A corona discharge is an electrical discharge brought on by the ionization of a fluid such as air surrounding a conductor, electrically charged. Spontaneous corona discharges occur in high-voltage systems unless care is taken to limit the electric field strength. A corona will occur when the strength of the electric field around a conductor is high enough to form a conductive region, but not high enough to cause electrical breakdown or arcing to nearby objects, it is seen as a bluish glow in the air adjacent to pointed metal conductors carrying high voltages, emits light by the same property as a gas discharge lamp. In many high voltage applications corona is an unwanted side effect. Corona discharge from high voltage electric power transmission lines constitutes an economically significant waste of energy for utilities. In high voltage equipment like Cathode Ray Tube televisions, radio transmitters, X-ray machines and particle accelerators the current leakage caused by coronas can constitute an unwanted load on the circuit.
In air, coronas generate gases such as ozone and nitric oxide, in turn nitrogen dioxide, thus nitric acid if water vapor is present. These gases are corrosive and can degrade and embrittle nearby materials, are toxic to humans and the environment. Corona discharges can be suppressed by improved insulation, corona rings, making high voltage electrodes in smooth rounded shapes. However, controlled corona discharges are used in a variety of processes such as air filtration and ozone generators. A corona discharge is a process by which a current flows from an electrode with a high potential into a neutral fluid air, by ionizing that fluid so as to create a region of plasma around the electrode; the ions generated pass charge to nearby areas of lower potential, or recombine to form neutral gas molecules. When the potential gradient is large enough at a point in the fluid, the fluid at that point ionizes and it becomes conductive. If a charged object has a sharp point, the electric field strength around that point will be much higher than elsewhere.
Air near the electrode can become ionized. When the air near the point becomes conductive, it has the effect of increasing the apparent size of the conductor. Since the new conductive region is less sharp, the ionization may not extend past this local region. Outside this region of ionization and conductivity, the charged particles find their way to an oppositely charged object and are neutralized. Along with the similar brush discharge, the corona is called a "single-electrode discharge", as opposed to a "two-electrode discharge". A corona only forms when the conductor is enough separated from conductors at opposite potential that an arc cannot jump between them. If the geometry and gradient are such that the ionized region continues to grow until it reaches another conductor at a lower potential, a low resistance conductive path between the two will be formed, resulting in an electric spark or electric arc, depending upon the source of the electric field. If the source continues to supply current, a spark will evolve into a continuous discharge called an arc.
Corona discharge only forms when the electric field at the surface of the conductor exceeds a critical value, the dielectric strength or disruptive potential gradient of the fluid. In air at atmospheric pressure it is 30 kilovolts per centimeter, but decreases with pressure, so corona is more of a problem at high altitudes. Corona discharge forms at curved regions on electrodes, such as sharp corners, projecting points, edges of metal surfaces, or small diameter wires; the high curvature causes a high potential gradient at these locations, so that the air breaks down and forms plasma there first. On sharp points in air corona can start at potentials of 2 - 6 kV. In order to suppress corona formation, terminals on high voltage equipment are designed with smooth large diameter rounded shapes like balls or toruses, corona rings are added to insulators of high voltage transmission lines. Coronas may be negative; this is determined by the polarity of the voltage on the curved electrode. If the curved electrode is positive with respect to the flat electrode, it has a positive corona, if it is negative, it has a negative corona.
