1.
Cloud chamber
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The cloud chamber, also known as the Wilson chamber, is a particle detector used for detecting ionizing radiation. In its most basic form, a chamber is a sealed environment containing a supersaturated vapor of water or alcohol. When a charged particle interacts with the mixture, the fluid is ionized, the resulting ions act as condensation nuclei, around which a mist will form. The high energies of alpha and beta particles mean that a trail is left, Cloud chambers played a prominent role in the experimental particle physics from the 1920s to the 1950s, until the advent of the bubble chamber. In particular, the discoveries of the positron in 1932, the muon in 1936, Anderson detected the positron and muon in cosmic rays. Charles Thomson Rees Wilson, a Scottish physicist, is credited with inventing the cloud chamber, inspired by sightings of the Brocken spectre while working on the summit of Ben Nevis in 1894, he began to develop expansion chambers for studying cloud formation and optical phenomena in moist air. Very rapidly he discovered that ions could act as centers for water droplet formation in such chambers and he pursued the application of this discovery and perfected the first cloud chamber in 1911. When an ionizing particle passes through the chamber, water condenses on the resulting ions. Wilson, along with Arthur Compton, received the Nobel Prize in Physics in 1927 for his work on the cloud chamber and this kind of chamber is also called a Pulsed Chamber because the conditions for operation are not continuously maintained. Further developments were made by Patrick Blackett who utilised a stiff spring to expand and compress the chamber very rapidly, a cine film was used to record the images. The diffusion cloud chamber was developed in 1936 by Alexander Langsdorf, instead of water vapor, alcohol is used because of its lower freezing point. Cloud chambers cooled by dry ice are a demonstration and hobbyist device. There are also water-cooled diffusion cloud chambers, using ethylene glycol, a simple cloud chamber consists of the sealed environment, radioactive source, dry ice or a cold plate and some kind of alcohol source. The alcohol falls as it cools down and the cold condenser provides a steep temperature gradient, the result is a supersaturated environment. The alcohol vapor condenses around ion trails left behind by the travelling ionizing particles, the result is cloud formation, seen in the cloud chamber by the presence of droplets falling down to the condenser. As particles pass through they leave ionization trails and because the vapor is supersaturated it condenses onto these trails. Since the tracks are emitted radially out from the source, their point of origin can easily be determined, just above the cold condenser plate there is an area of the chamber which is sensitive to radioactive tracks. At this height, most of the alcohol has not condensed and this means that the ion trail left by the radioactive particles provides an optimal trigger for condensation and cloud formation
2.
Carl David Anderson
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Carl David Anderson was an American physicist. He is best known for his discovery of the positron in 1932, an achievement for which he received the 1936 Nobel Prize in Physics, Anderson was born in New York City, the son of Swedish immigrants. He studied physics and engineering at Caltech, under the supervision of Robert A. This discovery, announced in 1932 and later confirmed by others, Anderson first detected the particles in cosmic rays. He then produced more conclusive proof by shooting gamma rays produced by the natural radioactive nuclide ThC into other materials, for this work, Anderson shared the 1936 Nobel Prize in Physics with Victor Hess. Anderson and Neddermeyer at first believed that they had seen the pion, when it became clear that what Anderson had seen was not the pion, the physicist I. I. Rabi, puzzled as to how the discovery could fit into any logical scheme of particle physics. The muon was the first of a long list of particles whose discovery initially baffled theoreticians who could not make the confusing zoo fit into some tidy conceptual scheme. Anderson spent all of his academic and research career at Caltech, during World War II, he conducted research in rocketry there. He was elected a Fellow of the American Academy of Arts and he died on January 11,1991, and his remains were interred in the Forest Lawn, Hollywood Hills Cemetery in Los Angeles, California. His wife Lorraine died in 1984, the Apparent Existence of Easily Deflectable Positives. The Strange Case of the Cosmic Rays,1983 Audio Interview with Carl Anderson by Martin Sherwin Voices of the Manhattan Project American National Biography, vol. Annotated bibliography for Carl David Anderson from the Alsos Digital Library for Nuclear Issues Carl David Anderson
3.
