J. Paul Getty Museum
The J. Paul Getty Museum referred to as the Getty, is an art museum in California housed on two campuses: the Getty Center and Getty Villa; the two locations received over two million visitors in 2016. The primary museum, the Getty Center, is located in Brentwood neighborhood of Los Angeles, on a hill top above the west side of the Sepulveda Pass and I-405 freeway, its collection features Western art from the Middle Ages to the present. The secondary museum, the Getty Villa, is in the Malibu neighborhood and displays art from Ancient Greece and Etruria. In 1974, J. Paul Getty opened a museum in a re-creation of the Villa of the Papyri at Herculaneum on his property in Malibu, California. In 1982, the museum became the richest in the world. In 1983, after an economic downturn in what was West Germany, the Getty Museum acquired 144 illuminated medieval manuscripts from the financially struggling Ludwig Collection in Aachen. In 1997, the museum moved to its current location in the Brentwood neighborhood of Los Angeles.
A suite of interactive multimedia tools called GettyGuide allows visitors to access information about exhibitions. Within the Museum, the GettyGuide multimedia player provides commentary from curators and conservators on many works of art. In the 1970s and 1980s, the curator, Jiří Frel, designed a tax manipulation scheme which expanded the museum collection of antiquities buying artifacts of dubious provenance, as well as a number of artifacts considered fakes, such as the Getty kouros. In 1984, Frel was demoted, in 1986, he resigned; the Getty is involved in a controversy regarding proper title to some of the artwork in its collection. The museum's previous curator of antiquities, Marion True, was indicted in Italy in 2005 on criminal charges relating to trafficking in stolen antiquities. Similar charges have been addressed by the Greek authorities; the primary evidence in the case came from the 1995 raid of a Geneva, warehouse which had contained a fortune in stolen artifacts. Italian art dealer Giacomo Medici was arrested in 1997.
In 2005 True was forced to tender her resignation by the Board of Trustees, which announced her early retirement. Italy allowed the statute of limitations of the charges filed against her to expire in October 2010. In a letter to the J. Paul Getty Trust on December 18, 2006, True stated that she was being made to "carry the burden" for practices which were known and condoned by the Getty's Board of Directors. True is under investigation by Greek authorities over the acquisition of a 2,500-year-old funerary wreath; the wreath, along with a 6th-century BC statue of a woman, have been returned to Greece and are exhibited at the Archaeological Museum of Thessaloniki. On November 20, 2006, the director of the museum, Michael Brand, announced that 26 disputed pieces were to be returned to Italy, but not the Victorious Youth, still claimed by the Italian authorities. In 2007, the Los Angeles J. Paul Getty Museum was forced to return 40 artifacts, including a 5th-century BC statue of the goddess Aphrodite, looted from Morgantina, an ancient Greek settlement in Sicily.
The Getty Museum resisted the requests of the Italian government for nearly two decades, only to admit that "there might be'problems'" attached to the acquisition." In 2006, Italian senior cultural official Giuseppe Proietti said: "The negotiations haven't made a single step forward." Only after he suggested the Italian government "to take cultural sanctions against the Getty, suspending all cultural cooperation," did the J. Paul Getty Museum return the antiquities. In another unrelated case in 1999, the Getty Museum had to hand over three antiquities to Italy after determining they were stolen; the objects included a Greek red-figure kylix from the 5th-century BC, signed by the painter Onesimos and the potter Euphronios as potter, looted from the Etruscan site of Cerveteri. In 2016, the terracotta head of the Greek god Hades was returned to Sicily; the archaeological artifact was looted from Morgantina in the 1970s. The Getty museum purchased the terracotta head of Hades in 1985 from the New York collector Maurice Tempelsman, who had purchased it from the London dealer Robin Symes.
