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133-610: VERITAS ( Very Energetic Radiation Imaging Telescope Array System ) is a major ground-based gamma-ray observatory with an array of four 12 meter optical reflectors for gamma-ray astronomy in the GeV – TeV photon energy range. VERITAS uses the Imaging Atmospheric Cherenkov Telescope technique to observe gamma rays that cause particle showers in Earth's atmosphere that are known as extensive air showers . The VERITAS array

266-455: A French chemist and physicist, discovered gamma radiation in 1900, while studying radiation emitted from radium . Villard knew that his described radiation was more powerful than previously described types of rays from radium, which included beta rays, first noted as "radioactivity" by Henri Becquerel in 1896, and alpha rays, discovered as a less penetrating form of radiation by Rutherford, in 1899. However, Villard did not consider naming them as

399-531: A celebration was held at the Whipple Observatory to celebrate ten years of VERITAS science. VERITAS has a broad science program that combines key aspects of astronomy, exploring the universe in the new waveband of VHE gamma rays, and physics, searching for new particles of phenomena beyond the standard model of particle physics. The basic questions pursued include: understanding cosmic particle acceleration in our Galaxy (with special emphasis on understanding

532-465: A certain medium. Knowing particle momentum, one can separate particles lighter than a certain threshold from those heavier than the threshold. The most advanced type of a detector is the RICH, or ring-imaging Cherenkov detector , developed in the 1980s. In a RICH detector, a cone of Cherenkov light is produced when a high-speed charged particle traverses a suitable medium, often called radiator. This light cone

665-419: A charged particle, most commonly an electron , travels through a dielectric (can be polarized electrically) medium with a speed greater than light's speed in that medium. The effect can be intuitively described in the following way. From classical physics, it is known that accelerating charged particles emit EM waves and via Huygens' principle these waves will form spherical wavefronts which propagate with

798-438: A crystal. The immobilization of nuclei at both ends of a gamma resonance interaction is required so that no gamma energy is lost to the kinetic energy of recoiling nuclei at either the emitting or absorbing end of a gamma transition. Such loss of energy causes gamma ray resonance absorption to fail. However, when emitted gamma rays carry essentially all of the energy of the atomic nuclear de-excitation that produces them, this energy

931-415: A different fundamental type. Later, in 1903, Villard's radiation was recognized as being of a type fundamentally different from previously named rays by Ernest Rutherford , who named Villard's rays "gamma rays" by analogy with the beta and alpha rays that Rutherford had differentiated in 1899. The "rays" emitted by radioactive elements were named in order of their power to penetrate various materials, using

1064-473: A few weeks, suggesting their relatively small size (less than a few light-weeks across). Such sources of gamma and X-rays are the most commonly visible high intensity sources outside the Milky Way galaxy. They shine not in bursts (see illustration), but relatively continuously when viewed with gamma ray telescopes. The power of a typical quasar is about 10 watts, a small fraction of which is gamma radiation. Much of

1197-448: A formidable radiation protection challenge, requiring shielding made from dense materials such as lead or concrete. On Earth , the magnetosphere protects life from most types of lethal cosmic radiation other than gamma rays. The first gamma ray source to be discovered was the radioactive decay process called gamma decay . In this type of decay, an excited nucleus emits a gamma ray almost immediately upon formation. Paul Villard ,

1330-479: A large, steerable optical reflector and a high-speed photomultiplier tube camera. Multiple telescopes in an array are needed for stereoscopic observations of the Cherenkov light produced in extensive air showers. These stereoscopic observations allow precise reconstruction of the particle shower geometry, thus giving greatly improved angular and energy resolution compared to a single telescope. The angular direction of

1463-583: A low energy threshold. Compared to the Whipple telescope, VERITAS employs larger 12 m diameter reflectors, improved optics and light collection efficiency, and a finer pixelated camera. Both the recording (using 500 MS/s custom-made Flash-ADCs) and trigger electronics (using a sophisticated three-level system) were significantly improved compared to earlier instruments. VERITAS was conceived in the 1990s, along with three other imaging atmospheric Cherenkov telescope (IACT) arrays: CANGAROO-III, H.E.S.S. and MAGIC . VERITAS

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1596-455: A magnetic field indicated that they had no charge. In 1914, gamma rays were observed to be reflected from crystal surfaces, proving that they were electromagnetic radiation. Rutherford and his co-worker Edward Andrade measured the wavelengths of gamma rays from radium, and found they were similar to X-rays , but with shorter wavelengths and thus, higher frequency. This was eventually recognized as giving them more energy per photon , as soon as

1729-457: A means for sources of GeV photons using lasers as exciters through a controlled interplay between the cascade and anomalous radiative trapping . Thunderstorms can produce a brief pulse of gamma radiation called a terrestrial gamma-ray flash . These gamma rays are thought to be produced by high intensity static electric fields accelerating electrons, which then produce gamma rays by bremsstrahlung as they collide with and are slowed by atoms in

1862-490: A non-imaging Cherenkov observatory, which was located in New Mexico . Astrophysics observatories using the Cherenkov technique to measure air showers are key to determining the properties of astronomical objects that emit very-high-energy gamma rays, such as supernova remnants and blazars . Cherenkov radiation is commonly used in experimental particle physics for particle identification. One could measure (or put limits on)

1995-408: A nuclear power plant, shielding can be provided by steel and concrete in the pressure and particle containment vessel, while water provides a radiation shielding of fuel rods during storage or transport into the reactor core. The loss of water or removal of a "hot" fuel assembly into the air would result in much higher radiation levels than when kept under water. When a gamma ray passes through matter,

2128-554: A number of astronomical processes in which very high-energy electrons are produced. Such electrons produce secondary gamma rays by the mechanisms of bremsstrahlung , inverse Compton scattering and synchrotron radiation . A large fraction of such astronomical gamma rays are screened by Earth's atmosphere. Notable artificial sources of gamma rays include fission , such as occurs in nuclear reactors , as well as high energy physics experiments, such as neutral pion decay and nuclear fusion . A sample of gamma ray-emitting material that

2261-717: A number of other institutions. The chair of the VERITAS Science Board is the Spokesperson. There is a Deputy Spokesperson to assist in the leadership of the collaboration. A chronological list of the VERITAS Spokespersons and Deputy Spokespersons is given in the table below. Starting in 2007, the Spokesperson/Deputy Spokesperson served a two-year term and may be re-elected. As of 2019, the following agencies provide operational funding for VERITAS:

