TNT equivalent
TNT equivalent is a convention for expressing energy used to describe the energy released in an explosion. The "ton of TNT" is a unit of energy defined by that convention to be 4.184 gigajoules, the approximate energy released in the detonation of a metric ton of TNT. In other words, for each gram of TNT exploded, 4,184 joules of energy are released; this convention intends to compare the destructiveness of an event with that of traditional explosive materials, of which TNT is a typical example, although other conventional explosives such as dynamite contain more energy. The "kiloton" is a unit of energy equal to 4.184 terajoules. The "megaton" is a unit of energy equal to 4.184 petajoules. The kiloton and megaton of TNT have traditionally been used to describe the energy output, hence the destructive power, of a nuclear weapon; the TNT equivalent appears in various nuclear weapon control treaties, has been used to characterize the energy released in such other destructive events as an asteroid impact.
Alternative values for TNT equivalency can be calculated according to which property is being compared and when in the two detonation processes the values are measured. Where for example the comparison is by energy yield, an explosive's energy is expressed for chemical purposes as the thermodynamic work produced by its detonation. For TNT this has been measured as 4686 J/g from a large sample of air blast experiments, theoretically calculated to be 4853 J/g, but on this basis, comparing the actual energy yields of a large nuclear device and an explosion of TNT can be inaccurate. Small TNT explosions in the open, don't tend to burn the carbon-particle and hydrocarbon products of the explosion. Gas-expansion and pressure-change effects tend to "freeze" the burn rapidly. A large open explosion of TNT may maintain fireball temperatures high enough so that some of those products do burn up with atmospheric oxygen; such differences can be substantial. For safety purposes a range as wide as 2673–6702 J has been stated for a gram of TNT upon explosion.
So, one can state. These complications have been sidestepped by convention; the energy liberated by one gram of TNT was arbitrarily defined as a matter of convention to be 4184 J, one kilocalorie. A kiloton of TNT can be visualized as a cube of TNT 8.46 metres on a side. 1 ton TNT equivalent is approximately: 1.0×109 calories 4.184×109 joules 3.96831×106 British thermal units 3.08802×109 foot pounds 1.162×103 kilowatt hours The relative effectiveness factor relates an explosive's demolition power to that of TNT, in units of the TNT equivalent/kg. 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 for TNT. For example, if a timber-cutting formula calls for a charge of 1 kg of TNT based on octanitrocubane's RE factor of 2.38, it would take only 1.0/2.38 kg of it to do the same job. 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 / 1.0 / 0.42 kg, respectively. Calculating a single RE factor for a explosive is, impossible, it depends on the specific case of use. Given a pair of explosives, one can produce 2× the shockwave output but the difference in direct metal cutting ability maybe 4× higher for one type of metal and 7× higher for another type of metal; the relative differences between two explosives in shaped charges will be greater. The table below should be taken as an example and not as a precise source of data. *: TBX or EBX, in a small, confined space, may have over twice the power of destruction. The total power of aluminized mixtures depends on the condition of explosions. Brisance Net explosive quantity Nuclear weapon yield Orders of magnitude Relative effectiveness factor Table of explosive detonation velocities Ton Tonne Tonne of oil equivalent, a unit of energy exactly 10 tonnes of TNT Thompson, A.. N.. Guide for the Use of the International System of Units.
