Scientific proof: security theater and dangerous lies

The forthcoming paper by UCSF researchers, Leon Kaufman and Joseph Carlson, got some attention from the right-wing media because it showed that the TSA scanners are not effective. But the findings of this paper are much more significant. It illustrates the shockingly opaque scientific review of these machines. Despite having access to only sparse information, these scientists have shown that the claim that the backscatter machines "do not penetrate the skin" is patently false. The full text of their research is already publicly available at Springer, but, because I think this is so important, I have highlighted some key points below.

Foiling backscatter scanners

The UCSF scientists performed some theoretical calculations in order to assess the capabilities of x-ray backscatter scanners that are in use at a growing number of airports. There are two types of scanners used: the (more abundant) x-ray backscatter and the millimeter wave scanners. This paper exclusively evaluated the x-ray scanners, not the millimeter wave scanners. They relied on information available at the manufacturers' websites to compile specs for their computations. There are two slightly different x-ray backscatter technologies being used such that the energy of the x-ray beams vary. For that reason, all of the calculations performed were repeated at the two different energies used, and the authors refer to them as simply "high" and "low" in their graphs and images. (Most of the images in this blog post are linked from the authors' paper.)

Kaufman and Carlson. J Transp Secur

First, a little background on x-ray backscatter scanners. The image at right shows the difference between the typical medical x-ray that you may receive and an x-ray backscatter device, such as that used in an airport scanner. If M is the person, then in a standard medical x-ray, the x-rays (from source S) come from one side of the person and the x-rays that penetrate through the body are detected on the other side of the person (at the vertical line labeled "I"). In a backscatter device, the purpose is not to look through the person, but to look at what non-human objects are under the clothes. For this purpose, the x-rays that bounce off of the person or object are measured, so the detector (I) is on the same side of the person as the x-ray source (S).

An airport scanner has 2 sources - one in front of the person, and one in back of the person. In this way, two images are created of the unclothed person, but both images are created from the x-rays that bounce back to the detector on the same side as the source. Thus, this is not a 360 image and there are not currently any scanners that capture images from the side. This is one obvious vulnerability: a very dense object (eg, a gun) placed strategically on one's side will blend in with the background and will be difficult to detect. Notice that the gun on the woman's left hip in the frontal image below is only visible because her arm is behind it. But, the posture that one is instructed to take at the airport is with arms raised (in the position of a criminal suspect).

 Okay, but that's easy enough because each person could walk through both the metal detector and the scanner, and then dense objects concealed on one's hip would be detected by the metal detector. But - don't forget! - our country's invalids with hip and knee replacements are going to be the next to be recruited by Al Qaeda, and they can just claim that their knee set off the alarm. So, I guess it's good that they get an aggressive custody search for good measure!


But the UCSF researchers point out a more alarming fact about these scanners. Based on the known energy of the x-rays used and analyzing the dimensions of the machines and the images produced, they determined that plastic explosives could be easily smuggled through these machines. They created the image below; it is simulated from the data that they had available and shows why plastic explosives molded in a certain way are unlikely to be detected. In this image the explosive is shaped like a brick and is easy to see in the center of each panel (one for high energy and one for low energy x-rays):

Kaufman and Carlson. J Transp Secur

Notice, however, that the center of each brick has a similar color to most of the surroundings outside of the brick. The brick is noticeable because of the scattering that occurs at the sharp edges. In contrast, a bottle of water, on the left side, is much lighter in color than the rest of the surroundings, and a stick of iron, on the right side, is much darker in color than the rest of the surroundings. This is because the x-rays are scattering off of the atoms in each object, and different atoms have different sizes (more correctly, masses and densities).

The surroundings in the image above are simulated human tissue. Living organisms are comprised mostly of carbon, hydrogen, and oxygen (and, to a lesser extent, nitrogen, sulfur, phosphorous, and some metals). Water is two parts hydrogen to one part oxygen, so it does not have very many heavy atoms and produces a lighter image. Iron, in contrast, is much heavier than most of the atoms found in a human body, and it produces a very dark image. (Bone, which has a greater density due to the high amounts of calcium, will therefore scatter x-rays in a manner intermediate to soft tissue and iron.)

But plastic explosives are made up of carbon, hydrogen, and oxygen. Thus, their composition is very similar to that of a person's skin. It is only the odd shape of a brick (or plexiglass knife) that makes it obvious. Contrast this to the images below:

Kaufman and Carlson. J Transp Secur

If you know to look for it, you can see the contoured, circular explosives in panel c and d. But just barely. (Panels a and b do not have any simulated explosives.)

Kaufman and Carlson. J Transp Secur

To illustrate the importance of the edge of the explosives, the authors use the image at right. We know what a woman's breasts look like, so we infer from the "shadow" under each breast that the area above the contour is thicker than the area below the contour. But, if you cover up this contour, you see that the color of the breast is indiscernable from the color of the abdomen. By shaping an explosive so that it does not have an edge, a would-be hijacker could conceal his weapon.


Furthermore, if the piece of metal in the simulated images above were not 1 centimeter thick but, rather, 1 millimeter thick (like a wire), it would not be discernable either. Thus, both the explosive and the wire needed for ignition could pass through these scanners without detection.

Lack of scientific review

All of the above was summed up in the media coverage of this research, but there is more to be learned from the UCSF scientists' article. One of the things that has bothered many scientists is the complete lack of scientific review and informed debate of these scanners. The public can not be informed because virtually no information about the scanners has been made available. Studies were conducted by federal researchers and the Johns Hopkins Applied Physics Laboratory (which specializes in confidential research commissioned by the federal government). However, these studies, by Johns Hopkins' own admission, did not address the safety of the scanners. Also, these studies have not been published, so concerned scientists are being forced to do something that no scientist is comfortable with: take another's word for it.

