1.
System of measurement
–
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
–
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.
Henri Becquerel
–
Antoine Henri Becquerel was a French physicist, Nobel laureate, and the first person to discover evidence of radioactivity. For work in this field he, along with Marie Skłodowska-Curie and Pierre Curie, the SI unit for radioactivity, the becquerel, is named after him. Roentgen discovered X-rays on November 8,1895, the press reported this on January 5,1896, shortly before Becquerel did his famous experiment. Thus radioactivity was discovered the year but within a year of the discovery of X-rays. Becquerel was born in Paris into a family which produced four generations of scientists, Becquerels grandfather, father. He studied engineering at the École Polytechnique and the École des Ponts et Chaussées, in 1890 he married Louise Désirée Lorieux. In 1892, he became the third in his family to occupy the chair at the Muséum National dHistoire Naturelle. In 1894, he became chief engineer in the Department of Bridges, Becquerels earliest works centered on the subject of his doctoral thesis, the plane polarization of light, with the phenomenon of phosphorescence and absorption of light by crystals. Becquerels discovery of radioactivity is a famous example of serendipity. Becquerel had long interested in phosphorescence, the emission of light of one color following a bodys exposure to light of another color. His first experiments appeared to show this, one places on the sheet of paper, on the outside, a slab of the phosphorescent substance, and one exposes the whole to the sun for several hours. When one then develops the photographic plate, one recognizes that the silhouette of the phosphorescent substance appears in black on the negative. If one places between the phosphorescent substance and the paper a piece of money or a metal screen pierced with a cut-out design, one must conclude from these experiments that the phosphorescent substance in question emits rays which pass through the opaque paper and reduce silver salts. But further experiments led him to doubt and then abandon this hypothesis, since the sun did not come out in the following days, I developed the photographic plates on the 1st of March, expecting to find the images very weak. Instead the silhouettes appeared with great intensity, however, the present experiments, without being contrary to this hypothesis, do not warrant this conclusion. I hope that the experiments which I am pursuing at the moment will be able to bring some clarification to this new class of phenomena. In 1903, Becquerel shared the Nobel Prize in Physics with Pierre, by 1861, Niepce de Saint-Victor realized that uranium salts produce a radiation that is invisible to our eyes. Niepce de Saint-Victor knew Edmond Becquerel, Henri Becquerels father, in 1868, Edmond Becquerel published a book, La lumière, ses causes et ses effets
4.
SI base unit
–
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.
Second
–
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
6.
Radioactive decay
–
A material containing such unstable nuclei is considered radioactive. Certain highly excited short-lived nuclear states can decay through neutron emission, or more rarely, however, for a collection of atoms, the collections expected decay rate is characterized in terms of their measured decay constants or half-lives. This is the basis of radiometric dating, the half-lives of radioactive atoms have no known upper limit, spanning a time range of over 55 orders of magnitude, from nearly instantaneous to far longer than the age of the universe. A radioactive nucleus with spin can have no defined orientation. If there are multiple particles produced during a single decay, as in decay, their relative angular distribution. Such a parent process could be a previous decay, or a nuclear reaction, the decaying nucleus is called the parent radionuclide, and the process produces at least one daughter nuclide. Except for gamma decay or internal conversion from an excited state. When the number of changes, an atom of a different chemical element is created. The first decay processes to be discovered were alpha decay, beta decay, alpha decay occurs when the nucleus ejects an alpha particle. This is the most common process of emitting nucleons, but highly excited nuclei can eject single nucleons, or in the case of cluster decay, specific light nuclei of other elements. Beta decay occurs when the nucleus emits an electron or positron, the nucleus may capture an orbiting electron, causing a proton to convert into a neutron in a process called electron capture. All of these result in a well-defined nuclear transmutation. By contrast, there are radioactive decay processes that do not result in a nuclear transmutation, another type of radioactive decay results in products that vary, appearing as two or more fragments of the original nucleus with a range of possible masses. For a summary table showing the number of stable and radioactive nuclides in each category, there are 29 naturally occurring chemical elements on Earth that are radioactive. They are those that contain 34 radionuclides that date before the time of formation of the solar system, well-known examples are uranium and thorium, but also included are naturally occurring long-lived radioisotopes, such as potassium-40. Radioactivity was discovered in 1896 by the French scientist Henri Becquerel and these materials glow in the dark after exposure to light, and he suspected that the glow produced in cathode ray tubes by X-rays might be associated with phosphorescence. He wrapped a photographic plate in black paper and placed various phosphorescent salts on it, all results were negative until he used uranium salts. The uranium salts caused a blackening of the plate in spite of the plate being wrapped in black paper and these radiations were given the name Becquerel Rays
7.
Atomic nucleus
–
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
8.
Nobel Prize in Physics
–
The Nobel Prize in Physics is a yearly award given by the Royal Swedish Academy of Sciences for those who conferred the most outstanding contributions for mankind in the field of physics. The first Nobel Prize in Physics was awarded to German/Dutch physicist Wilhelm Röntgen in recognition of the services he has rendered by the discovery of the remarkable rays. This award is administered by the Nobel Foundation and widely regarded as the most prestigious award that a scientist can receive in physics and it is presented in Stockholm at an annual ceremony on December 10, the anniversary of Nobels death. Through 2016, a total of 203 individuals have been awarded the prize, only two women have won the Nobel Prize in Physics, Marie Curie in 1903, and Maria Goeppert Mayer in 1963. Though Nobel wrote several wills during his lifetime, the last one was written a year before he died and was signed at the Swedish-Norwegian Club in Paris on 27 November 1895. Nobel bequeathed 94% of his assets,31 million Swedish kronor, to establish. Due to the level of surrounding the will, it was not until April 26,1897 that it was approved by the Storting. The executors of his will were Ragnar Sohlman and Rudolf Lilljequist, the members of the Norwegian Nobel Committee who were to award the Peace Prize were appointed shortly after the will was approved. The prize-awarding organisations followed, the Karolinska Institutet on June 7, the Swedish Academy on June 9, the Nobel Foundation then reached an agreement on guidelines for how the Nobel Prize should be awarded. In 1900, the Nobel Foundations newly created statutes were promulgated by King Oscar II, according to Nobels will, The Royal Swedish Academy of sciences were to award the Prize in Physics. A maximum of three Nobel laureates and two different works may be selected for the Nobel Prize in Physics, compared with other Nobel Prizes, the nomination and selection process for the prize in Physics is long and rigorous. This is a key reason why it has grown in importance over the years to become the most important prize in Physics, the Nobel laureates are selected by the Nobel Committee for Physics, a Nobel Committee that consists of five members elected by The Royal Swedish Academy of Sciences. In the first stage begins in September, around 3,000 people – selected university professors, Nobel Laureates in Physics and Chemistry. The completed nomination forms arrive at the Nobel Committee no later than 31 January of the following year and these nominees are scrutinized and discussed by experts who narrow it to approximately fifteen names. The committee submits a report with recommendations on the candidates into the Academy. The Academy then makes the selection of the Laureates in Physics through a majority vote. The names of the nominees are never announced, and neither are they told that they have been considered for the prize. Nomination records are sealed for fifty years, while posthumous nominations are not permitted, awards can be made if the individual died in the months between the decision of the prize committee and the ceremony in December
9.
