1.
Oak Ridge National Laboratory
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Oak Ridge National Laboratory is an American multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the largest science and energy national laboratory in the Department of Energy system by surface, ORNL is located in Oak Ridge, Tennessee, near Knoxville. ORNLs scientific programs focus on materials, neutron science, energy, high-performance computing, systems biology, ORNL partners with the state of Tennessee, universities and industries to solve challenges in energy, advanced materials, manufacturing, security and physics. ORNL hosts the Center for Nanophase Materials Sciences, the BioEnergy Science Center, Oak Ridge National Laboratory is managed by UT-Battelle, a limited liability partnership between the University of Tennessee and the Battelle Memorial Institute, formed in 2000 for that purpose. The annual budget is US$1.65 billion, 80% of which is from the Department of Energy, as of 2012 there are 4,400 staff working at ORNL,1,600 of whom are directly conducting research, and an additional 3,000 guest researchers annually. The total area of the reservation 150 square kilometres of which the lab takes up 18 square kilometres, the town of Oak Ridge was established by the Army Corps of Engineers as part of the Clinton Engineer Works in 1942 on isolated farm land as part of the Manhattan Project. During the war, advanced research for the government was managed at the site by the University of Chicago, in 1943, construction of the Clinton Laboratories was completed, later renamed to Oak Ridge National Laboratory. The site was chosen for the X-10 Graphite Reactor, used to show that plutonium can be extracted from enriched uranium, enrico Fermi and his colleagues developed the worlds second self-sustaining nuclear reactor after Fermis previous experiment, the Chicago Pile-1. The X-10 was the first reactor designed for continuous operation, in 1946 the first medical isotopes were produced in the X-10 reactor, by 1950 almost 20,000 samples had been shipped to various hospitals. As the demand for military science had fallen dramatically the future of the lab was uncertain, management of the lab was contracted by the US government to Monsanto, however, they withdrew in 1947. In 1950 the Oak Ridge School of Reactor Technology was established with two courses in operation and safety, almost 1000 students graduated. Another project was the worlds first light water reactor, with its principles of neutron moderation and fuel cooling by ordinary water it is the direct ancestor of most modern nuclear power stations. The US Military funded much of its development, for nuclear-powered submarines, the US Army contracted portable nuclear reactors in 1953 for heat and electricity generation in remote military bases. The reactors were designed at ORNL, produced by American Locomotive Company and used in Greenland, the United States Air Force also contributed funding to three reactors, the labs first computers, and its first particle accelerators. ORNL designed and tested an aircraft in 1954 as a proof-of-concept for a proposed USAF fleet of long-range bombers. The provision of radionuclides by X-10 for medicine grew steadily in the 1950s with more isotopes available, ORNL scientists lowered the immune systems of mice and performed the worlds first successful bone marrow transplant. In the early 1960s there was a push at ORNL to develop nuclear-powered desalination plants where deserts met the sea to provide water. The Health Physics Research Reactor built in 1962 was used for exposure experiments leading to more accurate dosage limits, dosimeters
2.