2394-469: A periodic medium, and in that case one can even achieve Cherenkov radiation with no minimum particle velocity, a phenomenon known as the Smith–Purcell effect . In a more complex periodic medium, such as a photonic crystal , one can also obtain a variety of other anomalous Cherenkov effects, such as radiation in a backwards direction (see below) whereas ordinary Cherenkov radiation forms an acute angle with

2527-509: A slow-wave structure, like in a traveling-wave tube (TWT), the phase velocity decreases and the velocity of charged particles can exceed the phase velocity while remaining lower than c {\displaystyle c} . In such a system, this effect can be derived from conservation of the energy and momentum where the momentum of a photon should be p = ℏ β {\displaystyle p=\hbar \beta } ( β {\displaystyle \beta }

2660-409: A substantial amount of Cherenkov light in the tissue being treated, due to electron beams or photon beams with energy in the 6 MV to 18 MV ranges. The secondary electrons induced by these high energy x-rays result in the Cherenkov light emission, where the detected signal can be imaged at the entry and exit surfaces of the tissue. The Cherenkov light emitted from patient's tissue during radiation therapy

2793-419: A subwavelength microstructure that gives them an effective "average" property very different from their constituent materials, in this case having negative permittivity and negative permeability ). This means that, when a charged particle (usually electrons) passes through a medium at a speed greater than the phase velocity of light in that medium, that particle emits trailing radiation from its progress through

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2926-470: A way that the intensity cannot continue to increase at ever shorter wavelengths, even for very relativistic particles (where v / c is close to 1). At X-ray frequencies, the refractive index becomes less than 1 (note that in media, the phase velocity may exceed c without violating relativity) and hence no X-ray emission (or shorter wavelength emissions such as gamma rays ) would be observed. However, X-rays can be generated at special frequencies just below

3059-507: Is phase constant ) rather than the de Broglie relation p = ℏ k {\displaystyle p=\hbar k} . This type of radiation (VCR) is used to generate high-power microwaves. Radiation with the same properties of typical Cherenkov radiation can be created by structures of electric current that travel faster than light. By manipulating density profiles in plasma acceleration setups, structures up to nanocoulombs of charge are created and may travel faster than

3192-403: Is speed of light in vacuum , and n {\displaystyle n} is the refractive index of the medium. If the medium is water, the condition is 0.75 c < v p < c {\displaystyle 0.75c<v_{\text{p}}<c} , since n ≈ 1.33 {\displaystyle n\approx 1.33} for water at 20 °C. We define

3325-423: Is a very low light level signal but can be detected by specially designed cameras that synchronize their acquisition to the linear accelerator pulses. The ability to see this signal shows the shape of the radiation beam as it is incident upon the tissue in real time. Cherenkov radiation is used to detect high-energy charged particles. In open pool reactors , beta particles (high-energy electrons) are released as

3458-518: Is about 1 to 2 mSv per year, and the average total amount of radiation received in one year per inhabitant in the USA is 3.6 mSv. There is a small increase in the dose, due to naturally occurring gamma radiation, around small particles of high atomic number materials in the human body caused by the photoelectric effect. Cherenkov radiation The radiation is named after the Soviet scientist Pavel Cherenkov,

3591-403: Is also a mode of relaxation of many excited states of atomic nuclei following other types of radioactive decay, such as beta decay, so long as these states possess the necessary component of nuclear spin . When high-energy gamma rays, electrons, or protons bombard materials, the excited atoms emit characteristic "secondary" gamma rays, which are products of the creation of excited nuclear states in

3724-555: Is also sufficient to excite the same energy state in a second immobilized nucleus of the same type. Gamma rays provide information about some of the most energetic phenomena in the universe; however, they are largely absorbed by the Earth's atmosphere. Instruments aboard high-altitude balloons and satellites missions, such as the Fermi Gamma-ray Space Telescope , provide our only view of the universe in gamma rays. Gamma-induced molecular changes can also be used to alter

3857-448: Is another possible mechanism of gamma ray production. Neutron stars with a very high magnetic field ( magnetars ), thought to produce astronomical soft gamma repeaters , are another relatively long-lived star-powered source of gamma radiation. More powerful gamma rays from very distant quasars and closer active galaxies are thought to have a gamma ray production source similar to a particle accelerator . High energy electrons produced by

3990-403: Is classified as X-rays and is the subject of X-ray astronomy . Gamma rays are ionizing radiation and are thus hazardous to life. They can cause DNA mutations , cancer and tumors , and at high doses burns and radiation sickness . Due to their high penetration power, they can damage bone marrow and internal organs. Unlike alpha and beta rays, they easily pass through the body and thus pose

4123-446: Is close to the edge of the visible universe . Due to their penetrating nature, gamma rays require large amounts of shielding mass to reduce them to levels which are not harmful to living cells, in contrast to alpha particles , which can be stopped by paper or skin, and beta particles , which can be shielded by thin aluminium. Gamma rays are best absorbed by materials with high atomic numbers ( Z ) and high density, which contribute to

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4256-446: Is continuous. Around the visible spectrum, the relative intensity per unit frequency is approximately proportional to the frequency. That is, higher frequencies (shorter wavelengths ) are more intense in Cherenkov radiation. This is why visible Cherenkov radiation is observed to be brilliant blue. In fact, most Cherenkov radiation is in the ultraviolet spectrum—it is only with sufficiently accelerated charges that it even becomes visible;

4389-545: Is currently the only IACT array operating in the western hemisphere. The first proposal for VERITAS (called VHEGRA at the time) was submitted by Trevor Weekes ( Smithsonian Astrophysical Observatory (SAO)) to the Smithsonian Institution in 1995; this proposal described an array of nine 10 m diameter Cherenkov telescopes. In 1998, the first VERITAS collaboration meeting was held at the University of Chicago . In 2000,

4522-427: Is defined as the probability of cancer induction and genetic damage. The International Commission on Radiological Protection says "In the low dose range, below about 100 mSv, it is scientifically plausible to assume that the incidence of cancer or heritable effects will rise in direct proportion to an increase in the equivalent dose in the relevant organs and tissues" High doses produce deterministic effects, which

4655-606: Is designed to introduce a gradient of phase retardation along the trajectory of the fast travelling particle ( d ϕ / d x {\displaystyle d\phi /dx} ), reversing or steering Cherenkov emission at arbitrary angles given by the generalized relation: cos ⁡ θ = 1 n β + n k 0 ⋅ d ϕ d x {\displaystyle \cos \theta ={\frac {1}{n\beta }}+{\frac {n}{k_{0}}}\cdot {\frac {d\phi }{dx}}} Note that since this ratio

