1.
System of measurement
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A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce, systems of measurement in modern use include the metric system, the imperial system, and United States customary units. The French Revolution gave rise to the system, and this has spread around the world. In most systems, length, mass, and time are base quantities, later science developments showed that either electric charge or electric current could be added to extend the set of base quantities by which many other metrological units could be easily defined. Other quantities, such as power and speed, are derived from the set, for example. Such arrangements were satisfactory in their own contexts, the preference for a more universal and consistent system only gradually spread with the growth of science. Changing a measurement system has substantial financial and cultural costs which must be offset against the advantages to be obtained using a more rational system. However pressure built up, including scientists and engineers for conversion to a more rational. The unifying characteristic is that there was some definition based on some standard, eventually cubits and strides gave way to customary units to met the needs of merchants and scientists. In the metric system and other recent systems, a basic unit is used for each base quantity. Often secondary units are derived from the units by multiplying by powers of ten. Thus the basic unit of length is the metre, a distance of 1.234 m is 1,234 millimetres. Metrication is complete or nearly complete in almost all countries, US customary units are heavily used in the United States and to some degree in Liberia. Traditional Burmese units of measurement are used in Burma, U. S. units are used in limited contexts in Canada due to the large volume of trade, there is also considerable use of Imperial weights and measures, despite de jure Canadian conversion to metric. In the United States, metric units are used almost universally in science, widely in the military, and partially in industry, but customary units predominate in household use. At retail stores, the liter is a used unit for volume, especially on bottles of beverages. Some other standard non-SI units are still in use, such as nautical miles and knots in aviation. Metric systems of units have evolved since the adoption of the first well-defined system in France in 1795, during this evolution the use of these systems has spread throughout the world, first to non-English-speaking countries, and then to English speaking countries
2.
SI derived unit
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The International System of Units specifies a set of seven base units from which all other SI units of measurement are derived. Each of these units is either dimensionless or can be expressed as a product of powers of one or more of the base units. For example, the SI derived unit of area is the metre. The degree Celsius has an unclear status, and is arguably an exception to this rule. The names of SI units are written in lowercase, the symbols for units named after persons, however, are always written with an uppercase initial letter. In addition to the two dimensionless derived units radian and steradian,20 other derived units have special names, some other units such as the hour, litre, tonne, bar and electronvolt are not SI units, but are widely used in conjunction with SI units. Until 1995, the SI classified the radian and the steradian as supplementary units, but this designation was abandoned, International System of Quantities International System of Units International Vocabulary of Metrology Metric prefix Metric system Non-SI units mentioned in the SI Planck units SI base unit I. Mills, Tomislav Cvitas, Klaus Homann, Nikola Kallay, IUPAC, Quantities, Units and Symbols in Physical Chemistry. CS1 maint, Multiple names, authors list
3.
Rolf Maximilian Sievert
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Rolf Maximilian Sievert was a medical physicist whose major contribution was in the study of the biological effects of radiation. Professor Sievert was born in Stockholm, Sweden and he served as head of the physics laboratory at Swedens Radiumhemmet from 1924 to 1937, when he became head of the department of radiation physics at the Karolinska Institute. He played a role in the measurement of doses of radiation especially in its use in the diagnosis. In later years, he focused his research on the effects of repeated exposure to low doses of radiation. In 1964, he founded the International Radiation Protection Association, serving for a time as its chairman and he also chaired the United Nations Scientific Committee on the Effects of Atomic Radiation. He invented a number of instruments for measuring radiation doses, the most widely known being the Sievert chamber, in 1979, at the Conférence Générale des Poids et Mesures, the SI unit for ionizing radiation dose equivalent was named after him and given the name sievert. Sievert integral Sievert chamber Rolf Sievert, the man and the unit
4.
SI base unit
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The International System of Units defines seven units of measure as a basic set from which all other SI units can be derived. The SI base units form a set of mutually independent dimensions as required by dimensional analysis commonly employed in science, thus, the kelvin, named after Lord Kelvin, has the symbol K and the ampere, named after André-Marie Ampère, has the symbol A. Many other units, such as the litre, are not part of the SI. The definitions of the units have been modified several times since the Metre Convention in 1875. Since the redefinition of the metre in 1960, the kilogram is the unit that is directly defined in terms of a physical artifact. However, the mole, the ampere, and the candela are linked through their definitions to the mass of the platinum–iridium cylinder stored in a vault near Paris. It has long been an objective in metrology to define the kilogram in terms of a fundamental constant, two possibilities have attracted particular attention, the Planck constant and the Avogadro constant. The 23rd CGPM decided to postpone any formal change until the next General Conference in 2011
5.
Metre
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The metre or meter, is the base unit of length in the International System of Units. The metre is defined as the length of the path travelled by light in a vacuum in 1/299792458 seconds, the metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole. In 1799, it was redefined in terms of a metre bar. In 1960, the metre was redefined in terms of a number of wavelengths of a certain emission line of krypton-86. In 1983, the current definition was adopted, the imperial inch is defined as 0.0254 metres. One metre is about 3 3⁄8 inches longer than a yard, Metre is the standard spelling of the metric unit for length in nearly all English-speaking nations except the United States and the Philippines, which use meter. Measuring devices are spelled -meter in all variants of English, the suffix -meter has the same Greek origin as the unit of length. This range of uses is found in Latin, French, English. Thus calls for measurement and moderation. In 1668 the English cleric and philosopher John Wilkins proposed in an essay a decimal-based unit of length, as a result of the French Revolution, the French Academy of Sciences charged a commission with determining a single scale for all measures. In 1668, Wilkins proposed using Christopher Wrens suggestion of defining the metre using a pendulum with a length which produced a half-period of one second, christiaan Huygens had observed that length to be 38 Rijnland inches or 39.26 English inches. This is the equivalent of what is now known to be 997 mm, no official action was taken regarding this suggestion. In the 18th century, there were two approaches to the definition of the unit of length. One favoured Wilkins approach, to define the metre in terms of the length of a pendulum which produced a half-period of one second. The other approach was to define the metre as one ten-millionth of the length of a quadrant along the Earths meridian, that is, the distance from the Equator to the North Pole. This means that the quadrant would have defined as exactly 10000000 metres at that time. To establish a universally accepted foundation for the definition of the metre, more measurements of this meridian were needed. This portion of the meridian, assumed to be the length as the Paris meridian, was to serve as the basis for the length of the half meridian connecting the North Pole with the Equator
6.
Second
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The second is the base unit of time in the International System of Units. It is qualitatively defined as the division of the hour by sixty. SI definition of second is the duration of 9192631770 periods of the corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. Seconds may be measured using a mechanical, electrical or an atomic clock, SI prefixes are combined with the word second to denote subdivisions of the second, e. g. the millisecond, the microsecond, and the nanosecond. Though SI prefixes may also be used to form multiples of the such as kilosecond. The second is also the unit of time in other systems of measurement, the centimetre–gram–second, metre–kilogram–second, metre–tonne–second. Absolute zero implies no movement, and therefore zero external radiation effects, the second thus defined is consistent with the ephemeris second, which was based on astronomical measurements. The realization of the second is described briefly in a special publication from the National Institute of Standards and Technology. 1 international second is equal to, 1⁄60 minute 1⁄3,600 hour 1⁄86,400 day 1⁄31,557,600 Julian year 1⁄, more generally, = 1⁄, the Hellenistic astronomers Hipparchus and Ptolemy subdivided the day into sixty parts. They also used an hour, simple fractions of an hour. No sexagesimal unit of the day was used as an independent unit of time. The modern second is subdivided using decimals - although the third remains in some languages. The earliest clocks to display seconds appeared during the last half of the 16th century, the second became accurately measurable with the development of mechanical clocks keeping mean time, as opposed to the apparent time displayed by sundials. The earliest spring-driven timepiece with a hand which marked seconds is an unsigned clock depicting Orpheus in the Fremersdorf collection. During the 3rd quarter of the 16th century, Taqi al-Din built a clock with marks every 1/5 minute, in 1579, Jost Bürgi built a clock for William of Hesse that marked seconds. In 1581, Tycho Brahe redesigned clocks that displayed minutes at his observatory so they also displayed seconds, however, they were not yet accurate enough for seconds. In 1587, Tycho complained that his four clocks disagreed by plus or minus four seconds, in 1670, London clockmaker William Clement added this seconds pendulum to the original pendulum clock of Christiaan Huygens. From 1670 to 1680, Clement made many improvements to his clock and this clock used an anchor escapement mechanism with a seconds pendulum to display seconds in a small subdial
7.