Pierre Curie
–
Pierre Curie was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity and radioactivity. Born in Paris on 15 May 1859, Pierre was the son of Eugène Curie and he was educated by his father, a doctor, and in his early teens showed a strong aptitude for mathematics and geometry. When he was 16, he earned his math degree, by the age of 18 he had completed the equivalent of a higher degree, but did not proceed immediately to a doctorate due to lack of money. Instead he worked as a laboratory instructor, in 1880, Pierre and his older brother Jacques demonstrated that an electric potential was generated when crystals were compressed, i. e. piezoelectricity. To provide accurate measurements needed for their work, Pierre created a highly sensitive instrument called the Curie Scale and he used weights, microscopic meter readers, and pneumatic dampeners to create the scale. Also, to aid their work, they invented the Piezoelectric Quartz Electrometer, shortly afterwards, in 1881, they demonstrated the reverse effect, that crystals could be made to deform when subject to an electric field. Almost all digital electronic circuits now rely on this in the form of crystal oscillators, Pierre Curie was introduced to Maria Skłodowska by their friend, physicist Józef Wierusz-Kowalski. Pierre took Maria into his laboratory as his student and his admiration for her grew when he realized that she would not inhibit his research. He began to regard her as his muse and she refused his initial proposal, but finally agreed to marry him on 26 July 1895. It would be a thing, a thing I dare not hope, if we could spend our life near each other hypnotized by our dreams, your patriotic dream, our humanitarian dream. Pierre Curie to Marie Skłodowska Prior to his famous studies on magnetism. Variations on this equipment were used by future workers in that area. Pierre Curie studied ferromagnetism, paramagnetism, and diamagnetism for his doctoral thesis, the material constant in Curies law is known as the Curie constant. He also discovered that ferromagnetic substances exhibited a critical temperature transition and this is now known as the Curie temperature. The Curie temperature is used to plate tectonics, treat hypothermia, measure caffeine. Pierre formulated what is now known as the Curie Dissymmetry Principle, for example, a random mixture of sand in zero gravity has no dissymmetry. Introduce a gravitational field, and there is a dissymmetry because of the direction of the field, then the sand grains can self-sort with the density increasing with depth. But this new arrangement, with the arrangement of sand grains
10.
Marie Curie
–
Marie Skłodowska Curie, born Maria Salomea Skłodowska, was a Polish and naturalized-French physicist and chemist who conducted pioneering research on radioactivity. She was also the first woman to become a professor at the University of Paris and she was born in Warsaw, in what was then the Kingdom of Poland, part of the Russian Empire. She studied at Warsaws clandestine Floating University and began her scientific training in Warsaw. In 1891, aged 24, she followed her older sister Bronisława to study in Paris and she shared the 1903 Nobel Prize in Physics with her husband Pierre Curie and with physicist Henri Becquerel. She won the 1911 Nobel Prize in Chemistry and her achievements included the development of the theory of radioactivity, techniques for isolating radioactive isotopes, and the discovery of two elements, polonium and radium. Under her direction, the worlds first studies were conducted into the treatment of neoplasms and she founded the Curie Institutes in Paris and in Warsaw, which remain major centres of medical research today. During World War I, she developed mobile radiography units to provide X-ray services to field hospitals, while a French citizen, Marie Skłodowska Curie never lost her sense of Polish identity. She taught her daughters the Polish language and took them on visits to Poland and she named the first chemical element that she discovered—polonium, which she isolated in 1898—after her native country. Maria Skłodowska was born in Warsaw, in the Russian partition of Poland, on 7 November 1867, the fifth and youngest child of well-known teachers Bronisława, née Boguska, the elder siblings of Maria were Zofia, Józef, Bronisława and Helena. On both the paternal and maternal sides, the family had lost their property and fortunes through patriotic involvements in Polish national uprisings aimed at restoring Polands independence. This condemned the subsequent generation, including Maria, her sisters and her brother. Marias paternal grandfather, Józef Skłodowski, had been a teacher in Lublin, where he taught the young Bolesław Prus. Her father, Władysław Skłodowski, taught mathematics and physics, subjects that Maria was to pursue, after Russian authorities eliminated laboratory instruction from the Polish schools, he brought much of the laboratory equipment home, and instructed his children in its use. Marias mother Bronisława operated a prestigious Warsaw boarding school for girls and she died of tuberculosis in May 1878, when Maria was ten years old. Less than three years earlier, Marias oldest sibling, Zofia, had died of typhus contracted from a boarder, Marias father was an atheist, her mother a devout Catholic. The deaths of Marias mother and sister caused her to give up Catholicism and become agnostic. When she was ten years old, Maria began attending the school of J. Sikorska, next she attended a gymnasium for girls. After a collapse, possibly due to depression, she spent the year in the countryside with relatives of her father, and the next year with her father in Warsaw
11.