4788-415: Is detected on a position sensitive planar photon detector, which allows reconstructing a ring or disc, whose radius is a measure for the Cherenkov emission angle. Both focusing and proximity-focusing detectors are in use. In a focusing RICH detector, the photons are collected by a spherical mirror and focused onto the photon detector placed at the focal plane. The result is a circle with a radius independent of

4921-404: Is dominated by the more common and longer-term production of gamma rays that emanate from pulsars within the Milky Way. Sources from the rest of the sky are mostly quasars . Pulsars are thought to be neutron stars with magnetic fields that produce focused beams of radiation, and are far less energetic, more common, and much nearer sources (typically seen only in our own galaxy) than are quasars or

5054-419: Is followed 99.88% of the time: Another example is the alpha decay of Am to form Np ; which is followed by gamma emission. In some cases, the gamma emission spectrum of the daughter nucleus is quite simple, (e.g. Co / Ni ) while in other cases, such as with ( Am / Np and Ir / Pt ),

5187-401: Is independent of time, one can take arbitrary times and achieve similar triangles . The angle stays the same, meaning that subsequent waves generated between the initial time t = 0 and final time t will form similar triangles with coinciding right endpoints to the one shown. A reverse Cherenkov effect can be experienced using materials called negative-index metamaterials (materials with

5320-513: Is located at the Fred Lawrence Whipple Observatory , in southern Arizona , United States . The VERITAS reflector design is similar to the earlier Whipple 10-meter gamma-ray telescope, located at the same site, but is larger in size and has a longer focal length for better control of optical aberrations. VERITAS consists of an array of imaging telescopes deployed to view atmospheric Cherenkov showers from multiple locations to give

5453-414: Is much slower in the case of a low-dose exposure. Studies have shown low-dose gamma radiation may be enough to cause cancer. In a study of mice, they were given human-relevant low-dose gamma radiation, with genotoxic effects 45 days after continuous low-dose gamma radiation, with significant increases of chromosomal damage, DNA lesions and phenotypic mutations in blood cells of irradiated animals, covering

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5586-409: Is sensitive to primary particles that produce sufficient atmospheric Cherenkov light to be detectable at the ground. Its full range of sensitivity is from 50 GeV to 50 TeV (although the spectral reconstruction does not start until at least 100 GeV, depending on source strength). The energy and angular resolution depend on the energy of the incident gamma ray but at 1 TeV the energy resolution is ~17%, and

5719-437: Is straight forward to construct and align. This design does cause some time spread in the arrival of Cherenkov photons at the camera, but this spread is small (~ 4 nanoseconds). The reflector consists of 350 individual mirror facets, hexagonal in shape, mounted on a rigid optical support structure. The camera on each telescope has 499 individual pixels (high-speed 26 mm-diameter photomultiplier tubes ). VERITAS, like other IACTs ,

5852-438: Is the index of refraction of the material the charged particle moves through. q {\displaystyle q} is the electric charge of the particle, v {\displaystyle v} is the speed of the particle, and c {\displaystyle c} is the speed of light in vacuum. Unlike fluorescence or emission spectra that have characteristic spectral peaks, Cherenkov radiation

5985-408: Is the severity of acute tissue damage that is certain to happen. These effects are compared to the physical quantity absorbed dose measured by the unit gray (Gy). When gamma radiation breaks DNA molecules, a cell may be able to repair the damaged genetic material, within limits. However, a study of Rothkamm and Lobrich has shown that this repair process works well after high-dose exposure but

6118-551: Is the array trigger which looks for a coincidence in the arrival time of the shower at multiple telescopes. The Cherenkov light that is produced by gamma rays in the upper atmosphere is very dim, so VERITAS observes best under clear, dark skies. Observations are not possible under cloudy or rainy skies, or when the Moon is very bright. However, observations are regularly made when the Moon is dim or moderate in brightness (typically less than 60% illumination). The total yearly observation time

6251-444: Is the threshold counter, which answers whether the velocity of a charged particle is lower or higher than a certain value ( v 0 = c / n {\displaystyle v_{0}=c/n} , where c {\displaystyle c} is the speed of light , and n {\displaystyle n} is the refractive index of the medium) by looking at whether this particle emits Cherenkov light in

6384-469: Is typically around 1,200 hours (of which around 200–250 hours is during brighter moonlight with illumination between 20 and 60%). The observatory does not generally collect data in July or August due to local monsoon conditions. VERITAS was designed to explore the very high energy (VHE) gamma-ray sky above 100 GeV , following up on the success of the Whipple 10 m gamma-ray telescope. The Whipple telescope pioneered

6517-499: Is used for irradiating or imaging is known as a gamma source. It is also called a radioactive source , isotope source, or radiation source, though these more general terms also apply to alpha and beta-emitting devices. Gamma sources are usually sealed to prevent radioactive contamination , and transported in heavy shielding. Gamma rays are produced during gamma decay, which normally occurs after other forms of decay occur, such as alpha or beta decay. A radioactive nucleus can decay by

6650-656: Is used for the same goal by the Extensive Air Shower experiment HAWC , the Pierre Auger Observatory and other projects. Similar methods are used in very large neutrino detectors, such as the Super-Kamiokande , the Sudbury Neutrino Observatory (SNO) and IceCube . Other projects operated in the past applying related techniques, such as STACEE , a former solar tower refurbished to work as

6783-510: Is widely used to facilitate the detection of small amounts and low concentrations of biomolecules . Radioactive atoms such as phosphorus-32 are readily introduced into biomolecules by enzymatic and synthetic means and subsequently may be easily detected in small quantities for the purpose of elucidating biological pathways and in characterizing the interaction of biological molecules such as affinity constants and dissociation rates. More recently, Cherenkov light has been used to image substances in

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6916-667: The Cygnus X-3 microquasar . Natural sources of gamma rays originating on Earth are mostly a result of radioactive decay and secondary radiation from atmospheric interactions with cosmic ray particles. However, there are other rare natural sources, such as terrestrial gamma-ray flashes , which produce gamma rays from electron action upon the nucleus. Notable artificial sources of gamma rays include fission , such as that which occurs in nuclear reactors , and high energy physics experiments, such as neutral pion decay and nuclear fusion . The energy ranges of gamma rays and X-rays overlap in