The physics of positive and negative coronas are strikingly different. This asymmetry is a result of the great difference in mass between electrons and positively charged ions, with only the electron having the ability to undergo a significant degree of ionising inelastic collision at common temperatures and pressures. An important reason for considering coronas is the production of ozone around conductors undergoing corona processes in air. A negative corona generates much more ozone than the corresponding positive corona. Corona discharge has a number of commercial and industrial applications: Removal of unwanted electric charges from the surface of aircraft in flight and thus avoiding the detrimental effect of uncontrolled electrical discharge pulses on the performance of avionic systems Manufacture of ozone Sanitization of pool water In an electrostatic precipitator, removal of solid pollutants from a waste gas stream, or scrubbing particles from air in air-conditioning systems Photocopying Air ionisers Production of photons for Kirlian photography to expose photographic film EHD thrusters and other ionic wind devices Nitrogen laser Ionization of a gaseous sample for subsequent analysis in a mass spectrometer or an ion mobility spectrometer Static charge neutrali
Sir John Douglas Cockcroft, was a British physicist who shared with Ernest Walton the Nobel Prize in Physics in 1951 for splitting the atomic nucleus, was instrumental in the development of nuclear power. After service on the Western Front with the Royal Field Artillery during the Great War, Cockcroft studied electrical engineering at Manchester Municipal College of Technology whilst he was an apprentice at Metropolitan Vickers Trafford Park and was a member of their research staff, he won a scholarship to St. John's College, where he sat the tripos exam in June 1924, becoming a wrangler. Ernest Rutherford accepted Cockcroft as a research student at the Cavendish Laboratory, Cockcroft completed his doctorate under Rutherford's supervision in 1928. With Ernest Walton and Mark Oliphant he built. Cockcroft and Walton used this to perform the first artificial disintegration of an atomic nucleus, a feat popularly known as splitting the atom. During the Second World War Cockcroft became Assistant Director of Scientific Research in the Ministry of Supply, working on radar.
He was a member of the committee formed to handle issues arising from the Frisch–Peierls memorandum, which calculated that an atomic bomb could be technically feasible, of the MAUD Committee which succeeded it. In 1940, as part of the Tizard Mission, he shared British technology with his counterparts in the United States. In the war, the fruits of the Tizard Mission came back to Britain in the form of the SCR-584 radar set and the proximity fuze, which were used to defeat the V-1 flying bomb. In May 1944, he became director of the Montreal Laboratory, oversaw the development of the ZEEP and NRX reactors, the creation of the Chalk River Laboratories. After the war Cockcroft became the director of the Atomic Energy Research Establishment at Harwell, where the low-powered, graphite-moderated GLEEP became the first nuclear reactor to operate in western Europe when it was started on 15 August 1947; this was followed by BEPO in 1948. Harwell was involved in the design of the chemical separation plant at Windscale.
Under his direction it took part including the ZETA program. His insistence that the chimney stacks of the Windscale reactors be fitted with filters was mocked as Cockcroft's Folly until the core of one of the reactors ignited and released radionuclides during the Windscale fire of 1957. From 1959 to 1967, he was the first Master of Cambridge, he was chancellor of the Australian National University in Canberra from 1961 to 1965. John Douglas Cockcroft, Also known as "Johnny W.", was born in Todmorden, West Riding of Yorkshire, England, on 27 May 1897, the eldest son of a mill owner, John Arthur Cockcroft, his wife Annie Maude née Fielden. He had four younger brothers, his early education was at the Church of England school in Walsden from 1901 to 1908, at Todmorden Elementary School from 1908 to 1909, at Todmorden Secondary School from 1909 to 1914, where he played football and cricket. Among the girls at the school was his future wife, Eunice Elizabeth Crabtree. In 1914, he won a County Major Scholarship, West Riding of Yorkshire, to the Victoria University of Manchester, where he studied mathematics.
The Great War broke out in August 1914. Cockcroft completed his first year at Manchester in June 1915, he did not wish to become an officer. During the summer break he worked at a YMCA canteen at Kinmel Camp in Wales, he enlisted in the British Army on 24 November 1915. On 29 March 1916, he joined the 59th Training Brigade, Royal Field Artillery, where he was trained as a signaller, he was posted to B Battery, 92nd Field Artillery Brigade, one of the units of the 20th Division, on the Western Front. Cockcroft participated in the Advance to the Third Battle of Ypres, he applied for a commission, despite not having attended a public school, was accepted. He was sent to Brighton in February 1918 to learn about gunnery, in April 1918, to the Officer Candidate School in Weedon Bec in Northamptonshire, where he was trained as a field artillery officer, he was commissioned as a lieutenant in the Royal Field Artillery on 17 October 1918. After the war ended, Cockcroft was released from the Army in January 1919.