Getty records show. On December 21, 2016, the head of Hades was added to the collection of the archaeological museum of Aidone, where it joined the statue of Demeter, the mother of his consort Persephone. Sicilian archaeologists found a blue curl, missing from Hades' beard, so it proved the origin of the terracotta head. Getty Conservation Institute Getty Foundation Getty Research Institute
Los Angeles the City of Los Angeles and known by its initials L. A. is the most populous city in California, the second most populous city in the United States, after New York City, the third most populous city in North America. With an estimated population of four million, Los Angeles is the cultural and commercial center of Southern California; the city is known for its Mediterranean climate, ethnic diversity and the entertainment industry, its sprawling metropolis. Los Angeles is the largest city on the West Coast of North America. Los Angeles is in a large basin bounded by the Pacific Ocean on one side and by mountains as high as 10,000 feet on the other; the city proper, which covers about 469 square miles, is the seat of Los Angeles County, the most populated county in the country. Los Angeles is the principal city of the Los Angeles metropolitan area, the second largest in the United States after that of New York City, with a population of 13.1 million. It is part of the Los Angeles-Long Beach combined statistical area the nation's second most populous area with a 2015 estimated population of 18.7 million.
Los Angeles is one of the most substantial economic engines within the United States, with a diverse economy in a broad range of professional and cultural fields. Los Angeles is famous as the home of Hollywood, a major center of the world entertainment industry. A global city, it has been ranked 6th in the Global Cities Index and 9th in the Global Economic Power Index; the Los Angeles metropolitan area has a gross metropolitan product of $1.044 trillion, making it the third-largest in the world, after the Tokyo and New York metropolitan areas. Los Angeles hosted the 1932 and 1984 Summer Olympics and will host the event for a third time in 2028; the city hosted the Miss Universe pageant twice, in 1990 and 2006, was one of 9 American cities to host the 1994 FIFA men's soccer World Cup and one of 8 to host the 1999 FIFA women's soccer World Cup, hosting the final match for both tournaments. Home to the Chumash and Tongva, Los Angeles was claimed by Juan Rodríguez Cabrillo for Spain in 1542 along with the rest of what would become Alta California.
The city was founded on September 4, 1781, by Spanish governor Felipe de Neve. It became a part of Mexico in 1821 following the Mexican War of Independence. In 1848, at the end of the Mexican–American War, Los Angeles and the rest of California were purchased as part of the Treaty of Guadalupe Hidalgo, becoming part of the United States. Los Angeles was incorporated as a municipality on April 4, 1850, five months before California achieved statehood; the discovery of oil in the 1890s brought rapid growth to the city. The completion of the Los Angeles Aqueduct in 1913, delivering water from Eastern California assured the city's continued rapid growth; the Los Angeles coastal area was settled by the Chumash tribes. A Gabrieleño settlement in the area was called iyáangẚ, meaning "poison oak place". Maritime explorer Juan Rodríguez Cabrillo claimed the area of southern California for the Spanish Empire in 1542 while on an official military exploring expedition moving north along the Pacific coast from earlier colonizing bases of New Spain in Central and South America.
Gaspar de Portolà and Franciscan missionary Juan Crespí, reached the present site of Los Angeles on August 2, 1769. In 1771, Franciscan friar Junípero Serra directed the building of the Mission San Gabriel Arcángel, the first mission in the area. On September 4, 1781, a group of forty-four settlers known as "Los Pobladores" founded the pueblo they called El Pueblo de Nuestra Señora la Reina de los Ángeles,'The Town of Our Lady the Queen of the Angels'; the present-day city has the largest Roman Catholic Archdiocese in the United States. Two-thirds of the Mexican or settlers were mestizo or mulatto, a mixture of African and European ancestry; the settlement remained a small ranch town for decades, but by 1820, the population had increased to about 650 residents. Today, the pueblo is commemorated in the historic district of Los Angeles Pueblo Plaza and Olvera Street, the oldest part of Los Angeles. New Spain achieved its independence from the Spanish Empire in 1821, the pueblo continued as a part of Mexico.
During Mexican rule, Governor Pío Pico made Los Angeles Alta California's regional capital. Mexican rule ended during the Mexican–American War: Americans took control from the Californios after a series of battles, culminating with the signing of the Treaty of Cahuenga on January 13, 1847. Railroads arrived with the completion of the transcontinental Southern Pacific line to Los Angeles in 1876 and the Santa Fe Railroad in 1885. Petroleum was discovered in the city and surrounding area in 1892, by 1923, the discoveries had helped California become the country's largest oil producer, accounting for about one-quarter of the world's petroleum output. By 1900, the population had grown to more than 102,000; the completion of the Los Angeles Aqueduct in 1913, under the supervision of William Mulholland, assured the continued growth of the city. Due to clauses in the city's charter that prevented the City of Los Angeles from selling or providing water from the aqueduct to any area outside its borders, many adjacent city and communities became compelled to annex themselves into Los Angeles.