Joule
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The joule, symbol J, is a derived unit of energy in the International System of Units. It is equal to the transferred to an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre. It is also the energy dissipated as heat when a current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule, one joule can also be defined as, The work required to move an electric charge of one coulomb through an electrical potential difference of one volt, or one coulomb volt. This relationship can be used to define the volt, the work required to produce one watt of power for one second, or one watt second. This relationship can be used to define the watt and this SI unit is named after James Prescott Joule. As with every International System of Units unit named for a person, note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, section 5.2. The CGPM has given the unit of energy the name Joule, the use of newton metres for torque and joules for energy is helpful to avoid misunderstandings and miscommunications. The distinction may be also in the fact that energy is a scalar – the dot product of a vector force. By contrast, torque is a vector – the cross product of a distance vector, torque and energy are related to one another by the equation E = τ θ, where E is energy, τ is torque, and θ is the angle swept. Since radians are dimensionless, it follows that torque and energy have the same dimensions, one joule in everyday life represents approximately, The energy required to lift a medium-size tomato 1 m vertically from the surface of the Earth. The energy released when that same tomato falls back down to the ground, the energy required to accelerate a 1 kg mass at 1 m·s−2 through a 1 m distance in space. The heat required to raise the temperature of 1 g of water by 0.24 °C, the typical energy released as heat by a person at rest every 1/60 s. The kinetic energy of a 50 kg human moving very slowly, the kinetic energy of a 56 g tennis ball moving at 6 m/s. The kinetic energy of an object with mass 1 kg moving at √2 ≈1.4 m/s, the amount of electricity required to light a 1 W LED for 1 s. Since the joule is also a watt-second and the unit for electricity sales to homes is the kW·h. For additional examples, see, Orders of magnitude The zeptojoule is equal to one sextillionth of one joule,160 zeptojoules is equivalent to one electronvolt. The nanojoule is equal to one billionth of one joule, one nanojoule is about 1/160 of the kinetic energy of a flying mosquito
8.
Kilogram
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The kilogram or kilogramme is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype of the Kilogram. The avoirdupois pound, used in both the imperial and US customary systems, is defined as exactly 0.45359237 kg, making one kilogram approximately equal to 2.2046 avoirdupois pounds. Other traditional units of weight and mass around the world are also defined in terms of the kilogram, the gram, 1/1000 of a kilogram, was provisionally defined in 1795 as the mass of one cubic centimeter of water at the melting point of ice. The final kilogram, manufactured as a prototype in 1799 and from which the IPK was derived in 1875, had an equal to the mass of 1 dm3 of water at its maximum density. The kilogram is the only SI base unit with an SI prefix as part of its name and it is also the only SI unit that is still directly defined by an artifact rather than a fundamental physical property that can be reproduced in different laboratories. Three other base units and 17 derived units in the SI system are defined relative to the kilogram, only 8 other units do not require the kilogram in their definition, temperature, time and frequency, length, and angle. At its 2011 meeting, the CGPM agreed in principle that the kilogram should be redefined in terms of the Planck constant, the decision was originally deferred until 2014, in 2014 it was deferred again until the next meeting. There are currently several different proposals for the redefinition, these are described in the Proposed Future Definitions section below, the International Prototype Kilogram is rarely used or handled. In the decree of 1795, the term gramme thus replaced gravet, the French spelling was adopted in the United Kingdom when the word was used for the first time in English in 1797, with the spelling kilogram being adopted in the United States. In the United Kingdom both spellings are used, with kilogram having become by far the more common, UK law regulating the units to be used when trading by weight or measure does not prevent the use of either spelling. In the 19th century the French word kilo, a shortening of kilogramme, was imported into the English language where it has used to mean both kilogram and kilometer. In 1935 this was adopted by the IEC as the Giorgi system, now known as MKS system. In 1948 the CGPM commissioned the CIPM to make recommendations for a practical system of units of measurement. This led to the launch of SI in 1960 and the subsequent publication of the SI Brochure, the kilogram is a unit of mass, a property which corresponds to the common perception of how heavy an object is. Mass is a property, that is, it is related to the tendency of an object at rest to remain at rest, or if in motion to remain in motion at a constant velocity. Accordingly, for astronauts in microgravity, no effort is required to hold objects off the cabin floor, they are weightless. However, since objects in microgravity still retain their mass and inertia, the ratio of the force of gravity on the two objects, measured by the scale, is equal to the ratio of their masses. On April 7,1795, the gram was decreed in France to be the weight of a volume of pure water equal to the cube of the hundredth part of the metre
9.
Ionizing radiation
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Ionizing radiation is radiation that carries enough energy to free electrons from atoms or molecules, thereby ionizing them. Ionizing radiation is made up of energetic particles, ions or atoms moving at high speeds. The boundary between ionizing and non-ionizing electromagnetic radiation that occurs in the ultraviolet is not sharply defined, since different molecules, conventional definition places the boundary at a photon energy between 10 eV and 33 eV in the ultraviolet. Typical ionizing subatomic particles from radioactivity include alpha particles, beta particles, almost all products of radioactive decay are ionizing because the energy of radioactive decay is typically far higher than that required to ionize. Cosmic rays are generated by stars and certain events such as supernova explosions. Cosmic rays may also produce radioisotopes on Earth, which in turn decay, cosmic rays and the decay of radioactive isotopes are the primary sources of natural ionizing radiation on Earth referred to as background radiation. Ionizing radiation can also be generated artificially using X-ray tubes, particle accelerators, ionizing radiation is invisible and not directly detectable by human senses, so radiation detection instruments such as Geiger counters are required to detect it. However, it can cause emission of light upon interaction with matter, such as in Cherenkov radiation. Exposure to ionizing radiation damage to living tissue, and can result in mutation, radiation sickness, cancer. Ionizing radiation is categorized by the nature of the particles or electromagnetic waves that create the ionizing effect and these have different ionization mechanisms, and may be grouped as directly or indirectly ionizing. Any charged massive particle can ionize atoms directly by fundamental interaction through the Coulomb force if it carries sufficient kinetic energy and this includes atomic nuclei, electrons, muons, charged pions, protons, and energetic charged nuclei stripped of their electrons. When moving at relativistic speeds these particles have enough energy to be ionizing. For example, an alpha particle is ionizing, but moves at about 5% c. Natural cosmic rays are made up primarily of protons but also include heavier atomic nuclei like helium ions. Pions can also be produced in large amounts in particle accelerators, alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus. Alpha particle emissions are produced in the process of alpha decay. Alpha particles are named after the first letter in the Greek alphabet, the symbol for the alpha particle is α or α2+. Because they are identical to helium nuclei, they are sometimes written as He2+ or 4 2He2+ indicating a Helium ion with a +2 charge
10.
International System of Units
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The International System of Units is the modern form of the metric system, and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units, the system also establishes a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system was published in 1960 as the result of an initiative began in 1948. It is based on the system of units rather than any variant of the centimetre-gram-second system. The motivation for the development of the SI was the diversity of units that had sprung up within the CGS systems, the International System of Units has been adopted by most developed countries, however, the adoption has not been universal in all English-speaking countries. The metric system was first implemented during the French Revolution with just the metre and kilogram as standards of length, in the 1830s Carl Friedrich Gauss laid the foundations for a coherent system based on length, mass, and time. In the 1860s a group working under the auspices of the British Association for the Advancement of Science formulated the requirement for a coherent system of units with base units and derived units. Meanwhile, in 1875, the Treaty of the Metre passed responsibility for verification of the kilogram, in 1921, the Treaty was extended to include all physical quantities including electrical units originally defined in 1893. The units associated with these quantities were the metre, kilogram, second, ampere, kelvin, in 1971, a seventh base quantity, amount of substance represented by the mole, was added to the definition of SI. On 11 July 1792, the proposed the names metre, are, litre and grave for the units of length, area, capacity. The committee also proposed that multiples and submultiples of these units were to be denoted by decimal-based prefixes such as centi for a hundredth, on 10 December 1799, the law by which the metric system was to be definitively adopted in France was passed. Prior to this, the strength of the magnetic field had only been described in relative terms. The technique used by Gauss was to equate the torque induced on a magnet of known mass by the earth’s magnetic field with the torque induced on an equivalent system under gravity. The resultant calculations enabled him to assign dimensions based on mass, length, a French-inspired initiative for international cooperation in metrology led to the signing in 1875 of the Metre Convention. Initially the convention only covered standards for the metre and the kilogram, one of each was selected at random to become the International prototype metre and International prototype kilogram that replaced the mètre des Archives and kilogramme des Archives respectively. Each member state was entitled to one of each of the prototypes to serve as the national prototype for that country. Initially its prime purpose was a periodic recalibration of national prototype metres. The official language of the Metre Convention is French and the version of all official documents published by or on behalf of the CGPM is the French-language version
11.