Hertz
–
The hertz is the unit of frequency in the International System of Units and is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide proof of the existence of electromagnetic waves. Hertz are commonly expressed in SI multiples kilohertz, megahertz, gigahertz, kilo means thousand, mega meaning million, giga meaning billion and tera for trillion. Some of the units most common uses are in the description of waves and musical tones, particularly those used in radio-. It is also used to describe the speeds at which computers, the hertz is equivalent to cycles per second, i. e. 1/second or s −1. In English, hertz is also used as the plural form, as an SI unit, Hz can be prefixed, commonly used multiples are kHz, MHz, GHz and THz. One hertz simply means one cycle per second,100 Hz means one hundred cycles per second, and so on. The unit may be applied to any periodic event—for example, a clock might be said to tick at 1 Hz, the rate of aperiodic or stochastic events occur is expressed in reciprocal second or inverse second in general or, the specific case of radioactive decay, becquerels. Whereas 1 Hz is 1 cycle per second,1 Bq is 1 aperiodic radionuclide event per second, the conversion between a frequency f measured in hertz and an angular velocity ω measured in radians per second is ω =2 π f and f = ω2 π. This SI unit is named after Heinrich Hertz, as with every International System of Units unit named for a person, the first letter of its symbol is upper case. Note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, the hertz is named after the German physicist Heinrich Hertz, who made important scientific contributions to the study of electromagnetism. The name was established by the International Electrotechnical Commission in 1930, the term cycles per second was largely replaced by hertz by the 1970s. One hobby magazine, Electronics Illustrated, declared their intention to stick with the traditional kc. Mc. etc. units, sound is a traveling longitudinal wave which is an oscillation of pressure. Humans perceive frequency of waves as pitch. Each musical note corresponds to a frequency which can be measured in hertz. An infants ear is able to perceive frequencies ranging from 20 Hz to 20,000 Hz, the range of ultrasound, infrasound and other physical vibrations such as molecular and atomic vibrations extends from a few femtoHz into the terahertz range and beyond. Electromagnetic radiation is described by its frequency—the number of oscillations of the perpendicular electric and magnetic fields per second—expressed in hertz. Radio frequency radiation is measured in kilohertz, megahertz, or gigahertz
12.
Joseph Fourier
–
The Fourier transform and Fouriers law are also named in his honour. Fourier is also credited with the discovery of the greenhouse effect. Fourier was born at Auxerre, the son of a tailor and he was orphaned at age nine. Fourier was recommended to the Bishop of Auxerre, and through this introduction, the commissions in the scientific corps of the army were reserved for those of good birth, and being thus ineligible, he accepted a military lectureship on mathematics. He took a prominent part in his own district in promoting the French Revolution and he was imprisoned briefly during the Terror but in 1795 was appointed to the École Normale, and subsequently succeeded Joseph-Louis Lagrange at the École Polytechnique. Fourier accompanied Napoleon Bonaparte on his Egyptian expedition in 1798, as scientific adviser, cut off from France by the English fleet, he organized the workshops on which the French army had to rely for their munitions of war. He also contributed several papers to the Egyptian Institute which Napoleon founded at Cairo. After the British victories and the capitulation of the French under General Menou in 1801, in 1801, Napoleon appointed Fourier Prefect of the Department of Isère in Grenoble, where he oversaw road construction and other projects. However, Fourier had previously returned home from the Napoleon expedition to Egypt to resume his academic post as professor at École Polytechnique when Napoleon decided otherwise in his remark. The Prefect of the Department of Isère having recently died, I would like to express my confidence in citizen Fourier by appointing him to this place, hence being faithful to Napoleon, he took the office of Prefect. It was while at Grenoble that he began to experiment on the propagation of heat and he presented his paper On the Propagation of Heat in Solid Bodies to the Paris Institute on December 21,1807. He also contributed to the monumental Description de lÉgypte, Fourier moved to England in 1816. Later, he returned to France, and in 1822 succeeded Jean Baptiste Joseph Delambre as Permanent Secretary of the French Academy of Sciences, in 1830, he was elected a foreign member of the Royal Swedish Academy of Sciences. In 1830, his health began to take its toll, Fourier had already experienced, in Egypt and Grenoble. At Paris, it was impossible to be mistaken with respect to the cause of the frequent suffocations which he experienced. A fall, however, which he sustained on the 4th of May 1830, while descending a flight of stairs, shortly after this event, he died in his bed on 16 May 1830. His name is one of the 72 names inscribed on the Eiffel Tower, a bronze statue was erected in Auxerre in 1849, but it was melted down for armaments during World War II. Joseph Fourier University in Grenoble is named after him and this book was translated, with editorial corrections, into English 56 years later by Freeman
13.
Cycle per second
–
The cycle per second was a once-common English name for the unit of frequency now known as the hertz. The plural form was used, often written cycles per second, cycles/second, c. p. s, c/s. The term comes from the fact that waves have a frequency measurable in their number of vibrations, or cycles. With the organization of the International System of Units in 1960, symbolically, cycle per second units are cycle/second, while hertz is 1/second or s −1. This particular mandate has been so widely adopted as to render the old cycle per second all, for higher frequencies, kilocycles, as an abbreviation of kilocycles per second were often used on components or devices. Other higher units like megacycle and less commonly kilomegacycle were used before 1960 and these have modern equivalents such as kilohertz, megahertz, and gigahertz. Thus,1 Bq is 1 event per second on average whereas 1 hertz is 1 event per second on a regular cycle. Cycle can also be a unit for measuring usage of reciprocating machines, especially presses, cycles per instruction Heinrich Hertz Instructions per cycle Instructions per second MKS system of units a predecessor of the SI set of units Normalized frequency Radian per second
14.
Gray (unit)
–
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
15.
Metric prefix
–
A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or fraction of the unit. While all metric prefixes in use today are decadic, historically there have been a number of binary metric prefixes as well. Each prefix has a symbol that is prepended to the unit symbol. The prefix kilo-, for example, may be added to gram to indicate multiplication by one thousand, the prefix milli-, likewise, may be added to metre to indicate division by one thousand, one millimetre is equal to one thousandth of a metre. Decimal multiplicative prefixes have been a feature of all forms of the system with six dating back to the systems introduction in the 1790s. Metric prefixes have even been prepended to non-metric units, the SI prefixes are standardized for use in the International System of Units by the International Bureau of Weights and Measures in resolutions dating from 1960 to 1991. Since 2009, they have formed part of the International System of Quantities, the BIPM specifies twenty prefixes for the International System of Units. Each prefix name has a symbol which is used in combination with the symbols for units of measure. For example, the symbol for kilo- is k, and is used to produce km, kg, and kW, which are the SI symbols for kilometre, kilogram, prefixes corresponding to an integer power of one thousand are generally preferred. Hence 100 m is preferred over 1 hm or 10 dam, the prefixes hecto, deca, deci, and centi are commonly used for everyday purposes, and the centimetre is especially common. However, some building codes require that the millimetre be used in preference to the centimetre, because use of centimetres leads to extensive usage of decimal points. Prefixes may not be used in combination and this also applies to mass, for which the SI base unit already contains a prefix. For example, milligram is used instead of microkilogram, in the arithmetic of measurements having units, the units are treated as multiplicative factors to values. If they have prefixes, all but one of the prefixes must be expanded to their numeric multiplier,1 km2 means one square kilometre, or the area of a square of 1000 m by 1000 m and not 1000 square metres. 2 Mm3 means two cubic megametres, or the volume of two cubes of 1000000 m by 1000000 m by 1000000 m or 2×1018 m3, and not 2000000 cubic metres, examples 5 cm = 5×10−2 m =5 ×0.01 m =0. The prefixes, including those introduced after 1960, are used with any metric unit, metric prefixes may also be used with non-metric units. The choice of prefixes with a unit is usually dictated by convenience of use. Unit prefixes for amounts that are larger or smaller than those actually encountered are seldom used
16.
