New way to find terrorist explosives

March 17, 2005
Israeli researchers have developed a device that identifies a previously undetectable explosive commonly used by terrorists.

The device is called a Peroxide Explosive Tester (PET). It determines whether or not a suspicious substance is triacetone triperoxide (TATP). The PET, which resembles a three-color ballpoint pen, releases three chemical mixtures that change color when they interact with TATP.

TATP and other explosives of the peroxide family are used extensively by terrorist organizations around the world because they are easy to prepare and difficult to detect. Many of the devastating suicide attacks by terrorists over the past few years involved TATP, including the bus explosions in Israel.

The researchers, who hail from the Technion-Israel Institute of Technology, are in negotiation to commercialize the PET, and they say interest from law-enforcement agencies has been high.

Most explosives are energetic materials, and they have a lot of energy chemically stored in them. In an explosion, that energy is released suddenly, generating a huge amount of heat. The heat, in turn, creates the explosive expansion. The usual technique for producing explosives is to add energy to the explosive substance in the form of heat. TNT, for example, must cook at a high temperature for its high-energy chemical bonds to form. Because nitrogen compounds are good at storing energy, most conventional explosives contain nitrogen, a property that makes them relatively easy to detect.

But TATP is different from most explosives. It is formed at room temperature and does not require any input of heat. Nor does TATP contain nitrogen compounds. It is in fact a carbohydrate-type compound somewhat related to sugar.

A key to the Israeli development was in understanding how TATP can explode even though energy is not pumped into it initially as heat.

The research team demonstrated that TATP explodes not by releasing thermal energy, but by suddenly breaking each molecule of solidstate TATP into four molecules of gas. Although the gas is at room temperature, it has the same density as the solid, and four times as many molecules, so it has 200 times the pressure of the surrounding air. This enormous pressure — one-and-a-half tons per square inch — pushes outward, creating an explosive force 80% greater than that of TNT. In a TATP explosion, the gas molecules give up their energy of motion to the surroundings, in the process creating the shock wave that does the damage.

The research team discovered TATP's secret by first analyzing the structure of the molecule. They found it is held together by weak oxygen-to-oxygen bonds that break when the substance sees mild heating or a chemical shock. So it is highly unstable. The team was then able of follow the decomposition of TATP with detailed calculations of the energy content of the intermediate products.

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