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.

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.

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.

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.

Do you mind me asking your experience in this area?

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.

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.

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.

I can't say too much. It is basically summarized in the comment. But ask anyway, I might be able to answer if it is general enough.

You (they) should have asked a few congress-critters to be on your board of directors. You still might not get a copy of the standards, but you'd likely have been selling machines.

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.

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.)

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.

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.

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...

Thankfully, Al-Qaeda has no familiarity with heroin smuggling 'mules'. Wait, what's that you say? They've got base camps in the world's major heroin-producing region and make money from heroin? Hmm.

Heroine is not smuggled out of Afghanistan through rectums, no, it goes out in caravan trucks with security detail.

why bother when you have 1000s of cleaners, baggage handlers, caterers etc who are allowed onto the plane unsearched and unchecked.

Of course they are subject to extensive background checks = are you willing to work for less than minimum wage?

I don't know about the other job categories, but fast food workers on the wrong side of the security checkpoint do get screened every day before work.

They go through the security checkpoint though - have you ever seen an xray machine and metal detector at the road entrance that all the tankers, food trucks, fedex and baggage arrives through?

Why bother removing it?

Given the clueless people usually used for bombings, the guy would probably drop it down the airplane toilet by accident and lose it.

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

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).

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?

This is one of Bruce Schneier's constant themes.