Health care
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It includes the work done in providing primary care, secondary care, and tertiary care, as well as in public health. Access to healthcare varies across countries, groups, and individuals, largely influenced by social, countries and jurisdictions have different policies and plans in relation to the personal and population-based health care goals within their societies. Healthcare systems are organizations established to meet the needs of target populations. Their exact configuration varies between national and subnational entities, in some countries and jurisdictions, healthcare planning is distributed among market participants, whereas in others, planning occurs more centrally among governments or other coordinating bodies. Healthcare can contribute to a significant part of a countrys economy. In 2011, the healthcare industry consumed an average of 9.3 percent of the GDP or US$3,322 per capita across the 34 members of OECD countries.1 years, a gain of 10 years since 1970. The USA ranges only on place 26 among the 34 OECD member countries, all OECD countries have achieved universal health coverage, except Mexico and the USA. Healthcare is conventionally regarded as an important determinant in promoting the general physical and mental health, an example of this was the worldwide eradication of smallpox in 1980, declared by the WHO as the first disease in human history to be completely eliminated by deliberate health care interventions. The delivery of health care depends on groups of trained professionals and paraprofessionals coming together as interdisciplinary teams. Healthcare can be defined as public or private. Primary care refers to the work of professionals who act as a first point of consultation for all patients within the health care system. Depending on the nature of the condition, patients may then be referred for secondary or tertiary care. Primary care is used as the term for the health care services which play a role in the local community. It can be provided in different settings, such as Urgent care centres which provide services to patients same day with appointment or walk-in bases, consequently, a primary care practitioner must possess a wide breadth of knowledge in many areas. The International Classification of Primary Care is a tool for understanding and analyzing information on interventions in primary care by the reason for the patient visit. Common chronic illnesses usually treated in primary care may include, for example, hypertension, diabetes, asthma, COPD, depression and anxiety, back pain, Primary care also includes many basic maternal and child health care services, such as family planning services and vaccinations. Physicians in this model bill patients directly for services, either on a monthly, quarterly, or annual basis. Examples of direct primary care practices include Foundation Health in Colorado, the World Health Organization attributes the provision of essential primary care as an integral component of an inclusive primary health care strategy
3.
X-ray generator
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An X-ray generator is a device that produces X-rays. It is commonly used in a variety of applications including medicine, fluorescence, electronic assembly inspection, in medical applications, X-ray generators are used by radiographers to acquire x-ray images of the internal structures of living organisms, and also in sterilization. X-rays are typically generated by an X-ray tube, when the electrons collide with the target, about 1% of the resulting energy is emitted as X-rays, with the remaining 99% released as heat. Due to the energy of the electrons that reach relativistic speeds the target is usually made of tungsten even if other material can be used particularly in XRF applications. A cooling system is necessary to cool the anode, many X-ray generators use water or oil recirculating systems, the discovery of X-rays came from experimenting with Crookes tubes, an early experimental electrical discharge tube invented by English physicist William Crookes around 1869-1875. In 1895, Wilhelm Röntgen discovered X-rays emanating from Crookes tubes, one of the first X-ray photographs was made of the hand of Röntgens wife. The image displayed both her wedding ring and bones, on January 18,1896 an X-ray machine was formally displayed by H. L. Smith. A fully functioning unit was introduced to the public at the 1904 Worlds Fair by Clarence Dally, in the 1940s and 1950s, X-ray machines were used in stores to help sell footwear. These were known as Shoe-fitting fluoroscopes, however, as the harmful effects of X-ray radiation were properly considered, they finally fell out of use. Shoe-fitting use of the device was first banned by the state of Pennsylvania in 1957, together with Robert J. Van de Graaff, John G. Trump developed one of the first million-volt X-ray generators. X-ray photons are produced by a beam that is accelerated to a very high speed. The electrons that make up the beam are emitted from a cathode filament. The electrons are focused and accelerated by an electrical field towards an angled anode target. The point where the beam strikes the target is called the focal spot. Most of the energy contained in the electron beam is converted to heat, but around 1% of the energy is converted into X-ray photons. There is a round window in the X-ray tube directly above the angled target. This window allows the X-rays to exit the tube with little attenuation while maintaining a vacuum seal required for the X-ray tube operation. Other than the tube window or port the remaining portion of the x-ray tube housing is lined with lead to absorb all remaining x-rays not usable for image creation
4.