7049-616: The Earth's atmosphere , it may produce an electron– positron pair with enormous velocities. The Cherenkov radiation emitted in the atmosphere by these charged particles is used to determine the direction and energy of the cosmic ray or gamma ray, which is used for example in the Imaging Atmospheric Cherenkov Technique ( IACT ), by experiments such as VERITAS , H.E.S.S. , MAGIC . Cherenkov radiation emitted in tanks filled with water by those charged particles reaching earth

7182-536: The English polymath Oliver Heaviside in papers published between 1888 and 1889 and by Arnold Sommerfeld in 1904, but both had been quickly dismissed following the relativity theory's restriction of superluminal particles until the 1970s. Marie Curie observed a pale blue light in a highly concentrated radium solution in 1910, but did not investigate its source. In 1926, the French radiotherapist Lucien Mallet described

7315-773: The National Science Foundation and the Smithsonian Institution in the U.S., the Natural Sciences and Engineering Research Council in Canada, the Helmholtz Association in Germany. Gamma ray A gamma ray , also known as gamma radiation (symbol γ ), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei . It consists of

7448-530: The United Kingdom . Improvements and upgrades to VERITAS have been made periodically since 2007. Telescope #1 was moved in the summer of 2009 to a new location for better array geometry (and improved gamma-ray sensitivity). Between 2009 and 2011 an upgrade program was carried out that improved the alignment of the VERITAS mirror facets and replaced the level 2 trigger system. Furthermore, in the summer of 2012 all of

7581-469: The Zooniverse platform. The project showed images taken with VERITAS and citizen volunteers had to classify the images as muon or non-muon events. The researchers then trained a machine learned algorithm that performed better than the standard analysis. In Muon Hunter 2.0 the project will try to improve the result with a different machine learning approach. The VERITAS collaboration was officially formed by

7714-409: The anisotropy of the radiation and came to the conclusion that the bluish glow was not a fluorescent phenomenon. A theory of this effect was later developed in 1937 within the framework of Einstein 's special relativity theory by Cherenkov's colleagues Igor Tamm and Ilya Frank , who also shared the 1958 Nobel Prize. Cherenkov radiation as conical wavefronts had been theoretically predicted by

7847-455: The electromagnetic spectrum , so the terminology for these electromagnetic waves varies between scientific disciplines. In some fields of physics, they are distinguished by their origin: gamma rays are created by nuclear decay while X-rays originate outside the nucleus. In astrophysics , gamma rays are conventionally defined as having photon energies above 100 keV and are the subject of gamma-ray astronomy , while radiation below 100 keV

7980-459: The extragalactic background light in the universe: The highest-energy rays interact more readily with the background light photons and thus the density of the background light may be estimated by analyzing the incoming gamma ray spectra. Gamma spectroscopy is the study of the energetic transitions in atomic nuclei, which are generally associated with the absorption or emission of gamma rays. As in optical spectroscopy (see Franck–Condon effect)

8113-421: The fission products decay. The glow continues after the chain reaction stops, dimming as the shorter-lived products decay. Similarly, Cherenkov radiation can characterize the remaining radioactivity of spent fuel rods. This phenomenon is used to verify the presence of spent nuclear fuel in spent fuel pools for nuclear safeguards purposes. When a high-energy ( TeV ) gamma photon or cosmic ray interacts with

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8246-450: The phase velocity of that medium (i.e. the speed of light in that medium given by c / n {\displaystyle c/n} , for n {\displaystyle n} , the refractive index ). When any charged particle passes through a medium, the particles of the medium will polarize around it in response. The charged particle excites the molecules in the polarizable medium and on returning to their ground state ,

8379-909: The speed of light and emit optical shocks at the Cherenkov angle. Electrons are still subluminal, hence the electrons that compose the structure at a time t = t 0 are different from the electrons in the structure at a time t > t 0 . The frequency spectrum of Cherenkov radiation by a particle is given by the Frank–Tamm formula : d 2 E d x d ω = q 2 4 π μ ( ω ) ω ( 1 − c 2 v 2 n 2 ( ω ) ) {\displaystyle {\frac {d^{2}E}{dx\,d\omega }}={\frac {q^{2}}{4\pi }}\mu (\omega )\omega {\left(1-{\frac {c^{2}}{v^{2}n^{2}(\omega )}}\right)}} The Frank–Tamm formula describes

8512-418: The velocity of an electrically charged elementary particle by the properties of the Cherenkov light it emits in a certain medium. If the momentum of the particle is measured independently, one could compute the mass of the particle by its momentum and velocity (see four-momentum ), and hence identify the particle. The simplest type of particle identification device based on a Cherenkov radiation technique

8645-547: The 1958 Nobel Prize winner, who was the first to detect it experimentally under the supervision of Sergey Vavilov at the Lebedev Institute in 1934. Therefore, it is also known as Vavilov–Cherenkov radiation . Cherenkov saw a faint bluish light around a radioactive preparation in water during experiments. His doctorate thesis was on luminescence of uranium salt solutions that were excited by gamma rays instead of less energetic visible light, as done commonly. He discovered

8778-420: The K shell electrons of the atom, causing it to be ejected from that atom, in a process generally termed the photoelectric effect (external gamma rays and ultraviolet rays may also cause this effect). The photoelectric effect should not be confused with the internal conversion process, in which a gamma ray photon is not produced as an intermediate particle (rather, a "virtual gamma ray" may be thought to mediate

8911-791: The VERITAS collaboration consists of ~80 scientists from institutions in Canada, Germany, Ireland and the U.S. The participating institutions are: Barnard College , Columbia University , Cork Institute of Technology , DESY , Georgia Institute of Technology , Iowa State University , McGill University , National University of Ireland, Galway , Purdue University , Smithsonian Astrophysical Observatory , University College Dublin , University of California, Los Angeles , University of California, Santa Cruz , University of Chicago , University of Delaware , University of Iowa , University of Minnesota , University of Utah , and Washington University in St. Louis . There are also non-affiliated and associate members from

9044-495: The absorption of gamma rays by a nucleus is especially likely (i.e., peaks in a "resonance") when the energy of the gamma ray is the same as that of an energy transition in the nucleus. In the case of gamma rays, such a resonance is seen in the technique of Mössbauer spectroscopy . In the Mössbauer effect the narrow resonance absorption for nuclear gamma absorption can be successfully attained by physically immobilizing atomic nuclei in

9177-435: The amount of energy E {\displaystyle E} emitted from Cherenkov radiation, per unit length traveled x {\displaystyle x} and per frequency ω {\displaystyle \omega } . μ ( ω ) {\displaystyle \mu (\omega )} is the permeability and n ( ω ) {\displaystyle n(\omega )}