NIST Special Publication. 811. National Institute of Standards and Technology. Version 3.2. Nuclear Weapons FAQ Part 1.3 Rhodes, Richard. The Making of the Atomic Bomb. Simon & Schuster. ISBN 978-1-4516-7761-4. Cooper, Paul W. Explosives Engineering, New York: Wiley-VCH, ISBN 978-0-471-18636-6 HQ Department of the Army, Field Manual 5-25: Explosives and Demolitions, Washington, D. C.: Pentagon Publishing, pp. 83–84, ISBN 978-0-9759009-5-6 Explosives - Compositions, Alexandria, VA: GlobalSecurity.org, retrieved September 1, 2010 Urbański, Tadeusz and Technology of Explosives, Volumes I–IV, Oxford: Pergamon Mathieu, Jörg. Thermobaric Explosives, Advanced Energetic Materials, 2004; the National Academies Press, nap.edu, 2004
Sievert
The sievert is a derived unit of ionizing radiation dose in the International System of Units and is a measure of the health effect of low levels of ionizing radiation on the human body. The sievert is of importance in dosimetry and radiation protection, is named after Rolf Maximilian Sievert, a Swedish medical physicist renowned for work on radiation dose measurement and research into the biological effects of radiation; the sievert is used for radiation dose quantities such as equivalent dose and effective dose, which represent the risk of external radiation from sources outside the body, committed dose which represents the risk of internal irradiation due to inhaled or ingested radioactive substances. The sievert is intended to represent the stochastic health risk, which for radiation dose assessment is defined as the probability of radiation-induced cancer and genetic damage. One sievert carries with it a 5.5% chance of developing cancer based on the linear no-threshold model. To enable consideration of stochastic health risk, calculations are performed to convert the physical quantity absorbed dose into equivalent dose and effective dose, the details of which depend on the radiation type and biological context.
For applications in radiation protection and dosimetry assessment the International Commission on Radiological Protection and International Commission on Radiation Units and Measurements have published recommendations and data which are used to calculate these. These are under continual review, changes are advised in the formal "Reports" of those bodies. Conventionally, the sievert is not used for high dose rates of radiation that produce deterministic effects, the severity of acute tissue damage, certain to happen, such as acute radiation syndrome. One sievert equals 100 rem; the rem is an older, non-SI unit of measurement. The SI definition given by the International Committee for Weights and Measures says: "The quantity dose equivalent H is the product of the absorbed dose D of ionizing radiation and the dimensionless factor Q defined as a function of linear energy transfer by the ICRU" H = Q × DThe value of Q is not defined further by CIPM, but it requires the use of the relevant ICRU recommendations to provide this value.
The CIPM says that "in order to avoid any risk of confusion between the absorbed dose D and the dose equivalent H, the special names for the respective units should be used, that is, the name gray should be used instead of joules per kilogram for the unit of absorbed dose D and the name sievert instead of joules per kilogram for the unit of dose equivalent H". In summary: The gray – quantity D 1 Gy = 1 joule/kilogram – a physical quantity. 1 Gy is the deposit of a joule of radiation energy per kg of tissue. The sievert – quantity H 1 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, 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 equivalent. Although the CIPM definition states that the linear energy transfer function of the ICRU is used in calculating the biological effect, the ICRP in 1990 developed the "protection" dose quantities effective and equivalent dose which are calculated from more complex computational models and are distinguished by not having the phrase dose equivalent in their name. 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; these were outlined at the 3rd International Symposium on Radiological Protection in October 2015, if implemented would make the naming of operational quantities more logical by introducing "dose to lens of eye" and "dose to local skin" as equivalent doses.
In the USA there are differently named dose quantities. 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 and dosimetry measurements. 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. The ICRU is responsible for the operational dose quantities, based upon the application of ionising radiation metrology, the ICRP is responsible for the protection quantities, based upon modelling of dose uptake and biological sensitivity of the human body; these are directly measurable physical quantities in which no allowance has been made for biological effects. Radiation fluence is the number of radiation particles impinging per unit area per unit time, kerma is the ionising effect of the radiation field, absorbed dose is the amount of radiation energy deposited per unit mass.