Los Angeles created the first municipal zoning ordinance in the United States. On September 14, 1908, the Los Angeles City Council promulgated residential and industrial land use zones; the new ordinance established three residential zones of a single type, where industrial uses were
X-ray fluorescence is the emission of characteristic "secondary" X-rays from a material, excited by being bombarded with high-energy X-rays or gamma rays. The phenomenon is used for elemental analysis and chemical analysis in the investigation of metals, glass and building materials, for research in geochemistry, forensic science and art objects such as paintings and murals; when materials are exposed to short-wavelength X-rays or to gamma rays, ionization of their component atoms may take place. Ionization consists of the ejection of one or more electrons from the atom, may occur if the atom is exposed to radiation with an energy greater than its ionization energy. X-rays and gamma rays can be energetic enough to expel held electrons from the inner orbitals of the atom; the removal of an electron in this way makes the electronic structure of the atom unstable, electrons in higher orbitals "fall" into the lower orbital to fill the hole left behind. In falling, energy is released in the form of a photon, the energy of, equal to the energy difference of the two orbitals involved.
Thus, the material emits radiation. The term fluorescence is applied to phenomena in which the absorption of radiation of a specific energy results in the re-emission of radiation of a different energy; each element has electronic orbitals of characteristic energy. Following removal of an inner electron by an energetic photon provided by a primary radiation source, an electron from an outer shell drops into its place. There are a limited number of ways in which this can happen, as shown in Figure 1; the main transitions are given names: an L→K transition is traditionally called Kα, an M→K transition is called Kβ, an M→L transition is called Lα, so on. Each of these transitions yields a fluorescent photon with a characteristic energy equal to the difference in energy of the initial and final orbital; the wavelength of this fluorescent radiation can be calculated from Planck's Law: λ = h c E The fluorescent radiation can be analysed either by sorting the energies of the photons or by separating the wavelengths of the radiation.
Once sorted, the intensity of each characteristic radiation is directly related to the amount of each element in the material. This is the basis of a powerful technique in analytical chemistry. Figure 2 shows the typical form of the sharp fluorescent spectral lines obtained in the wavelength-dispersive method. In order to excite the atoms, a source of radiation is required, with sufficient energy to expel held inner electrons. Conventional X-ray generators are most used, because their output can be "tuned" for the application, because higher power can be deployed relative to other techniques. However, gamma ray sources can be used without the need for an elaborate power supply, allowing an easier use in small portable instruments; when the energy source is a synchrotron or the X-rays are focused by an optic like a polycapillary, the X-ray beam can be small and intense. As a result, atomic information on the sub-micrometre scale can be obtained. X-ray generators in the range 20–60 kV are used, which allow excitation of a broad range of atoms.
The continuous spectrum consists of "bremsstrahlung" radiation: radiation produced when high-energy electrons passing through the tube are progressively decelerated by the material of the tube anode. A typical tube output spectrum is shown in Figure 3. In energy dispersive analysis, the fluorescent X-rays emitted by the material sample are directed into a solid-state detector which produces a "continuous" distribution of pulses, the voltages of which are proportional to the incoming photon energies; this signal is processed by a multichannel analyser which produces an accumulating digital spectrum that can be processed to obtain analytical data. In wavelength dispersive analysis, the fluorescent X-rays emitted by the material sample are directed into a diffraction grating monochromator; the diffraction grating used is a single crystal. By varying the angle of incidence and take-off on the crystal, a single X-ray wavelength can be selected; the wavelength obtained is given by Bragg's law: n ⋅ λ = 2 d ⋅ sin where d is the spacing of atomic layers parallel to the crystal surface.