Dosimetry
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Internal dosimetry due to the ingestion or inhalation of radioactive materials relies on a variety of physiological or imaging techniques. External dosimetry, due to irradiation from a source is based on measurements with a dosimeter. Dosimetry is used extensively for radiation protection and is applied to occupational radiation workers, where irradiation is expected. There are several ways of measuring absorbed doses from ionizing radiation, people in occupational contact with radioactive substances or who may be exposed to radiation routinely carry personal dosimeters. These are specifically designed to record and indicate the absorbed dose received, traditionally these were badges containing photographic film, which would be chemically developed, following exposure to indicate the total absorbed dose received. Film badges have now largely replaced with other devices such as the TLD badge which uses Thermoluminescent dosimetry or optically stimulated luminescence badges. A number of devices known as Electronic Personal Dosimeters have come into general use using semiconductor detection. These are worn as badges but can give an indication of instantaneous dose rate, a good deal of information can be made immediately available to the wearer of the recorded dose and current dose rate via a local display. They can be used as the main stand-alone dosimeter, or as a supplement to such as a TLD badge and these devices are particularly useful for real-time monitoring of dose where a high dose rate is expected which will time-limit the wearers exposure. In certain circumstances, a dose can be inferred from readings taken by fixed instrumentation in an area in which the person concerned has been working and this would generally only be used if personal dosimetry had not been issued, or a personal dosimeter has been damaged or lost. Such calculations would take a view of the likely received dose. Internal dosimetry is used to evaluate the dose due to the intake of radionuclides into the human body. Medical dosimetry is the calculation of absorbed dose and optimization of dose delivery in radiation therapy and it is often performed by a professional medical dosimetrist with specialized training in the field. In order to plan the delivery of radiation therapy, the produced by the sources is usually characterized with percentage depth dose curves. In radiation therapy, three-dimensional dose distributions are often evaluated using the technique known as gel dosimetry. Environmental Dosimetry is used where it is likely that the environment will generate a significant radiation dose, an example of this is radon monitoring. Radon is a radioactive gas generated by the decay of uranium, certain geographic areas, due to the underlying geology, continually generate radon which permeates its way to the earths surface. In some cases the dose can be significant in buildings where the gas can accumulate, a number of specialised dosimetry techniques are used to evaluate the dose that a buildings occupants may receive
12.
Radiation protection
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The IAEA also states The accepted understanding of the term radiation protection is restricted to protection of people. Suggestions to extend the definition to include the protection of species or the protection of the environment are controversial. Ionizing radiation is used in industry and medicine, and can present a significant health hazard. It causes microscopic damage to living tissue, which can result in burns and radiation sickness at high exposures. Fundamental to radiation protection is the reduction of expected dose and the measurement of dose uptake. The ICRP recommends, develops and maintains the International System of Radiological Protection based on evaluation of the body of scientific studies available, the recommendations it makes flow down to national regulators, which have the opportunity to incorporate them into law. This is shown in the accompanying diagram, the types of exposure, as well as government regulations and legal exposure limits are different for each of these groups, so they must be considered separately. There are three factors that control the amount, or dose, of radiation received from a source, Radiation exposure can be managed by a combination of these factors, Time, Reducing the time of an exposure reduces the effective dose proportionally. An example of reducing radiation doses by reducing the time of exposures might be improving operator training to reduce the time they take to handle a source, distance, Increasing distance reduces dose due to the inverse square law. Distance can be as simple as handling a source with forceps rather than fingers, Shielding, The term biological shield refers to a mass of absorbing material placed around a reactor, or other radioactive source, to reduce the radiation to a level safe for humans. Hence, shielding strength or thickness is measured in units of g/cm2. The radiation that manages to get through falls exponentially with the thickness of the shield, in x-ray facilities, walls surrounding the room with the x-ray generator may contain lead sheets, or the plaster may contain barium sulfate. Operators view the target through a glass screen, or if they must remain in the same room as the target. Almost any material can act as a shield from gamma or x-rays if used in sufficient amounts, practical radiation protection tends to be a job of juggling the three factors to identify the most cost effective solution. These use the overall principles, Justification, No unnecessary use of radiation is permitted. Limitation, Each individual must be protected against risks that are far too large through individual radiation dose limits, optimization, Radiation doses should all be kept as low as reasonably achievable. This means that it is not enough to remain under the radiation dose limits, as permit holder, you are responsible for ensuring that radiation doses are as low as reasonably achievable, which means that the actual radiation doses are often much lower than the permitted limit. ALARP is an acronym for an important principle in exposure to radiation and other health risks
13.
Sweden
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Sweden, officially the Kingdom of Sweden, is a Scandinavian country in Northern Europe. It borders Norway to the west and Finland to the east, at 450,295 square kilometres, Sweden is the third-largest country in the European Union by area, with a total population of 10.0 million. Sweden consequently has a low density of 22 inhabitants per square kilometre. Approximately 85% of the lives in urban areas. Germanic peoples have inhabited Sweden since prehistoric times, emerging into history as the Geats/Götar and Swedes/Svear, Southern Sweden is predominantly agricultural, while the north is heavily forested. Sweden is part of the area of Fennoscandia. The climate is in very mild for its northerly latitude due to significant maritime influence. Today, Sweden is a monarchy and parliamentary democracy, with a monarch as head of state. The capital city is Stockholm, which is also the most populous city in the country, legislative power is vested in the 349-member unicameral Riksdag. Executive power is exercised by the government chaired by the prime minister, Sweden is a unitary state, currently divided into 21 counties and 290 municipalities. Sweden emerged as an independent and unified country during the Middle Ages, in the 17th century, it expanded its territories to form the Swedish Empire, which became one of the great powers of Europe until the early 18th century. Swedish territories outside the Scandinavian Peninsula were gradually lost during the 18th and 19th centuries, the last war in which Sweden was directly involved was in 1814, when Norway was militarily forced into personal union. Since then, Sweden has been at peace, maintaining a policy of neutrality in foreign affairs. The union with Norway was peacefully dissolved in 1905, leading to Swedens current borders, though Sweden was formally neutral through both world wars, Sweden engaged in humanitarian efforts, such as taking in refugees from German-occupied Europe. After the end of the Cold War, Sweden joined the European Union on 1 January 1995 and it is also a member of the United Nations, the Nordic Council, Council of Europe, the World Trade Organization and the Organisation for Economic Co-operation and Development. Sweden maintains a Nordic social welfare system that provides health care. The modern name Sweden is derived through back-formation from Old English Swēoþēod and this word is derived from Sweon/Sweonas. The Swedish name Sverige literally means Realm of the Swedes, excluding the Geats in Götaland, the etymology of Swedes, and thus Sweden, is generally not agreed upon but may derive from Proto-Germanic Swihoniz meaning ones own, referring to ones own Germanic tribe
14.
Linear no-threshold model
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The linear no-threshold model is a model used in radiation protection to quantify radiation exposure and set regulatory limits. It assumes that the term, biological damage caused by ionizing radiation is directly proportional to the dose. This allows the summation by dosimeters of all radiation exposure, without taking into consideration dose levels or dose rates. In other words, radiation is considered harmful with no safety threshold. This is a reversal from previous recommendations by the same organization, there are three active challenges to the LNT model currently being considered by the US Nuclear Regulatory Commission. One was filed by Nuclear Medicine Professor Carol Marcus of UCLA, whether the model describes the reality for small-dose exposures is disputed. Because the current data are inconclusive, scientists disagree on which model should be used, such practice has been condemned by the International Commission on Radiological Protection. The LNT model is applied to other cancer hazards such as polychlorinated biphenyls in drinking water. The linear-no-threshold model was first expressed by John Gofman, and rejected by the Department of Energy, according to Gofman, the conclusion is that any given dose equivalent of radiation will produce the same number of cancers, no matter how thinly it is spread. For example, a hot particle embedded in an organ results in a high dose in the cells directly adjacent to the hot particle. The linear no-threshold model is used to extrapolate the number of extra deaths caused by exposure to environmental radiation. A linear model has long used in health physics to set maximum acceptable radiation exposures. Ramsar, located in Iran, is quoted as being a counter example to LNT. Actually, the population of the districts is small and only receive an average of 6 millisieverts per year. On the other hand, there may be non-cancer effects from the background such as chromosomal aberrations or female infertility. A2005 study of Ramsar, Iran showed that cancer incidence was lower in the high-radiation area than in seven surrounding regions with lower levels of natural background radiation. A fuller epidemiological study of the region showed no difference in mortality for males. However in medical journals, studies detail that in Sweden in the year of the chernobyl accident, more advanced maternal age in Swedish mothers was linked with a reduction in offspring IQ, in a paper published in 2012
15.