He elected not to return to Victoria University of Manchester, but to study electrical engineering at Manchester Municipal College of Technology. Because he had completed a year at Victoria University of Manchester, he was allowed to skip the first year of the course, he received his BSc in June 1920. Miles Walker, the professor of electrical engineering there, persuaded him to take up an apprenticeship with Metropolitan Vickers, he obtained a 1851 Exhibition Scholarship from the Royal Commission for the Exhibition of 1851, submitted his MSc thesis on the "Harmonic Analysis for Alternating Currents" in June 1922. Walker suggested Cockcroft sit for a scholarship to St. John's College, Walker's alma mater. Cockcroft was successful, winning a £30 scholarship and a £20 bursary awarded to undergraduates of limited means. Metropolitan Vickers gave. Walker and an aunt made up the balance of the £316 fee; as a graduate of another university, he was allowed to skip the first year of the tripos. He sat the tripos exam in June 1924, achieved a B* as a wrangler, was awarded his BA degree.
Cockcroft married Elizabeth Crabtree on 26 August 1925, in a ceremony at the Bridge Street United Methodist Church in Todmorden. They had six children; the first, a boy known as Timothy, died in infancy. They subsequently had four
Electrical breakdown or dielectric breakdown is when current flows through an electrical insulator when the voltage applied across it exceeds the breakdown voltage. This results in the insulator becoming electrically conductive. Electrical breakdown may be a momentary event, or may lead to a continuous arc if protective devices fail to interrupt the current in a power circuit. Under sufficient electrical stress, electrical breakdown can occur within solids, gases or vacuum. However, the specific breakdown mechanisms are different for each kind of dielectric medium. Electrical breakdown is associated with the failure of solid or liquid insulating materials used inside high voltage transformers or capacitors in the electricity distribution grid resulting in a short circuit or a blown fuse. Electrical breakdown can occur across the insulators that suspend overhead power lines, within underground power cables, or lines arcing to nearby branches of trees. Dielectric breakdown is important in the design of integrated circuits and other solid state electronic devices.
Insulating layers in such devices are designed to withstand normal operating voltages, but higher voltage such as from static electricity may destroy these layers, rendering a device useless. The dielectric strength of capacitors limits how much energy can be stored and the safe working voltage for the device. Breakdown mechanisms differ in solids and gasses. Breakdown is influenced by electrode material, sharp curvature of conductor material, the size of the gap between the electrodes, the density of the material in the gap. In solid materials a long-time partial discharge precedes breakdown, degrading the insulators and metals nearest the voltage gap; the partial discharge chars through a channel of carbonized material that conducts current across the gap. Possible mechanisms for breakdown in liquids include bubbles, small impurities, electrical super-heating; the process of breakdown in liquids is complicated by hydrodynamic effects, since additional pressure is exerted on the fluid by the non-linear electrical field strength in the gap between the electrodes.
In liquefied gases used as coolants for superconductivity – such as Helium at 4.2 K or Nitrogen at 77 K – bubbles can induce breakdown. In oil-cooled and oil-insulated transformers the field strength for breakdown is about 20 kV/mm. Despite the purified oils used, small particle contaminants are blamed. Electrical breakdown occurs within a gas. Regions of intense voltage gradients can cause nearby gas to ionize and begin conducting; this is done deliberately in low pressure discharges such as in fluorescent lights. The voltage that leads to electrical breakdown of a gas is approximated by Paschen's Law. Partial discharge in air causes the "fresh air" smell of ozone during thunderstorms or around high-voltage equipment. Although air is an excellent insulator, when stressed by a sufficiently high voltage, air can begin to break down, becoming conductive. Across small gaps, breakdown voltage in air is a function of gap length times pressure. If the voltage is sufficiently high, complete electrical breakdown of the air will culminate in an electrical spark or an electric arc that bridges the entire gap.
