Backscatter X-ray

Backscatter X-ray is an advanced imaging technology. Traditional X-ray machines detect hard and soft materials by the variation in transmission through the target; in contrast, backscatter X-ray detects the radiation that reflects back from the target. It has potential applications in situations where non-destructive examination is required, and can be used even if only one side of the target is available for examination.

The technology is one of two types of whole body imaging technologies being used to perform security scans of airline passengers. The other technology is the millimeter wave scanner‎.

Technology

Backscatter technology is based on the X-ray Compton scattering effect. Unlike a traditional X-ray machine which relies on the transmission of X-rays through the object material, backscatter X-ray detects the radiation that reflects back from the object to form an image. The backscatter pattern is dependent on the material property and is good for imaging organic material.

In contrast to millimeter wave scanners which create a 3D image, backscatter X-ray scanners will typically only create a 2D image. For airport screening, images are taken from both sides of the human body.^[1]

Backscatter X-ray was first applied in a commercial security scanning device by Dr. Steven W Smith.^[2][3] Dr. Smith developed the Secure 1000 whole body scanner in 1992 and subsequently sold the device and associated patents to Rapiscan Systems who now manufactures and distributes the device.

The following companies manufacture commercially available backscatter X-ray devices that are used in airports and security scanning applications:

1. American Science and Engineering^[4] (device name: Smartcheck)
2. Rapiscan Systems (a subsidiary of OSI Systems Inc.) ^[5] (device name: Secure 1000)
3. Tek84 (formerly Spectrum San Diego Inc.) ^[6] (device name: Castscope)

Some backscatter X-ray scanners are also used to search containers and trucks much more quickly than performing a physical search, and potentially allow a larger percentage of shipping to be checked for smuggled items or weapons. According to Farren Technology, the technology exists to scan areas as far as 50 meters away from the device, producing images of people's bodies and the weapons or other contrabands they might be hiding.^{[citation needed]}

Concerns

Privacy

The technology has been proposed as an alternative to personal searches at airport and other security checkpoints, since it can easily penetrate clothing and reveal concealed weapons; however, it raises privacy concerns in that it appears to screeners essentially as a nude picture of the subject, and may allow screeners to gain access to otherwise confidential medical information, such as the fact a passenger uses a colostomy bag.

The ACLU and the Electronic Privacy Information Center are opposed to this use of the technology, currently in use in the U.S. at 18 airports, four court houses, and a correctional facility.^[7] The ACLU refers to backscatter x-rays as a "virtual strip search". In one Transportation Security Administration (TSA) trial, 79 percent of the public opted to try backscatter over the traditional pat-down in secondary screening.^[8]

It is "possible for backscatter X-raying to produce photo-quality images of what's going on beneath our clothes", thus, according to the TSA, the images have been distorted with the private areas being blurred.^[9] According to the TSA further distortion is used in the Phoenix airport's trial system where photo-quality images are replaced by chalk outlines.^[10][11] The TSA has also commented^{[citation needed]} that setting up screening procedures such as having the screener viewing the image located far away from the person being screened could be a possibility.

In light of this, some journalists have however expressed concern that this blurring may allow people to carry weapons or certain explosives aboard by attaching the object or substance to their private parts.^[9][12]

The British newspaper The Guardian has revealed concern among British officials that the use of such scanners to scan children may be illegal under the Protection of Children Act 1978, which prohibits the creation and distribution of indecent images of children. This concern may delay the introduction routine backscatter scanning in UK airports, which had been planned in response to the attempted Christmas Day 2009 attack on Northwest Airlines Flight 253.^[13]

The Fiqh Council of North America have also issued the following fatwa

It is a violation of clear Islamic teachings that men or women be seen naked by other men and women. Islam highly emphasizes haya (modesty) and considers it part of faith. The Quran has commanded the believers, both men and women, to cover their private parts.^[14]

Health effects

Some people are concerned with exposure to radiation emitted by backscatter X-rays. At airports, lead vests are not used and people fear being exposed to "dangerous level of radiation if they get backscattered too often."^[9] Safety regulations and standards like ANSI N43.17 (see below) that govern the use of these systems and that are recognized by the HPS, FDA and Various US Government Agencies may indicate that these concerns are not warranted.

The Health Physics Society (HPS) reports that a person undergoing a backscatter scan receives approximately 0.005 millirems (or 0.05 μSv) of radiation; American Science and Engineering Inc. reports 0.009 mrems (0.09 μSv).^[9] According to U.S. regulatory agencies, "1 mrem per year is a negligible dose of radiation, and 25 mrem per year from a single source is the upper limit of safe radiation exposure".^[9]

According to a draft standard on the FDA website ^[15], the allowable dose from a scan would be 0.1 μSv, and that report uses a model whereby a 0.01 μSv dose results in a 5×10⁻¹⁰ additional risk of death by cancer. Since the dose limit is ten times higher than 0.01 μSv, their model would predict one additional cancer death per 200 million scans. Since the airports in the UK handled 218 million passengers in 2009 ^[16] , if all passengers were scanned in the UK, this would produce on average one additional death every year. (Presumably there would also be some people who are given cancer but survive due to treatments such as chemotherapy, which is also very unpleasant.) Whilst the anti-terrorism related killing of Jean Charles de Menezes was widely unpopular, people killed by being irradiated with low doses of x-rays may produce less public outcry because it is not possible to identify which cancer deaths are a result of x-ray scanners and which are due to other causes. It is also frequently argued that airline passengers are going to receive a larger dose of ionizing radiation due to the altitude at which aircraft fly, so that in comparison the dose due to the x-ray scanner may be small. On the other hand, imposing a small risk of cancer on someone by for example smoking near them in a public place is deemed to be illegal in many countries even though the risk due to smoking one cigarette near someone may be small and of a similar order to the airport x-ray scan.

Safety Regulations and Standards

In the United States, an X-ray system can be considered to comply with requirements for general purpose security screening of humans if the device complies with American National Standards Institute (ANSI) Standard #N43.17.^[17][18]

In the most general sense, N43.17 states that a device can be used for general purpose security screening of humans if the dose to the subject is less than 25 micro Rontgen per examination (25 micro Rontgen of x-rays = 25 micro Rem = 0.25 micro Sievert) and complies with other requirements of the standard. Twenty-five micro Rem is equal to the amount of background radiation every human is exposed to (from the air and soil) at sea level every 1.5 hours and is also equal to the radiation exposure from cosmic rays when travelling in an airplane at altitude for 2 minutes.^[19] However, radiation from cosmic rays is diffuse, likened to ambient light exposure. In contrast, by analogy a 2 millisecond burst of focused light from a laser can burn the eye, unlike the equivalent amount of diffuse light. A concern therefore exists because X-ray screeners use focused radiation, the effects of which are unknown particularly for pregnant women, rather than diffuse radiation of the sort travelers are naturally exposed to in an airplane.^[20]

Many types of X-ray systems can be designed to comply with ANSI N43.17 including transmission X-ray, backscatter X-ray and gamma ray systems. Not all backscatter X-ray devices necessarily comply with ANSI N43.17; only the manufacturer or end user can confirm compliance to the standard.

See also

• Security scan
• Millimeter wave scanner
• Puffer Machine

References

External links

• You are undie surveillance UK considers using backscatter X-ray machines to scan the public.
• American Science and Engineering - pioneers in the field.
• University of Florida Research - High Resolution Scatter X-ray Imaging
• Rapiscan Systems - Manufacturer of the SECURE 1000 People Screening System
• Backscatter X-ray technology and risks
• Dr. Steven W Smith / First Backscatter X-ray Security Device (Secure 1000)