Absorbed dose
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Absorbed dose is a physical dose quantity D representing the mean energy imparted to matter per unit mass by ionizing radiation. In the SI system of units, the unit of measure is joules per kilogram, the non-SI CGS unit rad is sometimes also used, predominantly in the USA. Absorbed dose is used in the calculation of dose uptake in living tissue in both radiation protection and radiology and it is also used to directly compare the effect of radiation on inanimate matter. The quantity absorbed dose is of importance in radiological protection for calculating radiation dose. However, absorbed dose is a quantity and used unmodified is not an adequate indicator of the likely health effects in humans. It has been found that for stochastic radiation risk consideration must be given to the type of radiation and the sensitivity of the irradiated tissues, which requires the use of modifying factors. Conventionally therefore, unmodified absorbed dose is not used for comparing stochastic risks, to represent stochastic risk the equivalent dose H T and effective dose E are used, and appropriate dose factors and coefficients are used to calculate these from the absorbed dose. Equivalent and effective dose quantities are expressed in units of the sievert or rem which implies that biological effects have been taken into account and these are usually in accordance with the recommendations of the International Committee on Radiation Protection and International Commission on Radiation Units and Measurements. The coherent system of protection quantities developed by them is shown in the accompanying diagram. Absorbed dose is used to rate the survivability of devices such as components in ionizing radiation environments. Absorbed dose is the physical quantity used to ensure irradiated food has received the correct dose to ensure effectiveness. Variable doses are used depending on the application and can be as high as 70 kGy, the absorbed dose is equal to the radiation exposure of the radiation beam multiplied by the ionization energy of the medium to be ionized. For example, the energy of dry air at 20 °C and 101.325 kPa of pressure is 33. 97±0.06 J/C. Therefore, an exposure of 2. 58×10−4 C/kg would deposit an absorbed dose of 8. 76×10−3 J/kg in dry air at those conditions, self-shielding means that the absorbed dose will be higher in the tissues facing the source than deeper in the body. The mass average can be important in evaluating the risks of radiotherapy treatments, since they are designed to very specific volumes in the body. For example, if 10% of a bone marrow mass is irradiated with 10 Gy of radiation locally. Bone marrow makes up 4% of the mass, so the whole-body absorbed dose would be 0.04 Gy. The first figure is indicative of the effects on the tumour, while the second
16.
Equivalent dose
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Equivalent dose is a dose quantity H representing the stochastic health effects of low levels of ionizing radiation on the human body. It is derived from the physical quantity absorbed dose, but also takes account the biological effectiveness of the radiation. In the SI system of units, the unit of measure is the sievert, to enable consideration of stochastic health risk, calculations are performed to convert the physical quantity absorbed dose into equivalent dose, the details of which depend on the radiation type. The ICRP has assigned radiation weighting factors to specified radiation types dependent on their relative biological effectiveness, to obtain the equivalent dose for a mix of radiation types and energies, a sum is taken over all types of radiation energy doses. This takes into account the contributions of the biological effect of different radiation types. The concept of equivalent dose was developed in the 1950s, in its 1990 recommendations, the ICRP revised the definitions of some radiation protection quantities, and provided new names for the revised quantities. This included a proposal to use of equivalent dose as a separate protection quantity. In the United States the roentgen equivalent man, equal to 0.01 sievert, is still in common use, equivalent dose HT is used for assessing stochastic health risk due to external radiation fields that penetrate uniformly through the whole body. However it needs further corrections when the field is applied only to part of the body, to enable this a further dose quantity called effective dose must be used to take into account the varying sensitivity of different organs and tissues to radiation. Whilst equivalent dose is used for the effects of external radiation. The ICRP defines an equivalent dose quantity for individual committed dose, a committed dose from an internal source represents the same effective risk as the same amount of equivalent dose applied uniformly to the whole body from an external source. This refers specifically to the dose in a tissue or organ. The ICRP states Radionuclides incorporated in the human body irradiate the tissues over time periods determined by their physical half-life, thus they may give rise to doses to body tissues for many months or years after the intake. The need to regulate exposures to radionuclides and the accumulation of radiation dose over extended periods of time has led to the definition of committed dose quantities, somebody says that There is no confusion between equivalent dose and dose equivalent. Somebody says, Indeed, they are same concepts, currently, the ICRPs definition of equivalent dose represents an average dose over an organ or tissue, and radiation weighting factors are used instead of quality factors. The International Committee for Weights and Measures and the US Nuclear Regulatory Commission continue to use the old terminology of quality factors, the NRC quality factors are independent of linear energy transfer, though not always equal to the ICRP radiation weighting factors. The NRCs definition of dose equivalent is the product of the dose in tissue, quality factor. However, it is apparent from their definition of dose equivalent that all other necessary modifying factors excludes the tissue weighting factor
17.
Effective dose (radiation)
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Effective dose is a dose quantity in the International Commission on Radiological Protection system of radiological protection. The SI unit for dose is the sievert which represents a 5. 5% chance of developing cancer. The name effective dose replaced the name effective dose equivalent in 1991, since 1977 it has been the central quantity for dose limitation in the ICRP international system of radiological protection. The effective dose is thus a central quantity for regulatory purposes. The calculation of dose is required for partial or non-uniform irradiation of the human body because equivalent dose does not consider the tissue irradiated. A radiation field irradiating only a portion of the body will carry lower risk if the same field irradiated the whole body. To take this account, the effective doses to the component parts of the body which have been irradiated are calculated and summed. This becomes the effective dose for the body, dose quantity E. It is a dose quantity which can be calculated. Effective dose can be calculated for committed dose which is the dose resulting from inhaling, ingesting. The commitment period is taken to be 50 years for adults, ionizing radiation deposits energy in the matter being irradiated. The quantity used to express this is the dose, a physical dose quantity that is dependent on the level of incident radiation. The sum of effective doses to all organs and tissues of the body represents the effective dose for the whole body, if only part of the body is irradiated, then only those regions are used to calculate the effective dose. The ICRP tissue weighting factors are given in the table. Some tissues like bone marrow are particularly sensitive to radiation, so they are given a weighting factor that is large relative to the fraction of body mass they represent. Other tissues like the bone surface are particularly insensitive to radiation and are assigned a disproportionally low weighting factor. Calculating from the equivalent dose, E = ∑ T W T ⋅ H T = ∑ T W T ∑ R W R ⋅ D ¯ T, R and these weighting factors have been revised twice, as shown in the chart above. The US Nuclear Regulatory Commission still endorses the ICRPs 1977 tissue weighting factors in their regulations, the US Nuclear Regulatory Commission has retained in the US regulation system the older term effective dose equivalent to refer to a similar quantity to the ICRP effective dose
18.
Gray (unit)
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The gray is a derived unit of ionizing radiation dose in the International System of Units. It is defined as the absorption of one joule of energy per kilogram of matter. It is used as a measure of absorbed dose, specific energy and it is a physical quantity, and does not take into account any biological context. Unlike the pre-1971 non-SI roentgen unit of exposure, the gray when used for absorbed dose is defined independently of any target material. However, when measuring kerma the reference target material must be defined explicitly, usually as dry air at standard temperature and pressure. The corresponding cgs unit, the rad, remains common in the United States, though strongly discouraged in the guide for U. S. National Institute of Standards. The gray was named after British physicist Louis Harold Gray, a pioneer in the measurement of X-ray and radium radiation and it was adopted as part of the International System of Units in 1975. One gray is the absorption of one joule of energy, in the form of ionizing radiation, measuring and controlling the value of absorbed dose is vital to ensuring correct operation of these processes. Kerma is a measure of the energy of ionisation due to irradiation. Importantly, kerma dose is different from absorbed dose, depending on the energies involved. The measurement of absorbed dose is a problem, and so many different dosimeters are available for these measurements. These dosimeters cover measurements that can be done in 1-D, 2-D and 3-D, in radiation therapy, the amount of radiation applied varies depending on the type and stage of cancer being treated. For curative cases, the dose for a solid epithelial tumor ranges from 60 to 80 Gy. Preventive doses are typically around 45–60 Gy in 1. 8–2 Gy fractions, the absorbed dose also plays an important role in radiation protection, as it is the starting point for calculating the effect of low levels of radiation. In radiation protection dose assessment, the health risk is defined as the probability of cancer induction. This probability is related to the equivalent dose in sieverts, which has the dimensions as the gray. It is related to the gray by weighting factors described in the articles on equivalent dose, to avoid any risk of confusion between the absorbed dose and the equivalent dose, the absorbed dose is stated in grays and the equivalent dose is stated in sieverts. The accompanying diagrams show how absorbed dose is first obtained by computational techniques, radiation poisoning - The gray is conventionally used to express the severity of what are known as tissue effects from doses received in acute exposure to high levels of ionizing radiation
19.