The color of the spark depends upon the gases. While the small sparks generated by static electricity may be audible, larger sparks are accompanied by a loud snap or bang. Lightning is an example of an immense spark. If a fuse or circuit breaker fails to interrupt the current through a spark in a power circuit, current may continue, forming a hot electric arc; the color of an arc depends upon the conducting gasses, some of which may have been solids before being vaporized and mixed into the hot plasma in the arc. The free ions in and around the arc recombine to create new chemical compounds, such as ozone, carbon monoxide, nitrous oxide. Ozone is most noticed due to its distinct odour. Although sparks and arcs are undesirable, they can be useful in applications such as spark plugs for gasoline engines, electrical welding of metals, or for metal melting in an electric arc furnace. Prior to gas discharge the gas glows with distinct colors that depend on the energy levels of the atoms. Not all mechanisms are understood.
The vacuum itself is expected to undergo electrical breakdown near the Schwinger limit. Before gas breakdown, there is a non-linear relation between voltage and current as shown in the figure. In region 1, there are free ions that can induce a current; these will be saturated after a certain voltage and give a constant current, region 2. Region 3 and 4 are caused by ion avalanche. Friedrich Paschen established the relation between the breakdown condition to breakdown voltage, he derived a formula that defines the breakdown voltage for uniform field gaps as a function of gap length and gap pressure. V b = B p d ln ( A p d ln ( 1 +
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or from a combination of fission and fusion reactions. Both bomb types release large quantities of energy from small amounts of matter; the first test of a fission bomb released an amount of energy equal to 20,000 tons of TNT. The first thermonuclear bomb test released energy equal to 10 million tons of TNT. A thermonuclear weapon weighing little more than 2,400 pounds can release energy equal to more than 1.2 million tons of TNT. A nuclear device no larger than traditional bombs can devastate an entire city by blast and radiation. Since they are weapons of mass destruction, the proliferation of nuclear weapons is a focus of international relations policy. Nuclear weapons have been used twice in war, both times by the United States against Japan near the end of World War II. On August 6, 1945, the U. S. Army Air Forces detonated a uranium gun-type fission bomb nicknamed "Little Boy" over the Japanese city of Hiroshima.
S. Army Air Forces detonated a plutonium implosion-type fission bomb nicknamed "Fat Man" over the Japanese city of Nagasaki; these bombings caused injuries that resulted in the deaths of 200,000 civilians and military personnel. The ethics of these bombings and their role in Japan's surrender are subjects of debate. Since the atomic bombings of Hiroshima and Nagasaki, nuclear weapons have been detonated over two thousand times for testing and demonstration. Only a few nations are suspected of seeking them; the only countries known to have detonated nuclear weapons—and acknowledge possessing them—are the United States, the Soviet Union, the United Kingdom, China, India and North Korea. Israel is believed to possess nuclear weapons, though, in a policy of deliberate ambiguity, it does not acknowledge having them. Germany, Turkey and the Netherlands are nuclear weapons sharing states. South Africa is the only country to have independently developed and renounced and dismantled its nuclear weapons.
The Treaty on the Non-Proliferation of Nuclear Weapons aims to reduce the spread of nuclear weapons, but its effectiveness has been questioned, political tensions remained high in the 1970s and 1980s. Modernisation of weapons continues to this day. There are two basic types of nuclear weapons: those that derive the majority of their energy from nuclear fission reactions alone, those that use fission reactions to begin nuclear fusion reactions that produce a large amount of the total energy output. All existing nuclear weapons derive some of their explosive energy from nuclear fission reactions. Weapons whose explosive output is from fission reactions are referred to as atomic bombs or atom bombs; this has long been noted as something of a misnomer, as their energy comes from the nucleus of the atom, just as it does with fusion weapons. In fission weapons, a mass of fissile material is forced into supercriticality—allowing an exponential growth of nuclear chain reactions—either by shooting one piece of sub-critical material into another or by compression of a sub-critical sphere or cylinder of fissile material using chemically-fueled explosive lenses.
