93-475: The Cherenkov Telescope Array , or CTA , is a multinational, worldwide project to build a new generation of ground-based gamma-ray instruments in the energy range extending from some tens of GeV to about 300 TeV . It is proposed as an open observatory and will consist of two arrays of imaging atmospheric Cherenkov telescopes (IACT), a first array at the Northern Hemisphere with emphasis on
186-462: 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
279-455: 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
372-456: A corresponding point on the rotational axis of the galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses , which is called Sagittarius A* , a compact radio source which is almost exactly at the galactic rotational center. The Galactic Center is approximately 8 kiloparsecs (26,000 ly) away from Earth in the direction of the constellations Sagittarius , Ophiuchus , and Scorpius , where
465-438: 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
558-415: 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
651-478: 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
744-448: 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 ,
837-455: 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
930-457: 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
1023-408: 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,
SECTION 10
#17327731562391116-554: 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
1209-481: A prominent Galactic bar. The bar may be surrounded by a ring called the 5- kpc ring that contains a large fraction of the molecular hydrogen present in the Milky Way, and most of the Milky Way's star formation activity. Viewed from the Andromeda Galaxy , it would be the brightest feature of the Milky Way. The complex astronomical radio source Sagittarius A appears to be located almost exactly at
1302-523: A search for the center with the 100-inch (250 cm) Hooker Telescope . He found that near the star Alnasl (Gamma Sagittarii), there is a one-degree-wide void in the interstellar dust lanes, which provides a relatively clear view of the swarms of stars around the nucleus of the Milky Way Galaxy. This gap has been known as Baade's Window ever since. At Dover Heights in Sydney, Australia,
1395-533: A team of radio astronomers from the Division of Radiophysics at the CSIRO , led by Joseph Lade Pawsey , used " sea interferometry " to discover some of the first interstellar and intergalactic radio sources, including Taurus A , Virgo A and Centaurus A . By 1954 they had built an 80-foot (24 m) fixed dish antenna and used it to make a detailed study of an extended, extremely powerful belt of radio emission that
1488-412: Is a "hole", or core , around the black hole. Several suggestions have been put forward to explain this puzzling observation, but none is completely satisfactory. For instance, although the black hole would eat stars near it, creating a region of low density, this region would be much smaller than a parsec. Because the observed stars are a fraction of the total number, it is theoretically possible that
1581-454: Is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei . It consists of 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 ,
1674-521: 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. Galactic Center The Galactic Center is the barycenter of the Milky Way and
1767-403: 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
1860-620: 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
1953-448: 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
SECTION 20
#17327731562392046-403: 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
2139-446: 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
2232-427: 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
2325-427: Is designed to detect gamma rays over a larger area and a wider range of views, with more than 100 telescopes located in the northern and southern hemispheres. At least three classes of telescopes are required to cover the full CTA energy range (20 GeV to 300 TeV): Large-Sized Telescope (LST), Medium-Sized Telescope (MST), and Small-Sized Telescope (SST). The project to build CTA is well advanced: prototypes exist for all
2418-404: 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
2511-491: Is even stronger for stars that are on very tight orbits around Sagittarius A*, such as S2 and S0-102 . The scenarios invoked to explain this formation involve either star formation in a massive star cluster offset from the Galactic Center that would have migrated to its current location once formed, or star formation within a massive, compact gas accretion disk around the central black-hole. Current evidence favors
2604-419: 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 ),
2697-522: Is hindered by numerous effects, which include: an ambiguous reddening law ; a bias for smaller values of the distance to the Galactic Center because of a preferential sampling of stars toward the near side of the Galactic bulge owing to interstellar extinction ; and an uncertainty in characterizing how a mean distance to a group of variable stars found in the direction of the Galactic bulge relates to
2790-414: 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
2883-678: Is on the roadmaps for the Aspera European Astroparticle network and Astronet . The cost for baseline design of the project is estimated at €300 million (US$ 350 million). As of December 2018, the CTA consortium includes more than 1,420 members from 210 institutes in 31 countries: Armenia, Australia, Austria, Brazil, Bulgaria, Canada, Chile, Croatia, Czech Republic, Finland, France, Germany, Greece, India, Ireland, Italy, Japan, Mexico, Namibia, Netherlands, Norway, Poland, Slovenia, South Africa, Spain, Sweden, Switzerland, Thailand,
Cherenkov Telescope Array - Misplaced Pages Continue
2976-408: 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
3069-499: 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
3162-673: 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
3255-601: The Max Planck Institute for Extraterrestrial Physics in Germany using Chilean telescopes have confirmed the existence of a supermassive black hole at the Galactic Center, on the order of 4.3 million solar masses . Later studies have estimated a mass of 3.7 million or 4.1 million solar masses. On 5 January 2015, NASA reported observing an X-ray flare 400 times brighter than usual, a record-breaker, from Sagittarius A*. The unusual event may have been caused by