Potassium-40
–
Potassium-40 is a radioactive isotope of potassium which has a very long half-life of 1. 251×109 years. It makes up 0. 012% of the amount of potassium found in nature. Potassium-40 is an example of an isotope that undergoes all three types of beta decay. About 89. 28% of the time, it decays to calcium-40 with emission of a particle with a maximum energy of 1.33 MeV. About 10. 72% of the time it decays to argon-40 by electron capture, with the emission of a 1.460 MeV gamma ray, the radioactive decay of this particular isotope explains the large abundance of argon in the earths atmosphere. Very rarely it will decay to 40Ar by emitting a positron, potassium-40 is especially important in potassium–argon dating. Argon is a gas that does not ordinarily combine with other elements, so, when a mineral forms – whether from molten rock, or from substances dissolved in water – it will be initially argon-free, even if there is some argon in the liquid. However, if the mineral contains any potassium, then decay of the 40K isotope present will create fresh argon-40 that will remain locked up in the mineral. Since the rate at which this occurs is known, it is possible to determine the elapsed time since the mineral formed by measuring the ratio of 40K. It follows that most of the terrestrial argon derives from potassium-40 that decayed into argon-40, the radioactive decay of 40K in the Earths mantle ranks third, after 232Th and 238U, as the source of radiogenic heat. The core also likely contains radiogenic sources, although how much is uncertain and it has been proposed that significant core radioactivity may be caused by high levels of U, Th, and K. 40K is the largest source of natural radioactivity in animals including humans
17.
Carbon-14
–
Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby, Carbon-14 was discovered on 27 February 1940, by Martin Kamen and Sam Ruben at the University of California Radiation Laboratory in Berkeley, California. Its existence had been suggested by Franz Kurie in 1934, carbon-12 and carbon-13 are both stable, while the half-life of carbon-14 is 5, 730±40 years. Carbon-14 decays into nitrogen-14 through beta decay, a gram of carbon containing 1 atom of carbon-14 per 1012 atoms will emit 0.40 beta particles per second. The primary natural source of carbon-14 on Earth is cosmic ray action on nitrogen in the atmosphere, however, open-air nuclear testing between 1955–1980 contributed to this pool. The different isotopes of carbon do not differ appreciably in their chemical properties, the emitted beta particles have a maximum energy of 156 keV, while their weighted mean energy is 49 keV. These are relatively low energies, the distance traveled is estimated to be 22 cm in air and 0.27 mm in body tissue. The fraction of the radiation transmitted through the dead layer is estimated to be 0.11. Liquid scintillation counting is the preferred method, the G-M counting efficiency is estimated to be 3%. The half-distance layer in water is 0.05 mm. Radiocarbon dating is a dating method that uses to determine the age of carbonaceous materials up to about 60,000 years old. The technique was developed by Willard Libby and his colleagues in 1949 during his tenure as a professor at the University of Chicago, in 1960, Libby was awarded the Nobel Prize in chemistry for this work. One of the frequent uses of the technique is to date organic remains from archaeological sites, plants fix atmospheric carbon during photosynthesis, so the level of 14C in plants and animals when they die approximately equals the level of 14C in the atmosphere at that time. However, it decreases thereafter from radioactive decay, allowing the date of death or fixation to be estimated. A calculation or a comparison of carbon-14 levels in a sample, with tree ring or cave-deposit carbon-14 levels of a known age. Carbon-14 is produced in the layers of the troposphere and the stratosphere by thermal neutrons absorbed by nitrogen atoms. When cosmic rays enter the atmosphere, they undergo various transformations, the resulting neutrons participate in the following reaction, n +14 7N →14 6C + p The highest rate of carbon-14 production takes place at altitudes of 9 to 15 km and at high geomagnetic latitudes. Production rates vary because of changes to the cosmic ray flux caused by the heliospheric modulation, the latter can create significant variations in 14C production rates, although the changes of the carbon cycle can make these effects difficult to tease out. Another extraordinarily large 14C increase has been associated with the 5480 BC event
18.
Atomic bombings of Hiroshima and Nagasaki
–
The United States dropped nuclear weapons on the Japanese cities of Hiroshima and Nagasaki on August 6 and 9,1945, respectively, during the final stage of World War II. The United States had dropped the bombs with the consent of the United Kingdom as outlined in the Quebec Agreement, the two bombings, which killed at least 129,000 people, remain the only use of nuclear weapons for warfare in history. In the final year of the war, the Allies prepared for what was anticipated to be a costly invasion of the Japanese mainland. This was preceded by a U. S. conventional and firebombing campaign that destroyed 67 Japanese cities, the war in Europe had concluded when Nazi Germany signed its instrument of surrender on May 8,1945, just after Hitler committed suicide. The Japanese, facing the fate, refused to accept the Allies demands for unconditional surrender. The Allies called for the surrender of the Japanese armed forces in the Potsdam Declaration on July 26, 1945—the alternative being prompt. The Japanese response to this ultimatum was to ignore it, orders for atomic bombs to be used on four Japanese cities were issued on July 25. Three days later, on August 9, a plutonium bomb was dropped on Nagasaki. During the following months, large numbers died from the effect of burns, radiation sickness, in both cities, most of the dead were civilians, although Hiroshima had a sizable military garrison. Japan announced its surrender to the Allies on August 15, six days after the bombing of Nagasaki, on September 2, the Japanese government signed the instrument of surrender, effectively ending World War II. The justification for the bombings of Hiroshima and Nagasaki is still debated to this day, in 1945, the Pacific War between the Empire of Japan and the Allies entered its fourth year. The Japanese fought fiercely, ensuring that U. S. victory would come at an enormous cost, December 1944 saw American battle casualties hit an all-time monthly high of 88,000 as a result of the German Ardennes Offensive. In the Pacific, the Allies returned to the Philippines, recaptured Burma, offensives were undertaken to reduce the Japanese forces remaining in Bougainville, New Guinea and the Philippines. In April 1945, American forces landed on Okinawa, where fighting continued until June. Along the way, the ratio of Japanese to American casualties dropped from 5,1 in the Philippines to 2,1 on Okinawa, although some Japanese were taken prisoner, most fought until they were killed or committed suicide. Nearly 99% of the 21,000 defenders of Iwo Jima were killed, of the 117,000 Japanese troops defending Okinawa in April–June 1945, 94% were killed. American military leaders used these figures to estimate high casualties among American soldiers in the invasion of Japan. As the Allies advanced towards Japan, conditions became steadily worse for the Japanese people, Japans merchant fleet declined from 5,250,000 gross tons in 1941 to 1,560,000 tons in March 1945, and 557,000 tons in August 1945
19.
