Using Radio Waves to Detect Explosives

deadmantyping writes "A Japanese research group published a paper describing a method to detect explosives in luggage using radio waves. The method relies upon nitrogen nuclear quadrapole resonance (NQR) and is able to distinguish between different white powders, whereas currently used x-ray technology is not."

Comments

Interesting...

[thedarknite]

It appears to be a slightly more advanced system than SNUPA http://www.abc.net.au/quantum/stories/s112369.htm developed at the University of Melbourne, which I believe didn't differentiate between different explosive compounds.

nuclear resonance is MRI without the "imaging"

[kris_lang]

so this is called nuclear magnetic resonance spectroscopy.

Doing it with a gradient field and a special pulse sequence lets you get the
vibrational amplitudes of your protons based on their position within the gradient field.
That's what gets you MRI images. Before MRI images, nuclear spectroscopy was used to
resonate the "nucleus" of atoms/molecules/conglomerations of molecules at varying radio-frequencies to see if there was any resulting resonance and output RF (radiofrequency) signal.

Protons resonate at 2.4 GHz approximately (which is the frequency used in microwaves to resonate the H's in the {H}_2{0} molecules in your food and heat it.

Re:nuclear resonance is MRI without the "imaging"

[Anonymous Coward]

... but this is NQR which is examing the 4th order (as I can recall, maybe is was 2nd-order, I don't remember anymore:-p) of the nucleus. It's very similar underlying principles as MRI and NMR (and thus implementatin scheme is similar) but the physical interaction mechanism is the quadrapole momeent rather than the dipole moment of the nucleus.

The problem with NQR and SQUID is that the measurement is extremely sensitive and it is difficult to filter out false positives. SQUIDs are very sensitive to magnetic perturbations and noise. Heck in the lab it can pick up the noise caused by the underground train. So the design has to be extremely precise and the filters need to be carefully designed. Also NQR technique only can detect certain substances that contain the molecular signature of interest (in this case N14 (i think?)). You need to induce a very large magnetic field (relative to the nucleus) to induce NQR. The SQUID can pick up the magnetic distrubance, but you still need to induce the field. DARPA showed some demos of remote systems that could acheive this. The problem was the false positives were pretty high, because it turns out shoe soles haave N14 which can trigger a false positive.

Nevertheless, it's a great acheivement and I hope they can iron out the kinks in this technology.

So don't put those shoes in your baggage! :-)

Re:nuclear resonance is MRI without the "imaging"

[candover]

Protons resonate at 2.4 GHz approximately

No they don't. Nuclear magnetic resonance requires a strong external magnetic field. The strongest superconducting magnet you can buy today induces a resonance (the Larmor frequency) in protons at 950 MHz... but it costs about ten million dollars and only does that over a tube about five centimeters wide. The absolute strongest MRI magnets today top out at about 1/3 of that magnetic field, and most are far less.

Microwaves heat food via RF heating, which is an electric effect, not a magnetic one. No relationship to the mechanism of NMR at all.

As for the article topic, nuclear quadrupole resonance is similar to NMR except that, instead of using a magnetic field to induce an energy splitting (which gives you the Larmor frequency), you take advantage of electric field splitting instead. This only works in atoms that have a quadrupole moment, and the only one of those that's present at high concentrations in explosives (and living things too) is nitrogen-14.

Only thing new is using a SQUID

[calidoscope]

Research into using NQR for explosive detection dates back to the 1970's. The first NQR baggage scanner was built by Al Garroway's group at NRL in the early 1990's using room temperature coils and room temperature electronics.

Ron Sager and Alan Sheldon of Quantum Design used a SQUID in 1992 for detecting the NQR response of ammonium perchlorate (~38kHz), so the Japanese group isn't even the first to use SQUIDs for NQR...

Re:It's not a cure-all

[calidoscope]

I see the nitrogen nuclear quadrupole resonance as have more potential in finding IED in the road beds in places like Iraq.

Snicker....

As was pointed out by 'Entrope', NQR is probably not the best choice for detecting roadside IED's - there are other methods better suited for rapid scanning. What NQR would be good for is confirming whether or not a non-conducting anomaly picked up ground penetrating radar contains explosives.

You are correct in stating that NQR would be ineffective against peroxide explosives. The explosives that NQR is especially effective at detecting are also the ones with essentially zero vapor pressure that give problems for trace detectors.

Re:White powders?

[Romwell]

Then you get what is called "Brown-brown"