3348-609: The Solar System and the Galactic Center is not certain, although estimates since 2000 have remained within the range 24–28.4 kilolight-years (7.4–8.7 kiloparsecs ). The latest estimates from geometric-based methods and standard candles yield the following distances to the Galactic Center: An accurate determination of the distance to the Galactic Center as established from variable stars (e.g. RR Lyrae variables ) or standard candles (e.g. red-clump stars)
3441-455: 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
3534-459: 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)
3627-528: The Galactic Center and contains an intense compact radio source, Sagittarius A* , which coincides with a supermassive black hole at the center of the Milky Way. Accretion of gas onto the black hole , probably involving an accretion disk around it, would release energy to power the radio source, itself much larger than the black hole. A study in 2008 which linked radio telescopes in Hawaii, Arizona and California ( Very-long-baseline interferometry ) measured
3720-411: The Galactic Center is also rich in massive stars . More than 100 OB and Wolf–Rayet stars have been identified there so far. They seem to have all been formed in a single star formation event a few million years ago. The existence of these relatively young stars was a surprise to experts, who expected the tidal forces from the central black hole to prevent their formation. This paradox of youth
3813-657: The Galactic Center, although the Circumnuclear Disk of molecular gas that orbits the Galactic Center at two parsecs seems a fairly favorable site for star formation. Work presented in 2002 by Antony Stark and Chris Martin mapping the gas density in a 400- light-year region around the Galactic Center has revealed an accumulating ring with a mass several million times that of the Sun and near the critical density for star formation . They predict that in approximately 200 million years, there will be an episode of starburst in
Cherenkov Telescope Array - Misplaced Pages Continue
3906-433: The Galactic Center, with many stars forming rapidly and undergoing supernovae at a hundred times the current rate. This starburst may also be accompanied by the formation of galactic relativistic jets , as matter falls into the central black hole . It is thought that the Milky Way undergoes a starburst of this sort every 500 million years. In addition to the paradox of youth, there is a "conundrum of old age" associated with
3999-462: The Galactic Center. The galaxy's diffuse gamma-ray fog hampered prior observations, but the discovery team led by D. Finkbeiner, building on research by G. Dobler, worked around this problem. The 2014 Bruno Rossi Prize went to Tracy Slatyer , Douglas Finkbeiner , and Meng Su "for their discovery, in gamma rays, of the large unanticipated Galactic structure called the Fermi bubbles ". The origin of
4092-581: The Heavens (1755) that a large star was at the center of the Milky Way Galaxy, and that Sirius might be the star. Harlow Shapley stated in 1918 that the halo of globular clusters surrounding the Milky Way seemed to be centered on the star swarms in the constellation of Sagittarius, but the dark molecular clouds in the area blocked the view for optical astronomy. In the early 1940s Walter Baade at Mount Wilson Observatory took advantage of wartime blackout conditions in nearby Los Angeles, to conduct
4185-529: The IAC to host CTA's northern-hemisphere array. On 19 December 2018, final agreements were signed for the southern array as well. CTA's northern hemisphere site is located on the existing site of the IAC's Roque de los Muchachos Observatory on the island of La Palma, the fifth largest island in the Canary Islands. At 2,200 metres of altitude and nestled on a plateau below the rim of an extinct volcanic crater,
4278-420: 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
4371-543: The Milky Way appears brightest, visually close to the Butterfly Cluster (M6) or the star Shaula , south to the Pipe Nebula . There are around 10 million stars within one parsec of the Galactic Center, dominated by red giants , with a significant population of massive supergiants and Wolf–Rayet stars from star formation in the region around 1 million years ago. The core stars are a small part within
4464-987: The United Kingdom, Ukraine, and the United States. On 15 and 16 July 2015, the CTA decided to enter into detailed contract negotiations for hosting CTA at the European Southern Observatory (ESO) of Paranal Observatory , in Chile, and at the Instituto de Astrofisica de Canarias (IAC), Roque de los Muchachos Observatory in La Palma, Spain. On 19 September 2016, the Council of the Cherenkov Telescope Array Observatory (CTAO) concluded negotiations with
4557-500: 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
4650-715: 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
4743-441: 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
SECTION 50
#17327731562394836-470: 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
4929-482: 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
5022-480: The breaking apart of an asteroid falling into the black hole or by the entanglement of magnetic field lines within gas flowing into Sagittarius A*, according to astronomers. In November 2010, it was announced that two large elliptical lobe structures of energetic plasma , termed bubbles , which emit gamma- and X-rays, were detected astride the Milky Way galaxy's core. Termed Fermi or eRosita bubbles, they extend up to about 25,000 light years above and below
5115-615: The bubbles is being researched. The bubbles are connected and seemingly coupled, via energy transport, to the galactic core by columnar structures of energetic plasma termed chimneys . In 2020, for the first time, the lobes were seen in visible light and optical measurements were made. By 2022, detailed computer simulations further confirmed that the bubbles were caused by the Sagittarius A* black hole. The central cubic parsec around Sagittarius A* contains around 10 million stars . Although most of them are old red giant stars ,
5208-496: 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
5301-496: 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
5394-615: 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
5487-458: The diameter of Sagittarius A* to be 44 million kilometers (0.3 AU ). For comparison, the radius of Earth's orbit around the Sun is about 150 million kilometers (1.0 AU ), whereas the distance of Mercury from the Sun at closest approach ( perihelion ) is 46 million kilometers (0.3 AU). Thus, the diameter of the radio source is slightly less than the distance from Mercury to the Sun. Scientists at
