Energetic Gamma Ray Experiment Telescope
Encyclopedia
The Energetic Gamma Ray Experiment Telescope (EGRET) was one of four instruments outfitted on NASA’s Compton Gamma Ray Observatory
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.
To accomplish its task, EGRET was equipped with a spark chamber, calorimeter
, and plastic scintillator
anti-coincidence dome. The spark chamber was used to induce a process called electron-positron pair production
as a gamma ray
entered the telescope. The calorimeter on the telescope was then used record the data from the electron
or positron
. To reject other energy rays that would skew the data, scientists covered the telescope with a plastic scintillator anti-coincidence dome. The dome acted as a shield for the telescope and blocked out any unwanted energy rays.
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 and recorded its data, such as energy level.
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 pulsar
s. Scientists were able to map an entire sky of gamma rays with EGRET's results as well as find out interesting facts about Earth’s Moon and the Sun.
EGRET is a predecessor of the Fermi Gamma-ray Space Telescope LAT.
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 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 (Na(TI)) calorimeter at its base. The calorimeter captured the resolution of the gamma rays that entered EGRET.
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 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.
Compton Gamma Ray Observatory
The Compton Gamma Ray Observatory was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000. It featured four main telescopes in one spacecraft covering x-rays and gamma-rays, including various specialized sub-instruments and detectors...
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.
To accomplish its task, EGRET was equipped with a spark chamber, calorimeter
Calorimeter
A calorimeter is a device used for calorimetry, the science of measuring the heat of chemical reactions or physical changes as well as heat capacity. Differential scanning calorimeters, isothermal microcalorimeters, titration calorimeters and accelerated rate calorimeters are among the most common...
, and plastic scintillator
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...
anti-coincidence dome. The spark chamber was used to induce a process called electron-positron pair production
Pair production
Pair production refers to the creation of an elementary particle and its antiparticle, usually from a photon . For example an electron and its antiparticle, the positron, may be created...
as a gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
entered the telescope. The calorimeter on the telescope was then used record the data from the electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
or positron
Positron
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...
. To reject other energy rays that would skew the data, scientists covered the telescope with a plastic scintillator anti-coincidence dome. The dome acted as a shield for the telescope and blocked out any unwanted energy rays.
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 and recorded its data, such as energy level.
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 pulsar
Pulsar
A pulsar is a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The radiation can only be observed when the beam of emission is pointing towards the Earth. This is called the lighthouse effect and gives rise to the pulsed nature that gives pulsars their name...
s. Scientists were able to map an entire sky of gamma rays with EGRET's results as well as find out interesting facts about Earth’s Moon and the Sun.
EGRET is a predecessor of the Fermi Gamma-ray Space Telescope LAT.
Design
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. The sensor would capture and record the characteristics of the gamma ray. Finally the protective covering would block out any unwanted energy rays.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 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 (Na(TI)) calorimeter at its base. The calorimeter captured the resolution of the gamma rays that entered EGRET.
Function
Since NASA scientists only wanted 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 into the spark chamber. As the gamma ray travels through the spark chamber, it has of striking one of the metal plates within the spark chamber. Once the gamma ray comes in contact a plate of metal, it initiates the process of electron-positron pair production and creates an electron and positron. Once both the electron and positron have been created, if one of these particles is still moving down throughout the telescope and a signal from the anticoincidence scintillator isn’t fired, the particle is imaged and its energy level is recorded. With each gamma ray having to pass all of these systems of checks, the results of EGRET are supported to be the most valuable out of the other CGRO instruments.Findings
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 mapping of the universe, scientists were able to reaffirm many long holding theories about gamma rays and their origins. NASANASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
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 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.