Linear energy transfer
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Linear energy transfer is a term used in dosimetry. It describes the action of radiation upon matter and it is identical to the retarding force acting on a charged ionizing particle travelling through the matter. It describes how much energy an ionizing particle transfers to the material traversed per unit distance, by definition, LET is a positive quantity. LET depends on the nature of the radiation as well as on the material traversed, a high LET will attenuate the radiation more quickly, generally making shielding more effective and preventing deep penetration. On the other hand, the concentration of deposited energy can cause more severe damage to any microscopic structures near the particle track. Dosimetry attempts to factor in this effect with radiation weighting factors, linear energy transfer is closely related to stopping power, since both equal the retarding force. The unrestricted linear energy transfer is identical to linear electronic stopping power, but the stopping power and LET concepts are different in the respect that total stopping power has the nuclear stopping power component, and this component does not cause electronic excitations. Hence nuclear stopping power is not contained in LET, the appropriate SI unit for LET is the newton, but it is most typically expressed in units of kiloelectronvolts per micrometre or megaelectronvolts per centimetre. While medical physicists and radiobiologists usually speak of energy transfer. Many studies focus upon the energy transferred in the vicinity of the particle track. This energy limit is meant to exclude secondary electrons that carry energy far from the particle track. This approximation neglects the directional distribution of radiation and the non-linear path of delta rays. Here, the use of the term infinity is not to be literally, it simply means that no energy transfers. During his investigations of radioactivity, Ernest Rutherford coined the terms alpha rays, beta rays and gamma rays for the three types of emissions that occur during radioactive decay. Linear energy transfer is best defined for monoenergetic ions, i. e. protons, alpha particles, and these particles cause frequent direct ionizations within a narrow diameter around a relatively straight track, thus approximating continuous deceleration. At equilibrium, the incident particle essentially comes to rest or is absorbed, since the LET varies over the particle track, an average value is often used to represent the spread. Averages weighted by track length or weighted by absorbed dose are present in the literature and these averages are not widely separated for heavy particles with high LET, but the difference becomes more important in the other type of radiations discussed below. Electrons produced in nuclear decay are called beta particles, because of their low mass relative to atoms, they are strongly scattered by nuclei, much more so than heavier particles
20.
United states of america
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Forty-eight of the fifty states and the federal district are contiguous and located in North America between Canada and Mexico. The state of Alaska is in the northwest corner of North America, bordered by Canada to the east, the state of Hawaii is an archipelago in the mid-Pacific Ocean. The U. S. territories are scattered about the Pacific Ocean, the geography, climate and wildlife of the country are extremely diverse. At 3.8 million square miles and with over 324 million people, the United States is the worlds third- or fourth-largest country by area, third-largest by land area. It is one of the worlds most ethnically diverse and multicultural nations, paleo-Indians migrated from Asia to the North American mainland at least 15,000 years ago. European colonization began in the 16th century, the United States emerged from 13 British colonies along the East Coast. Numerous disputes between Great Britain and the following the Seven Years War led to the American Revolution. On July 4,1776, during the course of the American Revolutionary War, the war ended in 1783 with recognition of the independence of the United States by Great Britain, representing the first successful war of independence against a European power. The current constitution was adopted in 1788, after the Articles of Confederation, the first ten amendments, collectively named the Bill of Rights, were ratified in 1791 and designed to guarantee many fundamental civil liberties. During the second half of the 19th century, the American Civil War led to the end of slavery in the country. By the end of century, the United States extended into the Pacific Ocean. The Spanish–American War and World War I confirmed the status as a global military power. The end of the Cold War and the dissolution of the Soviet Union in 1991 left the United States as the sole superpower. The U. S. is a member of the United Nations, World Bank, International Monetary Fund, Organization of American States. The United States is a developed country, with the worlds largest economy by nominal GDP. It ranks highly in several measures of performance, including average wage, human development, per capita GDP. While the U. S. economy is considered post-industrial, characterized by the dominance of services and knowledge economy, the United States is a prominent political and cultural force internationally, and a leader in scientific research and technological innovations. In 1507, the German cartographer Martin Waldseemüller produced a map on which he named the lands of the Western Hemisphere America after the Italian explorer and cartographer Amerigo Vespucci
21.
Computational human phantom
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Computational human phantoms are models of the human body used in computerized analysis. Since the 1960s, the science community has developed and applied these models for ionizing radiation dosimetry studies. These models have become increasingly accurate with respect to the structure of the human body. As computing evolved, so did the phantoms, graduating from phantoms based on simple quadratic equations to voxelized phantoms, which were based on actual medical images of the human body, was a major step. Phantoms have been developed for a variety of humans, from children to adolescents to adults, male and female. With such a variety of phantoms, many kinds of simulations can be run, over the years, the results of these simulations have created an assortment of standards that have been adopted in the International Commission on Radiological Protection recommendations. The very first generation computational phantoms were developed to address the need to better assess organ doses from internally deposited radioactive materials in workers, until the late 1950s, the ICRP still used very simple models. In these calculations, each organ of the body was assumed to be represented as a sphere with an effective radius, the radionuclide of interest was assumed to be located at the center of the sphere and the effective absorbed energy was calculated for each organ. Phantoms such as the Shepp-Logan Phantom were used as models of a head in the development. The feature of stylized computational phantom is finely tuned by adjusting individual parameters of the equations, which describes the volume, position. Stylized computational phantom has a history of development through the 1960s to 1980s. The MIRD phantom was developed by Fisher and Snyder at Oak Ridge National Laboratory in 1960s with 22 internal organs and it is the first anthropomorphic phantom representing a hermaphrodite adult for internal dosimetry. Based on MIRD phantom, many derivations of phantoms were developed for the following decades, although many efforts were undertaken to diversify and extend its applications in radiation protection, radiation therapy, and medical imaging, one cannot overcome its inborn limitation. The representation of internal organs in this mathematical phantom was crude, by capturing only the most general description of the position, with the powerful computer and tomographic imaging technologies became available in the late 1980s, the history launched a new era of voxel phantoms. The stylized phantoms provided only basic information with a degree of error. More accurate methods of simulating a human body were necessary to advance, to allow further research, the computer technology had to become more powerful and more readily available. This did not occur until the 1980s, the real breakthrough occurred when computed tomography and magnetic resonance imaging devices could generate highly accurate images of internal organs in three dimensions and in digital format. Researchers discovered that they could take that diagnostic data and transform it into a voxel format, today there are over 38 human phantoms in voxel format, for many different uses
22.
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
23.
Dosimeter
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A radiation dosimeter is a device that measures exposure to ionizing radiation. It has two uses, for human radiation protection and for measurement of dose in both medical and industrial processes. Ionising radiation damage to the body is cumulative, and is related to the total dose received. Such devices are known as legal if they have been approved for use in recording personnel dose for regulatory purposes. These are especially useful in high dose areas where residence time of the wearer is limited due to dose constraints, the dosimeter can be reset, usually after taking a reading for record purposes, and thereby re-used multiple times. MOSFET dosimeters are now used as clinical dosimeters for radiotherapy radiation beams, the main advantages of MOSFET devices are,1. The MOSFET dosimeter is direct reading with a thin active area. The physical size of the MOSFET when packaged is less than 4 mm.3, the post radiation signal is permanently stored and is dose rate independent. Gate oxide of MOSFET which is conventionally silicon dioxide is an active sensing material in MOSFET dosimeters, radiation creates defects in oxide, which in turn affects the threshold voltage of the MOSFET. This change in voltage is proportional to radiation dose. Alternate high-k gate dielectrics like Hafnium dioxide and Aluminum oxides are also proposed as a radiation dosimeters, film badge dosimeters are for one-time use only. The level of absorption is indicated by a change to the film emulsion. Quartz fiber dosimeters are charged to a high voltage, as the gas in the dosimeter chamber becomes ionized by radiation the charge leaks away, causing the fiber indicator to change against a graduated scale. A thermoluminescent dosimeter measures ionizing radiation exposure by measuring the intensity of light emitted from a crystal in the detector when heated. The intensity of light emitted is dependent upon the radiation exposure, both the quartz fiber and film badge types are being superseded by the TLD and the EPD. This is shown in the accompanying diagram and these quantities cannot be practically measured and are a calculated value of irradiation of organs of the human body, which is arrived at by using an anthropomorphic phantom. This is a 3D computational model of the body which attempts to take into account a number of complex effects such as body self-shielding. As protection quantities cannot practically be measured, operational quantities are used to them to practical radiation instrument
24.