Hiroshima
–
Hiroshima is the capital of Hiroshima Prefecture and the largest city in the Chūgoku region of western Honshu - the largest island of Japan. The citys name, 広島, means Broad Island in Japanese, Hiroshima gained city status on April 1,1889. On April 1,1980, Hiroshima became a designated city, as of August 2016, the city had an estimated population of 1,196,274. The GDP in Greater Hiroshima, Hiroshima Metropolitan Employment Area, is US$61.3 billion as of 2010, kazumi Matsui has been the citys mayor since April 2011. Hiroshima was established on the river delta coastline of the Seto Inland Sea in 1589 by powerful warlord Mōri Terumoto, Hiroshima Castle was quickly built, and in 1593 Terumoto moved in. Terumoto was on the side at the Battle of Sekigahara. The winner of the battle, Tokugawa Ieyasu, deprived Mōri Terumoto of most of his fiefs, including Hiroshima and gave Aki Province to Masanori Fukushima, after the han was abolished in 1871, the city became the capital of Hiroshima Prefecture. Hiroshima became an urban center during the imperial period, as the Japanese economy shifted from primarily rural to urban industries. During the 1870s, one of the seven government-sponsored English language schools was established in Hiroshima, Ujina Harbor was constructed through the efforts of Hiroshima Governor Sadaaki Senda in the 1880s, allowing Hiroshima to become an important port city. The Sanyō Railway was extended to Hiroshima in 1894, and a line from the main station to the harbor was constructed for military transportation during the First Sino-Japanese War. During that war, the Japanese government moved temporarily to Hiroshima, New industrial plants, including cotton mills, were established in Hiroshima in the late 19th century. Further industrialization in Hiroshima was stimulated during the Russo-Japanese War in 1904, the Hiroshima Prefectural Commercial Exhibition Hall was constructed in 1915 as a center for trade and exhibition of new products. Later, its name was changed to Hiroshima Prefectural Product Exhibition Hall, during World War I, Hiroshima became a focal point of military activity, as the Japanese government entered the war on the Allied side. About 500 German prisoners of war were held in Ninoshima Island in Hiroshima Bay, during World War II, the 2nd General Army and Chugoku Regional Army were headquartered in Hiroshima, and the Army Marine Headquarters was located at Ujina port. The city also had large depots of supplies, and was a key center for shipping. The bombing of Tokyo and other cities in Japan during World War II caused widespread destruction, there were no such air raids on Hiroshima. However, a real threat existed and was recognized, in order to protect against potential firebombings in Hiroshima, school children aged 11–14 years were mobilized to demolish houses and create firebreaks. On Monday, August 6,1945, at 8,15 a. m, by the end of the year, injury and radiation brought the total number of deaths to 90, 000–166,000
20.
TNT equivalent
–
TNT equivalent is a convention for expressing energy, typically used to describe the energy released in an explosion. The ton of TNT is a unit of energy defined by convention to be 4.184 gigajoules. The convention intends to compare the destructiveness of an event with that of conventional explosives, the kiloton is a unit of energy equal to 4.184 terajoules. The megaton is a unit of equal to 4.184 petajoules. The kiloton and megaton of TNT have traditionally used to describe the energy output. The TNT equivalent appears in various nuclear weapon control treaties, and has used to characterize the energy released in such other highly destructive events as an asteroid impact. A gram of TNT releases 2673–6702 J upon explosion, the energy liberated by one gram of TNT was arbitrarily defined as a matter of convention to be 4184 J, which is exactly one kilocalorie. The measured, pure heat output of a gram of TNT is only 2724 J, alternative TNT equivalency can be calculated as a function of when in the detonation the value is measured and which property is being compared. A kiloton of TNT can be visualized as a cube of TNT8.46 metres on a side, the RE factor is the relative mass of TNT to which an explosive is equivalent, the greater the RE, the more powerful the explosive. This enables engineers to determine the proper masses of different explosives when applying blasting formulas developed specifically for TNT. For example, if a timber-cutting formula calls for a charge of 1 kg of TNT, then based on octanitrocubanes RE factor of 2.38, using PETN, engineers would need 1. 0/1.66 kg to obtain the same effects as 1 kg of TNT. With ANFO or ammonium nitrate, they would require 1. 0/0.74 kg or 1. 0/0.42 kg, *, TBX or EBX, in a small, confined space, may have over twice the power of destruction. The total power of aluminized mixtures strictly depends on the condition of explosions, guide for the Use of the International System of Units. National Institute of Standards and Technology, nuclear Weapons FAQ Part 1.3 Rhodes, Richard. The Making of the Atomic Bomb, cooper, Paul W. Explosives Engineering, New York, Wiley-VCH, ISBN 0-471-18636-8 HQ Department of the Army, Field Manual 5-25, Explosives and Demolitions, Washington, D. C. Pentagon Publishing, pp. 83–84, ISBN 0-9759009-5-1 Explosives - Compositions, Alexandria, VA, thermobaric Explosives, Advanced Energetic Materials,2004. THE NATIONAL ACADEMIES PRESS, nap. edu, retrieved September 2004
21.
