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With airports around the world working hard to increase their security, X-ray
machines that can tell different metals apart could be on the list of
most-wanted technologies. Ordinary X-rays generally show a mish-mash of metal
objects so a bomb could be hidden by the surrounding objects. Now Jim Raistrick
from Keele University in Staffordshire has found a way to tweak X-ray machines
so that they only emit at a few well-defined energies. By comparing the
absorption patterns at different energies he can pick out a single element such
as silver or lead, which are often used to make bomb detonators.