9310-542: The angular resolution is 0.08 degrees (65% containment radius). The entire array has a peak effective area of 100,000 square meters above 1 TeV. A very weak astrophysical source with a gamma-ray flux only 1% of the Crab Nebula can be detected by VERITAS in under 25 hours of observation. Stronger sources can be detected in significantly less time. In order to distinguish between the background events (i.e. hadronic showers and muons ) or noise (i.e. starlight and moonlight) and

9443-706: The annihilating electron and positron are at rest, each of the resulting gamma rays has an energy of ~ 511 keV and frequency of ~ 1.24 × 10  Hz . Similarly, a neutral pion most often decays into two photons. Many other hadrons and massive bosons also decay electromagnetically. High energy physics experiments, such as the Large Hadron Collider , accordingly employ substantial radiation shielding. Because subatomic particles mostly have far shorter wavelengths than atomic nuclei, particle physics gamma rays are generally several orders of magnitude more energetic than nuclear decay gamma rays. Since gamma rays are at

9576-508: The annihilation of dark matter particles. Most of these searches target the Galactic Center and dwarf spheroidal galaxies . Starting in 2017, the VERITAS science program was expanded to include observations in the optical waveband through high-time-resolution measurements of asteroid occultations and stellar intensity interferometry. As of 2020, VERITAS research had led to 58 Ph.D. 's and more than 100 peer-reviewed publications. As shown in

9709-441: The atmosphere. Gamma rays up to 100 MeV can be emitted by terrestrial thunderstorms, and were discovered by space-borne observatories. This raises the possibility of health risks to passengers and crew on aircraft flying in or near thunderclouds. The most effusive solar flares emit across the entire EM spectrum, including γ-rays. The first confident observation occurred in 1972 . Extraterrestrial, high energy gamma rays include

9842-470: The average 10 seconds. Such relatively long-lived excited nuclei are termed nuclear isomers , and their decays are termed isomeric transitions . Such nuclei have half-lifes that are more easily measurable, and rare nuclear isomers are able to stay in their excited state for minutes, hours, days, or occasionally far longer, before emitting a gamma ray. The process of isomeric transition is therefore similar to any gamma emission, but differs in that it involves

9975-546: The body. These discoveries have led to intense interest around the idea of using this light signal to quantify and/or detect radiation in the body, either from internal sources such as injected radiopharmaceuticals or from external beam radiotherapy in oncology. Radioisotopes such as the positron emitters F and N or beta emitters P or Y have measurable Cherenkov emission and isotopes F and I have been imaged in humans for diagnostic value demonstration. External beam radiation therapy has been shown to induce

10108-482: The bombarded atoms. Such transitions, a form of nuclear gamma fluorescence , form a topic in nuclear physics called gamma spectroscopy . Formation of fluorescent gamma rays are a rapid subtype of radioactive gamma decay. In certain cases, the excited nuclear state that follows the emission of a beta particle or other type of excitation, may be more stable than average, and is termed a metastable excited state, if its decay takes (at least) 100 to 1000 times longer than

10241-399: The camera photomultiplier tubes were upgraded to high-quantum-efficiency tubes, which again increased the sensitivity, especially near the low end of the gamma-ray energy range. Compared to its initial design sensitivity, the actual achieved sensitivity of VERITAS is significantly better with the time required to detect weak gamma-ray sources reduced by more than a factor of two. In June 2017,

10374-496: The cancer often has a higher metabolic rate than the surrounding tissues. The most common gamma emitter used in medical applications is the nuclear isomer technetium-99m which emits gamma rays in the same energy range as diagnostic X-rays. When this radionuclide tracer is administered to a patient, a gamma camera can be used to form an image of the radioisotope's distribution by detecting the gamma radiation emitted (see also SPECT ). Depending on which molecule has been labeled with

10507-496: The cancerous cells. The beams are aimed from different angles to concentrate the radiation on the growth while minimizing damage to surrounding tissues. Gamma rays are also used for diagnostic purposes in nuclear medicine in imaging techniques. A number of different gamma-emitting radioisotopes are used. For example, in a PET scan a radiolabeled sugar called fluorodeoxyglucose emits positrons that are annihilated by electrons, producing pairs of gamma rays that highlight cancer as

10640-660: The collision of pairs of neutron stars, or a neutron star and a black hole . The so-called long-duration gamma-ray bursts produce a total energy output of about 10 joules (as much energy as the Sun will produce in its entire life-time) but in a period of only 20 to 40 seconds. Gamma rays are approximately 50% of the total energy output. The leading hypotheses for the mechanism of production of these highest-known intensity beams of radiation, are inverse Compton scattering and synchrotron radiation from high-energy charged particles. These processes occur as relativistic charged particles leave

10773-514: The concept of VERITAS as a seven telescope array was recommended by the 2000 Decadal Survey in Astronomy and Astrophysics as a moderate-sized project. Delays were incurred due to difficulties with two proposed sites in Arizona (Montosa Canyon at the base of Mount Hopkins and Kitt Peak ) and due to a reduction in available funding. The proposal for a four telescope array (now with 12 m diameter reflectors)

10906-505: The effects had never been experimentally observed. While the speed of light in vacuum is a universal constant ( c = 299,792,458 m/s ), the speed in a material may be significantly less, as it is perceived to be slowed by the medium. For example, in water it is only 0.75 ‍ c . Matter can accelerate to a velocity higher than this (although still less than c , the speed of light in vacuum) during nuclear reactions and in particle accelerators . Cherenkov radiation results when

11039-499: The emission of Cherenkov radiation. The angle takes on a maximum as the particle speed approaches the speed of light. Hence, observed angles of incidence can be used to compute the direction and speed of a Cherenkov radiation-producing charge. Cherenkov radiation can be generated in the eye by charged particles hitting the vitreous humour , giving the impression of flashes, as in cosmic ray visual phenomena and possibly some observations of criticality accidents . Cherenkov radiation

11172-479: The emission of an α or β particle. The daughter nucleus that results is usually left in an excited state. It can then decay to a lower energy state by emitting a gamma ray photon, in a process called gamma decay. The emission of a gamma ray from an excited nucleus typically requires only 10 seconds. Gamma decay may also follow nuclear reactions such as neutron capture , nuclear fission , or nuclear fusion. Gamma decay