UK
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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
25.
Ionising Radiations Regulations 1999
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The Ionising Radiations Regulations 1999 are a statutory instrument which form the main legal requirements for the use and control of ionising radiation in the United Kingdom. The regulations came into force on 1 January 2000, replacing the Ionising Radiations Regulations 1985 and they effectively implement the majority of the European Basic Safety Standards Directive 96/29/Euratom under the auspices of the Health and Safety at Work etc. This European Directive is in turn a reflection of the recommendations of the International Commission on Radiological Protection, the regulations are aimed at employers and are enforced by the Health and Safety Executive. Local rules including the designation of controlled areas, defined as places where special procedures are needed to restrict significant exposure, in 2013 the European Union adopted directive 2013/59/Euratom which requires updated Ionising Radiations Regulations to implement the directive in UK law by 2018. Changes include reduced eye dose limits as a result of updated ICRP recommendations, the regulations impose duties on employers to protect employees and anyone else from radiation arising from work with radioactive substances and other forms of ionising radiation. In the United Kingdom the Health and Safety Executive is one of a number of bodies which regulates workplaces which could expose workers to radiation. Radiation itself is energy that travels either as electromagnetic waves, or as subatomic particles, Ionising radiation occurs naturally but can also be artificially created. Generally people can be exposed to radiation externally from radioactive material or internally by inhaling or ingesting radioactive substances, exposure to electromagnetic rays such as x-rays and gamma rays can, depending on the time exposed, cause sterility, genetic defects, premature ageing and death. Health risks caused by exposure to this type of radiation will often be as a result of too much exposure to light either from the sun or from sunbeds which could lead to skin cancer. The regulations are split into seven parts containing 41 regulations, dose limits do not apply to people undergoing a medical exposure or to those acting as comforters and carers to such. The following table shows radiation quantities in SI and non-SI units, the European Union European units of measurement directives required that non-SI units use for public health. Purposes be phased out by 31 December 1985, sievert - SI unit of radiation dose
26.
Relative biological effectiveness
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In radiobiology, the relative biological effectiveness is the ratio of biological effectiveness of one type of ionizing radiation relative to another, given the same amount of absorbed energy. The RBE is a value that varies depending on the particles, energies involved. It is a set of experimental measurements, in dosimetry, the RBE is represented in regulations by the radiation weighting factor, or formerly, the quality factor. These weighting factors, arrived at by consensus of governments, industry, the higher the RBE or weighting factor numbers for a type of radiation, the more damaging is the type of radiation, per unit of energy deposited in biological tissues. Different types of radiation have different biological effectiveness mainly because they transfer their energy to the tissue in different ways. Photons and beta particles have a low energy transfer coefficient, meaning that they ionize atoms in the tissue that are spaced by several hundred nanometers apart. In contrast, the more massive alpha particles and neutrons leave a denser trail of ionized atoms in their wake. Radiation weighting factors that go from physical energy to biological effect must not be confused with tissue weighting factors, the radiation weighting factors will be approximately the same as the RBEs that result from some experiments, but may be quite different from RBEs that result from other experiments. Both doses are quantified by the amount of energy absorbed in the cells, for some kinds of radiation, the RBE is strongly dependent on the energy of the individual particles. Early on it was found that X-rays, gamma radiation, therefore, the standard radiation type X is generally an X-ray beam with 250 keV photons. As a result, the biological effectiveness of beta and photon radiation is essentially 1. For other radiation types, the RBE is not a physical quantity, since it varies somewhat with the type of tissue. Thus, for example, the RBE for alpha radiation is 2–3 when measured on bacteria, 4–6 for simple eukaryotic cells, the RBE of neutrons is 4–6 for bacteria, 8–12 for simple eukaryotic cells, and 12–16 for higher eukaryotic cells. In the early experiments, the sources of radiation were all external to the cells that were irradiated, however, since alpha particles cannot traverse the outermost dead layer of human skin, they can do significant damage only if they come from the decay of atoms inside the body. Since the range of a particle is typically about the diameter of a single eukaryotic cell. For this reason, it has suggested that the health impact of contamination by alpha emitters might have been substantially underestimated. Measurements of RBE with external sources also neglect the ionization caused by the recoil of the due to the alpha decay. The parent nucleus is required to recoil, upon emission of an alpha particle, the bulk of studies, using sources that are external to the cell, have yielded RBEs between 10 and 20
27.
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
28.
Beta particle
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Two forms of beta decay, β− and β+, respectively produce electrons and positrons. Beta particles are a type of ionizing radiation, the neutron turns into a proton through the emission of a virtual W− boson. At the quark level, W− emission turns a down quark into an up quark, the virtual W− boson then decays into an electron and an antineutrino. Beta decay commonly occurs among the neutron-rich fission byproducts produced in nuclear reactors, free neutrons also decay via this process. Both of these contribute to the copious numbers of beta rays. The daughter nucleus is a lower-energy state, of the three common types of radiation given off by radioactive materials, alpha, beta and gamma, beta has the medium penetrating power and the medium ionising power. Although the beta particles given off by different radioactive materials vary in energy, shielding composed of materials with lower atomic weight generates gammas with lower energy, making such shields somewhat more effective per unit mass than ones made of high-Z materials such as lead. Being composed of charged particles, beta radiation is more strongly ionizing than gamma radiation, when passing through matter, a beta particle is decelerated by electromagnetic interactions and may give off bremsstrahlung x-rays. In water, beta radiation from nuclear fission products typically exceeds the speed of light in that material. The intense beta radiation from the rods of pool-type reactors can thus be visualized through the transparent water that covers. The ionizing or excitation effects of particles on matter are the fundamental processes by which radiometric detection instruments detect. The ionization of gas is used in ion chambers and Geiger-Muller counters, beta particles can be used to treat health conditions such as eye and bone cancer and are also used as tracers. Strontium-90 is the material most commonly used to produce beta particles, beta particles are also used in quality control to test the thickness of an item, such as paper, coming through a system of rollers. Some of the radiation is absorbed while passing through the product. If the product is too thick or thin, a correspondingly different amount of radiation will be absorbed. A computer program monitoring the quality of the paper will then move the rollers to change the thickness of the final product. An illumination device called a betalight contains tritium and a phosphor, as tritium decays, it emits beta particles, these strike the phosphor, causing the phosphor to give off photons, much like the cathode ray tube in a television. Beta-plus decay of a radioactive isotope is the source of the positrons used in positron emission tomography
29.
Muon
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The muon is an elementary particle similar to the electron, with an electric charge of −1 e and a spin of 1/2, but with a much greater mass. It is classified as a lepton, as is the case with other leptons, the muon is not believed to have any sub-structure—that is, it is not thought to be composed of any simpler particles. The muon is a subatomic particle with a mean lifetime of 2.2 µs. Muon decay almost always produces at least three particles, which must include an electron of the charge as the muon and two neutrinos of different types. Like all elementary particles, the muon has a corresponding antiparticle of opposite charge but equal mass and spin, muons are denoted by μ− and antimuons by μ+. Muons were previously called mu mesons, but are not classified as mesons by modern particle physicists, muons have a mass of 105.7 MeV/c2, which is about 207 times that of the electron. Due to their mass, muons are not as sharply accelerated when they encounter electromagnetic fields. As an example, so-called secondary muons, generated by cosmic rays hitting the atmosphere, can penetrate to the Earths surface, because muons have a very large mass and energy compared with the decay energy of radioactivity, they are never produced by radioactive decay. These interactions usually produce pi mesons initially, which most often decay to muons, muons were discovered by Carl D. Anderson and Seth Neddermeyer at Caltech in 1936, while studying cosmic radiation. Anderson noticed particles that curved differently from electrons and other known particles when passed through a magnetic field and they were negatively charged but curved less sharply than electrons, but more sharply than protons, for particles of the same velocity. Thus Anderson initially called the new particle a mesotron, adopting the prefix meso- from the Greek word for mid-, the existence of the muon was confirmed in 1937 by J. C. The transition of a particle from neutron state to proton state is not always accompanied by the emission of light particles. The transition is taken up by another heavy particle. Because of its mass, the mu meson was initially thought to be Yukawas particle, with two particles now known with the intermediate mass, the more general term meson was adopted to refer to any such particle within the correct mass range between electrons and nucleons. The difference, in part, was that mu mesons did not interact with the nuclear force, newer mesons also showed evidence of behaving like the pi meson in nuclear interactions, but not like the mu meson. Also, the mu mesons decay products included both a neutrino and an antineutrino, rather than just one or the other, as was observed in the decay of other charged mesons. In the quark model, a meson was no longer defined by mass, mu mesons, however, had shown themselves to be fundamental particles like electrons, with no quark structure. Thus, mu mesons were not mesons at all, in the new sense and use of the term used with the quark model of particle structure
30.