The latter approach, the "implosion" method, is more sophisticated than the former. A major challenge in all nuclear weapon designs is to ensure that a significant fraction of the fuel is consumed before the weapon destroys itself; the amount of energy released by fission bombs can range from the equivalent of just under a ton to upwards of 500,000 tons of TNT. All fission reactions generate the remains of the split atomic nuclei. Many fission products are either radioactive or moderately radioactive, as such, they are a serious form of radioactive contamination. Fission products are the principal radioactive component of nuclear fallout. Another source of radioactivity is the burst of free neutrons produced by the weapon; when they collide with other nuclei in surrounding material, the neutrons transmute those nuclei into other isotopes, altering their stability and making them radioactive. The most used fissile materials for nuclear weapons applications have been uranium-235 and plutonium-239.
Less used has been uranium-233. Neptunium-237 and some isotopes of americium may be usable for nuclear explosives as well, but it is not clear that this has been implemented, their plausible use in nuclear weapons is a matter of dispute; the other basic type of nuclear weapon produces a large proportion of its energy in nuclear fusion reactions. Such fusion weapons are referred to as thermonuclear weapons or more colloquially as hydrogen bombs, as they rely on fusion reactions between isotopes of hydrogen. All such weapons derive a significant portion of their energy from fission reactions used to "trigger" fusion reactions, fusion reactions can themselves trigger additional fission reactions. Only six countries—United States, United Kingdom, China and India—have conducted thermonuclear weapon tests. North Korea claims to have tested a fusion weapon as of January 2016. Thermonuclear weapons a
Photochemistry is the branch of chemistry concerned with the chemical effects of light. This term is used to describe a chemical reaction caused by absorption of ultraviolet, visible light or infrared radiation. In nature, photochemistry is of immense importance as it is the basis of photosynthesis and the formation of vitamin D with sunlight. Photochemical reactions proceed differently than temperature-driven reactions. Photochemical paths access high energy intermediates that cannot be generated thermally, thereby overcoming large activation barriers in a short period of time, allowing reactions otherwise inaccessible by thermal processes. Photochemistry is destructive, as illustrated by the photodegradation of plastics. Photoexcitation is the first step in a photochemical process where the reactant is elevated to a state of higher energy, an excited state; the first law of photochemistry, known as the Grotthuss–Draper law, states that light must be absorbed by a chemical substance in order for a photochemical reaction to take place.
According to the second law of photochemistry, known as the Stark-Einstein law, for each photon of light absorbed by a chemical system, no more than one molecule is activated for a photochemical reaction, as defined by the quantum yield. When a molecule or atom in the ground state absorbs light, one electron is excited to a higher orbital level; this electron maintains its spin according to the spin selection rule. The excitation to a higher singlet state can be from HOMO to LUMO or to a higher orbital, so that singlet excitation states S1, S2, S3… at different energies are possible. Kasha's rule stipulates that higher singlet states would relax by radiationless decay or internal conversion to S1. Thus, S1 is but not always, the only relevant singlet excited state; this excited state S1 can further relax to S0 by IC, but by an allowed radiative transition from S1 to S0 that emits a photon. Alternatively, it is possible for the excited state S1 to undergo spin inversion and to generate a triplet excited state T1 having two unpaired electrons with the same spin.
This violation of the spin selection rule is possible by intersystem crossing of the vibrational and electronic levels of S1 and T1. According to Hund's rule of maximum multiplicity, this T1 state would be somewhat more stable than S1; this triplet state can relax to the ground state S0 by radiationless IC or by a radiation pathway called phosphorescence. This process implies a change of electronic spin, forbidden by spin selection rules, making phosphorescence much slower than fluorescence. Thus, triplet states have longer lifetimes than singlet states; these transitions are summarized in a state energy diagram or Jablonski diagram, the paradigm of molecular photochemistry. These excited species, either S1 or T1, have a half empty low-energy orbital, are more oxidizing than the ground state, but at the same time, they have an electron in a high energy orbital, are thus more reducing. In general, excited species are prone to participate in electron transfer processes. Photochemical reactions require a light source that emits wavelengths corresponding to an electronic transition in the reactant.
