[Michael_Voyageur]

Des scientifiques japonais decouvrent un nouveau moyen de detecter les explosifs plastiques, dont le C4, au moyen des ondes terahertz.

Source : Yomiuri Shimbun

Scientists discover way to detect plastic explosives


Composition 4 (C4), a powerful plastic explosive often used in terrorist attacks, can be detected even if it is concealed inside baggage or other packages using special electromagnetic waves called terahertz waves, according to researchers at Osaka University's Research Center for Superconductor Photonics and Osaka Prefectural Police's Forensic Science Laboratory.

If the technology is adapted for practical use, it will enable security authorities to prevent attacks using C4--a substance that cannot currently be detected by metal detectors or X-ray inspection machines.

Terahertz waves, which have a frequency between infrared rays and radio waves, penetrate plastic, vinyl, paper, timber and glass just like X-rays. Unlike X-rays, they pose no radiation risk.

Terahertz waves of specific frequencies are absorbed at different rates depending on the molecular structure of the substances through which they pass. Consequently, the waves can be used to identify different substances.

University research associate Koji Yamamoto and other researchers found that C4 showed a distinctive absorption spectrum pattern. The degree of absorption reached its peak when waves of six particular frequencies were applied.

Through calculating changes in absorption rates when C4 was hidden in plastic containers or wooden boxes, researchers found they could consistently locate the substance regardless of the material that contained it.

Researchers will soon start a comprehensive program of irradiating C4 in different containers with terahertz waves to measure rates of absorption.

The destructive capability of C4, developed for military purposes, is about 1.4 times that of dynamite.

The plastic explosive was used in the 1987 Korean Air bombing and the bombing at Davao International Airport in the Philippines in March.

Prof. Masanori Hangyo of the university's research center said the scientists now had an electromagnetic fingerprint for C4, adding that the terahertz waves would be a powerful tool to detect the explosive
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