Piece work

A team at Liverpool University is building a gamma-ray scanner for airports that creates clear images of hidden drugs and explosives by piecing together their components like a jigsaw.

The researchers will work with BAE Systems, Manchester Airport and the Police Scientific Development Branch to build a prototype of the gamma-ray scanner.

Explosives or drugs universally comprise oxygen, nitrogen, hydrogen and carbon in different quantities, and have a unique fingerprint based on the ratios of these four elements.

The Liverpool researchers’ device will bombard the bag or suitcase with neutrons, and any hidden explosives or drugs will release gamma rays from each of their four components at different energy levels. A detector measures the specific energy of the gamma rays from each substance to identify it, and the device’s fast electronics calculate the amount to yield the unique fingerprint and an image.

The detector itself is made from germanium, a semiconductor used in the nuclear industry to warn of stray radioactivity. Gamma rays react with the germanium and leave a charge, which is then collected with an electric field with a voltage across the detector.