In the early experiments, sunlight was the light source. Mercury-vapor lamps are more common in the laboratory. Low pressure mercury vapor lamps emit at 254 nm. For polychromatic sources, wavelength ranges can be selected using filters. Alternatively, laser beams are monochromatic and LEDs have a narrowband that can be efficiently used, as well as Rayonet lamps, to get monochromatic beams; the emitted light must of course reach the targeted functional group without being blocked by the reactor, medium, or other functional groups present. For many applications, quartz is used for the reactors as well as to contain the lamp. Pyrex absorbs at wavelengths shorter than 275 nm; the solvent is an important experimental parameter. Solvents are potential reactants and for this reason, chlorinated solvents are avoided because the C-Cl bond can lead to chlorination of the substrate. Absorbing solvents prevent photons from reaching the substrate. Hydrocarbon solvents absorb only at short wavelengths and are thus preferred for photochemical experiments requiring high energy photons.
Solvents containing unsaturation absorb at longer wavelengths and can usefully filter out short wavelengths. For example and acetone "cut off" at wavelengths shorter than 215 and 330 nm, respectively. Continuous flow photochemistry offers multiple advantages over batch photochemistry. Photochemical reactions are driven by the number of photons that are able to activate molecules causing the desired reaction; the large surface area to volume ratio of a microreactor maximizes the illumination, at the same time allows for efficient cooling, which decreases the thermal side products. In the case of photochemical reactions, light provides the activation energy. Simplistically, light is one mechanism for providing the activation energy required for many reactions. If laser light is employed, it is possible to selectively excite a molecule so as to produce a desired electronic and vibrational state; the emission from a particular state may be selectively monitored, providing a measure of the population of that state
A streamer discharge known as filamentary discharge, is a type of transient electrical discharge. Streamer discharges can form; when the electric field created by the applied voltage is sufficiently large, accelerated electrons strike air molecules with enough energy to knock other electrons off them, ionizing them, the freed electrons go on to strike more molecules in a chain reaction. These electron avalanches create ionized, electrically conductive regions in the air near the electrode creating the electric field; the space charge created by the electron avalanches gives rise to an additional electric field. This field can enhance the growth of new avalanches in a particular direction; the ionized region grows in that direction, forming a finger-like discharge called a streamer. Streamers are filamentary, which makes them different from corona discharges, they are used in applications such as air purification or plasma medicine. Streamers pave the way for arcs and lightning leaders, in which the ionized paths created by streamers are heated by large currents.
Streamers can be observed as sprites in the upper atmosphere. Due to the low pressure, sprites are much larger than streamers at ground pressure, see the similarity laws below; the theory of streamer discharges was preceded by John Sealy Townsend's discharge theory from around 1900. However, it became clear; this was true for discharges that were longer or at higher pressure. In 1939, Loeb and Raether independently described a new type of discharge, based on their experimental observations. Shortly thereafter, in 1940, Meek presented the theory of spark discharge, which quantitatively explained the formation of a self-propagating streamer; this new theory of streamer discharges explained the experimental observations. Streamers are used in applications such as ozone generation, air purification and plasma-assisted combustion. An important property is that the plasma they generate is non-equilibrium: the electrons have much higher energies than the ions. Therefore, chemical reactions can be triggered in a gas without heating it.
This is important for plasma medicine, where "plasma bullets", or guided streamers, can be used for wound treatment, although this is still experimental. Streamers can emerge when a strong electric field is applied to an insulating material a gas. Streamers can only form in areas where the electric field exceeds the dielectric strength of the medium. For air at atmospheric pressure, this is 30 kV per centimeter; the electric field accelerates the few electrons and ions that are always present in air, due to natural processes such as cosmic rays, radioactive decay, or photoionization. Ions are much heavier, so they move slowly compared to electrons; as the electrons move through the medium, they collide with the neutral atoms. Important collisions are: Elastic collisions. Excitations, where the neutral particle is excited, the electron loses the corresponding energy. Impact ionization, where the neutral particle becomes ionized, with the incident electron losing the energy. Attachment, where the electron attaches to the neutral to form a negative ion.
