Japanese scientists use radio waves to detect TNT

Published 29 January 2007

Airport luggage screening to benefit from this breakthrough approach; nitrogen nuclear quadrupole resonance solves the problem of low nitrogen resonance levels; distinghuishing between cocaine and explosives the key challenge

Airport security officials take note: scientists in Japan have developed a new technique for detecting explosives hidden in airline luggage, one that relies on radio waves rather than X-rays to perform the task. Researchers have long observed X-rays’s limitations — among them the inability to sufficiently distinguish between cocaine, baby powder, and explosives — but even radio waves have so far not been as effective as desired. “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 of Osaka University. The lower a substance’s resonant frequency, the more challenging it is to identify it.

Such is the problem. Now the solution. The approach offered by Itozaki and his collegues relies on what is called nitrogen nuclear quadrupole resonance (NQR) — an established method that detects atoms of nitrogen in different positions in a molecule. An atom of nitrogen attached to a carbon atom, for instance, will have a different resonance to one attached to an oxygen atom. Because the molecular structure of each explosive is different, the resonant frequency will be different. Said Itozaki:“We have successfully developed a machine that can pick up very low resonant frequencies by using a SQUID (superconducting quantum interference device). The SQUID operates at a temperature of 77 Kelvin (minus 196 degrees centigrade) which we achieve by using liquid nitrogen.”

-read more in this university news release