Terrorists Beware: Device Identifies Previously Undetectable Explosives

Newswise — Israeli researchers have developed a device that identifies a previously undetectable explosive commonly used by terrorists. Once a suspicious substance is located, a small sample is placed in the device, named Peroxide Explosive Tester (PET), to determine whether or not it is in fact triacetone triperoxide (TATP). The PET " which resembles a three-color ballpoint pen " then 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 very difficult to detect. Many of the devastating suicide attacks by terrorists over the past few years involved TATP, including the bus explosions in Israel," said lead researcher Professor Ehud Keinan of the Technion-Israel Institute of Technology. "They are also dangerous to those who prepare them. This is the reason for the frequent 'work accidents' that have occurred in the terrorists' labs."

The researchers are in negotiations to commercialize the PET, and interest from law enforcement agencies has been high, according to Keinan.

Findings (see sidebar below) detailing the unique qualities of TATP, published January 6, 2005 in the Journal of the American Chemical Society, result from collaborative research by Technion Prof. Keinan, who is also a faculty member at The Scripps Research Institute; Prof. Yehuda Zeiri of Israel's Nuclear Research Center in the Negev; Professors Ronnie Kosloff and Joseph Almog of the Hebrew University of Jerusalem; and their co-workers.

Sidebar: The science behind TATP

An explosive favored by suicide bombers " triacetone triperoxide(TATP) -- is extremely unstable and prone to explode unexpectedly, a disadvantage that has made it useless for other applications. But it is hard to detect and extremely easy to make from two widely available chemicals: acetone and hydrogen peroxide. Now, an international team of scientists led by Ehud Keinan of the Institute of Catalysis Science and Technology of the Technion-Israel Institute of Technology has discovered the surprising reason why TATP is so easy to make--it's a different kind of explosive than practically any in use.

"Most explosives are energetic materials," explains Keinan. "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." To get the energy into the explosive in the first place, it has to be supplied from something, generally in the form of heat. TNT, for example, has to cooked at high temperature for its high-energy chemical bonds to form. Since 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. It is formed at room temperature and does not require any input of heat. Nor does it contain nitrogen compounds. It is in fact a carbohydrate-type compound somewhat related to sugar. So the question is--how can it explode if the energy is not pumped into it in the first place?

The research team demonstrated that TATP exploded not by releasing thermal energy, but by suddenly breaking each molecule of TATP in the solid state 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-a-half tons per square inch " then pushes outward, creating an explosive force 80% greater than that of TNT.

"There is no increase in energy when the molecules break apart," says Keinan, "but there is a sudden increase in entropy." Entropy is a measure of the degree of disorder in a system, and the randomly moving gas molecules have far more entropy than the orderly TATP crystal from which they are produced. When entropy increases in a system, energy can be derived from it, such as the kinetic energy of an explosion. 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 that it is held together by weak oxygen-to-oxygen bonds that are broken when the substance is subjected to mild heating or a chemical shock " thus making it highly unstable.

The team was then able of follow the decomposition of TATP with detailed calculations of the energy content of the intermediate products.

The Technion-Israel Institute of Technology is Israel's leading science and technology university. Home to the country's only winners of a Nobel Prize in science, it commands a worldwide reputation for its pioneering work in computer science, biotechnology, water-resource management, materials engineering, aerospace and medicine. The majority of the founders and managers of Israel's high-tech companies are alumni. Based in New York City, the American Technion Society is the leading American organization supporting higher education in Israel, with 17 offices around the country.