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Fast, Accurate Detection of Explosives
It doesn't come easy writes "Fast, highly reliable detection of residues that could indicate the presence of explosives and other hazardous materials inside luggage is now possible with technology under development at Purdue University. Recent improvements to a previously developed prototype have proven successful at detecting at the picogram (trillionths of a gram) level in lab tests, about 1,000 times less material than previously required. From the article: 'In the amount of time it requires to take a breath, this technology can sniff the surface of a piece of luggage and determine whether a hazardous substance is likely to be inside, based on residual chemicals brushed from the hand of someone loading the suitcase.'"
Ok, here's something I've always wondered about. If you have these exquisitly sensitive machines that can detect even a few molecules of material, aren't they by the same token super-vulnerable to being attacked by "chaffing" or overloading?
Its worse than that. You have to look at the false positive and negative rates for detection. If you have a test that is 99.9% specific, it will still fail in practical use in an airport, as that means that 1/1000 people will come up positive. (I think I have the right statistical measure here, but apologies if not). If you have alot of people going through you will still have a big problem -London had 1 000 000 FLIGHTS last year, so the equivalent of 1000 plane loads of people will come up positive per year. This is the same issue as using automatic detection of terrorists - Its one thing to match/no match a known ID (eg biometric passport) to a person, its another to match every passer by to every known terrorist.
Coming back to chemical detection, this level of sensitivity will mean that every person who uses GTN for angina (commonly known as "Anginine" tablets or sprays) runs the risk of coming up positive. This amounts probably about a million people in US, and lots more elsewhere in the world. GTN (used in microgram doses in the treatment of poor blood supply to the heart; the precursor to a heart attack) is actually tri nitro glycerine, and is just a wee touch explosive in larger quantities.
Just my 2c worth.
Michael
There is no cryptographic solution to the problem where the intended receiver and the attacker are the same entity.
I'm surprised - very surprised - that there's no reference to the recent bombings in Bali in the article post. I mean, an article about instantly detecting explosives, three days after a serious terrorist attack... I can't help but feel that if it had been Hawaii and US citizens killed rather than Bali and Indonesian/Australian citizens killed this link would have been made.
Anyway, this is an interesting development, but should not lead us to stop traditional methods of bomb detection, particularly searches and x-rays. These machines sound wonderful *so long as* you are using an explosive with which they are familiar.
Read Pynchon.
Regarding the article, nanogram sensitivity (a trillion molecules of TNT) is utterly unimpressive. The vapor pressure of most explosives is so low that you need femtogram sensitivity to directly sense vapor. For an explosive like RDX that has an absurdly low vapor pressure, you really want attogram sensitivity (about a million molecules). You can heat up dust and surfaces to vaporize more explosive, but with a mass spectrometer you then run into a problem with selectivity: many ordinary boring compounds will have the same molecular weight as the explosive--the signal will be swamped by the noise. (Hmmm ... the article says they're using clever ionization, and tandem spectrometry. That helps a lot, but they still have a hell of a problem to solve.)
The article says "'If you tried to detect a particular compound out of a mixture of thousands of different substances, you might begin to see the limitations of this method,' Talaty said. 'But real-world explosives are not that complex.'" What, people walk through airports with purified blocks of luggage? No! You get a suitcase drenched with sweat (which includes urea), solvents, ammonium nitrate from natural sources, perfumes, plasticizers, plastic monomers and short chain polymers, various mineral oils, a whole boat-load of volatiles from living things, and many more. The background signal is a freaking nightmare. I work in the explosive detection field, and I sure wish it was as easy as they say.
Just in case there are any chemical physicists reading this...
Assumedly, if this system is small enough to be backpack-sized, it's not a time-of-flight mass spec... right? The article's short on details on the actual mass spec--they seem to focus on their ionization technique more than on the spectrometer itself. But, then again, I guess that's where they're focusing their research.
I'm not too impressed by this "reactive chemical spray" system, but maybe that's because I'd be more concerned with airborne rather than adsorbed/adhered molecules. It seems needlessly destructive to be spraying corrosives onto a person's luggage, unless we're talking, like, microgram quantities--although if you're just taking off a few molecular layers, and if the reactive components are rarefied in a less reactive gas, maybe it's not a big deal. Still, couldn't the same sort of "wipes" that you see used with modern airport ion mobility spectrometers be used to spare travelers from being exposed to these "reactive" compounds? Too, it seems a bad idea to require that airports keep machines sitting around in terminals with cylinders of reactive gasses. Once again, the quantities one would be dealing with are what concern me.
They mention that their system suffers low selectivity. Selectivity, from what I understand, is pretty important in other fields, like nerve-gas detection, for instance, in order to force down false positives. What's keeping their system at a low rate of false positives as they claim?
I suppose I could read their papers; this article really is just a press release, after all. Being a lasers sort of guy, I guess maybe I'm just biased towards photoionization.