5580-469: The distance to the Galactic Center. The nature of the Milky Way's bar , which extends across the Galactic Center, is also actively debated, with estimates for its half-length and orientation spanning between 1–5 kpc (short or a long bar) and 10–50°. Certain authors advocate that the Milky Way features two distinct bars, one nestled within the other. The bar is delineated by red-clump stars (see also red giant ); however, RR Lyrae variables do not trace
5673-409: The distribution of the old stars at the Galactic Center. Theoretical models had predicted that the old stars—which far outnumber young stars—should have a steeply-rising density near the black hole, a so-called Bahcall–Wolf cusp . Instead, it was discovered in 2009 that the density of the old stars peaks at a distance of roughly 0.5 parsec from Sgr A*, then falls inward: instead of a dense cluster, there
SECTION 60
#17327731562395766-479: 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
5859-562: 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,
5952-425: 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
6045-583: 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
6138-423: 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
6231-513: 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)
6324-539: The impact of high-energy particles in the evolution of cosmic systems and to gain insight into the most extreme and unusual phenomena in the Universe. It will also search for annihilating dark matter particles and deviations from Einstein's theory of special relativity , even conducting a census of particle acceleration in the Universe. Research at the CTA will seek to address questions in and beyond astrophysics that fall under three major themes of study: understanding
6417-494: 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
6510-551: 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
6603-466: The latter theory, as formation through a large accretion disk is more likely to lead to the observed discrete edge of the young stellar cluster at roughly 0.5 parsec. Most of these 100 young, massive stars seem to be concentrated within one or two disks, rather than randomly distributed within the central parsec. This observation however does not allow definite conclusions to be drawn at this point. Star formation does not seem to be occurring currently at
6696-402: 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
6789-623: 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
6882-518: The much wider galactic bulge . Because of interstellar dust along the line of sight, the Galactic Center cannot be studied at visible , ultraviolet , or soft (low-energy) X-ray wavelengths . The available information about the Galactic Center comes from observations at gamma ray , hard (high-energy) X-ray, infrared , submillimetre, and radio wavelengths. Immanuel Kant stated in Universal Natural History and Theory of
6975-468: The origin and role of relativistic cosmic particles, probing extreme environments, and exploring frontiers in lhysics. To address these themes, CTA will observe the following key targets: Galactic Center , Large Magellanic Cloud , Galactic Plane, galaxy clusters, cosmic ray PeVatrons, star-forming systems, active galactic nuclei , and transient phenomena. Gamma-ray A gamma ray , also known as gamma radiation (symbol γ ),
7068-424: 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
7161-471: 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
7254-466: 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
7347-530: The proposed telescope designs, and significant site characterization and preparations are underway. An intergovernmental agreement for construction and subsequent operation of the observatory—a European Research Infrastructure Consortium (ERIC)—is in preparation, and the financial threshold is expected to be reached in 2019. The project was promoted to a landmark on the roadmap of the European Strategy Forum on Research Infrastructures (ESFRI) and
7440-553: 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
7533-553: 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),
7626-638: 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
7719-523: 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
7812-422: 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
7905-556: 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
7998-582: The site currently hosts an operating gamma-ray observatory, the Major Atmospheric Gamma Ray Imaging Cherenkov (MAGIC) telescopes, as well as a variety of optical telescopes of various sizes. CTA will look at higher-energy photons than ever measured before. Its cosmic particle accelerators can reach energies inaccessible to such accelerators as the Large Hadron Collider. CTA will seek to understand
8091-682: The study of extragalactic objects at the lowest possible energies, and a second array at the Southern Hemisphere , which is to cover the full energy range and concentrate on galactic sources. The physics program of CTA goes beyond high-energy astrophysics into cosmology and fundamental physics. Building on the technology of current-generation ground-based gamma-ray detectors ( MAGIC , HESS , and VERITAS ), CTA will be ten times more sensitive and have unprecedented accuracy in its detection of high-energy gamma rays. Current gamma-ray telescope arrays host up to five individual telescopes, but CTA
8184-475: The system of galactic latitude and longitude . In the equatorial coordinate system the location is: RA 17 45 40.04 , Dec −29° 00′ 28.1″ ( J2000 epoch ). In July 2022, astronomers reported the discovery of massive amounts of prebiotic molecules , including some associated with RNA , in the Galactic Center of the Milky Way Galaxy . The exact distance between
8277-452: 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
8370-813: 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
8463-523: 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
8556-446: 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
8649-606: Was detected in Sagittarius. They named an intense point-source near the center of this belt Sagittarius A , and realised that it was located at the very center of the Galaxy, despite being some 32 degrees south-west of the conjectured galactic center of the time. In 1958 the International Astronomical Union (IAU) decided to adopt the position of Sagittarius A as the true zero coordinate point for
#238761