In energy dispersive analysis and detection are a single operation, as mentioned above. Proportional counters or various types of solid-state detectors are used, they all share the same detection principle: An incoming X-ray photon ionises a large number of detector atoms with the amount of charge produced being proportional to the energy of the incoming photon. The charge is collected and the process repeats itself for the next photon. Detector speed is critical, as all charge carriers measured have to come from the same photon to measure the photon energy correctly; the spectrum is built up by dividing the energy spectrum into discrete bins and counting the number of pulses registered within each energy bin. EDXRF detector types vary in resolution and the means of cooling
The Getty Villa is one of two locations of the J. Paul Getty Museum. Located at the easterly end of the Malibu coast in the Pacific Palisades neighborhood of Los Angeles, United States, the Getty Villa is an educational center and museum dedicated to the study of the arts and cultures of ancient Greece and Etruria; the collection has 44,000 Greek and Etruscan antiquities dating from 6,500 BC to 400 AD, including the Lansdowne Heracles and the Victorious Youth. The UCLA/Getty Master's Program in Archaeological and Ethnographic Conservation is housed on this campus; the collection is documented and presented through the online GettyGuide as well as through audio tours. In 1954, oil tycoon J. Paul Getty opened a gallery adjacent to his home in Pacific Palisades. Running out of room, he built a second museum, the Getty Villa, on the property down the hill from the original gallery; the villa design was inspired by the Villa of the Papyri at Herculaneum and incorporated additional details from several other ancient sites.
It was designed by architects Robert E. Langdon, Jr. and Ernest C. Wilson, Jr. in consultation with archeologist Norman Neuerburg. It opened in 1974, but was never visited by Getty, who died in 1976. Following his death, the museum inherited $661 million and began planning a much larger campus, the Getty Center, in nearby Brentwood; the museum overcame neighborhood opposition to its new campus plan by agreeing to limit the total size of the development on the Getty Center site. To meet the museum's total space needs, the museum decided to split between the two locations with the Getty Villa housing the Greek and Etruscan antiquities. In 1993, the Getty Trust selected Rodolpho Machado and Jorge Silvetti to design the renovation of the Getty Villa and its campus. In 1997, portions of the museum's collection of Greek and Etruscan antiquities were moved to the Getty Center for display, the Getty Villa was closed for renovation; the collection was restored during the renovation. Starting in 2004, the museum and the University of California, Los Angeles hold summer institutes in Turkey, studying the conservation of Middle Eastern Art.
Reopened on January 28, 2006, the Getty Villa shows Greek and Etruscan antiquities within Roman-inspired architecture and surrounded by Roman-style gardens. The art is arranged by themes, e.g. Gods and Goddesses and the Theater, Stories of the Trojan War; the new architectural plan surrounding the Villa –, conceived by Boston architects Machado and Silvetti Associates – is designed to simulate an archaeological dig. Architectural Record has praised their work on the Getty Villa as "a near miracle – a museum that elicits no smirks from the art world... a masterful job... crafting a sophisticated ensemble of buildings and landscaping that provides a real home for a relic of another time and place."In 2016–18 the collection was reinstalled in a chronological arrangement emphasizing art-historical themes. There has been controversy surrounding the Greek and Italian governments' claim that objects in the collection were looted and should be repatriated. In 2006, the Getty returned or promised to return four looted objects to Greece: a stele, a marble relief, a gold funerary wreath, a marble statue.
In 2007, the Getty signed an agreement to return 40 looted items to Italy. Admission to the Getty Villa is free, but timed tickets must be obtained in advance via phone or the museum's website; as of June 2010, there is a $15.00 charge for parking during the day, but parking is free for evening performances. The museum is open Wednesday to 10 a.m. to 5 p.m.. It is on New Year's Day, July 4, Thanksgiving and Christmas; the Getty Villa hosts live performances in both its outdoor theatre. Indoor play-readings included The Trojan Women, Aristophanes' The Frogs, Euripides' Helen. Indoor musical performances, which relate to art exhibits, included: Musica Angelica, De Organographia, Songs from the Fifth Age: Sones de México in Concert; the auditorium held a public reading of Homer's Iliad. Outdoor performances included Aristophanes' Peace, Aeschylus's Agamemnon, Sophocles' Elektra; the Getty Villa hosts visiting exhibitions beyond its own collections. For example, in March 2011 "In Search of Biblical Lands" was a photographic exhibition which included scenes of the Middle East dating back to the 1840s.