Atomic mass
–
The atomic mass is the mass of an atom. Its unit is the atomic mass units where 1 unified atomic mass unit is defined as 1⁄12 of the mass of a single carbon-12 atom. For atoms, the protons and neutrons of the account for almost all of the mass. When divided by unified atomic mass units or daltons to form a pure numeric ratio, thus, the atomic mass of a carbon-12 atom is 12 u or 12 daltons, but the relative isotopic mass of a carbon-12 atom is simply 12. By contrast, atomic mass figures refer to an individual species, as atoms of the same species are identical. Atomic mass figures are commonly reported to many more significant figures than atomic weights. Standard atomic weight is related to atomic mass by the ranking of isotopes for each element. It is usually about the value as the atomic mass of the most abundant isotope. The atomic mass of atoms, ions, or atomic nuclei is slightly less than the sum of the masses of their constituent protons, neutrons, and electrons, due to binding energy mass loss. Relative isotopic mass is similar to mass and has exactly the same numerical value as atomic mass. The only difference in case, is that relative isotopic mass is a pure number with no units. This loss of results from the use of a scaling ratio with respect to a carbon-12 standard. The relative isotopic mass, then, is the mass of an isotope, when this value is scaled by the mass of carbon-12. Equivalently, the isotopic mass of an isotope or nuclide is the mass of the isotope relative to 1/12 of the mass of a carbon-12 atom. For example, the isotopic mass of a carbon-12 atom is exactly 12. For comparison, the mass of a carbon-12 atom is exactly 12 daltons or 12 unified atomic mass units. Alternately, the mass of a carbon-12 atom may be expressed in any other mass units, for example. As in the case of mass, no nuclides other than carbon-12 have exactly whole-number values of relative isotopic mass
22.
Half-life
–
Half-life is the time required for a quantity to reduce to half its initial value. The term is used in nuclear physics to describe how quickly unstable atoms undergo. The term is used more generally to characterize any type of exponential or non-exponential decay. For example, the medical sciences refer to the biological half-life of drugs, the converse of half-life is doubling time. The original term, half-life period, dating to Ernest Rutherfords discovery of the principle in 1907, was shortened to half-life in the early 1950s. Rutherford applied the principle of a radioactive elements half-life to studies of age determination of rocks by measuring the period of radium to lead-206. Half-life is constant over the lifetime of an exponentially decaying quantity, the accompanying table shows the reduction of a quantity as a function of the number of half-lives elapsed. A half-life usually describes the decay of discrete entities, such as radioactive atoms, in that case, it does not work to use the definition that states half-life is the time required for exactly half of the entities to decay. For example, if there are 3 radioactive atoms with a half-life of one second, instead, the half-life is defined in terms of probability, Half-life is the time required for exactly half of the entities to decay on average. In other words, the probability of a radioactive atom decaying within its half-life is 50%, for example, the image on the right is a simulation of many identical atoms undergoing radioactive decay. Note that after one half-life there are not exactly one-half of the remaining, only approximately. Nevertheless, when there are many identical atoms decaying, the law of large numbers suggests that it is a good approximation to say that half of the atoms remain after one half-life. There are various simple exercises that demonstrate probabilistic decay, for example involving flipping coins or running a computer program. The three parameters t1⁄2, τ, and λ are all related in the following way. Amount approaches zero as t approaches infinity as expected, some quantities decay by two exponential-decay processes simultaneously. There is a half-life describing any exponential-decay process, for example, The current flowing through an RC circuit or RL circuit decays with a half-life of RCln or lnL/R, respectively. For this example, the half time might be used instead of half life. In a first-order chemical reaction, the half-life of the reactant is ln/λ, in radioactive decay, the half-life is the length of time after which there is a 50% chance that an atom will have undergone nuclear decay
23.
Avogadro constant
–
In chemistry and physics, the Avogadro constant is the number of constituent particles, usually atoms or molecules, that are contained in the amount of substance given by one mole. Thus, it is the proportionality factor that relates the mass of a compound to the mass of a sample. Avogadros constant, often designated with the symbol NA or L, has the value 7023602214085700000♠6. 022140857×1023 mol−1 in the International System of Units and this number is also known as Loschmidt constant in German literature. The constant was later redefined as the number of atoms in 12 grams of the isotope carbon-12, for instance, to a first approximation,1 gram of hydrogen element, having the atomic number 1, has 7023602200000000000♠6. 022×1023 hydrogen atoms. Similarly,12 grams of 12C, with the mass number 12, has the number of carbon atoms. Avogadros number is a quantity, and has the same numerical value of the Avogadro constant given in base units. In contrast, the Avogadro constant has the dimension of reciprocal amount of substance, the Avogadro constant can also be expressed as 0.602214. ML mol−1 Å−3, which can be used to convert from volume per molecule in cubic ångströms to molar volume in millilitres per mole, revisions in the base set of SI units necessitated redefinitions of the concepts of chemical quantity. Avogadros number, and its definition, was deprecated in favor of the Avogadro constant, the French physicist Jean Perrin in 1909 proposed naming the constant in honor of Avogadro. Perrin won the 1926 Nobel Prize in Physics, largely for his work in determining the Avogadro constant by several different methods, accurate determinations of Avogadros number require the measurement of a single quantity on both the atomic and macroscopic scales using the same unit of measurement. This became possible for the first time when American physicist Robert Millikan measured the charge on an electron in 1910, the electric charge per mole of electrons is a constant called the Faraday constant and had been known since 1834 when Michael Faraday published his works on electrolysis. By dividing the charge on a mole of electrons by the charge on a single electron the value of Avogadros number is obtained, since 1910, newer calculations have more accurately determined the values for the Faraday constant and the elementary charge. Perrin originally proposed the name Avogadros number to refer to the number of molecules in one gram-molecule of oxygen, with this recognition, the Avogadro constant was no longer a pure number, but had a unit of measurement, the reciprocal mole. While it is rare to use units of amount of other than the mole, the Avogadro constant can also be expressed in units such as the pound mole. NA = 7026273159734000000♠2. 73159734×1026 −1 = 7025170724843400000♠1. 707248434×1025 −1 Avogadros constant is a factor between macroscopic and microscopic observations of nature. As such, it provides the relationship between other physical constants and properties. The Avogadro constant also enters into the definition of the atomic mass unit. The earliest accurate method to measure the value of the Avogadro constant was based on coulometry
24.
