We've heard the various stories of folks getting weapons past the TSA's new scanners -- such as Adam Savage's famous video
from earlier this year, or the more recent report of a guy getting past the scanners with a 6" hunting knife
. Both of those stories appeared to just be about the bag
scanners missing stuff on the conveyor belt. But what about the new backscanner x-ray machines? Well, Jay
points us to some new research by two UCSF professors that indicates getting dangerous weapons or explosives past the new machines
isn't that hard. They look at how the machines work and the various images currently out there, as well as their understanding of x-ray technology, and point out that since the x-rays need to pass through your body, if you flattened out some plastic explosives, they probably won't be noticed, or if you just put the weapon on your side
the new machines probably won't spot them:
It is very likely that a large (15–20 cm in diameter), irregularly-shaped, cm-thick
pancake with beveled edges, taped to the abdomen, would be invisible to this
technology, ironically, because of its large volume, since it is easily confused with
normal anatomy. Thus, a third of a kilo of PETN, easily picked up in a competent pat
down, would be missed by backscatter "high technology". Forty grams of PETN, a
purportedly dangerous amount, would fit in a 1.25 mm-thick pancake of the
dimensions simulated here and be virtually invisible. Packed in a compact mode,
say, a 1 cm×4 cm×5 cm brick, it would be detected.
The images are very sensitive to the presence of large pieces of high Z material, e.
g., iron, but unless the spatial resolution is good, thin wires will be missed because
of partial volume effects. It is also easy to see that an object such as a wire or a boxcutter blade, taped to the side of the body, or even a small gun in the same location,
will be invisible. While there are technical means to mildly increase the conspicuity
of a thick object in air, they are ineffective for thin objects such as blades when they
are aligned close to the beam direction.
Feeling safer? Once again, this isn't to say that there shouldn't be a security screening process, but if we have to go through all this trouble, shouldn't we at least have a system that is at least somewhat