Neutron
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The neutron is a subatomic particle, symbol n or n0, with no net electric charge and a mass slightly larger than that of a proton. Protons and neutrons, each with approximately one atomic mass unit, constitute the nucleus of an atom. Their properties and interactions are described by nuclear physics, the nucleus consists of Z protons, where Z is called the atomic number, and N neutrons, where N is the neutron number. The atomic number defines the properties of the atom. The terms isotope and nuclide are often used synonymously, but they are chemical and nuclear concepts, the atomic mass number, symbol A, equals Z+N. For example, carbon has atomic number 6, and its abundant carbon-12 isotope has 6 neutrons, some elements occur in nature with only one stable isotope, such as fluorine. Other elements occur with many stable isotopes, such as tin with ten stable isotopes, even though it is not a chemical element, the neutron is included in the table of nuclides. Within the nucleus, protons and neutrons are bound together through the nuclear force, neutrons are produced copiously in nuclear fission and fusion. They are a contributor to the nucleosynthesis of chemical elements within stars through fission, fusion. The neutron is essential to the production of nuclear power, in the decade after the neutron was discovered in 1932, neutrons were used to induce many different types of nuclear transmutations. These events and findings led to the first self-sustaining nuclear reactor, free neutrons, or individual neutrons free of the nucleus, are effectively a form of ionizing radiation, and as such, are a biological hazard, depending upon dose. A small natural background flux of free neutrons exists on Earth, caused by cosmic ray showers. Dedicated neutron sources like neutron generators, research reactors and spallation sources produce free neutrons for use in irradiation, neutrons and protons are both nucleons, which are attracted and bound together by the nuclear force to form atomic nuclei. The nucleus of the most common isotope of the atom is a lone proton. The nuclei of the hydrogen isotopes deuterium and tritium contain one proton bound to one. All other types of nuclei are composed of two or more protons and various numbers of neutrons. The most common nuclide of the chemical element lead, 208Pb has 82 protons and 126 neutrons. The free neutron has a mass of about 1. 675×10−27 kg, the neutron has a mean square radius of about 0. 8×10−15 m, or 0.8 fm, and it is a spin-½ fermion
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Proton
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A proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and mass slightly less than that of a neutron. Protons and neutrons, each with masses of one atomic mass unit, are collectively referred to as nucleons. One or more protons are present in the nucleus of every atom, the number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number. Since each element has a number of protons, each element has its own unique atomic number. The word proton is Greek for first, and this name was given to the nucleus by Ernest Rutherford in 1920. In previous years, Rutherford had discovered that the nucleus could be extracted from the nuclei of nitrogen by atomic collisions. Protons were therefore a candidate to be a particle, and hence a building block of nitrogen. In the modern Standard Model of particle physics, protons are hadrons, and like neutrons, although protons were originally considered fundamental or elementary particles, they are now known to be composed of three valence quarks, two up quarks and one down quark. The rest masses of quarks contribute only about 1% of a protons mass, the remainder of a protons mass is due to quantum chromodynamics binding energy, which includes the kinetic energy of the quarks and the energy of the gluon fields that bind the quarks together. At sufficiently low temperatures, free protons will bind to electrons, however, the character of such bound protons does not change, and they remain protons. A fast proton moving through matter will slow by interactions with electrons and nuclei, the result is a protonated atom, which is a chemical compound of hydrogen. In vacuum, when electrons are present, a sufficiently slow proton may pick up a single free electron, becoming a neutral hydrogen atom. Such free hydrogen atoms tend to react chemically with other types of atoms at sufficiently low energies. When free hydrogen atoms react with other, they form neutral hydrogen molecules. Protons are spin-½ fermions and are composed of three quarks, making them baryons. Protons have an exponentially decaying positive charge distribution with a mean square radius of about 0.8 fm. Protons and neutrons are both nucleons, which may be together by the nuclear force to form atomic nuclei. The nucleus of the most common isotope of the atom is a lone proton
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Pion
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Protein pigeon homolog also known as gamma-secretase activating protein is a protein that in humans is encoded by the PION gene. The human PION gene is located on the arm of chromosome 7 at band 11.23. Highly conserved PION orthologs have been identified in most vertebrates for which complete genome data are available, more distantly related orthologs are also expressed in insects including the pigeon gene in Drosophila melanogaster that when mutated produces the pigeon phenotype. The name of the human PION gene derives the corresponding Drosophila gene, the transcribed human pigeon homolog protein is 854 amino acid residues in length. A16 kDa fragment derived from 121 residues from the C-terminus region of the full length protein is known as the activating protein. γ-secretase activating protein increases β-amyloid production through a mechanism involving its interactions with both γ-secretase and its substrate, the precursor protein. By binding to both the enzyme and its APP substrate, GSAP increases the affinity and the selectivity of the enzyme for this particular substrate. Imatinib itself does not get into the brain so imatinib could not be used as an AD therapeutic, however it may be possible to identify imatinib-like drugs that do get into the brain. Hence GSAP represents a potential target for the treatment of Alzheimers disease. The drug semagacestat in contrast to imatinib, works by inhibiting the γ-secretase. While semagacestat reduces β-amyloid plaque formation in AD patients, γ-secretase is also needed to other important proteins. The failure of semagacestat to improve the function of AD patients may be due to its non-selective blockade of γ-secretase. The more selective blockade of γ-secretase provided by inhibiting GSAP may make GSAP a more efficacious, the PION gene was originally discovered through a large scale genome sequencing effort. However the function of the PION gene product remained a mystery, in the laboratory of Paul Greengard, a screen of compounds that could inhibit the formation of β-amyloid identified imatinib, however it was not immediately known how it accomplished this. Later it was discovered by Greengards lab that imatinib inhibited the function of GSAP and that GSAP in turn functions as an activator of γ-secretase
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Alpha particle
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Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus. They are generally produced in the process of decay. Alpha particles are named after the first letter in the Greek alphabet, the symbol for the alpha particle is α or α2+. Because they are identical to helium nuclei, they are sometimes written as He2+ or 4 2He2+ indicating a helium ion with a +2 charge. If the ion gains electrons from its environment, the particle can be written as a normal helium atom 4 2He. Some science authors may use doubly ionized helium nuclei and alpha particles as interchangeable terms, the nomenclature is not well defined, and thus not all high-velocity helium nuclei are considered by all authors to be alpha particles. As with beta and gamma rays/particles, the used for the particle carries some mild connotations about its production process and energy. Thus, alpha particles may be used as a term when referring to stellar helium nuclei reactions. A higher energy version of alphas than produced in alpha decay is a product of an uncommon nuclear fission result called ternary fission. However, helium nuclei produced by particle accelerators are less likely to be referred to as alpha particles, alpha particles, like helium nuclei, have a net spin of zero. Due to the mechanism of their production in standard alpha radioactive decay, alpha particles generally have an energy of about 5 MeV. They are a highly ionizing form of radiation, and have low penetration depth. They are able to be stopped by a few centimeters of air, however, so-called long range alpha particles from ternary fission are three times as energetic, and penetrate three times as far. To a lesser extent, this is true of very high-energy helium nuclei produced by particle accelerators. The best-known source of particles is alpha decay of heavier atoms. When an atom emits an alpha particle in alpha decay, the mass number decreases by four due to the loss of the four nucleons in the alpha particle. The atomic number of the atom goes down by two, as a result of the loss of two protons – the atom becomes a new element. Examples of this sort of nuclear transmutation are when uranium becomes thorium, or radium becomes radon gas, alpha particles are commonly emitted by all of the larger radioactive nuclei such as uranium, thorium, actinium, and radium, as well as the transuranic elements
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Nuclear fission product