11305-422: The emission point along the particle track. This scheme is suitable for low refractive index radiators—i.e. gases—due to the larger radiator length needed to create enough photons. In the more compact proximity-focusing design, a thin radiator volume emits a cone of Cherenkov light which traverses a small distance—the proximity gap—and is detected on the photon detector plane. The image is a ring of light whose radius

11438-553: The emitted electromagnetic waves are constricted to travel the distance x em = v em t = c n t . {\displaystyle x_{\text{em}}=v_{\text{em}}t={\frac {c}{n}}t.} So the emission angle results in cos ⁡ θ = 1 n β {\displaystyle \cos \theta ={\frac {1}{n\beta }}} Cherenkov radiation can also radiate in an arbitrary direction using properly engineered one dimensional metamaterials . The latter

11571-562: The energy of the gamma rays, the thicker the shielding made from the same shielding material is required. Materials for shielding gamma rays are typically measured by the thickness required to reduce the intensity of the gamma rays by one half (the half-value layer or HVL). For example, gamma rays that require 1 cm (0.4 inch) of lead to reduce their intensity by 50% will also have their intensity reduced in half by 4.1 cm of granite rock, 6 cm (2.5 inches) of concrete , or 9 cm (3.5 inches) of packed soil . However,

11704-425: The energy range from a few kilo electronvolts (keV) to approximately 8 megaelectronvolts (MeV), corresponding to the typical energy levels in nuclei with reasonably long lifetimes. The energy spectrum of gamma rays can be used to identify the decaying radionuclides using gamma spectroscopy . Very-high-energy gamma rays in the 100–1000 teraelectronvolt (TeV) range have been observed from astronomical sources such as

11837-555: The enigmatic gamma-ray source at the Galactic Center . Extragalactic sources include active galactic nuclei , starburst galaxies , and gamma-ray bursts . An important component of VERITAS observations is that associated with multi-wavelength and multi-messenger follow up, including fast radio burst (FRB), high energy neutrino , and gravitational wave events. VERITAS has an extensive dark matter program, in which indirect searches are conducted to find VHE gamma rays resulting from

11970-527: The fact that an electron moving in a medium does radiate light even if it is moving uniformly provided that its velocity is greater than the velocity of light in the medium." In the figure on the geometry, the particle (red arrow) travels in a medium with speed v p {\displaystyle v_{\text{p}}} such that c n < v p < c , {\displaystyle {\frac {c}{n}}<v_{\text{p}}<c,} where c {\displaystyle c}

12103-453: The figure, VERITAS has detected 63 astrophysical sources of very high energy gamma rays (as of January 2020). The first VERITAS source catalog had only six sources. Some of the scientific highlights of VERITAS include: VERITAS researchers have also pioneered the use of an IACT to carry out Citizen Science . To improve the detection of muon events, the Muon Hunter project was created on

12236-579: The first three letters of the Greek alphabet: alpha rays as the least penetrating, followed by beta rays, followed by gamma rays as the most penetrating. Rutherford also noted that gamma rays were not deflected (or at least, not easily deflected) by a magnetic field, another property making them unlike alpha and beta rays. Gamma rays were first thought to be particles with mass, like alpha and beta rays. Rutherford initially believed that they might be extremely fast beta particles, but their failure to be deflected by

12369-405: The frequencies corresponding to core electronic transitions in a material, as the index of refraction is often greater than 1 just below a resonant frequency (see Kramers–Kronig relation and Anomalous dispersion ) . As in sonic booms and bow shocks, the angle of the shock cone is directly related to the velocity of the disruption. The Cherenkov angle is zero at the threshold velocity for

12502-423: The gamma emission spectrum is complex, revealing that a series of nuclear energy levels exist. Gamma rays are produced in many processes of particle physics . Typically, gamma rays are the products of neutral systems which decay through electromagnetic interactions (rather than a weak or strong interaction). For example, in an electron–positron annihilation , the usual products are two gamma ray photons. If

12635-462: The gamma ray background produced when cosmic rays (either high speed electrons or protons) collide with ordinary matter, producing pair-production gamma rays at 511 keV. Alternatively, bremsstrahlung are produced at energies of tens of MeV or more when cosmic ray electrons interact with nuclei of sufficiently high atomic number (see gamma ray image of the Moon near the end of this article, for illustration). The gamma ray sky (see illustration at right)

12768-409: The ground had it not interacted. The energy of the primary particle is determined from the total amount of Cherenkov light measured in each telescope, along with the distance of that telescope from the shower core. Each of the individual telescopes has a 12 m diameter aperture and a 3.5 degree field of view. The telescopes are built on a Davies-Cotton optical design, which uses a spherical reflector and

12901-599: The highest sensitivity in the 100 GeV – 10 TeV band (with sensitivity from 50 GeV to up to 50 TeV). This very high energy observatory, completed in 2007, effectively complements the Large Area Telescope (LAT) of the Fermi Gamma-ray Space Telescope due to its larger collection area as well as coverage in a higher energy band. VERITAS is constructed of four 12 m diameter Imaging Atmospheric Cherenkov Telescopes with an approximate separation of 100 m (330 ft) between each adjacent telescope. Each telescope comprises

13034-421: The incoming shower is determined by finding the central axis of the spread of the shower on each telescope and tracing those axes until they cross. The intersection of these axes determines the incoming direction of the primary particle (cosmic ray or gamma ray) that initiated the air shower in the upper atmosphere. It also determines the shower core position, i.e. the extrapolated position of the primary particle on

13167-494: The intermediate metastable excited state(s) of the nuclei. Metastable states are often characterized by high nuclear spin , requiring a change in spin of several units or more with gamma decay, instead of a single unit transition that occurs in only 10 seconds. The rate of gamma decay is also slowed when the energy of excitation of the nucleus is small. An emitted gamma ray from any type of excited state may transfer its energy directly to any electrons , but most probably to one of

13300-551: The latter term became generally accepted. A gamma decay was then understood to usually emit a gamma photon. Natural sources of gamma rays on Earth include gamma decay from naturally occurring radioisotopes such as potassium-40 , and also as a secondary radiation from various atmospheric interactions with cosmic ray particles. Natural terrestrial sources that produce gamma rays include lightning strikes and terrestrial gamma-ray flashes , which produce high energy emissions from natural high-energy voltages. Gamma rays are produced by

13433-593: The luminous radiation of radium irradiating water having a continuous spectrum. In 2019, a team of researchers from Dartmouth's and Dartmouth-Hitchcock 's Norris Cotton Cancer Center discovered Cherenkov light being generated in the vitreous humor of patients undergoing radiotherapy . The light was observed using a camera imaging system called a CDose, which is specially designed to view light emissions from biological systems. For decades, patients had reported phenomena such as "flashes of bright or blue light" when receiving radiation treatments for brain cancer, but