Protection quantities are cal
Potassium
Potassium is a chemical element with symbol K and atomic number 19. It was first isolated from the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals. All of the alkali metals have a single valence electron in the outer electron shell, removed to create an ion with a positive charge – a cation, which combines with anions to form salts. Potassium in nature occurs only in ionic salts. Elemental potassium is a soft silvery-white alkali metal that oxidizes in air and reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, burning with a lilac-colored flame, it is found dissolved in sea water, is part of many minerals. Potassium is chemically similar to sodium, the previous element in group 1 of the periodic table, they have a similar first ionization energy, which allows for each atom to give up its sole outer electron. That they are different elements that combine with the same anions to make similar salts was suspected in 1702, was proven in 1807 using electrolysis.
Occurring potassium is composed of three isotopes, of which 40K is radioactive. Traces of 40K are found in all potassium, it is the most common radioisotope in the human body. Potassium ions are vital for the functioning of all living cells; the transfer of potassium ions across nerve cell membranes is necessary for normal nerve transmission. Fresh fruits and vegetables are good dietary sources of potassium; the body responds to the influx of dietary potassium, which raises serum potassium levels, with a shift of potassium from outside to inside cells and an increase in potassium excretion by the kidneys. Most industrial applications of potassium exploit the high solubility in water of potassium compounds, such as potassium soaps. Heavy crop production depletes the soil of potassium, this can be remedied with agricultural fertilizers containing potassium, accounting for 95% of global potassium chemical production; the English name for the element potassium comes from the word "potash", which refers to an early method of extracting various potassium salts: placing in a pot the ash of burnt wood or tree leaves, adding water and evaporating the solution.
When Humphry Davy first isolated the pure element using electrolysis in 1807, he named it potassium, which he derived from the word potash. The symbol "K" stems from kali, itself from the root word alkali, which in turn comes from Arabic: القَلْيَه al-qalyah "plant ashes". In 1797, the German chemist Martin Klaproth discovered "potash" in the minerals leucite and lepidolite, realized that "potash" was not a product of plant growth but contained a new element, which he proposed to call kali. In 1807, Humphry Davy produced the element via electrolysis: in 1809, Ludwig Wilhelm Gilbert proposed the name Kalium for Davy's "potassium". In 1814, the Swedish chemist Berzelius advocated the name kalium for potassium, with the chemical symbol "K"; the English and French speaking countries adopted Davy and Gay-Lussac/Thénard's name Potassium, while the Germanic countries adopted Gilbert/Klaproth's name Kalium. The "Gold Book" of the International Union of Physical and Applied Chemistry has designated the official chemical symbol as K.
Potassium is the second least dense metal after lithium. It is a soft solid with a low melting point, can be cut with a knife. Freshly cut potassium is silvery in appearance, but it begins to tarnish toward gray on exposure to air. In a flame test 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; because of this and its low first ionization energy of 418.8 kJ/mol, the potassium atom is much more to lose the last electron and acquire a positive charge than to gain one and acquire a negative charge. This process requires so little energy that potassium is oxidized by atmospheric oxygen. In contrast, the second ionization energy is high, because removal of two electrons breaks the stable noble gas electronic configuration. Potassium therefore does not form compounds with the oxidation state of higher. Potassium is an active metal that reacts violently with oxygen in water and air.
With oxygen it forms potassium peroxide, 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; this reaction requires only traces of water. Because of the sensitivity of potassium to water and air, reactions with other elements are possible only in an inert atmosphere such as argon gas using air-free techniques. Potassium does not react with most hydrocarbons such as mineral kerosene, it dissolves in liquid ammonia, up to 480 g per 1000 g of ammonia at 0 °C. Depending on the concentration, the ammonia solutions are blue to yellow, their electrical conductivity is similar to that of liquid metals. In a pure solution, potassium reacts with ammonia to form KNH2, but this reaction is accelerated by minute amounts of transition metal s
Curie
The curie is a non-SI unit of radioactivity defined in 1910. According to a notice in Nature at the time, it was named in honour of Pierre Curie, but was considered at least by some to be in honour of Marie Curie as well, it was defined as "the quantity or mass of radium emanation in equilibrium with one gram of radium" but is defined as: 1 Ci = 3.7×1010 decays per second after more accurate measurements of the activity of 226Ra In 1975 the General Conference on Weights and Measures gave the becquerel, defined as one nuclear decay per second, official status as the SI unit of activity. Therefore: 1 Ci = 3.7×1010 Bq = 37 GBqand 1 Bq ≅ 2.703×10−11 Ci ≅ 27 pCiWhile its continued use is discouraged by National Institute of Standards and Technology and other bodies, the curie is still used throughout the government and medicine in the United States and in other countries. At the 1910 meeting which defined the curie, it was proposed to make it equivalent to 10 nanograms of radium, but Marie Curie, after accepting this, changed her mind and insisted on one gram of radium.
