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dome. The dome acted as a shield, blocking any unwanted energy waves from entering the telescope and skewing the data. To actually create recordable, usable data, scientists used a process called electron-positron pair production, which is creating an electron and positron simultaneously near a nucleus or subatomic particle. In order to induce this process, scientists assembled a multilevel thin-plate spark chamber within the telescope. A spark chamber is basically a chamber with many plates of metal and gases such as helium or neon. Finally, to record the data from the electron or positron about the gamma ray, scientists equipped EGRET with a thallium-activated sodium iodide (NaI(Tl)) calorimeter at its base. The calorimeter captured the spectrum of the gamma rays that EGRET detected.
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into the spark chamber. As the gamma ray travelled through the spark chamber, it struck one of the metal plates within the spark chamber. Once the gamma ray came in contact with a plate of metal, it initiated the process of electron-positron pair production and created an electron and positron. Once both the electron and positron were created, if one of these particles was still moving down throughout the telescope and a signal from the anticoincidence scintillator was not fired, the particle was imaged and its energy level recorded. With each gamma ray having to pass all of these systems of checks, the results of EGRET were supported to be the most valuable out of the other CGRO instruments.
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scientists also discovered that pulsars, which are “rotating neutron stars that emit a beam of electromagnetic radiation,” are the best sources of gamma rays. Scientists have also been able to detect and characterize the properties of 4 pulsars. EGRET's results also pointed out to scientists that the
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Throughout EGRET's active life span, which went from 1991 to 2000, all of the gamma rays it collected and recorded were done one at a time. From each individual gamma ray that entered EGRET, scientists were able to create a detailed map of the “entire high-energy gamma-ray sky.” From its findings and
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The basic design of EGRET was basically a chamber filled with a special type of metal, a sensor at the bottom of the chamber to capture and record gamma rays, and finally a protective covering over the entire instrument. The chamber would manipulate the gamma ray into a way that it could be recorded.
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The telescope was calibrated to only record gamma rays entering the telescope at certain angles. As these gamma rays entered the telescope, the rays went through the telescopes spark chamber and started the production of an electron and positron. The calorimeter then detected the electron or positron
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Fichtel, C.E; Bertsch, D.L; Dingus, B; Hartman, R.C; Hunter, S.D; Kanbach, G; Kniffen, D.A; Kwok, P.W; Lin, Y.C; Mattox, J.R; Mayer-Hasselwander, H.A; Michelson, P.F; von
Montigny, C; Nolan, P.L; Pinkau, K; Rothermel, H; Schneid, E.J; Sommer, M; Sreekumar, P; Thompson, D.J (1993), "Results from the
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Since NASA scientists wanted only certain types of gamma rays to be processed and recorded, they set up EGRET with many systems of checks to filter out any unwanted information. The most basic type of filter EGRET had was only allowing gamma rays entering the telescope from certain angles to be let
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With the purpose of detecting individual gamma rays ranging from 30 MeV to 30 GeV, EGRET was equipped with a plastic scintillator anti-coincidence dome, spark chamber, and calorimeter. Starting from the outside of the telescope, scientists covered EGRET with a plastic scintillator anti-coincidence
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satellite. Since lower energy gamma rays cannot be accurately detected on Earth's surface, EGRET was built to detect gamma rays while in space. EGRET was created for the purpose of detecting and collecting data on gamma rays ranging in energy level from 30 MeV to 30 GeV.
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Thompson, D. J., D. L. Bertsch, D. J. Morris, and R. Mukherjee. "Energetic gamma ray experiment telescope high-energy gamma ray observations of the Moon and quiet Sun." Journal of
Geophysical Research A7 102 (1997): 14730-4740.
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Thompson, D. J., D. L. Bertsch, D. J. Morris, and R. Mukherjee. "Energetic gamma ray experiment telescope high-energy gamma ray observations of the Moon and quiet Sun." JOURNAL OF GEOPHYSICAL RESEARCH A7 102 (1997): 14730-4740.
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Earth's Moon is particularly brighter than the Sun the majority of the time. EGRET provided scientists with information that allowed them into a new understanding of the universe.
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From EGRET's finds, scientists have affirmed many long-standing theories about energy waves in space. Scientists have also been able to categorize and characterize four
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The sensor would capture and record the characteristics of the gamma ray. Finally, an anticoincidence identifies unwanted particles.
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mapping of the universe, scientists were able to reaffirm many long holding theories about gamma rays and their origins.
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Energetic Gamma-Ray
Experiment Telescope (EGRET) on the Compton Observatory",
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HEASARC: NASA's
Archive of Data on Energetic Phenomena. Web. 23 Jan. 2010.
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HEASARC: NASA's
Archive of Data on Energetic Phenomena. Web. 23 Jan. 2010.
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The EGRET home page at the
Compton Observatory Science Center
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Instrument on NASA's
Compton Gamma Ray Observatory satellite
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30:"EGRET" redirects here. For the type of bird, see
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49:The sky as seen in high-energy gamma rays.
55:Energetic Gamma Ray Experiment Telescope
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180:CGRO SSC EGRET Technical Information
168:CGRO SSC EGRET Technical Information
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113:Fermi Gamma-ray Space Telescope
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63:Compton Gamma Ray Observatory
225:10.1016/0273-1177(93)90175-B
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