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RF pulses at 890 kHz detect explosives

From "Scientists use radio waves to detect explosives," by Reuters, 26 January 2007:

"Scientists in Japan have developed a new technique for detecting explosives such as TNT in landmines or luggage using radio waves.

"Writing in Superconductor Science and Technology journal this week, they said the technique is superior to conventional methods of detection such as X-rays, and can identify different types of white powder, from flour and salt to drugs and explosives. The technique can also identify landmines, an improvement from traditional metal detectors that cannot tell bits of metal in the ground from an actual mine.

" 'Until now it has been very difficult to detect specific explosives such as TNT because they contain atoms of nitrogen that vibrate at very low frequencies,' said Professor Hideo Itozaki at Osaka University, one of the authors of the paper. 'The natural frequency at which the nucleus of an atom vibrates is called its resonant frequency and the lower this is, the harder it is to detect what atoms are present in a molecule which in turn makes it harder to define what the molecule or substance is.'

"The scientists created a device called superconducting quantum interference device (SQUID), which has a very sensitive magnetic field sensor that detects nitrogen, an element found in many explosives, including TNT.

" 'The SQUID chip itself is very small, only in the order of 1 cm. But it needs liquid nitrogen for cooling,' another researcher He Dongfeng told Reuters in an email. The SQUID operates at a temperature of 77 Kelvin, or minus 196 degrees Celsius.

" 'This will not hinder the equipment from being used in places such as airports as liquid nitrogen is becoming much easier to deal with and is already routinely used in hospitals and laboratories,' said Itozaki.

"One hitch for now, though, is that the screening time takes 'several minutes', something the team is working to improve. 'We are improving our system. If the sensitivity becomes better, the measuring time can be reduced,' He Dongfeng said."

© Reuters 2007. All Rights Reserved.
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The article by He, Tachiki and Itozaki says typical resonance frequencies for explosives are between 0.5 and 5 MHz, and vary with the temperature of the sample. The resonance detected in this experiment was 887.1 kHz, activated with 890 kHz pulses sent once per second.

[NMR - 28 January 2007]