Also, even though this isn't really germane to my post here, I found another press release here is an article from just about a year ago that talks about this same DESI system.
>Someone remind me what the point of this whizz-bang technology is again?
High explosives are not exactly stable.
Your plan will not really keep the volatile materials fully *inside* the suitcase.
Any kind of bomb worth using is going to be pretty noisy, chemically speaking. You're pretty much going to have a cloud of nitrates around you. If you've got enough of an oxidizer in your bag to be an effective bomb, it's going to be very difficult to keep it from being detected.
You could probably seal an organic explosive like C4 or TNT well enough to avoid detection by the swab test (which is looking for nitrates, sodium chlorate, etc.) but those have an obvious x-ray signature.
I sometimes work with my laptop in an environment that has all kinds of lawn and garden products (e.g., fertilizer), and if I take that laptop through security, they swab it every time, it comes up positive (!) and I get to explain to them why (!!). More than once, I've had to endure questioning by several levels of security people, and once, they made me sign something declaring that I didn't have any explosives (like that would matter?)
-fb Everything not expressly forbidden is now mandatory.
"If you declare that before you went through security, I'm sure they would just let you pass through after a peekinto your bags."
Oh, no, not at all.
*Nothing* you say to TSA people is going to hasten your experience. I have a similar problem as the miner's. Nitrate residues off the scale from my bag, due to my work environment.
Do not overestimate the level of intuition of security personnel or cops, ever. Anything you try to say to them will merely be regarded as suspicious.
The last time I flew, I had to deal with two different people who did not speak English... at Logan.
Another thing to consider... Just about the entire TSA staff has been hired in the last 4 years, and I'm being generous with that. For many of them, it's their first job after getting their GED. Don't expect them to regard ANYTHING you tell them as anything but a threat.
-fb Everything not expressly forbidden is now mandatory.
If you have these exquisitly sensitive machines that can detect even a few molecules of material, aren't they by the same token super-vulnerable to being attacked by "chaffing" or overloading?
I think a few molecules might be a bit of an over statement. Nitroglycerin has a weight of 227g/mole. A mole is 6.02*10^23. So one molecule of nitroglycerin weighs 3.77 * 10^-22 grams.
A picogram = 1*10^-12 grams.
1*10^-12/(3.77*10^-22)=2.65* 10^9, or 2.65 billion molecules. That's a ways from a few.
I think your point still is valid though. Could someone contaminate an area such that it couldn't be cleaned sufficiently? My guess is it probbably could be. You don't have to get rid of all the material, just enough so that you're below the level of detection.
AccountKiller
http://www.airportguides.co.uk/guides/heathrow/fac tsandfigures.html
64e6 passengers per year = 175,000 passengers per day.
Pretend these are all commercial 737s with 130 seats, all filled. That's 1349 flights per day which is pretty much one per minute (1440 minutes per day). Having once stayed with a friend whose house was in the flight path, that seems feasible!
Plus, London has "three" major airports - Heathrow, Gatwick and Luton (not really London, IMHO). There's also "London city airport" too, but that's pretty small.
When you install the machine and periodically thereafter you would "null" it. That means you adjust the needle to read zero when there is nothing in the detection chamber. I used an oxigen sensor resently. The first step is to expose it to just plain air and adjust it to read 21% (air is about 21% oxigen, 79% nitrogen) After doing this it can detect very small amounts In both cases you have to tell the machine "This is the normal background." After this the machine detects changes.
Firecrackers are filled with flash power which is a mix of Potasium perchlorate and aluminum powder (dust), Illegal stuff made by Jed and Clem in the barn sometimes contains Potasium Chlorate instead, it's unstable but they don't care (it makes a slightly louder bang). There is no sulphur.
I don't know what is in caps but it sure is not ammonium tri-iodide. If it was, everything near it would turn purple! ahh, the joys of a misspent youth. It would make it easy to tell though as it won't wash off.
The ping pong paddle is a metal detector. A couple of times my laptop has been tested for explosives at London Heathrow, they take a swab cloth, wipe it over the laptop then place the cloth in a little machine (I assume a digital nose) to see if there are any banned trace elements.
First of all: you don't use tomato juice as it is ineffective. The best way to neutralize mercaptan is to use a mix of baking soda and hydrogen peroxide solution, which will oxidize the mercaptan and destroy it, without staining whatever you are cleaning.
.22 blank to drive nails into concrete.
Now, as for the explosive detector: I have a real problem with this, as if it is so sensitive as to be able to detect explosives after M. Random Terrorist has carefully cleaned up, it is probably sensitive enough to trigger on the residue left on me if I have done some home construction with my powder activated nail driver - which uses a
It will probably also trigger on any heart patient using, or even carrying, medical nitroglycerin. So, obviously, the next bunch of Al Qeidea terrorists will all have very convincing papers indicating they are heart patients.
www.eFax.com are spammers
El Al??
Israeli airline.