Radioactive waste
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Radioactive waste is waste that contains radioactive material. Radioactive waste is usually a by-product of nuclear generation and other applications of nuclear fission or nuclear technology, such as research. Radioactive waste is hazardous to most forms of life and the environment, and is regulated by government agencies in order to protect human health and the environment. Radioactivity naturally decays over time, so radioactive waste has to be isolated and confined in appropriate facilities for a sufficient period until it no longer poses a threat. The time radioactive waste must be stored for depends on the type of waste, Radioactive waste typically comprises a number of radionuclides, unstable configurations of elements that decay, emitting ionizing radiation which can be harmful to humans and the environment. These isotopes emit different types and levels of radiation, which last for different periods of time, the radioactivity of all radioactive waste diminishes with time. Certain radioactive elements will remain hazardous to humans and other creatures for hundreds or thousands of years, other radionuclides remain radioactive for millions of years. Thus, these wastes must be shielded for centuries and isolated from the environment for millennia. Since radioactive decay follows the rule, the rate of decay is inversely proportional to the duration of decay. In other words, the radiation from a long-lived isotope like iodine-129 will be less intense than that of a short-lived isotope like iodine-131. The two tables show some of the radioisotopes, their half-lives, and their radiation yield as a proportion of the yield of fission of uranium-235. The energy and the type of the radiation emitted by a radioactive substance are also important factors in determining its threat to humans. The chemical properties of the element will determine how mobile the substance is and how likely it is to spread into the environment. Exposure to radioactive waste may cause harm or death. In humans, a dose of 1 sievert carries a 5. 5% risk of developing cancer, ionizing radiation causes deletions in chromosomes. If a developing organism such as a child is irradiated, it is possible a birth defect may be induced. The incidence of radiation-induced mutations in humans is small, as in most mammals, because of natural cellular-repair mechanisms, Radioactive waste comes from a number of sources. Waste from the front end of the fuel cycle is usually alpha-emitting waste from the extraction of uranium
5.
Radioactive contamination
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Such contamination presents a hazard because of the radioactive decay of the contaminants, which emit harmful ionising radiation such as alpha particles or beta particles, gamma rays or neutrons. It is important to be clear that the contamination gives rise to the hazard. Contamination may affect a person, a place, an animal, a spilled vial of radioactive material like uranyl nitrate may contaminate the floor and any rags used to wipe up the spill. Radioactive contamination is typically the result of a spill or accident during the production, or use of, radionuclides, less typically, nuclear fallout is the distribution of radioactive contamination by a nuclear explosion. The amount of material released in an accident is called the source term. Contamination may occur from radioactive gases, liquids or particles, for example, if a radionuclide used in nuclear medicine is spilled, the material could be spread by people as they walk around. Radioactive contamination may also be a result of certain processes. In cases that radioactive material cannot be contained, it may be diluted to safe concentrations, for a discussion of environmental contamination by alpha emitters please see actinides in the environment. Contamination does not include residual radioactive material remaining at a site after the completion of decommissioning, therefore, radioactive material in sealed and designated containers is not properly referred to as contamination, although the units of measurement might be the same. Containment is the way of preventing contamination being released into the environment or coming into contact or being ingested by humans. Being within the intended Containment differentiates radioactive material from radioactive contamination, when radioactive materials are concentrated to a detectable level outside a containment, the area affected is generally referred to as contaminated. There are a number of techniques for containing radioactive material so that it does not spread beyond the containment. In the case of liquids this is by the use of high integrity tanks or containers, where material is likely to become airborne, then extensive use is made of the glovebox, which is a common technique in hazardous laboratory and process operations in many industries. A variety of radionuclides occur naturally in the environment, elements like uranium and thorium, and their decay products, are present in rock and soil. Potassium-40, a nuclide, makes up a small percentage of all potassium and is present in the human body. Other nuclides, like carbon-14, which is present in all living organisms, are created by cosmic rays. These levels of radioactivity pose little danger but can confuse measurement, a particular problem is encountered with naturally generated radon gas which can affect instruments which are set to detect contamination close to normal background levels and can cause false alarms. Because of this skill is required by the operator of radiological survey equipment to differentiate between background radiation and the radiation emanates from contamination
6.