Potassium
–
Potassium is a chemical element with symbol K and atomic number 19. It was first isolated from potash, the ashes of plants, in the periodic table, potassium is one of the alkali metals. Potassium in nature only in ionic salts. It is found dissolved in sea water, and is part of many minerals, naturally occurring potassium is composed of three isotopes, of which 40K is radioactive. Traces of 40K are found in all potassium, and it is the most common radioisotope in the human body, Potassium is chemically very similar to sodium, the previous element in Group 1 of the periodic table. They have a similar energy, which allows for each atom to give up its sole outer electron. That they are different elements combine with the same anions to make similar salts was suspected in 1702. Most industrial applications of potassium exploit the high solubility in water of potassium compounds, heavy crop production rapidly depletes the soil of potassium, and this can be remedied with agricultural fertilizers containing potassium, accounting for 95% of global potassium chemical production. Potassium ions are necessary for the function of all living cells, fresh fruits and vegetables are good dietary sources of potassium. Potassium is the second least dense metal after lithium and it is a soft solid with a low melting point, and can be easily cut with a knife. Freshly cut potassium is silvery in appearance, but it begins to tarnish toward gray immediately on exposure to air, in a flame test, potassium and its compounds emit a lilac color with a peak emission wavelength of 766.5 nanometers. Neutral potassium atoms have 19 electrons, one more than the stable configuration of the noble gas argon. This process requires so little energy that potassium is readily oxidized by atmospheric oxygen, in contrast, the second ionization energy is very high, because removal of two electrons breaks the stable noble gas electronic configuration. Potassium therefore does not readily form compounds with the state of +2 or higher. Potassium is an active metal that reacts violently with oxygen in water. With oxygen it forms potassium peroxide, and with water potassium forms potassium hydroxide, the reaction of potassium with water is dangerous because of its violent exothermic character and the production of hydrogen gas. Hydrogen reacts again with atmospheric oxygen, producing water, which reacts with the remaining potassium and this reaction requires only traces of water, because of this, potassium and the liquid sodium-potassium — NaK — are potent desiccants that can be used to dry solvents prior to distillation. Because of the sensitivity of potassium to water and air, reactions with other elements are only in an inert atmosphere such as argon gas using air-free techniques
25.
International System of Units
–
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
26.
Roentgen (unit)
–
The roentgen or röntgen is a legacy unit of measurement for the exposure of X-rays and gamma rays up to several megaelectronvolts. It is a measure of the ionization produced in air by X-rays or gamma radiation and it is named after the German physicist Wilhelm Röntgen, who discovered X-rays. Originating in 1908, this unit has been redefined and renamed over the years. It was last defined by the US National Institute of Standards and Technology in 1998 as 2. 58×10−4 C/kg, one roentgen of air kerma deposits 0.00877 grays of absorbed dose in dry air, or 0.0096 Gy in soft tissue. One roentgen of X-rays may deposit anywhere from 0.01 to 0.04 Gy in bone depending on the beam energy and this tissue-dependent conversion from kerma to absorbed dose is called the F-factor in radiotherapy contexts. The conversion depends on the energy of a reference medium. Even where the medium is fully defined, the ionizing energy of the calibration. Using 1 esu ≈3. 33564×10−10 C and the air density of ~1.293 kg/m³ at 0 °C and 101 kPa, this converts to 2.58 × 10−4 C/kg, which is the modern value given by NIST. 1 esu/cm3 ×3.33564 × 10−10 C/esu ×1,000,000 cm3/m3 ÷1.293 kg/m3 =2.58 × 10−4 C/kg This definition was used under different names for the next 20 years. In the meantime, the French Roentgen was given a different definition which amounted to 0.444 German R. The stated 1 cc of air would have a mass of 1.293 mg at the given, so in 1937 the ICR rewrote this definition in terms of this mass of air instead of volume. The 1937 definition was extended to gamma rays, but later capped at 3 MeV in 1950. The USSR all-union committee of standards had meanwhile adopted a different definition of the roentgen in 1934. The distinction of physical dose from dose caused confusion, some of which may have led Cantrill and they named this derivative quantity the roentgen equivalent physical to distinguish it from the ICR roentgen. Towards the middle of the 20th century, roentgens were used for the purpose of radiation protection and this replaced earlier practices that relied on time, film exposure, or fluorescence. The National Council on Radiation Protection established the first formal dose limit in 1931 as 0.1 roentgen per day. The International X-ray and Radium Protection Committee, now known as the International Commission on Radiological Protection soon followed with a limit of 0.2 roentgen per day in 1934. The 3 MeV cap was no part of the definition
27.
Absorbed dose
–
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
28.
Joule
–
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
29.
Equivalent dose
–
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
30.
Sievert
–
The sievert, named after Rolf Maximilian Sievert, is a derived unit of ionizing radiation dose in the International System of Units. It is a measure of the effect of low levels of ionizing radiation on the human body. These are under review, and changes are advised in the formal Reports of those bodies. The sievert is used for radiation dose quantities such as equivalent dose, effective dose and it is used to represent both the risk of the effect of external radiation from sources outside the body and the effect of internal irradiation due to inhaled or ingested radioactive substances. Conventionally, the sievert is not used for high rates of radiation that produce deterministic effects. Such effects are compared to the physical quantity absorbed dose measured by the unit gray, one sievert carries with it a 5. 5% chance of eventually developing cancer based on the linear no-threshold model. The rem is an older, non-SI unit of measurement, in summary, The gray - quantity D1 Gy =1 joule/kilogram - a physical quantity. 1 Gy is the deposit of a joule of energy in a kg of matter or tissue. The sievert - quantity H1 Sv =1 joule/kilogram - a biological effect, the sievert represents the equivalent biological effect of the deposit of a joule of radiation energy in a kilogram of human tissue. The equivalence to absorbed dose is denoted by Q, the ICRP definition of the sievert is, The sievert is the special name for the SI unit of equivalent dose, effective dose, and operational dose quantities. The unit is joule per kilogram, the sievert is used for a number of dose quantities which are described in this article and are part of the international radiological protection system devised and defined by the ICRP and ICRU. The ICRU/ICRP dose quantities have specific purposes and meanings, but some use common words in a different order, there can be confusion between, for instance, equivalent dose and dose equivalent. Only the operational dose quantities which still use Q for calculation retain the phrase dose equivalent, however, there are joint ICRU/ICRP proposals to simplify this system by changes to the operational dose definitions to harmonise with those of protection quantities. In the USA there are differently named dose quantities which are not part of the ICRP nomenclature, the sievert is used to represent the biological effects of different forms of external ionizing radiation on various types of human tissue. Some quantities cannot be measured, but they must be related to actual instrumentation. The resultant complexity has required the creation of a number of different dose quantities within a coherent system developed by the ICRU working with the ICRP, the external dose quantities and their relationships are shown in the accompanying diagram. These are directly measurable physical quantities in which no allowance has been made for biological effects and these quantities cannot be practically measured but are a calculated value of dose of organs of the human body, which is arrived at by using anthropomorphic phantoms. These are 3D computational models of the body which take into account a number of complex effects such as body self-shielding
31.