The Getty Villa offers special educational programs for children. A special Family Forum gallery offers activities including decorating Greek vases and projecting shadows onto a screen that represents a Greek urn; the room has polystyrene props from Greek and Roman culture for children to handle and use to cast shadows. The Getty Villa offers children's guides to the other exhibits; the Getty Conservation Institute offers a Master's Program in Archaeological and Ethnographic Conservation in association with the Cotsen Institute of Archaeology at UCLA. Classes and research are conducted in the museum wing of the ranch house; the program was the first of its kind in the United States. The Villa self-identifies with Malibu as it is located just east of the city limits of Malibu in the city of Los Angeles in the community of Pacific Palisades; the 64 acres museum complex sits on a hill overlooking the Pacific Ocean, about 100 feet from the entrance to the property. An outdoor 2,500-square-foot entry pavilion is built into the hill near the 248-car, four story, South Parking garage at the southern end of the Outer Peristyle.
The Outer Peristyle is a formal garden with roses and English ivy that includes a number o
Architectural conservation describes the process through which the material and design integrity of any built heritage are prolonged through planned interventions. The individual engaged in this pursuit is known as an architectural conservator-restorer. Decisions of when and how to engage in an intervention are critical to the ultimate conservation-restoration of cultural heritage; the decision is value based: a combination of artistic and informational values is considered. In some cases, a decision to not intervene may be the most appropriate choice; the Conservation Architect must consider factors that deal with issues of prolonging the life and preserving the integrity of architectural character, such as form and style, and/or its constituent materials, such as stone, glass and wood. In this sense, the term refers to the "professional use of a combination of science, art and technology as a preservation tool" and is allied with - and equated to - its parent fields, of historic environment conservation and art conservation.
In addition to the design and art/science definition described above, architectural conservation refers to issues of identification, policy and advocacy associated with the entirety of the cultural and built environment. This broader scope recognizes that society has mechanisms to identify and value historic cultural resources, create laws to protect these resources, develop policies and management plans for interpretation and education; this process operates as a specialized aspect of a society's planning system, its practitioners are termed built or historic environment conservation professionals. Architectural conservation is the process by which individuals or groups attempt to protect valued buildings from unwanted change; as a movement, architectural conservation in general, the preservation of ancient structures gained momentum during the 18th and 19th centuries. It was a response to Modernism and its corresponding architectural perspective, which eschewed sentimental attachment to old buildings and structures in favor of technological and architectural progress and change.
Prior to this time most of the ancient buildings that were still standing had only survived because they either had significant cultural or religious import, or they had yet to be discovered. The growth of the architectural conservation movement took place at a time of significant archaeological discovery and scientific advancement; those educated in the field began to see various examples of architecture as either being "correct" or "incorrect". Because of this, two schools of thought began to emerge within the field of building conservation. Preservation/Conservation were used interchangeably to refer to the architectural school of thought that either encouraged measures that would protect and maintain buildings in their current state, or would prevent further damage and deterioration to them; this school of thought saw the original design of old buildings as correct of themselves. Two of the main proponents of preservation and conservation in the 19th century were art critic John Ruskin and artist William Morris.
Restoration was the conservationist school of thought that believed historic buildings could be improved, sometimes completed, using current day materials and techniques. In this way it is similar to the Modernist architectural theory, except it does not advocate the destruction of ancient structures. One of the most ardent supporters of this school of thought in the 19th century was the French architect Eugène Viollet-le-Duc. Victorian restoration of medieval churches was widespread in England and elsewhere, with results that were deplored at the time by William Morris and are now regretted; the Department of the Interior of the United States defined the following treatment approaches to architectural conservation: Preservation, "places a high premium on the retention of all historic fabric through conservation and repair. It reflects a building's continuum over time, through successive occupancies, the respectful changes and alterations that are made." Rehabilitation "emphasizes the retention and repair of historic materials, but more latitude is provided for replacement because it is assumed the property is more deteriorated prior to work.
(Both Preservation and Rehabilitation standards focus attention on the preservation of those materials, finishes and spatial relationships that, give a property its historic character." See adaptive reuse. Restoration "focuses on the retention of materials from the most significant time in a property's history, while permitting the removal of materials from other periods." Reconstruction, "establishes limited opportunities to re-create a non-surviving site, building, structure, or object in all new materials."Other nations recognize some or all of these as potential treatments for historic structures. Canada recognizes preservation and restoration; the Burra Charter, for Australia, identifies preservation and reconstruction. The earliest building materials used by ancient peoples, such as wood and mud, were organic. Organic materials were used because they were renewable; the organic materials used were very susceptible to the two most significant impediments to preservation and conservation: the elements and life.