Engineering
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The term Engineering is derived from the Latin ingenium, meaning cleverness and ingeniare, meaning to contrive, devise. Engineering has existed since ancient times as humans devised fundamental inventions such as the wedge, lever, wheel, each of these inventions is essentially consistent with the modern definition of engineering. The term engineering is derived from the engineer, which itself dates back to 1390 when an engineer originally referred to a constructor of military engines. In this context, now obsolete, a referred to a military machine. Notable examples of the obsolete usage which have survived to the present day are military engineering corps, the word engine itself is of even older origin, ultimately deriving from the Latin ingenium, meaning innate quality, especially mental power, hence a clever invention. The earliest civil engineer known by name is Imhotep, as one of the officials of the Pharaoh, Djosèr, he probably designed and supervised the construction of the Pyramid of Djoser at Saqqara in Egypt around 2630–2611 BC. Ancient Greece developed machines in both civilian and military domains, the Antikythera mechanism, the first known mechanical computer, and the mechanical inventions of Archimedes are examples of early mechanical engineering. In the Middle Ages, the trebuchet was developed, the first steam engine was built in 1698 by Thomas Savery. The development of this gave rise to the Industrial Revolution in the coming decades. With the rise of engineering as a profession in the 18th century, similarly, in addition to military and civil engineering, the fields then known as the mechanic arts became incorporated into engineering. The inventions of Thomas Newcomen and the Scottish engineer James Watt gave rise to mechanical engineering. The development of specialized machines and machine tools during the revolution led to the rapid growth of mechanical engineering both in its birthplace Britain and abroad. John Smeaton was the first self-proclaimed civil engineer and is regarded as the father of civil engineering. He was an English civil engineer responsible for the design of bridges, canals, harbours and he was also a capable mechanical engineer and an eminent physicist. Smeaton designed the third Eddystone Lighthouse where he pioneered the use of hydraulic lime and his lighthouse remained in use until 1877 and was dismantled and partially rebuilt at Plymouth Hoe where it is known as Smeatons Tower. The United States census of 1850 listed the occupation of engineer for the first time with a count of 2,000, there were fewer than 50 engineering graduates in the U. S. before 1865. In 1870 there were a dozen U. S. mechanical engineering graduates, in 1890 there were 6,000 engineers in civil, mining, mechanical and electrical. There was no chair of applied mechanism and applied mechanics established at Cambridge until 1875, the theoretical work of James Maxwell and Heinrich Hertz in the late 19th century gave rise to the field of electronics
7.
National Physical Laboratory (United Kingdom)
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The National Physical Laboratory is the national measurement standards laboratory for the United Kingdom, based at Bushy Park in Teddington, London, England. It is the largest applied physics organisation in the UK, NPL is an internationally respected centre of excellence in measurement and materials science. Since 1900, when Bushy House was selected as the site of NPL, today it provides the scientific resources for the National Measurement System financed by the Department for Business, Innovation and Skills. NPL also offers a range of services, applying scientific skills to industrial measurement problems. The NPL cooperates with professional networks such as those of the IET to support scientists, NPL is at the forefront of new developments in metrology, such as researching metrology for, and standardizing, nanotechnology. NPL is mainly based on the Teddington site but also has a site in Huddersfield for dimensional metrology, Teddington was also home to the UK National Chemical Laboratory but this was closed in 1965 and some of its work was transferred to NPL. The laboratory was run by the UK government, with members of staff being part of the civil service. Administration of the NPL was contracted out in 1995 under a GOCO model, with Serco winning the bid, under this regime, overhead costs halved, third party revenues grew by 16% per annum, and the number of peer-reviewed research papers published doubled. It was decided in 2012 to change the model for NPL from 2014 onward to include academic partners. The date of the changeover was postponed for up to a year. The laboratory transferred back to Department for Business, Innovation and Skills ownership on 1 January 2015, NPL was initially sited entirely within Bushy House but grew to fill a large selection of buildings on the Teddington site. Many of these buildings were demolished and the moved to a large state-of-the-art laboratory for NPL that was built between 1998 and 2007. In January 2013 funding for a new £25m Advanced Metrology Laboratory was announced that will be built on the footprint of an unused building. H. J. Gough one of the pioneers of research into metal fatigue worked at NPL for 19 years from 1914-38, the inventor Sir Barnes Wallis did early development work there on the Bouncing Bomb used in the Dam Busters wartime raids. Sydney Goldstein and Sir James Lighthill worked in NPLs aerodynamics division during World War II researching boundary layer theory, dr Clifford Hodge also worked there and was engaged in research on semiconductors
8.
