Airport X-Ray Scanners: Do They Check Our Bags?

Airport security is a complex and multifaceted operation, employing various methods and technologies to ensure the safety of passengers and prevent illegal activities. One crucial aspect of this security network is the use of baggage scanners, which utilise X-ray technology to inspect checked luggage and carry-on bags. These scanners are designed to detect potential threats and prohibited items, such as metallic and non-metallic objects, organic materials, and hazardous substances. With approximately 1.3 million checked bags and 3.3 million carry-on bags screened daily in the US alone, the role of these scanners in maintaining aviation security cannot be overstated.

X-ray technology

X-ray Systems for Cargo and Checked Luggage

Most airports utilise one of three x-ray systems to scan cargo and checked luggage: medium x-ray systems, mobile x-ray systems, and fixed-site systems. Medium x-ray systems are fixed installations that can scan an entire pallet of cargo or luggage. Mobile x-ray systems involve a large truck carrying the x-ray equipment, which drives alongside a stationary truck to scan its contents. Fixed-site systems are entire buildings dedicated to x-ray scanning, where a tractor-trailer can be pulled inside for scanning.

X-ray scanners emit high-energy x-ray beams that penetrate luggage and create detailed images on a monitor. These images show the dense and light areas inside the bag, allowing security officers to differentiate between various materials. Metals, for example, absorb a lot of x-rays and appear as dark orange or blue on the screen, while organic materials like food, paper, or drugs are depicted in shades of green or lighter colours.

Detection of Metallic and Non-Metallic Objects

X-ray scanners can easily detect metallic objects such as guns, knives, and other weapons due to their interaction with metal. However, they are also capable of identifying non-metallic objects made of plastics, ceramics, or glass through their density and atomic number. This makes it possible to detect items like plastic explosives or other contraband that could threaten aircraft security.

Identifying Organic Materials

Airport scanners are equipped with advanced technology to sensitively identify organic materials, which is crucial for detecting drugs and explosives. These substances have unique densities and compositions that stand out on an x-ray scan, appearing as orange on the monitor. Security officers are trained to spot visual clues that may indicate the presence of narcotics or explosives.

Ensuring Safety and Privacy

Detecting drugs and other illegal substances

One significant challenge is that narcotics often lack a distinct shape or form, making it difficult for algorithms to identify them through object recognition. Additionally, drugs such as heroin and cocaine are often mixed with other substances, altering their physical characteristics and making material discrimination more complex.

To address these challenges, a combination of object recognition and material discrimination algorithms can be utilised. This approach can identify narcotics based on physical characteristics, density, or effective atomic number, especially when the drugs are relatively pure. Advanced imaging technologies, such as Computed Tomography (CT) scans, also enhance the detection of drugs transported inside the body, on the body surface, or within luggage.

Another effective method for drug detection is the use of trained dogs, known as K-9 units. These dogs are specialised in sniffing out specific odours associated with drugs and explosives, providing fast and accurate detection.

While X-ray diffraction technology, which provides detailed information about the physical composition of materials, holds promise for narcotics detection, it is not yet widely available. In the meantime, the ongoing collaboration between authorities and the security screening industry to gather images of substances for algorithm training will contribute to the development of more effective drug detection solutions.

Scanning for weapons

X-ray scanning is a widely used technique for screening checked bags and carry-on luggage. These X-ray systems come in different configurations, such as medium X-ray systems that scan fixed pallets, mobile X-ray systems mounted on trucks, and fixed-site systems that can accommodate large vehicles. The X-rays penetrate bags and generate images based on the density of the contents, which helps identify potential weapons or other prohibited items.

Metal detectors are another crucial tool for detecting weapons. They generate and measure low-strength magnetic fields, which, when altered by metallic objects, indicate the presence of metal. This technology is safe and does not cause biological damage. Additionally, metal detectors can identify even the smallest amounts of metal, helping to uncover potential weapons or dangerous items.

To enhance security further, some airports employ explosive detection systems, often utilizing trained dogs, or K-9 units, that can sniff out explosives and drugs with remarkable speed and accuracy. These dogs are trained to detect specific odors associated with explosives and illegal substances, providing an effective layer of security.

Full-body scanners are also becoming more common in airports to detect weapons and explosives that might be concealed under clothing. These include backscatter scanners, which use low-energy X-rays, and millimeter-wave scanners, which use radiofrequency waves. Both types create images of the person's body and any hidden items without causing health risks to the individual being scanned.

Overall, the combination of these scanning technologies and techniques plays a vital role in ensuring the safety of passengers and staff by effectively detecting weapons and other prohibited items during the security screening process at airports.

Checking for explosives

Checking luggage for explosives is a key part of airport security. The Transportation Security Administration (TSA) screens approximately 1.3 million checked bags for explosives and other dangerous items daily.

X-ray systems

Most airports use one of three X-ray systems to check cargo for explosives: medium X-ray systems, mobile X-ray systems, and fixed-site systems. Medium X-ray systems are fixed systems that can scan an entire pallet of cargo for suspicious items. Mobile X-ray systems are large trucks that carry a complete X-ray scanning system. The truck drives slowly next to another stopped truck to scan its entire contents. Fixed-site systems are buildings that function as one huge X-ray scanner. A tractor-trailer is pulled into the building and the entire truck is scanned at once. Some airports also have medium X-ray facilities set up to scan an entire pallet of luggage at a time.

Full-body scanners

Full-body scanners are used to detect threatening items and contraband such as weapons, explosives, and drugs under multiple layers of clothing. The most common type is the millimeter-wave scanner, which uses a special type of electromagnetic wave to detect a wide range of items, including plastic explosives. Full-body scanners are now commonplace in the U.S., and travelers passing through airports where they are in use will be subject to scanning unless they specifically opt out.

Explosive trace detection

This process involves swabbing the outside of a piece of luggage, or a traveler's hands or clothes, to check for trace amounts of explosives, which may indicate contact with, or carriage of, a restricted substance or item. The technology checks for chemicals such as glycerin and nitrates, which are present in soaps, shampoos, and hair products, and often cause false positives.

Detection dogs

Also known as sniffer dogs, these dogs are trained to detect the specific odors emitted by chemicals used to make bombs, as well as the odors of other items such as drugs, live animals, animal manure, organic matter, ivory, currency, blood, and electronic contraband. They can find items that may slip past other detection methods, making them an excellent additional security measure.

Scanning for organic materials

X-ray scanning is a common method for security screening at airports. There are two main types of X-ray imaging modalities used for security screening: transmission imaging and backscatter imaging. Transmission imaging uses an X-ray beam that passes through the object being scanned, which is then detected by a linear array of pixels. On the other hand, backscatter imaging uses a moving, collimated beam of X-rays, known as a "flying spot", that is rastered across the object. This type of imaging is particularly effective at detecting low-atomic-number (low-Z) elements, which give the strongest X-ray backscatter signal.

A forward/backscatter scanner can be used to differentiate between organic and inorganic materials. This type of scanner uses a pencil beam X-ray that is rastered over the object, with detectors on both sides to collect transmitted and backscattered X-rays. By analyzing the forward and backscatter signals, it is possible to determine the atomic number of the material being scanned. Organic materials, which are typically low-Z, produce a strong backscatter signal and relatively weak attenuation, while inorganic materials, which are usually high-Z, produce a weak backscatter signal and strong attenuation.

Z Backscatter technology is a specific type of backscatter imaging that is highly effective at detecting organic materials. It captures the data from X-rays that are scattered back towards a near-sided detector, which is known as Compton Scattering. The resulting images show organic matter as bright white areas, making it easy for operators to identify potential threats.

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