X-Ray Vision: What Airport Scanners See

Airport X-ray machines are used to scan carry-on luggage and detect any dangerous or prohibited items. The machines use electromagnetic waves to scan luggage, and the resulting image is coloured according to the range of energy that passes through the object. Organic materials, including explosives, are typically coloured orange. Full-body scanners are also used in some airports to detect objects on or inside a person's body, without physical contact. These scanners have been the subject of controversy, with critics arguing that they violate privacy and human rights.

X-ray systems use orange to represent organic items as most explosives are organic

Airport X-ray systems are used to scan carry-on items and detect any threats or contraband. These machines use X-rays, which are electromagnetic waves with high energy that can penetrate many materials. The X-rays pass through the items, and a detector picks them up. This detector then passes the X-rays through a filter that blocks out the lower-energy X-rays, and the remaining high-energy X-rays hit a second detector. This process allows the machine to better represent low-energy objects, such as organic materials.

The X-ray system then colours the items on the display monitor based on the range of energy that passes through them, categorising them into three main groups: organic, inorganic, and metal. While the colours for inorganic and metal may vary between manufacturers, all X-ray systems use shades of orange to represent organic items. This is because most explosives are organic, and operators are trained to look for anything that could be a component of an improvised explosive device (IED).

It is important to note that not all explosives are organic, and some inorganic explosives can be popular with terrorists and have been widely used in homemade explosive (HME) mixtures. Therefore, relying solely on the colour orange to identify potential threats may be flawed. However, organic items are typically represented by orange on airport X-ray systems to help operators identify potential dangers.

Additionally, electronic items, such as laptops, may require further inspection as it can be challenging to determine if a bomb is hidden within them. Passengers may be asked to turn their devices on, but even this may not be sufficient as skilled criminals can conceal bombs within functioning electronics. As a result, some airports employ additional measures, such as chemical sniffers, to enhance security and detect potential explosive threats.

The dual-energy X-ray system has a single X-ray source that can penetrate many materials

Airport security uses a dual-energy X-ray system to scan carry-on items. This system has a single X-ray source that emits X-rays in the range of 140 to 160 kilovolt peak (KVP). KVP refers to the amount of penetration an X-ray makes, with a higher KVP allowing the X-ray to penetrate further. The dual-energy X-ray system works by passing X-rays through a detector, a filter, and then another detector. The detector picks up the X-rays after they have passed through the scanned item, and then passes them to the filter, which blocks out the lower-energy X-rays. The remaining high-energy X-rays then hit the second detector.

A computer circuit compares the readings of the two detectors to better represent low-energy objects, such as organic materials. Different materials absorb X-rays at different levels, so the image on the monitor allows the operator to see distinct items inside the bag. Items are typically coloured based on the range of energy that passes through them, with all X-ray systems using shades of orange to represent organic items as most explosives fall into this category.

Dual-energy X-ray systems are also used in medical settings to measure bone mineral density (BMD) and diagnose osteoporosis. This is known as dual-energy X-ray absorptiometry (DXA or DEXA). DXA uses two X-ray beams with different energy levels aimed at the patient's bones. By subtracting the soft tissue absorption, the bone mineral density can be determined from the absorption of each beam by bone.

X-rays are electromagnetic waves with more energy than light, allowing them to penetrate materials

X-rays are a type of electromagnetic radiation, like light, but with more energy. This higher energy allows X-rays to penetrate materials that light cannot. This property of X-rays is exploited in airport security systems, where they are used to scan carry-on luggage for prohibited items.

X-rays are a form of electromagnetic radiation, which is a broad category that includes other types of radiation such as radio waves, microwaves, ultraviolet light, and gamma rays. These different types of radiation are distinguished by their frequencies and wavelengths, with radio waves having the lowest photon energy and the longest wavelengths, and gamma rays possessing the highest photon energies and shortest wavelengths. X-rays fall somewhere in the middle of the electromagnetic spectrum, with more energy than visible light but less than gamma rays.

The ability of X-rays to penetrate materials is due to their higher energy compared to light. This energy allows them to pass through many substances that light cannot, such as human skin and luggage. The amount of penetration an X-ray can achieve is measured in kilovolt peak (KVP), with higher KVP values corresponding to greater penetration. This property is crucial for their application in airport security, where they need to be able to pass through various materials to create an image of the contents of a bag.