Scientific research is premised on the idea that other scientists have the opportunity to review and, if warranted or desired, to try to duplicate others' results. It's not a perfect system as it is currently implemented, but it is certainly held as an ideal by practitioners, funding organizations, including the federal government, and the public. The federal government, however, has not made the scanners available to researchers for analysis and publication of their findings. It has also not made certain basic specifications available. Thus, Kaufman and Carlson had to infer many of their baseline inputs from information on the manufacturers' websites. For instance, they had to estimate the size of the detectors from the dimensions of the machine and the quality of the data from only a handful of available images (and they did not have specific information as to whether the images were doctored-up).

Despite this, they did a remarkable job of covering their bases and accounting for a variety of scenarios. At the very least, their research calls into question the claim that these scanners are effective. Why aren't there more calls for scientific review and transparency (no pun intended) of these scanners? The little bit of reporting that has been done on this paper has not acknowledged this gaping hole. The researchers practically had to bend over backwards to complete a study on a machine that is costing a lot of tax-payer money, causing a public backlash, infringes on basic human rights, is technically illegal, and - as I argue next - unsafe for use on the general population. But the information that is needed to determine the safety of the scanners has not been made available. As the authors say:

Knowledge of the generator and x-ray tube used, kVp setting and filtration. location with respect to collimation, collimator crossection and length, and scanning area and speed, information of little use to a someone intent on passing contraband, as we shall see below-, would permit an accurate evaluation of dose. Of these, kVp settings and filtration, scanning area and scan speed are known ... Lacking the other parameters, a direct calculation is not possible.

"It doesn't penetrate the skin"

As a skeptic of the state, I am never surprised to hear that my government is lying to me. Wikileaks should dis-spell any remaining believers of their naive assumption that the US government doesn't lie (but it is often more comforting to believe that the emperor is indeed wearing clothes).

This research provides convincing evidence that the radiation in the x-ray scanners - that are being used on the elderly, the sick, children, and pregnant women - not only penetrates the skin, but likely penetrates through the body of our skinnier fellow men, women, and children. 

According to the calculations performed by Kaufman and Carlson, in order to create the images provided online, the x-ray beam penetrates approximately 6 inches into human tissue. Because there are two beams - one in front and one behind - the entire width of the torso may be exposed to radiation:

Kaufman and Carlson. J Transp Secur

In this graph, the authors show that both high- and low-energy x-rays penetrate human tissue. The left axis is a measure of the x-ray exposure, where 0 is no radiation exposure and higher numbers mean greater radiation exposure. Across the bottom is the depth of penetration of the radiation into the body (1 inch is approximately 2.5 centimeters). Their calculations are based on established knowledge about how x-ray backscattering works, and the plot shows what happens when two x-rays are aimed at one person (from front and back - ie, from the left of the graph and from the right of the graph). Because the exposure value never goes all the way down to zero, you can see that a person who is about 10 inches thick will have some x-ray exposure at every point of their body. The radiation at the mid-way point (5 inches under the person's skin) is lower than at the surface of their skin, but it does not ever drop off to zero.


Are you less than 12 inches thick through your torso? Is your child? Remember that your abdomen has very little bone to slow down this penetration, so it is the most likely area for complete penetration to occur. This also happens to be the location of a number of vital organs. Also, although your rib cage will provide some protection for your heart and lungs, the air in your lungs will allow even greater penetration to occur. Finally, although the authors did not calculate penetration through bone, it seems reasonable that the surfaces of bones are exposed (which is obvious from scanner images where the tibia are outlined) and exposure of bones to radiation is also problematic from a health point of view.

The authors state clearly at the beginning of their article that they are not trained to assess safety of radiation to humans. However, they do note that the does values that are reported for "safe" exposure to scanner radiation are modified by assumptions, including which organs are exposed. Therefore, the issue of penetration is very important. If the scanners (laughably) "do not penetrate," then these dose values will be, by definition, below the threshold for safe exposure. Does a 6-inch penetration of 3% of the radiation pose a risk? What about a half-inch penetration at 50% of the radiation? Does it matter if it is a pregnant woman? What happens if the x-rays penetrate a newlywed's testicles? None of these questions have been addressed and it is absolutely irresponsible of the TSA to continue to use these scanners from a public health perspective.

Irresponsible MSM

No surprises here, but the authors of the UCSF paper (from my perspective) planted a number of gems for a journalist with integrity to follow-up on, and no one has. I touched on some above. I think there is another one, though. The authors question whether the available images could be created using the claimed "safe" exposure levels and still detect plastic explosives (as is claimed):

It is worth noting that [the backscatter image from Rapiscan's website], with a pixel dimension of 2.1 mm and a [signal-to-noise] of 12, this simulation requires an entrance exposure of 170 nGy, 70% higher than the [American National Standards Institute] guideline [for the dose limit of these devices].

So, either explosives can easily get past the scanner (whether or not it is contoured to the body), or they are cranking up the radiation so they can see these explosives. Furthermore, the skin penetration issue that is being ignored by the MSM is clearly stated by the authors in the article:

The results indicate that the radiation used penetrates throughout the body, a not surprising fact to those familiar with radiologic imaging [at energies comparable to CT scans and mammography].

This research indicates that someone is lying, but journalists are only focusing on the fact that a clever terrorist with some sculpting ability could foil the scanners. There's more than enough in this paper to indict the TSA. This criminal organization should be disbanded immediately - it has no credibility and is endangering our lives and our freedoms.