According to Bertram Boltwood, Marie Curie thought that'the use of the name "curie" for so infinitesimally small quantity of anything was altogether inappropriate.'The power in milliwatts emitted by one curie of radiation can be calculated by taking the number of MeV for the radiation times 5.93. A radiotherapy machine may have 1000 Ci of a radioisotope such as caesium-137 or cobalt-60; this quantity of radioactivity can produce serious health effects with only a few minutes of close-range, unshielded exposure. Ingesting a millicurie is fatal. For example, the LD-50 for ingested polonium-210 is about 53.5 nanograms. The typical human body contains 0.1 μCi of occurring potassium-40. A human body containing 16 kg of carbon would have about 24 nanograms or 0.1 μCi of carbon-14. Together, these would result in a total of 0.2 μCi or 7400 decays per second inside the person's body. Units of activity refer to a quantity of radioactive atoms; because the probability of decay is a fixed physical quantity, for a known number of atoms of a particular radionuclide, a predictable number will decay in a given time.
The number of decays that will occur in one second in one gram of atoms of a particular radionuclide is known as the specific activity of that radionuclide. The activity of a sample decreases with time because of decay; the rules of radioactive decay may be used to convert activity to an actual number of atoms. They state that 1 Ci of radioactive atoms would follow the expression: N × λ = 1 Ci = 3.7 × 1010 Bqand so, N = 3.7 × 1010 Bq / λ,where λ is the decay constant in s−1. We can express activity in moles: 1 Ci = 3.7 × 10 10 N A moles × t 1 / 2 in seconds ≈ 8.8639 × 10 − 14 moles × t 1 / 2 in seconds ≈ 5.3183 × 10 − 12 moles × t 1 / 2 in minutes ≈ 3.1910 × 10 − 10 moles × t 1 / 2 in hours ≈ 7.6584 × 10 − 9 moles × t 1 / 2 in days ≈ 2.7972 × 10 − 6 moles × t 1 / 2 in years where NA is Avogadro's number and t1/2 is the half life. The number of moles may be converted to grams by multiplying by the atomic mass. Here are some examples, ordered by half-life: The following table shows radiation quantities in SI and non-SI units: Geiger counter Ionizing radiat
Joseph Fourier
Jean-Baptiste Joseph Fourier was a French mathematician and physicist born in Auxerre and best known for initiating the investigation of Fourier series and their applications to problems of heat transfer and vibrations. The Fourier transform and Fourier's law are named in his honour. Fourier is generally credited with the discovery of the greenhouse effect. Fourier was born at the son of a tailor, he was orphaned at the age of nine. Fourier was recommended to the Bishop of Auxerre and, through this introduction, he was educated by the Benedictine Order of the Convent of St. Mark; the commissions in the scientific corps of the army were reserved for those of good birth, being thus ineligible, he accepted a military lectureship on mathematics. He took a prominent part in his own district in promoting the French Revolution, serving on the local Revolutionary Committee, he was imprisoned 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, was appointed secretary of the Institut d'Égypte. Cut off from France by the British fleet, he organized the workshops on which the French army had to rely for their munitions of war, he contributed several mathematical papers to the Egyptian Institute which Napoleon founded at Cairo, with a view of weakening British influence in the East. After the British victories and the capitulation of the French under General Menou in 1801, Fourier returned to France. In 1801, Napoleon appointed Fourier Prefect of the Department of Isère in Grenoble, where he oversaw road construction and other projects. However, Fourier had 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 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, he presented his paper On the Propagation of Heat in Solid Bodies to the Paris Institute on December 21, 1807. He contributed to the monumental Description de l'Égypte. In 1822, Fourier 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 diminished health began to take its toll: Fourier had experienced, in Egypt and Grenoble, some attacks of aneurism of the heart. At Paris, it was impossible to be mistaken with respect to the primary cause of the frequent suffocations which he experienced. A fall, which he sustained on the 4th of May 1830, while descending a flight of stairs, aggravated the malady to an extent beyond what could have been feared. Shortly after this event, he died in his bed on 16 May 1830. Fourier was buried in the Père Lachaise Cemetery in Paris, a tomb decorated with an Egyptian motif to reflect his position as secretary of the Cairo Institute, his collation of Description de l'Égypte.
