The Large Area Telescope (LAT) detects gamma rays by using Einstein's famous equation (E=mc(squared)) in a technique known as pair production. When a gamma ray, which is pure energy, slams into a layer of tungsten in one of the Tracker's towers, it can create a pair of subatomic particles (an electron and its antimatter counterpart, a positron). The direction of the incoming gamma ray is determined by projecting the direction of these particles back to their source using several layers of high-precision silicon tracking detectors. A separate detector, called a calorimeter, absorbs and measures the energy of the particles. Working on gamma ray at a time, the LAT will make gamma-ray images of astronomical objects, while also determining the energy for each detected gamma ray.
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