

Backscatter Machines Not Effective at Detecting Plastic Explosives - pmichaud
http://springerlink.com/content/g6620thk08679160/

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goalieca
I was waiting for this paper to be published. Basically, xrays are deflected
more by higher "Z" materials and this contrast is what creates the pixel
values in the image. This means the heavier nuclei like that in calcium in our
bones (z=20) deflect them a lot better than the carbon in our soft tissues.
I'm no explosives expert but I understand that these are made from the same
elements in our soft tissue like H,C,N,O (z=1,6,7,8).

edit: Drugs too. Generally they are just organic molecules.

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karzeem
It's disconcerting that this — the most thorough public study of the machines'
effectiveness — is a _simulation_. In a sane environment, we'd be allowed to
know what happens when you actually, you know, test the machines.

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physcab
I used to develop explosives detection technology that we were hoping to sell
to Smiths or TSA in a government contract. We were a research laboratory
hoping to get our technology out into "industry". TSA and Smiths have their
own "standards" for what they will use as basis for whether the detection
methodology is viable, but they don't give those numbers or those materials
out. There was a leaked document earlier this year (last year?) that contained
some of this information and that was a Big Deal. I remember it took months to
get something as simple as a Limit of Detection threshold that TSA benchmarks
for each machine they procure.

In fact, one of the main reasons why I left is because it seemed so futile. We
had very few customers to sell to, and yet we could never determine what they
wanted or what channels were available to us to get it tested.

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rdtsc
That happens quite often with government contracts. There is a lot of back-
room deals, knock-knock, wink-wink, "I'm a friend of a friend" kind of stuff.
There is some superficial formality and fake fairness tot the bidding process
but it ultimately comes to who you know. Requirements are kept vague and only
the "friends" are notified of what they are. Later during the review surprise!
one company just happens to exactly read the mind of the buyers and gets
picked.

This is even worse in the security related areas as the vagueness of
requirements is justified to be security related.

Your best bet would have been to hire an ex-General or an ex-TSA high ranking
official. Or at least hire someone who was a college roommate of some TSA
official.

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scotth
Do you mind me asking your experience in this area?

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throwaway80935
While I am not the person you are asking this question of, I can personally
corroborate their story.

During my enlisted years, I saw plenty of this type of behaviour. Some G.S. or
officer would be taken to lunch/dinner by the rep from a major defense
contractor; guess which company gets the inside scoop on what the military is
looking for? Due to multiple deltas between what I believed to be true and
what the military was pushing as truth, I got out and went to work for a
company doing web-related work.

A few years later, after I had allowed myself to forget how bad the military
was, I took a position with a small defense contractor. This contractor had a
couple decades of experience working in a particular field of research and
were widely regarded as experts in that field. A few years after I joined the
company, a major defense contractor got wind of how successful this company
was and decided they wanted the pie for themselves.

First, they regularly took the G.S. in charge of the project out to lunch and
the golf course. Then they planted the idea that the military needed fail-over
redundancy for such a "mission-critical" position held by the company I worked
for. The G.S. then ordered the company I worked for to hand over a copy of all
production code to this major defense contractor; after all, the military
needed fail-over redundancy for this "mission-critical" position.

It doesn't take too many brain cells to figure out what happened next. So,
based on my past experience, I would be very happy with never working anywhere
near a government institution again. On the bright side, working so close to
government allows you to realize the vast majority of taxes are actually
legalized theft.

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ams6110
By the same token, I've been told that unless you have an "inside track" it's
a waste of time to respond to a government RFP. 80% of the time, maybe more,
they already know who they're going to give the work to. The RFP is just a
formality.

~~~
rdtsc
I agree with that. Some buyers even have the nerve to call to inquire "how we
do things?" just to turn around and tell it to our competitors (their friends
who they were going to pick anyway).

Next thing we know those competitors are implementing things pretty much the
way we described to the buyers.

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pmichaud
Would it be difficult to simply shape the plastic explosive around a part of
your body to make it blend? I don't mean to be crass, but for example, what if
you created a penis shaped sheath around your real penis? Wouldn't that just
look like a larger penis to the scanner? Breasts would be easier maybe. But
what about just fat rolls on the belly of a fat man?

This technology is unworkable in practice.

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Estragon
Anyway, this is ignoring the obvious hiding place which the backscatter
machine can't possibly resolve: the rectum. You could store a huge amount of
plastic explosive in there in a form which would be very easy to retrieve
(just shape it like a stiff shit.)

Can't wait till they plug this hole. (So to speak.)

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tptacek
Christopher Hitchens wrote an article for Slate a week ago pointing out that a
recent (successful) assassination in Saudi was carried out with a body cavity
PETN bomb.

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slug
If it's I think it is, it was an unsuccessful attempt of assassination of a
Saudi prince, with a high rank in the anti-terrorism agency, although he
barely escaped.

Supposedly the assailant was thoroughly searched and finding nothing
suspicious , the security people let him approach the prince. The bomb was
detonated by remote control, through a message or call to his cellphone.

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scdlbx
The assailant's body did a pretty good job of containing the explosion. The
assailant didn't make it, but everyone else relatively okay.

[http://www.cbsnews.com/stories/2009/09/28/eveningnews/main53...](http://www.cbsnews.com/stories/2009/09/28/eveningnews/main5347847.shtml)

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Bud
The machines are, however, extremely effective at making money for Michael
Chertoff. Which is their intended function.

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electromagnetic
Honestly I'm not surprised, given the binders low density it was always going
to be possible to dilute the explosive while keeping it still dangerously
explosive and reduce its density down to water density (IE body).

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noamsml
I've always wondered if airport security in general is ultimately a detriment.
After all, it involves getting tons of people together at one spot. What's
stopping a terrorist from blowing themselves up in the line for security?

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Nick_C
This is one of Bruce Schneier's constant themes.