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. In 1822 Fourier published his work on heat flow in Théorie analytique de la chaleur, in which he based his reasoning on Newton's law of cooling, that the flow of heat between two adjacent molecules is proportional to the small difference of their temperatures; this book was translated, with editorial'corrections', into English 56 years by Freeman. The book was edited, with many editorial corrections, by Darboux and republished in French in 1888. There were three important contributions in this work, one purely mathematical, two physical. In mathematics, Fourier claimed that any function of a variable, whether continuous or discontinuous, can be expanded in a series of sines of multiples of the variable. Though this result is not correct without additional conditions, Fourier's observation that some discontinuous functions are the sum of infinite series was a breakthrough.
The question of determining when a Fourier series converges has been fundamental for centuries. Joseph-Louis Lagrange had given particular cases of this theorem, had implied that the method was general, but he had not pursued the subject. Peter Gustav Lejeune Dirichlet was the first to give a satisfactory demonstration of it with some restrictive conditions; this work provides the foundation for. One important physical contribution in the book was the concept of dimensional homogeneity in equations; the other physical contribution was Fourier's proposal of his partial differential equation for conductive diffusion of heat. This equation is now taught to every student of mathematical physics. Fourier left an unfinished work on determining and locating real roots of polynomials, edited by Claude-Louis Navier and published in 1831; this work contains much original matter—in particular, Fourier's theorem on polynomial real roots, published in 1820. François Budan, in 1807 and 1811, had published independently his theorem, which
Henri Becquerel
Antoine Henri Becquerel was a French engineer, Nobel laureate, the first person to discover evidence of radioactivity. For work in this field he, along with Marie Skłodowska-Curie and Pierre Curie, received the 1903 Nobel Prize in Physics; the SI unit for radioactivity, the becquerel, is named after him. Becquerel was born in Paris into a wealthy family which produced four generations of physicists: Becquerel's grandfather and son. Henri started off his education by attending the Lycée Louis-le-Grand school, a prep school in Paris, he studied engineering at the École des Ponts et Chaussées. In 1874, Henri married Lucie Zoé Marie Jamin, who would die while giving birth to Jean. In 1890 he married Louise Désirée Lorieux. In Becquerel's early career, he became the third in his family to occupy the physics chair at the Muséum National d'Histoire Naturelle in 1892. On in 1894, Becquerel became chief engineer in the Department of Bridges and Highways before he started with his early experiments. Becquerel's 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.