13566-402: The mass of this much concrete or soil is only 20–30% greater than that of lead with the same absorption capability. Depleted uranium is sometimes used for shielding in portable gamma ray sources , due to the smaller half-value layer when compared to lead (around 0.6 times the thickness for common gamma ray sources, i.e. Iridium-192 and Cobalt-60) and cheaper cost compared to tungsten . In

13699-623: The material (atomic density) and σ the absorption cross section in cm . As it passes through matter, gamma radiation ionizes via three processes: The secondary electrons (and/or positrons) produced in any of these three processes frequently have enough energy to produce much ionization themselves. Additionally, gamma rays, particularly high energy ones, can interact with atomic nuclei resulting in ejection of particles in photodisintegration , or in some cases, even nuclear fission ( photofission ). High-energy (from 80 GeV to ~10 TeV ) gamma rays arriving from far-distant quasars are used to estimate

13832-405: The medium rather than in front of it (as is the case in normal materials with, both permittivity and permeability positive). One can also obtain such reverse-cone Cherenkov radiation in non-metamaterial periodic media where the periodic structure is on the same scale as the wavelength, so it cannot be treated as an effectively homogeneous metamaterial. The Cherenkov effect can occur in vacuum. In

13965-435: The molecules re-emit the energy given to them to achieve excitation as photons. These photons form the spherical wavefronts which can be seen originating from the moving particle. If v p < c / n {\displaystyle v_{\text{p}}<c/n} , that is the velocity of the charged particle is less than that of the speed of light in the medium, then the polarization field which forms around

14098-403: The moving particle is usually symmetric. The corresponding emitted wavefronts may be bunched up, but they do not coincide or cross, and there are therefore no interference effects to consider. In the reverse situation, i.e. v p > c / n {\displaystyle v_{\text{p}}>c/n} , the polarization field is asymmetric along the direction of motion of

14231-437: The origin of cosmic rays ) and beyond our Galaxy, probing extreme environments near compact objects such as neutron stars and black holes , the nature of dark matter and the intergalactic magnetic field, and whether the speed of light is constant at these extreme gamma-ray energies. The VERITAS observational program includes Galactic sources such as supernova remnants , pulsars , pulsar wind nebulae , binary systems and

14364-445: The particle velocity. In their original work on the theoretical foundations of Cherenkov radiation, Tamm and Frank wrote, "This peculiar radiation can evidently not be explained by any common mechanism such as the interaction of the fast electron with individual atom or as radiative scattering of electrons on atomic nuclei. On the other hand, the phenomenon can be explained both qualitatively and quantitatively if one takes into account

14497-419: The particle, as the particles of the medium do not have enough time to recover to their "normal" randomized states. This results in overlapping waveforms (as in the animation) and constructive interference leads to an observed cone-like light signal at a characteristic angle: Cherenkov light. A common analogy is the sonic boom of a supersonic aircraft . The sound waves generated by the aircraft travel at

14630-424: The probability for absorption is proportional to the thickness of the layer, the density of the material, and the absorption cross section of the material. The total absorption shows an exponential decrease of intensity with distance from the incident surface: where x is the thickness of the material from the incident surface, μ= n σ is the absorption coefficient, measured in cm , n the number of atoms per cm of

14763-471: The process). One example of gamma ray production due to radionuclide decay is the decay scheme for cobalt-60, as illustrated in the accompanying diagram. First, Co decays to excited Ni by beta decay emission of an electron of 0.31  MeV . Then the excited Ni decays to the ground state (see nuclear shell model ) by emitting gamma rays in succession of 1.17 MeV followed by 1.33 MeV . This path

14896-466: The properties of semi-precious stones , and is often used to change white topaz into blue topaz . Non-contact industrial sensors commonly use sources of gamma radiation in refining, mining, chemicals, food, soaps and detergents, and pulp and paper industries, for the measurement of levels, density, and thicknesses. Gamma-ray sensors are also used for measuring the fluid levels in water and oil industries. Typically, these use Co-60 or Cs-137 isotopes as

15029-553: The quasar, and subjected to inverse Compton scattering, synchrotron radiation , or bremsstrahlung, are the likely source of the gamma rays from those objects. It is thought that a supermassive black hole at the center of such galaxies provides the power source that intermittently destroys stars and focuses the resulting charged particles into beams that emerge from their rotational poles. When those beams interact with gas, dust, and lower energy photons they produce X-rays and gamma rays. These sources are known to fluctuate with durations of

15162-538: The radiation source. In the US, gamma ray detectors are beginning to be used as part of the Container Security Initiative (CSI). These machines are advertised to be able to scan 30 containers per hour. Gamma radiation is often used to kill living organisms, in a process called irradiation . Applications of this include the sterilization of medical equipment (as an alternative to autoclaves or chemical means),

15295-638: The rarer gamma-ray burst sources of gamma rays. Pulsars have relatively long-lived magnetic fields that produce focused beams of relativistic speed charged particles, which emit gamma rays (bremsstrahlung) when those strike gas or dust in their nearby medium, and are decelerated. This is a similar mechanism to the production of high-energy photons in megavoltage radiation therapy machines (see bremsstrahlung ). Inverse Compton scattering , in which charged particles (usually electrons) impart energy to low-energy photons boosting them to higher energy photons. Such impacts of photons on relativistic charged particle beams

15428-400: The ratio between the speed of the particle and the speed of light as β = v p c . {\displaystyle \beta ={\frac {v_{\text{p}}}{c}}.} The emitted light waves (denoted by blue arrows) travel at speed v em = c n . {\displaystyle v_{\text{em}}={\frac {c}{n}}.} The left corner of

15561-523: The region of the event horizon of a newly formed black hole created during supernova explosion. The beam of particles moving at relativistic speeds are focused for a few tens of seconds by the magnetic field of the exploding hypernova . The fusion explosion of the hypernova drives the energetics of the process. If the narrowly directed beam happens to be pointed toward the Earth, it shines at gamma ray frequencies with such intensity, that it can be detected even at distances of up to 10 billion light years, which

15694-422: The removal of decay-causing bacteria from many foods and the prevention of the sprouting of fruit and vegetables to maintain freshness and flavor. Despite their cancer-causing properties, gamma rays are also used to treat some types of cancer , since the rays also kill cancer cells. In the procedure called gamma-knife surgery, multiple concentrated beams of gamma rays are directed to the growth in order to kill