The X-ray systems used in airports are typically dual-energy systems, which employ a single X-ray source with energies ranging from 140 to 160 kilovolt peak (KVP). As the luggage is passed through the X-ray machine on a conveyor belt, the X-rays penetrate the bag and its contents. After passing through, the X-rays are detected and analysed to create an image that reveals distinct items inside the bag.

The image produced by the X-ray system uses colours to differentiate between different types of materials. Typically, organic materials are represented by shades of orange since most explosives fall into this category. Inorganic materials and metals are also colour-coded, allowing security personnel to identify potential threats. This process enables the detection of prohibited items, such as scissors, cigarette lighters, guns, knives, and explosives.

Full-body scanners can detect non-metal objects and items inside body cavities

Full-body scanners have been used in airports since 2007, supplementing metal detectors. They are used to detect objects on or inside a person's body without the need for physical contact or the removal of clothing. This is done through the use of different technologies, including:

• Millimeter wave scanners, which use non-ionizing electromagnetic radiation to detect objects.
• Backscatter X-ray scanners, which use low-dose radiation to detect objects hidden under clothing or in body cavities.
• Transmission X-ray scanners, which use higher-dose radiation to detect objects hidden under clothing or inside the body.
• Infrared thermal conductivity scanners, which detect objects based on temperature differences on the surface of clothing.

Full-body scanners can detect non-metal objects, such as plastic weapons, explosives, drugs, and other prohibited substances, that metal detectors cannot. They can also detect items hidden in body cavities, such as drugs swallowed by drug couriers. This enhanced detection capability makes them effective security measures in airports and other high-security areas.

The use of full-body scanners has sparked debates about privacy and health concerns. Critics argue that the imaging produced by these scanners amounts to virtual strip searches without probable cause, violating basic human rights. To address these concerns, operators are typically located in separate rooms and view cartoon-like representations or alternate-wavelength images of scanned individuals, with indicators of suspicious items.

Health concerns have also been raised, particularly regarding the use of X-ray scanners. While radiation safety authorities claim that there is "no evidence" of health risks, critics argue that long-term studies are lacking. The use of X-ray scanners has been banned in multiple countries due to safety investigations.

Millimeter wave scanners use non-ionizing electromagnetic radiation and are considered safer than X-ray scanners

X-ray machines are used at airport security to scan both passengers and their carry-on luggage. Dual-energy X-ray systems are used to scan luggage, and backscatter X-ray machines are used to scan passengers.

Backscatter X-ray machines produce detailed full-body images of passengers, using low-energy X-rays that bounce off the passenger's body and any concealed items. These X-rays have enough energy to penetrate many materials, and they can also penetrate the skin and strike deeper tissues.

However, there are concerns about the safety of X-ray scanners. X-rays are a form of ionizing radiation, which has the potential to alter the structure of biological molecules, and there are worries that this could increase cancer rates.

An alternative to X-ray scanners is the millimeter-wave scanner, which uses non-ionizing electromagnetic radiation. Millimeter-wave scanners produce detailed full-body images, but they do so with ultra-high-frequency millimeter-wave radiation, similar to microwaves. This type of radiation has much less impact on small structures in the body, such as human proteins and nucleic acids.

Millimeter-wave scanners are considered safer than X-ray scanners because they do not use ionizing radiation. No known safety issues have been found with this type of scanner. The waves produced by millimeter-wave scanners are much larger than X-rays, and they do not have the ability to remove electrons from atoms or alter biological molecules.

In addition to safety concerns, X-ray scanners have also faced criticism for privacy invasion. While measures have been put in place to protect passenger privacy, such as privacy algorithms and remote image viewing, there have been reports of images being stored and disseminated. Millimeter-wave scanners have also faced similar privacy criticisms, but these scanners now typically use automated target recognition (ATR) software, which produces a generic body outline rather than a detailed image.

Millimeter-wave scanners are widely used, with hundreds of devices installed at major airports in the US and internationally. They are considered a safer and more privacy-respecting alternative to X-ray scanners, and they are particularly useful for detecting both metallic and non-metallic objects.

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