Early in his career, Becquerel studied the Earth's magnetic fields. Becquerel's discovery of spontaneous radioactivity is a famous example of serendipity, of how chance favors the prepared mind. Becquerel had long been interested in phosphorescence, the emission of light of one color following a body's exposure to light of another color. In early 1896, there was a wave of excitement following Wilhelm Conrad Röntgen's discovery of X-rays on the 5th of January. During the experiment, Röntgen "found that the Crookes tubes he had been using to study cathode rays emitted a new kind of invisible ray, capable of penetrating through black paper." Learning of Röntgen's discovery from earlier that year during a meeting of the French Academy of Sciences caused Becquerel to be interested, soon "began looking for a connection between the phosphorescence he had been investigating and the newly discovered x-rays" of Röntgen, thought that phosphorescent materials, such as some uranium salts, might emit penetrating X-ray-like radiation when illuminated by bright sunlight.
By May 1896, after other experiments involving non-phosphorescent uranium salts, he arrived at the correct explanation, namely that the penetrating radiation came from the uranium itself, without any need for excitation by an external energy source. There followed a period of intense research into radioactivity, including the determination that the element thorium is radioactive and the discovery of additional radioactive elements polonium and radium by Marie Skłodowska-Curie and her husband Pierre Curie; the intensive research of radioactivity led to Henri publishing seven papers on the subject in 1896. Becquerel's other experiments allowed him to research more into radioactivity and figure out different aspects of the magnetic field when radiation is introduced into the magnetic field. "When different radioactive substances were put in the magnetic field, they deflected in different directions or not at all, showing that there were three classes of radioactivity: negative and electrically neutral."As happens in science, radioactivity came close to being discovered nearly four decades earlier in 1857, when Abel Niépce de Saint-Victor, investigating photography under Michel Eugène Chevreul, observed that uranium salts emitted radiation that could darken photographic emulsions.
By 1861, Niepce de Saint-Victor realized that uranium salts produce "a radiation, invisible to our eyes". Niepce de Saint-Victor knew Henri Becquerel's father. In 1868, Edmond Becquerel published La lumière: ses causes et ses effets. On page 50 of volume 2, Edmond noted that Niepce de Saint-Victor had observed that some objects, exposed to sunlight could expose photographic plates in the dark. Niepce further noted that on the one hand, the effect was diminished if an obstruction were placed between a photographic plate and the object, exposed to the sun, but " … d'un autre côté, l'augmentation d'effet quand la surface insolée est couverte de substances facilement altérables à la lumière, comme le nitrate d'urane … ". Describing them to the French Academy of Sciences on 27 February 1896, he said: One wraps a Lumière photographic plate with a bromide emulsion in two sheets of thick black paper, such that the plate does not become clouded upon being exposed to the sun for a day. One places on the sheet of paper, on the outside, a slab of the phosphorescent substance, one exposes the whole to the sun for several hours.
When one 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 sees the image of these objects appear on the negative... 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 abandon this hypothesis. On 2 March 1896 he reported: I will insist upon the following fact, which seems to me quite important and beyond the phenomena which one could expec
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 written cycles per second, cycles/second, c.p.s. c/s, ~, or, just cycles. The term comes from the fact that sound waves have a frequency measurable in their number of oscillations, or cycles, per second. With the organization of the International System of Units in 1960, the cycle per second was replaced by the hertz, or reciprocal second, "s−1" or "1/s". Symbolically, "cycle per second" units are "cycle/second", while hertz is "Hz" or "s−1". For higher frequencies, kilocycles, as an abbreviation of kilocycles per second were used on components or devices. Other higher units like megacycle and less kilomegacycle were used before 1960 and in some documents; these have modern equivalents such as kilohertz and gigahertz. The rate at which aperiodic or stochastic events occur may be expressed in becquerels, not hertz, since although the two are mathematically similar, by convention hertz implies regularity where becquerels implies the requirement of a time averaging operation.
Thus, one becquerel is one event per second on average, whereas one hertz is one event per second on a regular cycle. Cycle can be a unit for measuring usage of reciprocating machines presses, in which cases cycle refers to one complete revolution of the mechanism being measured. Derived units include cycles per day and cycles per year. Revolutions per minute 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