Geiger counter
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It detects ionizing radiation such as alpha particles, beta particles and gamma rays using the ionization effect produced in a Geiger–Müller tube, which gives its name to the instrument. In wide and prominent use as a radiation survey instrument. Since then it has very popular due to its robust sensing element. However, there are limitations in measuring high radiation rates and the energy of incident radiation, a Geiger counter consists of a Geiger-Müller tube, the sensing element which detects the radiation, and the processing electronics, which displays the result. The Geiger-Müller tube is filled with a gas such as helium, neon, or argon at low pressure. The tube briefly conducts electrical charge when a particle or photon of incident radiation makes the gas conductive by ionization, the ionization is considerably amplified within the tube by the Townsend discharge effect to produce an easily measured detection pulse, which is fed to the processing and display electronics. This large pulse from the tube makes the G-M counter relatively cheap to manufacture, the electronics also generates the high voltage, typically 400–600 volts, that has to be applied to the Geiger-Müller tube to enable its operation. There are two types of radiation readout, counts or radiation dose, the counts display is the simplest and is the number of ionizing events displayed either as a count rate, commonly counts per second, or as a total over a set time period. The counts readout is normally used when alpha or beta particles are being detected, more complex to achieve is a display of radiation dose rate, displayed in a unit such as the sievert which is normally used for measuring gamma or X-ray dose rates. A G-M tube can detect the presence of radiation, but not its energy influences the radiations ionising effect. Consequently, instruments measuring dose rate require the use of an energy compensated G-M tube, the electronics will apply known factors to make this conversion, which is specific to each instrument and is determined by design and calibration. The readout can be analog or digital, and increasingly, modern instruments are offering serial communications with a host computer or network, there is usually an option to produce audible clicks representing the number of ionization events detected. This is the distinctive sound associated with hand held or portable Geiger counters. The purpose of this is to allow the user to concentrate on manipulation of the instrument whilst retaining auditory feedback on the radiation rate, there are two main limitations of the Geiger counter. Because the output pulse from a Geiger-Müller tube is always the same regardless of the energy of the incident radiation. A further limitation is the inability to measure radiation rates due to the dead time of the tube. This is a period after each ionization of the gas during which any further incident radiation will not result in a count. Typically the dead time will reduce indicated count rates above about 104 to 105 counts per second depending on the characteristic of the tube being used, whilst some counters have circuitry which can compensate for this, for accurate measurements ion chamber instruments are preferred for high radiation rates
9.