Over time inorganic materials like brick, metal and terra cotta began to be used by ancient people instead of organic ones, due to their durability. In fact, we know that these materials are durable because many ancient structures that are composed of them some built a
Rome is the capital city and a special comune of Italy. Rome serves as the capital of the Lazio region. With 2,872,800 residents in 1,285 km2, it is the country's most populated comune, it is the fourth most populous city in the European Union by population within city limits. It is the centre of the Metropolitan City of Rome, which has a population of 4,355,725 residents, thus making it the most populous metropolitan city in Italy. Rome is located in the central-western portion of the Italian Peninsula, within Lazio, along the shores of the Tiber; the Vatican City is an independent country inside the city boundaries of Rome, the only existing example of a country within a city: for this reason Rome has been defined as capital of two states. Rome's history spans 28 centuries. While Roman mythology dates the founding of Rome at around 753 BC, the site has been inhabited for much longer, making it one of the oldest continuously occupied sites in Europe; the city's early population originated from a mix of Latins and Sabines.
The city successively became the capital of the Roman Kingdom, the Roman Republic and the Roman Empire, is regarded by some as the first metropolis. It was first called The Eternal City by the Roman poet Tibullus in the 1st century BC, the expression was taken up by Ovid and Livy. Rome is called the "Caput Mundi". After the fall of the Western Empire, which marked the beginning of the Middle Ages, Rome fell under the political control of the Papacy, in the 8th century it became the capital of the Papal States, which lasted until 1870. Beginning with the Renaissance all the popes since Nicholas V pursued over four hundred years a coherent architectural and urban programme aimed at making the city the artistic and cultural centre of the world. In this way, Rome became first one of the major centres of the Italian Renaissance, the birthplace of both the Baroque style and Neoclassicism. Famous artists, painters and architects made Rome the centre of their activity, creating masterpieces throughout the city.
In 1871, Rome became the capital of the Kingdom of Italy, which, in 1946, became the Italian Republic. Rome has the status of a global city. In 2016, Rome ranked as the 14th-most-visited city in the world, 3rd most visited in the European Union, the most popular tourist attraction in Italy, its historic centre is listed by UNESCO as a World Heritage Site. The famous Vatican Museums are among the world's most visited museums while the Colosseum was the most popular tourist attraction in world with 7.4 million visitors in 2018. Host city for the 1960 Summer Olympics, Rome is the seat of several specialized agencies of the United Nations, such as the Food and Agriculture Organization, the World Food Programme and the International Fund for Agricultural Development; the city hosts the Secretariat of the Parliamentary Assembly of the Union for the Mediterranean as well as the headquarters of many international business companies such as Eni, Enel, TIM, Leonardo S.p. A. and national and international banks such as Unicredit and BNL.
Its business district, called EUR, is the base of many companies involved in the oil industry, the pharmaceutical industry, financial services. Rome is an important fashion and design centre thanks to renowned international brands centered in the city. Rome's Cinecittà Studios have been the set of many Academy Award–winning movies. According to the founding myth of the city by the Ancient Romans themselves, the long-held tradition of the origin of the name Roma is believed to have come from the city's founder and first king, Romulus. However, it is a possibility that the name Romulus was derived from Rome itself; as early as the 4th century, there have been alternative theories proposed on the origin of the name Roma. Several hypotheses have been advanced focusing on its linguistic roots which however remain uncertain: from Rumon or Rumen, archaic name of the Tiber, which in turn has the same root as the Greek verb ῥέω and the Latin verb ruo, which both mean "flow". There is archaeological evidence of human occupation of the Rome area from 14,000 years ago, but the dense layer of much younger debris obscures Palaeolithic and Neolithic sites.
