A new airport security system is proving five times better than X-ray machines in trials at Heathrow Airport, London. The system, invented by scientists at King's College in London, uses radio waves to detect molecules of prohibited substances. It relies on quadrapole resonance (QR) to detect nitrogen, found in all stable explosives. Drugs such as heroin and cocaine also contain nitrogen. In the QR system, baggage goes along a conveyor, which passes through a coil where a transmitter irradiates it with a burst of radio-frequency. Nitrogen atoms in the baggage respond to the irradiation by changing their orientation. When the signal stops, they revert to their original position and emit a small radio signature.