.

Atomic Number (Z)

Number of protons in an atom's nucleus. Dual-energy X-ray systems calculate effective atomic number (Z_eff) to classify materials as organic (low Z) or inorganic (high Z), enabling automated threat recognition.

ATR (Automated Threat Recognition)

Machine learning algorithms that analyze X-ray imagery to identify potential threats without human intervention. Modern systems use convolutional neural networks trained on millions of threat images to achieve detection rates exceeding 95%.

B

Backscatter X-Ray

Imaging technique that detects X-rays reflected from an object rather than transmitted through it. Primarily used for body scanners and vehicle inspection. Sensitive to low-density organic materials concealed on surfaces. TSA phased out backscatter body scanners in 2013 in favor of millimeter wave technology.

Basis Material Decomposition

Mathematical technique in dual-energy CT that separates material composition into two basis components (typically water and bone, or aluminum and polyethylene) to enable precise material discrimination independent of thickness.

C

Computed Tomography (CT) Screening

Advanced 3D imaging technology that creates volumetric reconstructions of bag contents using multiple X-ray projections. Enables automated explosive detection and allows laptops/liquids to remain in bags. TSA approved CT for checkpoint deployment in 2018.

Compton Scattering

Interaction between X-ray photons and outer shell electrons resulting in photon deflection and energy loss. Dominant interaction mechanism at the energy levels used in security screening (60-160 keV). The Compton scatter profile provides material density information.

D

DEXRT (Dual-Energy X-Ray Transmission)

Imaging system that transmits X-rays at two distinct energy levels to enable material discrimination. Low-energy beam (60-80 keV) and high-energy beam (120-160 keV) produce differential absorption signatures used to classify organic vs. inorganic materials.

DHS (Department of Homeland Security)

U.S. federal agency responsible for security screening standards and certification. Oversees TSA operations and the Safety Act program for anti-terrorism technology qualification.

E

ECAC (European Civil Aviation Conference)

International organization that establishes aviation security standards for European nations. ECAC certification is required for screening equipment deployment in EU airports. Standards often align with but may differ from TSA requirements.

EDS (Explosive Detection System)

Certified screening technology capable of detecting explosive materials and devices. TSA certifies EDS equipment for checked baggage, cargo, and checkpoint applications based on detection probability and false alarm rate performance metrics.

ETD (Explosive Trace Detection)

Secondary screening method that uses mass spectrometry or ion mobility spectrometry to detect microscopic explosive residue. Deployed when X-ray imaging flags suspicious items or for random secondary screening protocols.

F

False Alarm Rate (FAR)

Percentage of benign items incorrectly flagged as threats. TSA requires FAR <5% to maintain operational throughput. High false alarm rates increase screening time and reduce passenger flow efficiency.

I

ICAO (International Civil Aviation Organization)

United Nations specialized agency that establishes international aviation security standards and recommended practices. Member states implement ICAO Annex 17 security protocols through national regulatory authorities.

L

LINAC (Linear Accelerator)

High-energy X-ray source operating at 3-9 MeV for cargo container penetration. Requires radiation shielding infrastructure and certified radiation safety programs. Used for fully loaded ISO containers and large vehicle inspection.

M

Millimeter Wave Scanner

Non-ionizing body scanner technology using electromagnetic waves in the 24-30 GHz frequency range. Replaced backscatter X-ray systems for passenger screening. Detects concealed objects through radio frequency reflection without radiation exposure.

N

NDT (Non-Destructive Testing)

Inspection methodology that evaluates material properties and structural integrity without causing damage. Industrial X-ray applications include weld inspection, composite analysis, and defect identification in aerospace, automotive, and manufacturing sectors.

P

Photoelectric Effect

Complete absorption of an X-ray photon by an inner shell electron, ejecting the electron from the atom. Dominant at low X-ray energies (<60 keV) and strongly dependent on atomic number (Z³ relationship), making it crucial for material discrimination.

Probability of Detection (Pd)

Statistical measure of a system's ability to correctly identify threat items. TSA requires Pd >95% for standardized threat articles. Certified through independent testing using representative threat materials and configurations.

Q

QATT (Qualified Anti-Terrorism Technology)

DHS Safety Act designation providing liability protection for approved security technologies. Requires demonstration of effectiveness and safety standards. Certification facilitates commercial deployment and procurement.

R

Radiographic Testing (RT)

NDT technique using X-rays or gamma rays to inspect internal structures. Common in pipeline integrity assessment, pressure vessel certification, and aerospace component qualification. Digital radiography (DR) replacing film-based methods.

S

Steel Penetration Equivalency

Standard metric for X-ray system capability measured in millimeters of steel thickness the system can effectively image. TSA requires minimum 34mm for checkpoint baggage systems, 38mm for checked baggage, and up to 300mm for cargo applications.

T

TIP (Threat Image Projection)

TSA-mandated quality assurance protocol that superimposes synthetic threat objects onto live X-ray feeds to test operator vigilance and detection performance. System records operator responses for training and certification metrics.

TSA (Transportation Security Administration)

U.S. federal agency responsible for civil aviation security. Certifies screening equipment, establishes operational protocols, and maintains the ACSTL database. Created in 2001 under the Aviation and Transportation Security Act.

Z

Z_eff (Effective Atomic Number)

Weighted average atomic number calculated from dual-energy X-ray data. Organic materials (explosives, narcotics) typically exhibit Z_eff 6-8, while inorganic materials (metals, ceramics) show Z_eff >12. Primary parameter for automated material classification algorithms.