Background radiation
–
Background radiation is the ionizing radiation present in the environment. Background radiation originates from a variety of sources, both natural and artificial, sources include cosmic radiation, naturally occurring radioactive materials such as radon, and fallout from nuclear weapons testing and nuclear accidents. For example, in considering radiation safety, background radiation is defined by the International Atomic Energy Agency as Dose or dose rate attributable to all other than the one specified. So a distinction is made between sources of dose which are incidentally in a location, which are defined here as being background, and this is important where radiation measurements are taken of a specified radiation source, and the incidental background may affect this measurement. An example would be detection of radioactive contamination in a gamma ray background, background radiation varies with location and time, and the following table gives examples, Radioactive material is found throughout nature. Detectable amounts occur naturally in soil, rocks, water, air, in addition to this internal exposure, humans also receive external exposure from radioactive materials that remain outside the body and from cosmic radiation from space. The worldwide average natural dose to humans is about 2.4 millisievert per year and this is four times the worldwide average artificial radiation exposure, which in 2008 amounted to about 0.6 mSv per year. In some rich countries, like the US and Japan, artificial exposure is, on average, greater than the natural exposure, due to greater access to medical imaging. In Europe, average natural background exposure by country ranges from under 2 mSv annually in the United Kingdom to more than 7 mSv annually for some groups of people in Finland. The International Atomic Energy Agency states, Exposure to radiation from natural sources is a feature of everyday life in both working and public environments. These situations have become the focus of attention by the Agency in recent years. The biggest source of background radiation is airborne radon, a radioactive gas that emanates from the ground. Radon and its isotopes, parent radionuclides, and decay products all contribute to an average inhaled dose of 1.26 mSv/a. Radon is unevenly distributed and varies with weather, such that higher doses apply to many areas of the world. Concentrations over 500 times the average have been found inside buildings in Scandinavia, the United States, Iran. Radon is a product of uranium, which is relatively common in the Earths crust. Radon seeps out of these ores into the atmosphere or into water or infiltrates into buildings. It can be inhaled into the lungs, along with its decay products, although radon is naturally occurring, exposure can be enhanced or diminished by human activity, notably house construction
32.
Banana equivalent dose
–
Bananas contain naturally occurring radioactive isotopes, particularly potassium-40. One BED is often correlated to 0.1 µSv, however, in practice, the BED is only meant to inform the public about the existence of very low levels of natural radioactivity within a natural food and is not a formally adopted dose measurement. For example, the exposure from consuming a banana is approximately 1% of the average daily exposure to radiation. The maximum permitted radiation leakage for a power plant is equivalent to 2,500 BED per year. A lethal dose of radiation is approximately 35,000,000 BED, a person living 16 kilometres from the Three Mile Island nuclear reactor received an average of 800 BED of exposure to radiation during the 1979 accident. The concept probably originated on the RadSafe nuclear safety mailing list in 1995, although this unit is not formally adopted, the use of the word equivalent may still cause confusion. Properly, any quantity, which is a measure of the health effect of radiation on the whole body, is known as an effective dose. Equivalent doses only relate to specific organs of the body, the major natural source of radioactivity in plant tissue is potassium,0. 0117% of the naturally occurring potassium is the unstable isotope potassium-40. Plants naturally contain radioactive carbon-14, but in a banana containing 15 grams of carbon this would give off only about 3 to 5 beta rays per second. Since a typical banana contains about half a gram of potassium and this is typically given as the net dose over a period of 50 years resulting from the intake of radioactive material. According to the US Environmental Protection Agency, isotopically pure potassium-40 will give a committed dose equivalent of 5.02 nanosieverts over 50 years per becquerel ingested by an average adult. Using this factor, one banana equivalent dose comes out as about 5.02 nSv/Bq ×31 Bq/g ×0.5 g ≈78 nSv =0.078 μSv, in informal publications, one often sees this estimate rounded up to 0.1 μSv. If the assumed time of residence in the body is reduced by a factor of ten, for example, the estimated equivalent absorbed dose due to the banana will be reduced in the same proportion. These amounts may be compared to the due to the normal potassium content of the human body,2.5 g per kg. This potassium will naturally generate 175 g ×31 Bq/g ≈5400 Bq of radioactive decays, other food rich in potassium include potatoes, kidney beans, sunflower seeds, and nuts. Brazil nuts in particular are not only rich in 40K but may contain significant amounts of radium. Some types of salt can contain trace amounts of radium. Background radiation Committed dose List of humorous units of measurement Naturally occurring radioactive material Radioactivity in food, your questions answered, Food Standards Agency
33.
Counts per minute
–
Count rate measurements are associated with the detection of particles, such as alpha particles and beta particles. However, for gamma ray and X-ray dose measurements a unit such as the sievert is normally used, both cpm and cps are the rate of detection events registered by the measuring instrument, not the rate of emission from the source of radiation. For radioactive decay measurements it must not be confused with disintegrations per unit time, the count rates of cps and cpm are generally accepted and convenient practical rate measurements. They are not SI units, but are de facto units of measure in widespread use. Counts per minute is a measure of the rate of ionization events per minute. Counts are only manifested in the reading of the measuring instrument, whilst an instrument will display a rate of cpm, it does not have to detect counts for one minute, as it can infer the total per minute from a smaller sampling period. Count rate does not universally equate to dose rate, and there is no simple conversion factor. Counts is the number of events detected, but dose rate relates to the amount of ionising energy deposited in the sensor of the radiation detector, the conversion calculation is dependent on the radiation energy levels, the type of radiation being detected and the radiometric characteristic of the detector. The continuous current ion chamber instrument can easily measure dose but cannot measure counts, however the Geiger counter can measure counts but not the energy of the radiation, so a technique known as energy compensation of the detector tube is used to produce a dose reading. This modifies the characteristic so each count resulting from a particular radiation type is equivalent to a specific quantity of deposited dose. More can be found on radiation dose and dose rate at absorbed dose, disintegrations per minute and disintegrations per second are measures of the activity of the source of radioactivity. The SI unit of radioactivity, the becquerel, is equivalent to one disintegration per second and this unit should not be confused with cps, which is the number of counts received by an instrument from the source. One dps is the number of atoms that have decayed in one second, the efficiency of the radiation detector and its relative position to the source of radiation must be accounted for when relating cpm to dpm. This is known as the Counting efficiency, the factors affecting counting efficiency are shown in the accompanying diagram. The Surface Emission Rate is used as a measure of the rate of particles emitted from a source which is being used as a calibration standard. When the source is of plate or planar construction and the radiation of interest is emitting from one face, when the emissions are from a point source and the radiation of interest is emitting from all faces, it is known as 4 π emission. These terms correspond to the geometry over which the emissions are being measured. The SER is the emission rate from the source, and is related
34.
Ionizing radiation
–
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
