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The Energetic Gamma Ray Experiment Telescope (EGRET)
The Energetic Gamma Ray Experiment Telescope (EGRET) provides the
highest energy gamma-ray window for the Compton Observatory. Its
energy range is from 30 million electron volts (20 MeV) to 30 billion
electron volts (30 GeV). EGRET is 10 to 20 times larger and more
sensitive than previous detectors operating at these high energies and
has made detailed observations of high energy processes associated with
diffuse gamma-ray emission, gamma-ray bursts, cosmic rays, pulsars,
and active galaxies known as
gamma-ray blazars.
The EGRET instrument produces images at these energies using high
voltage, gas filled, spark chambers. High energy gamma rays enter the
chambers and produce an electron-positron pair of particles which cause
sparks. The path of the particles is recorded allowing the
determination of the direction of the original gamma ray. The particle
energies are recorded by a NaI crystal beneath the spark chambers
providing a measure of the original gamma-ray energy.
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