Evidence of stone tools and stone weapons attest to about 10,000 years of human presence. Several excavations support the view that Rome grew from pastoral settlements on the Palatine Hill built above the area of the future Roman Forum. Between the end of the bronze age and the beginning of the Iron age, each hill between the sea and the Capitol was topped by a village. However, none of them had yet an urban quality. Nowadays, there is a wide consensus that the city developed through the aggregation of several villages around the largest one, placed above the Palatine; this aggregation was facilitated by the increase of agricultural productivity above the subsistence level, which allowed the establishment of secondary and tertiary activities. These in turn boosted the development of trade with the Greek colonies of southern Italy; these developments, which according to archaeological ev
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: electromagnetic radiation, such as radio waves, infrared, visible light, ultraviolet, x-rays, gamma radiation particle radiation, such as alpha radiation, beta radiation, neutron radiation acoustic radiation, such as ultrasound and seismic waves gravitational radiation, radiation that takes the form of gravitational waves, or ripples in the curvature of spacetime. Radiation is categorized as either ionizing or non-ionizing depending on the energy of the radiated particles. Ionizing radiation carries more than 10 eV, enough to ionize atoms and molecules, break chemical bonds; this is an important distinction due to the large difference in harmfulness to living organisms. A common source of ionizing radiation is radioactive materials that emit α, β, or γ radiation, consisting of helium nuclei, electrons or positrons, photons, respectively.
Other sources include X-rays from medical radiography examinations and muons, positrons and other particles that constitute the secondary cosmic rays that are produced after primary cosmic rays interact with Earth's atmosphere. Gamma rays, X-rays and the higher energy range of ultraviolet light constitute the ionizing part of the electromagnetic spectrum; the word "ionize" refers to the breaking of one or more electrons away from an atom, an action that requires the high energies that these electromagnetic waves supply. Further down the spectrum, the non-ionizing lower energies of the lower ultraviolet spectrum cannot ionize atoms, but can disrupt the inter-atomic bonds which form molecules, thereby breaking down molecules rather than atoms; the waves of longer wavelength than UV in visible light and microwave frequencies cannot break bonds but can cause vibrations in the bonds which are sensed as heat. Radio wavelengths and below are not regarded as harmful to biological systems; these are not sharp delineations of the energies.
The word radiation arises from the phenomenon of waves radiating from a source. This aspect leads to a system of measurements and physical units that are applicable to all types of radiation; because such radiation expands as it passes through space, as its energy is conserved, the intensity of all types of radiation from a point source follows an inverse-square law in relation to the distance from its source. Like any ideal law, the inverse-square law approximates a measured radiation intensity to the extent that the source approximates a geometric point. Radiation with sufficiently high energy can ionize atoms. Ionization occurs when an electron is stripped from an electron shell of the atom, which leaves the atom with a net positive charge; because living cells and, more the DNA in those cells can be damaged by this ionization, exposure to ionizing radiation is considered to increase the risk of cancer. Thus "ionizing radiation" is somewhat artificially separated from particle radiation and electromagnetic radiation due to its great potential for biological damage.
While an individual cell is made of trillions of atoms, only a small fraction of those will be ionized at low to moderate radiation powers. The probability of ionizing radiation causing cancer is dependent upon the absorbed dose of the radiation, is a function of the damaging tendency of the type of radiation and the sensitivity of the irradiated organism or tissue. If the source of the ionizing radiation is a radioactive material or a nuclear process such as fission or fusion, there is particle radiation to consider. Particle radiation is subatomic particle accelerated to relativistic speeds by nuclear reactions; because of their momenta they are quite capable of knocking out electrons and ionizing materials, but since most have an electrical charge, they don't have the penetrating power of ionizing radiation. The exception is neutron particles. There are several different kinds of these particles, but the majority are alpha particles, beta particles and protons. Speaking and particles with energies above about 10 electron volts are ionizing.
Particle radiation from radioactive material or cosmic rays invariably carries enough energy to be ionizing. Most ionizing radiation originates from radioactive materials and space, as such is present in the environment, since most rocks and soil have small concentrations of radioactive materials. Since this radiation is invisible and not directly detectable by human senses, instruments such as Geiger counters are required to detect its presence. In some cases, it may lead to secondary emission of visible light upon its interaction with matter, as in the case of Cherenkov radiation and radio-luminescence. Ionizing radiation has many practical uses in medicine and construction, but presents a health hazard if used improperly. Exposure to radiation causes damage to living tissue.