United Kingdom
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The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom or Britain, is a sovereign country in western Europe. Lying off the north-western coast of the European mainland, the United Kingdom includes the island of Great Britain, Northern Ireland is the only part of the United Kingdom that shares a land border with another sovereign state—the Republic of Ireland. The Irish Sea lies between Great Britain and Ireland, with an area of 242,500 square kilometres, the United Kingdom is the 78th-largest sovereign state in the world and the 11th-largest in Europe. It is also the 21st-most populous country, with an estimated 65.1 million inhabitants, together, this makes it the fourth-most densely populated country in the European Union. The United Kingdom is a monarchy with a parliamentary system of governance. The monarch is Queen Elizabeth II, who has reigned since 6 February 1952, other major urban areas in the United Kingdom include the regions of Birmingham, Leeds, Glasgow, Liverpool and Manchester. The United Kingdom consists of four countries—England, Scotland, Wales, the last three have devolved administrations, each with varying powers, based in their capitals, Edinburgh, Cardiff and Belfast, respectively. The relationships among the countries of the UK have changed over time, Wales was annexed by the Kingdom of England under the Laws in Wales Acts 1535 and 1542. A treaty between England and Scotland resulted in 1707 in a unified Kingdom of Great Britain, which merged in 1801 with the Kingdom of Ireland to form the United Kingdom of Great Britain and Ireland. Five-sixths of Ireland seceded from the UK in 1922, leaving the present formulation of the United Kingdom of Great Britain, there are fourteen British Overseas Territories. These are the remnants of the British Empire which, at its height in the 1920s, British influence can be observed in the language, culture and legal systems of many of its former colonies. The United Kingdom is a country and has the worlds fifth-largest economy by nominal GDP. The UK is considered to have an economy and is categorised as very high in the Human Development Index. It was the worlds first industrialised country and the worlds foremost power during the 19th, the UK remains a great power with considerable economic, cultural, military, scientific and political influence internationally. It is a nuclear weapons state and its military expenditure ranks fourth or fifth in the world. The UK has been a permanent member of the United Nations Security Council since its first session in 1946 and it has been a leading member state of the EU and its predecessor, the European Economic Community, since 1973. However, on 23 June 2016, a referendum on the UKs membership of the EU resulted in a decision to leave. The Acts of Union 1800 united the Kingdom of Great Britain, Scotland, Wales and Northern Ireland have devolved self-government
10.
Energy
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In physics, energy is the property that must be transferred to an object in order to perform work on – or to heat – the object, and can be converted in form, but not created or destroyed. The SI unit of energy is the joule, which is the transferred to an object by the mechanical work of moving it a distance of 1 metre against a force of 1 newton. Mass and energy are closely related, for example, with a sensitive enough scale, one could measure an increase in mass after heating an object. Living organisms require available energy to stay alive, such as the humans get from food. Civilisation gets the energy it needs from energy resources such as fuels, nuclear fuel. The processes of Earths climate and ecosystem are driven by the radiant energy Earth receives from the sun, the total energy of a system can be subdivided and classified in various ways. It may also be convenient to distinguish gravitational energy, thermal energy, several types of energy, electric energy. Many of these overlap, for instance, thermal energy usually consists partly of kinetic. Some types of energy are a mix of both potential and kinetic energy. An example is energy which is the sum of kinetic. Whenever physical scientists discover that a phenomenon appears to violate the law of energy conservation. Heat and work are special cases in that they are not properties of systems, in general we cannot measure how much heat or work are present in an object, but rather only how much energy is transferred among objects in certain ways during the occurrence of a given process. Heat and work are measured as positive or negative depending on which side of the transfer we view them from, the distinctions between different kinds of energy is not always clear-cut. In contrast to the definition, energeia was a qualitative philosophical concept, broad enough to include ideas such as happiness. The modern analog of this property, kinetic energy, differs from vis viva only by a factor of two, in 1807, Thomas Young was possibly the first to use the term energy instead of vis viva, in its modern sense. Gustave-Gaspard Coriolis described kinetic energy in 1829 in its modern sense, the law of conservation of energy was also first postulated in the early 19th century, and applies to any isolated system. It was argued for years whether heat was a physical substance, dubbed the caloric, or merely a physical quantity. In 1845 James Prescott Joule discovered the link between mechanical work and the generation of heat and these developments led to the theory of conservation of energy, formalized largely by William Thomson as the field of thermodynamics
11.