15827-556: The rest is emitted as electromagnetic waves of all frequencies, including radio waves. The most intense sources of gamma rays, are also the most intense sources of any type of electromagnetic radiation presently known. They are the "long duration burst" sources of gamma rays in astronomy ("long" in this context, meaning a few tens of seconds), and they are rare compared with the sources discussed above. By contrast, "short" gamma-ray bursts of two seconds or less, which are not associated with supernovae, are thought to produce gamma rays during

15960-458: The sensitivity of the human eye peaks at green, and is very low in the violet portion of the spectrum. There is a cut-off frequency above which the equation cos ⁡ θ = 1 / ( n β ) {\displaystyle \cos \theta =1/(n\beta )} can no longer be satisfied. The refractive index n {\displaystyle n} varies with frequency (and hence with wavelength) in such

16093-792: The shortest wavelength electromagnetic waves, typically shorter than those of X-rays . With frequencies above 30 exahertz ( 3 × 10  Hz ) and wavelengths less than 10 picometers ( 1 × 10  m ), gamma ray photons have the highest photon energy of any form of electromagnetic radiation. Paul Villard , a French chemist and physicist , discovered gamma radiation in 1900 while studying radiation emitted by radium . In 1903, Ernest Rutherford named this radiation gamma rays based on their relatively strong penetration of matter ; in 1900, he had already named two less penetrating types of decay radiation (discovered by Henri Becquerel ) alpha rays and beta rays in ascending order of penetrating power. Gamma rays from radioactive decay are in

16226-554: The signing of a teaming agreement in 2000 between nine member institutions in three countries. The member institutions were: Iowa State University , Purdue University , Smithsonian Astrophysical Observatory , University of California, Los Angeles , University of Chicago , University of Utah , and Washington University in St. Louis in the U.S., University of Leeds in the U.K. and National University of Ireland Dublin in Ireland. A tenth member institution, McGill University in Canada,

16359-430: The speed of sound, which is slower than the aircraft, and cannot propagate forward from the aircraft, instead forming a conical shock front . In a similar way, a charged particle can generate a "shock wave" of visible light as it travels through an insulator. The velocity that must be exceeded is the phase velocity of light rather than the group velocity of light. The phase velocity can be altered dramatically by using

16492-427: The targeted data (i.e. electromagnetic showers produced by gamma rays), VERITAS uses a three-level trigger system. Level one corresponds to a level crossing on each pixel using constant fraction discriminators . Level two is a pattern selection trigger, which selects photon-like showers, which have compact shapes, and eliminates most of the background showers, which produce more random shapes in each camera. Level three

16625-509: The three types of genotoxic activity. Another study studied the effects of acute ionizing gamma radiation in rats, up to 10 Gy , and who ended up showing acute oxidative protein damage, DNA damage, cardiac troponin T carbonylation, and long-term cardiomyopathy . The natural outdoor exposure in the United Kingdom ranges from 0.1 to 0.5 μSv/h with significant increase around known nuclear and contaminated sites. Natural exposure to gamma rays

16758-809: The top of the electromagnetic spectrum in terms of energy, all extremely high-energy photons are gamma rays; for example, a photon having the Planck energy would be a gamma ray. A few gamma rays in astronomy are known to arise from gamma decay (see discussion of SN1987A ), but most do not. Photons from astrophysical sources that carry energy in the gamma radiation range are often explicitly called gamma-radiation. In addition to nuclear emissions, they are often produced by sub-atomic particle and particle-photon interactions. Those include electron-positron annihilation , neutral pion decay , bremsstrahlung , inverse Compton scattering , and synchrotron radiation . In October 2017, scientists from various European universities proposed

16891-523: The total stopping power. Because of this, a lead (high Z ) shield is 20–30% better as a gamma shield than an equal mass of another low- Z shielding material, such as aluminium, concrete, water, or soil; lead's major advantage is not in lower weight, but rather its compactness due to its higher density. Protective clothing, goggles and respirators can protect from internal contact with or ingestion of alpha or beta emitting particles, but provide no protection from gamma radiation from external sources. The higher

17024-446: The tracer, such techniques can be employed to diagnose a wide range of conditions (for example, the spread of cancer to the bones via bone scan ). Gamma rays cause damage at a cellular level and are penetrating, causing diffuse damage throughout the body. However, they are less ionising than alpha or beta particles, which are less penetrating. Low levels of gamma rays cause a stochastic health risk, which for radiation dose assessment

17157-405: The triangle represents the location of the superluminal particle at some initial moment ( t = 0 ). The right corner of the triangle is the location of the particle at some later time t. In the given time t , the particle travels the distance x p = v p t = β c t {\displaystyle x_{\text{p}}=v_{\text{p}}t=\beta \,ct} whereas

17290-472: The use of an imaging Cherenkov camera, coupled with a large 10 m diameter reflector, to make the first definitive detection of a VHE gamma-ray source, the Crab Nebula in 1989. Subsequently, the HEGRA telescope on La Palma demonstrated good sensitivity above 1 TeV using an array of imaging atmospheric Cherenkov telescopes. VERITAS combines the benefits of stereoscopic observations in an array with large reflectors for

17423-827: Was added with an updated agreement in 2008. Representatives from the member institutions form the VERITAS Executive Council (VEC), that serves as the ultimate decision-making authority within the collaboration. In 2008, the collaboration was enlarged by the addition of collaborating institutions that have representation on the VERITAS Science Board, that directs the science program of VERITAS. The initial collaborating institutions were: Adler Planetarium , Barnard College , Cork Institute of Technology , DePauw University , Galway-Mayo Institute of Technology , Grinnell College , National University of Ireland, Galway , University of California, Santa Cruz , University of Iowa and University of Massachusetts, Amherst . As of 2019,

17556-427: Was favorably reviewed in 2002 and construction of VERITAS started in 2003 at the Fred Lawrence Whipple Observatory . An initial prototype telescope was completed as Telescope #1 and saw first light in 2004. The construction of Telescope #2 was completed in 2005 and first stereo observations started that year. Telescopes #3 and #4 were completed by early 2007 and the first light celebration for the full for telescope array

17689-519: Was on 27-28 April 2007. Regular science operations for VERITAS started in September 2007. The construction of VERITAS was largely funded in the U.S. by Department of Energy , the National Science Foundation , and the Smithsonian Institution . Additional construction funding was provided by Enterprise Ireland (now Science Foundation Ireland ) and the Particle Physics and Astronomy Research Council in

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