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Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release of heat energy. The two smaller nuclei are the fission products, about 0. 2% to 0. 4% of fissions are ternary fissions, producing a third light nucleus such as helium-4 or tritium. The fission products themselves are often unstable and radioactive, due to being relatively neutron-rich for their atomic number and this releases additional energy in the form of beta particles, antineutrinos, and gamma rays. Thus, fission events normally result in radiation and antineutrinos. Many of these nuclides have a very short half-life, and therefore are very radioactive, for instance, strontium-90, strontium-89 and strontium-94 are all fission products, they are produced in similar quantities, and each nucleus decays by shooting off one beta particle. But Sr-90 has a 30-year half-life, Sr-89 a 50. 5-day half-life, the same number of atoms of Sr-89 will decay 10,600 times faster than Sr-90, and Sr-94 will do so 915 million times faster. It is these short-half-life nuclides that make spent fuel so dangerous, in addition to generating much heat, immediately after the reactor itself has been shut down. The most radioactive also decay the fastest, after 50 days, Sr-94 has had 58,000 half-lives and is gone, Sr-89 is at half its original quantity. As there are hundreds of different nuclides created, the radioactivity level fades quickly. The sum of the mass of the two atoms produced by the fission of one fissile atom is always less than the atomic mass of the original atom. Since the nuclei that can undergo fission are particularly neutron-rich. The initial fission products therefore may be unstable and typically undergo beta decay to move towards a stable configuration, a few neutron-rich and short-lived initial fission products decay by ordinary beta decay, followed by immediate emission of a neutron by the excited daughter-product. This process is the source of so-called delayed neutrons, which play an important role in control of a nuclear reactor, the first beta decays are rapid and may release high energy beta particles or gamma radiation. However, as the fission products approach stable nuclear conditions, the last one or two decays may have a long half-life and release less energy. Fission products have half-lives of 90 years or less, except for seven long-lived fission products that have lives of 211,100 years. This behavior of pure fission products with actinides removed, contrasts with the decay of fuel that still contains actinides and this fuel is produced in the so-called open nuclear fuel cycle. A number of these actinides have half lives in the range of about 100 to 200,000 years
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Atomic nucleus
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After the discovery of the neutron in 1932, models for a nucleus composed of protons and neutrons were quickly developed by Dmitri Ivanenko and Werner Heisenberg. Almost all of the mass of an atom is located in the nucleus, protons and neutrons are bound together to form a nucleus by the nuclear force. The diameter of the nucleus is in the range of 6985175000000000000♠1.75 fm for hydrogen to about 6986150000000000000♠15 fm for the heaviest atoms and these dimensions are much smaller than the diameter of the atom itself, by a factor of about 23,000 to about 145,000. The branch of physics concerned with the study and understanding of the nucleus, including its composition. The nucleus was discovered in 1911, as a result of Ernest Rutherfords efforts to test Thomsons plum pudding model of the atom, the electron had already been discovered earlier by J. J. Knowing that atoms are electrically neutral, Thomson postulated that there must be a charge as well. In his plum pudding model, Thomson suggested that an atom consisted of negative electrons randomly scattered within a sphere of positive charge, to his surprise, many of the particles were deflected at very large angles. This justified the idea of an atom with a dense center of positive charge. The term nucleus is from the Latin word nucleus, a diminutive of nux, in 1844, Michael Faraday used the term to refer to the central point of an atom. The modern atomic meaning was proposed by Ernest Rutherford in 1912, the adoption of the term nucleus to atomic theory, however, was not immediate. In 1916, for example, Gilbert N, the nuclear strong force extends far enough from each baryon so as to bind the neutrons and protons together against the repulsive electrical force between the positively charged protons. The nuclear strong force has a short range, and essentially drops to zero just beyond the edge of the nucleus. The collective action of the charged nucleus is to hold the electrically negative charged electrons in their orbits about the nucleus. The collection of negatively charged electrons orbiting the nucleus display an affinity for certain configurations, which chemical element an atom represents is determined by the number of protons in the nucleus, the neutral atom will have an equal number of electrons orbiting that nucleus. Individual chemical elements can create more stable electron configurations by combining to share their electrons and it is that sharing of electrons to create stable electronic orbits about the nucleus that appears to us as the chemistry of our macro world. Protons define the entire charge of a nucleus, and hence its chemical identity, neutrons are electrically neutral, but contribute to the mass of a nucleus to nearly the same extent as the protons. Neutrons explain the phenomenon of isotopes – varieties of the chemical element which differ only in their atomic mass. They are sometimes viewed as two different quantum states of the particle, the nucleon
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Conservation of energy
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In physics, the law of conservation of energy states that the total energy of an isolated system remains constant—it is said to be conserved over time. Energy can neither be created nor destroyed, rather, it transforms from one form to another, for instance, chemical energy can be converted to kinetic energy in the explosion of a stick of dynamite. A consequence of the law of conservation of energy is that a perpetual motion machine of the first kind cannot exist and that is to say, no system without an external energy supply can deliver an unlimited amount of energy to its surroundings. Ancient philosophers as far back as Thales of Miletus c.550 BCE had inklings of the conservation of some underlying substance of everything is made. However, there is no reason to identify this with what we know today as mass-energy. Empedocles wrote that in his system, composed of four roots, nothing comes to be or perishes, instead. In 1605, Simon Stevinus was able to solve a number of problems in statics based on the principle that perpetual motion was impossible. Essentially, he pointed out that the height a moving body rises is equal to the height from which it falls, and used this observation to infer the idea of inertia. The remarkable aspect of this observation is that the height that a moving body ascends to does not depend on the shape of the surface that the body is moving on. In 1669, Christian Huygens published his laws of collision, among the quantities he listed as being invariant before and after the collision of bodies were both the sum of their linear momentums as well as the sum of their kinetic energies. However, the difference between elastic and inelastic collision was not understood at the time and this led to the dispute among later researchers as to which of these conserved quantities was the more fundamental. In his Horologium Oscillatorium, he gave a much clearer statement regarding the height of ascent of a moving body, Huygens study of the dynamics of pendulum motion was based on a single principle, that the center of gravity of heavy objects cannot lift itself. The fact that energy is scalar, unlike linear momentum which is a vector. It was Leibniz during 1676–1689 who first attempted a mathematical formulation of the kind of energy which is connected with motion. Using Huygens work on collision, Leibniz noticed that in mechanical systems. He called this quantity the vis viva or living force of the system, the principle represents an accurate statement of the approximate conservation of kinetic energy in situations where there is no friction. Many physicists at that time, such as Newton, held that the conservation of momentum and it was later shown that both quantities are conserved simultaneously, given the proper conditions such as an elastic collision. In 1687, Isaac Newton published his Principia, which was organized around the concept of force and momentum
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Colon (anatomy)
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The large intestine, or the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the waste material is stored as feces before being removed by defecation. Most sources define the large intestine as the combination of the cecum, colon, rectum, some other sources exclude the anal canal. In humans, the large intestine begins in the right region of the pelvis, just at or below the waist. It then continues as the colon ascending the abdomen, across the width of the cavity as the transverse colon. Overall, in humans, the intestine is about 1.5 metres long. The colon is the last part of the digestive system and it extracts water and salt from solid wastes before they are eliminated from the body and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a role in absorption of foods. About 1.5 litres or 45 ounces of water arrives in the each day. The length of the human male colon is 166 cm, on average. In mammals, the colon consists of five sections, the cecum plus the colon, the transverse colon, the descending colon, the sigmoid colon. Retroperitoneal organs in general do not have a covering of peritoneum. Intraperitoneal organs are completely surrounded by peritoneum and are therefore mobile, of the colon, the ascending colon, descending colon and rectum are retroperitoneal, while the cecum, appendix, transverse colon and sigmoid colon are intraperitoneal. This is important as it affects which organs can be accessed during surgery. The ascending colon is the first of four sections of the large intestine and it is connected to the small intestine by a section of bowel called the cecum. The ascending colon runs upwards through the abdominal cavity toward the transverse colon for approximately eight inches, one of the main functions of the colon is to remove the water and other key nutrients from waste material and recycle it. As the waste material exits the small intestine through the valve, it will move into the cecum. The unwanted waste material is moved upwards toward the transverse colon by the action of peristalsis, the ascending colon is sometimes attached to the appendix via Gerlachs valve
. PMID 22355606. doi:10.1038/srep00087. Retrieved 19 May 2012.
