Misplaced Pages

#69930

22-406: 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 to record the data from the electron or positron . To reject other energy rays that would skew

44-690: A particle accelerator . Detectors can measure the particle energy and other attributes such as momentum, spin, charge, particle type, in addition to merely registering the presence of the particle. Many of the detectors invented and used so far are ionization detectors (of which gaseous ionization detectors and semiconductor detectors are most typical) and scintillation detectors ; but other, completely different principles have also been applied, like Čerenkov light and transition radiation. Historical examples The following types of particle detector are widely used for radiation protection, and are commercially produced in large quantities for general use within

66-540: 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. Spark chamber A spark chamber

88-401: 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

110-405: A spark chamber one looks at a stack of parallel plates edge-on. For this reason, best viewing is afforded when the particle comes in perpendicularly to the plates. A streamer chamber, in contrast, typically has only two plates, at least one of which is transparent (e.g. wire mesh or a conductive glass). Particles come in roughly parallel to the plane of these plates. A much shorter high-voltage pulse

132-434: A stack of metal plates placed in a sealed box filled with a gas such as helium , neon or a mixture of the two. When a charged particle from a cosmic ray travels through the box, it ionises the gas between the plates. Ordinarily this ionisation would remain invisible. However, if a high enough voltage can be applied between each adjacent pair of plates before that ionisation disappears, then sparks can be made to form along

154-492: Is a particle detector : a device used in particle physics for detecting electrically charged particles . They were most widely used as research tools from the 1930s to the 1960s and have since been superseded by other technologies such as drift chambers and silicon detectors . Today, working spark chambers are mostly found in science museums and educational organisations, where they are used to demonstrate aspects of particle physics and astrophysics. Spark chambers consist of

176-493: Is a predecessor of the Fermi Gamma-ray Space Telescope LAT. 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

198-403: Is radiation measurement, they are called radiation detectors , but as photons are also (massless) particles, the term particle detector is still correct. Beyond their experimental implementations, theoretical models of particle detectors are also of great importance to theoretical physics. These models consider localized non-relativistic quantum systems coupled to a quantum field. They receive

220-529: Is used than with a spark chamber, so there is insufficient time for sparks to form. Instead very dim streamers of ionised gas are formed. These can be seen when image enhancement is applied. Particle detector In experimental and applied particle physics , nuclear physics , and nuclear engineering , a particle detector , also known as a radiation detector , is a device used to detect, track, and/or identify ionizing particles , such as those produced by nuclear decay , cosmic radiation , or reactions in

242-422: The characteristics of the gamma ray. Finally, an anticoincidence identifies unwanted particles. 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

SECTION 10

#1732786730070

264-459: 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

286-406: 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 pulsars . 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

308-440: 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. NASA scientists also discovered that pulsars, which are “rotating neutron stars that emit

330-530: The model, giving rise to the Unruh-DeWitt detector model. Beyond their applications to theoretical physics, particle detector models are related to experimental fields such as quantum optics , where atoms can be used as detectors for the quantum electromagnetic field via the light-matter interaction. From a conceptual side, particle detectors also allow one to formally define the concept of particles without relying on asymptotic states, or representations of

352-417: The name of particle detectors because when the non-relativistic quantum system is measured in an excited state, one can claim to have detected a particle. The first instance of particle detector models in the literature dates from the 80's, where a particle in a box was introduced by W. G. Unruh in order to probe a quantum field around a black hole. Shortly after, Bryce DeWitt proposed a simplification of

374-573: The nuclear, medical, and environmental fields. Commonly used detectors for particle and nuclear physics Modern detectors in particle physics combine several of the above elements in layers much like an onion . Detectors designed for modern accelerators are huge, both in size and in cost. The term counter is often used instead of detector when the detector counts the particles but does not resolve its energy or ionization. Particle detectors can also usually track ionizing radiation (high energy photons or even visible light ). If their main purpose

396-411: The plates permanently, as this would lead to arc formation and continuous discharging. As research devices, spark chamber detectors have lower resolution than bubble chamber detectors. However they can be made highly selective with the help of auxiliary detectors, making them useful in searching for very rare events. A streamer chamber is a type of detector closely related to the spark chamber . In

418-590: 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. 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

440-421: The trajectory taken by the ray, and the cosmic ray in effect becomes visible as a line of sparks. In order to control when this voltage is applied, a separate detector (often containing a pair of scintillators placed above and below the box) is needed. When this trigger senses that a cosmic ray has just passed, it fires a fast switch to connect the high voltage to the plates. The high voltage cannot be connected to

462-453: Was only allowing gamma rays entering the telescope from certain angles to be let 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

SECTION 20

#1732786730070

484-405: 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. Throughout EGRET's active life span, which went from 1991 to 2000, all of

#69930