X-ray
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X-radiation is a form of electromagnetic radiation. Most X-rays have a wavelength ranging from 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz, X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. Spelling of X-ray in the English language includes the variants x-ray, xray, X-rays with high photon energies are called hard X-rays, while those with lower energy are called soft X-rays. Due to their ability, hard X-rays are widely used to image the inside of objects, e. g. in medical radiography. The term X-ray is metonymically used to refer to an image produced using this method. Since the wavelengths of hard X-rays are similar to the size of atoms they are useful for determining crystal structures by X-ray crystallography. By contrast, soft X-rays are easily absorbed in air, the length of 600 eV X-rays in water is less than 1 micrometer. There is no consensus for a definition distinguishing between X-rays and gamma rays, one common practice is to distinguish between the two types of radiation based on their source, X-rays are emitted by electrons, while gamma rays are emitted by the atomic nucleus. This definition has problems, other processes also can generate these high-energy photons. One common alternative is to distinguish X- and gamma radiation on the basis of wavelength, with radiation shorter than some arbitrary wavelength, such as 10−11 m and this criterion assigns a photon to an unambiguous category, but is only possible if wavelength is known. Occasionally, one term or the other is used in specific contexts due to precedent, based on measurement technique. Thus, gamma-rays generated for medical and industrial uses, for radiotherapy, in the ranges of 6–20 MeV. X-ray photons carry enough energy to ionize atoms and disrupt molecular bonds and this makes it a type of ionizing radiation, and therefore harmful to living tissue. A very high radiation dose over a period of time causes radiation sickness. In medical imaging this increased risk is generally greatly outweighed by the benefits of the examination. The ionizing capability of X-rays can be utilized in treatment to kill malignant cells using radiation therapy. It is also used for material characterization using X-ray spectroscopy, hard X-rays can traverse relatively thick objects without being much absorbed or scattered. For this reason, X-rays are widely used to image the inside of visually opaque objects, the most often seen applications are in medical radiography and airport security scanners, but similar techniques are also important in industry and research
12.
Gamma ray
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Gamma ray, denoted by the lower-case Greek letter gamma, is penetrating electromagnetic radiation of a kind arising from the radioactive decay of atomic nuclei. It consists of photons in the highest observed range of photon energy, 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, Rutherford had previously discovered two other types of radioactive decay, which he named alpha and beta rays. Gamma rays are able to ionize atoms, and are thus biologically hazardous. The decay of a nucleus from a high energy state to a lower energy state. Natural sources of gamma rays on Earth are observed in the decay of radionuclides. There are rare terrestrial natural sources, such as lightning strikes and terrestrial gamma-ray flashes, However, a large fraction of such astronomical gamma rays are screened by Earths atmosphere and can only be detected by spacecraft. Gamma rays typically have frequencies above 10 exahertz, and therefore have energies above 100 keV and wavelengths less than 10 picometers, However, this is not a strict definition, but rather only a rule-of-thumb description for natural processes. Electromagnetic radiation from radioactive decay of nuclei is referred to as gamma rays no matter its energy. This radiation commonly has energy of a few hundred keV, in astronomy, gamma rays are defined by their energy, and no production process needs to be specified. The energies of gamma rays from astronomical sources range to over 10 TeV, a notable example is the extremely powerful bursts of high-energy radiation referred to as long duration gamma-ray bursts, of energies higher than can be produced by radioactive decay. These bursts of gamma rays are thought to be due to the collapse of stars called hypernovae, the first gamma ray source to be discovered historically was the radioactive decay process called gamma decay. In this type of decay, a nucleus emits a gamma ray almost immediately upon formation. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900, However, Villard did not consider naming them as a different fundamental type. Rutherford also noted that gamma rays were not deflected by a field, another property making them unlike alpha. Gamma rays were first thought to be particles with mass, like alpha, Rutherford initially believed that they might be extremely fast beta particles, but their failure to be deflected by a magnetic field indicated that they had no charge. In 1914, gamma rays were observed to be reflected from crystal surfaces, Rutherford and his coworker Edward Andrade measured the wavelengths of gamma rays from radium, and found that they were similar to X-rays, but with shorter wavelengths and higher frequency. This was eventually recognized as giving them more energy per photon
