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An energy-dispersive x-ray analyzer (EDX) is a common accessory which gives the scanning electron microscope (SEM) a very valuable capability for elemental analysis. The figure to the right illustrates the interaction of an electron beam (in red) with a specimen (shaded blue). The electron beam in an SEM has an energy typically between 5,000 and 20,000 electron volts (eV). The energy holding electrons in atoms (the binding energy) ranges from a few eV up to many kilovolts. Many of these atomic electrons are dislodged as the incident electrons pass through the specimen, thus ionizing atoms of the specimen. This process is illustrated schematically in the inset box of the figure. Ejection of an atomic electron by an electron in the beam ionizes the atom, which is then quickly neutralized by other electrons. In the neutralization process an x-ray with an energy characteristic of the parent atom is emitted. By collecting and analyzing the energy of these x-rays, the constituent elements of the specimen can be determined.

The now standard forensic laboratory test for the identification of gunshot residue is based on the use of an electron microscope equipped with an EDX analyzer. This test was developed at the Aerospace Corporation in the 1970's. The analyzer produces a spectrum, like this example from a gunshot residue particle collected from the hand of a person who had fired a .380 Browning automatic. The peaks of lead, barium, and antimony (together with the shape of the particle) are quite specific and show that the subject in the test had indeed fired a weapon.