Seeing Through Steel: New Technology Identifies Chemical Weapons

In 1988, people in the Solomon Islands discovered rusty, World War II-era U.S. artillery projectiles. The markings on the steel casings were eroded and illegible. No one knew what was in them, but something inside sloshed. A team of explosives experts realized they were dealing with chemical weapons.

The U.S. Army boxed up the munitions in airtight containers and shipped them to nearby Johnston Atoll. The 600-acre coral island, 800 miles southwest of Hawaii, has served the U.S. military since World War II as an airbase and a place to store chemical weapons.

INEEL nuclear physicist Gus Caffrey has developed a system for evaluating what's inside a projectile -- without opening it up. Caffrey and three INEEL colleagues, Don Verrill, Alan Snyder, and Brian Harlow, flew out to Johnston Atoll late this summer to assess the recovered weapons.

On Johnston Atoll, the military operates an incinerator specifically designed to destroy chemical weapons. Before a weapon can be fed into the furnace, however, the operators must know what it contains. If a warhead contained explosives rather than chemical weapons, it could destroy the incinerator. Furthermore, the incinerator operators must know what kind of chemical weapon agent is being disposed of (such as mustard gas, a nerve gas, or an arsenic compound), in order to install the correct monitors on the incinerator's filter system to check for breakdown products.

Caffrey and his colleagues tested the warheads discovered on the Solomon Islands in two ways. First, they X-rayed them with a portable, fast, digitized prototype system that they developed recently. Chemical weapon projectiles contain a distinctive blasting tube down their centers, which can be seen in an X-ray.

Second, the team used a system they developed called PINS (for Portable Isotopic Neutron Spectroscopy) to find out which kind of chemical agent filled the projectile cavities. The PINS system shoots a beam of neutrons into the projectile. The neutrons bounce into the elements that make up the chemical weapon agent, and the interaction produces gamma rays. The gamma rays are recorded as they pass back through the projectile's steel casing.

Each type of warhead fill is made up of a different set of elements. Explosives contain a lot of nitrogen; nerve gases are composed partly of phosphorus, and mustard gas is chlorine-based. When assessed with PINS, each type of weapon emits a signature pattern of gamma rays. A computer program compares the pattern to a library of chemical weapons and determines what the projectiles are filled with.

The team concluded that 75% of the Solomon Island projectiles contained mustard gas. The rest were empty or contained mustard gas breakdown products.

PINS technology is needed surprisingly often. "The Army digs up old rusty munitions all the time," said Caffrey. Such weapons may have been lost or buried, their markings may have rusted away, or their records lost. PINS can tell what is in the weapons -- and therefore how to dispose of them safely.

The team's next goal is to make a PINS prototype that is smaller and cheaper than the current model. The technology could be used by law enforcement or fire departments to detect hazardous materials, for example in drug labs or traffic accidents.