Spectroscopy technique improves destruction of chemical weapons

Disposing of ancient chemical weapons is a considerable problem. Unused ammunitions can be left in dumps for years, even decades - rusting away; forgotten; but still potentially lethal.

The US army's disposal programme is dedicated to destroying any old munitions found in the field. It runs several units dedicated to this task, and each has access to a variety of techniques to render the various substances contained in ammunition harmless. But shells are frequently corroded so badly that there's no way that their contents can be identified from just looking at them.

The Idaho National Engineering and Environment Laboratory, whose staff have the job of identifying ancient munitions for the army, has been working on methods to identify the contents of shells without opening them. A team led by nuclear physicist Gus Caffrey has now developed a device known as PINS - portable isotropic neutron spectroscopy - which appears to fulfil this task.

PINS works by shooting a beam of neutrons through the casing of the shell. The neutrons interact with the molecules of active ingredient inside the shell, and this interaction produces a gamma radiation pattern which is characteristic of a particular element.

For example, the team explains, explosives contain a lot of nitrogen, so the nitrogen pattern will predominate in the gamma signal picked up by the PIMS unit's detectors. If the shell contains nerve gases, the signal will be dominated by phosphorus; for mustard gases, chlorine signals will predominate. A built-in computer compares the signal with a database of elemental signals and determines which substances are inside the shells. The INEEL staff then know how to handle the shells safely, and which processes to apply to them to extract and destroy their active ingredients.

Caffrey's team's next project is to develop a smaller, cheaper version of PIMS which could be used to detect flammable materials or contraband drugs.