Comment by scq
11 hours ago
From my understanding, the new CT machines are able to characterise material composition using dual-energy X-ray, and this is how they were able to relax the rules.
11 hours ago
From my understanding, the new CT machines are able to characterise material composition using dual-energy X-ray, and this is how they were able to relax the rules.
I am not up-to-date on the bleeding edge but that explanation doesn’t seem correct? The use of x-rays in analytical chemistry is for elemental analysis, not molecular analysis. (There are uses for x-rays in crystallography that but that is unrelated to this application.)
At an elemental level, the materials of a suitcase are more or less identical to an explosive. You won’t easily be able to tell them apart with an x-ray. This is analogous to why x-ray assays of mining ores can’t tell you what the mineral is, only the elements that are in the minerals.
FWIW, I once went through an airport in my travels that took an infrared spectra of everyone’s water! They never said that, I recognized the equipment. I forget where, I was just impressed that the process was scientifically rigorous. That would immediately identify anything weird that was passed off as water.
There's still no evidence that peroxide-based explosives are stable enough to be practical. And nobody every explained why the few liquid ones are so dangerous, but the solid ones get a pass when they are more stable.
It's a good thing that airport brought some machinery to apply the rule in a sane way. But it's still an insane rule, and if it wasn't the US insisting on it, the entire world would just laugh it off.
Here's an article that talks about Dual-energy CT [1]. And another one talking about material discrimination using DECT [2].
[1] https://en.wikipedia.org/wiki/Spectral_imaging_(radiography)
[2] https://pmc.ncbi.nlm.nih.gov/articles/PMC2719491/
Neither of those articles seem to support the idea that you can do molecular analysis with x-rays. They are all about elemental analysis, which is not useful for the purpose of detecting explosives.
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> FWIW, I once went through an airport in my travels that took an infrared spectra of everyone’s water! They never said that, I recognized the equipment. I forget where, I was just impressed that the process was scientifically rigorous. That would immediately identify anything weird that was passed off as water.
Something like 10 years ago, I had my water checked in a specialised "bottle of water checker" equipment in Japan. I had to put my bottle there, it took a second and that was it. I have been wondering why this isn't more common ever since :-).
No idea if it was an "infrared spectra machine" of course.
Cynically, it's so they can sell you another bottle on the secure side. If they spend money to give themselves a working mechanism to distinguish water from not-water, they lose the ability to create retail demand.
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Yes. The first step was upgrading to the new machines, now the size limits can be relaxed.