When the electric field approaches the breakdown field, the electrons gain enough energy between collisions to ionize the gas atoms, knocking an electron off the atom. At the breakdown field, there is a balance between the production of new electrons and the loss of electrons. Above the breakdown field, the number of electrons starts to grow exponentially, an electron avalanche forms; the electron avalanches leave behind positive ions, so in time more and more space charge is building up.. The electric field from all the space charge becomes comparable to the background electric field; this is sometimes referred to as the "avalanche to streamer transition". In some regions the total electric field will be smaller than before, but in other regions it will get larger, called electric field enhancement. New avalanches predominantly grow in the high-field regions, so a self-propagating structure can emerge: a streamer. There are negative streamers. Negative streamers propagate against the direction of the electric field, that is, in the same direction as the electrons drift velocity.
Positive streamers propagate in the opposite direction. In both cases, the streamer channel is electrically neutral, it is shielded by a thin space charge layer; this leads to an enhanced electric field at the end of the "head" of the streamer. Both positive and negative streamers grow by impact ionization in this high-field region, but the source of electrons is different. For negative streamers, free electrons are accelerated from the channel to the head region. However, for positive streamers, these free electrons have to come from farther away, as they accelerate into the streamer channel. Therefore, negative streamers grow in a more diffuse way than positive streamers; because a diffuse streamer has less field enhancement, negative streamers require higher electric fields than positive streamers. In nature and in applications, positive streamers are therefore much more common; as noted above, an important difference is that positive streamers need a source of free electrons for their propagation.
In many cases ph
Hendrik Anthony "Hans" Kramers was a Dutch physicist who worked with Niels Bohr to understand how electromagnetic waves interact with matter. Hans Kramers was born in Rotterdam; the son of Hendrik Kramers, a physician, Jeanne Susanne Breukelman. In 1912 Hans finished secondary education in Rotterdam, studied mathematics and physics at the University of Leiden, where he obtained a master's degree in 1916. Kramers wanted to obtain foreign experience during his doctoral research, but his first choice of supervisor, Max Born in Göttingen, was not reachable because of the first world war; because Denmark was neutral in this war, as was the Netherlands, he travelled to Copenhagen, where he visited unannounced the still unknown Niels Bohr. Bohr took him on as a Ph. D. candidate and Kramers prepared his dissertation under Bohr's direction. Although Kramers did most of his doctoral research in Copenhagen, he obtained his formal Ph. D. under Ehrenfest in Leiden, on 8 May 1919. Kramers enjoyed music and could play the cello and the piano.
After working for ten years in Bohr's group and becoming an associate professor at the University of Copenhagen, Kramers left Denmark in 1926 and returned to the Netherlands. He became a full professor in theoretical physics at Utrecht University, where he supervised Tjalling Koopmans. In 1934 he left Utrecht and succeeded Paul Ehrenfest in Leiden. From 1931 until his death he held a cross appointment at Delft University of Technology. Kramers was one of the founders of the Mathematisch Centrum in Amsterdam. In 1925, with Werner Heisenberg he developed the Kramers–Heisenberg dispersion formula, he is credited with introducing in 1948 the concept of renormalization into quantum field theory, although his approach was nonrelativistic.. He is credited for the Kramers–Kronig relations with Ralph Kronig which are mathematical equations relating real and imaginary parts of complex functions constrained by causality. On 25 October 1920 he was married to Anna Petersen, they had one son. Kramers became member of the Royal Netherlands Academy of Arts and Sciences in 1929, he was forced to resign in 1942.
He joined the Academy again in 1945. Kramers won the Lorentz Medal in 1947 and Hughes Medal in 1951. Dresden, Max. H. A. Kramers – Between Tradition and Revolution. Springer. ISBN 0-387-96282-4. Belinfante, F. J.. "Hendrik Anthony Kramers: 1894–1952". Science. 116: 555–556. Bibcode:1952Sci...116..555B. Doi:10.1126/science.116.3021.555. H. B. G. Casimir, Hendrik Anthony, in Biografisch Woordenboek van Nederland. J. M. Romein, Hendrik Anthony Kramers, in: Jaarboek van de Maatschappij der Nederlandse Letterkunde te Leiden, 1951–1953, pp. 83–91. Ph. D. candidates of H. A. Kramers: 1929-1952 Publications of H. A. Kramers