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Using Radio Waves to Detect Explosives

Posted by samzenpus on from the tuned-to-boom dept.

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."

2 of 99 comments (clear)

  1. nuclear resonance is MRI without the "imaging" by kris_lang · · Score: 5, Informative

    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.

    1. Re:nuclear resonance is MRI without the "imaging" by Anonymous Coward · · Score: 5, Informative

      ... 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! :-)