Particle
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A particle is a minute fragment or quantity of matter. In the physical sciences, a particle is a small localized object to which can be ascribed several physical or chemical properties such as volume or mass. Particles can also be used to create models of even larger objects depending on their density. The term particle is rather general in meaning, and is refined as needed by various scientific fields, something that is composed of particles may be referred to as being particulate. However, the particulate is most frequently used to refer to pollutants in the Earths atmosphere. The concept of particles is particularly useful when modelling nature, as the treatment of many phenomena can be complex. It can be used to make simplifying assumptions concerning the processes involved, francis Sears and Mark Zemansky, in University Physics, give the example of calculating the landing location and speed of a baseball thrown in the air. The treatment of large numbers of particles is the realm of statistical physics, the term particle is usually applied differently to three classes of sizes. The term macroscopic particle, usually refers to particles much larger than atoms and these are usually abstracted as point-like particles, or even invisible. This is even though they have volumes, shapes, structures, examples of macroscopic particles would include powder, dust, sand, pieces of debris during a car accident, or even objects as big as the stars of a galaxy. Another type, microscopic particles usually refers to particles of sizes ranging from atoms to molecules, such as carbon dioxide, nanoparticles and these particles are studied in chemistry, as well as atomic and molecular physics. The smallest of particles are the particles, which refer to particles smaller than atoms. These particles are studied in particle physics, because of their extremely small size, the study of microscopic and subatomic particles fall in the realm of quantum mechanics. Particles can also be classified according to composition, composite particles refer to particles that have composition – that is particles which are made of other particles. For example, an atom is made of six protons, eight neutrons. By contrast, elementary particles refer to particles that are not made of other particles, according to our current understanding of the world, only a very small number of these exist, such as the leptons, quarks or gluons. However it is possible some of these might turn up to be composite particles after all. While composite particles can very often be considered point-like, elementary particles are truly punctual, both elementary and composite particles, are known to undergo particle decay
4.
Elementary particle
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In particle physics, an elementary particle or fundamental particle is a particle whose substructure is unknown, thus, it is unknown whether it is composed of other particles. A particle containing two or more elementary particles is a composite particle, soon, subatomic constituents of the atom were identified. As the 1930s opened, the electron and the proton had been observed, along with the photon, via quantum theory, protons and neutrons were found to contain quarks—up quarks and down quarks—now considered elementary particles. And within a molecule, the three degrees of freedom can separate via wavefunction into three quasiparticles. Yet a free electron—which, not orbiting a nucleus, lacks orbital motion—appears unsplittable. Meanwhile, an elementary boson mediating gravitation—the graviton—remains hypothetical, all elementary particles are—depending on their spin—either bosons or fermions. These are differentiated via the theorem of quantum statistics. Particles of half-integer spin exhibit Fermi–Dirac statistics and are fermions, Particles of integer spin, in other words full-integer, exhibit Bose–Einstein statistics and are bosons. In the Standard Model, elementary particles are represented for predictive utility as point particles, though extremely successful, the Standard Model is limited to the microcosm by its omission of gravitation and has some parameters arbitrarily added but unexplained. According to the current models of big bang nucleosynthesis, the composition of visible matter of the universe should be about 75% hydrogen. Neutrons are made up of one up and two down quark, while protons are made of two up and one down quark. Since the other elementary particles are so light or so rare when compared to atomic nuclei. Therefore, one can conclude that most of the mass of the universe consists of protons and neutrons. Some estimates imply that there are roughly 1080 baryons in the observable universe, the number of protons in the observable universe is called the Eddington number. Other estimates imply that roughly 1097 elementary particles exist in the universe, mostly photons, gravitons. However, the Standard Model is widely considered to be a theory rather than a truly fundamental one. The 12 fundamental fermionic flavours are divided into three generations of four particles each, six of the particles are quarks. The remaining six are leptons, three of which are neutrinos, and the three of which have an electric charge of −1, the electron and its two cousins, the muon and the tau
5.
Particle statistics
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Particle statistics is a particular description of multiple particles in statistical mechanics. Its core concept is an ensemble that emphasizes properties of a large system as a whole at the expense of knowledge about parameters of separate particles. When an ensemble consists of particles with similar properties, their number is called the particle number, in classical mechanics, all particles in the system are considered distinguishable. This means that particles in a system can be tracked. As a consequence, changing the position of any two particles in the leads to a completely different configuration of the entire system. Furthermore, there is no restriction on placing more than one particle in any given state accessible to the system and these characteristics of classical positions are called Maxwell–Boltzmann statistics. The fundamental feature of quantum mechanics that distinguishes it from classical mechanics is that particles of a type are indistinguishable from one another. This means that in an assembly consisting of particles, interchanging any two particles does not lead to a new configuration of the system. In the case of a system consisting of particles of different kinds, all quantum particles, such as leptons and baryons, in the universe have three translational motion degrees of freedom and one discrete degree of freedom, known as spin. Thats why quantum statistics is useful when one considers, say, helium liquid or ammonia gas, the spin–statistics theorem binds two particular kinds of combinatorial symmetry with two particular kinds of spin symmetry, namely bosons and fermions. In Bose–Einstein statistics interchanging any two particles of the leaves the resultant system in a symmetric state. That is, the function of the system before interchanging equals the wave function of the system after interchanging. It is important to emphasize that the function of the system has not changed itself. This has very important consequences on the state of the system and it is found that the particles that obey Bose–Einstein statistics are the ones which have integer spins, which are therefore called bosons. Examples of bosons include photons and helium-4, one type of system obeying B–E statistics is the Bose–Einstein condensate where all particles of the assembly exist in the same state. In Fermi–Dirac statistics interchanging any two particles of the leaves the resultant system in an antisymmetric state. That is, the function of the system before interchanging is the wave function of the system after interchanging. Again, the function of the system itself does not change
6.
Fermion
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In particle physics, a fermion is any subatomic particle characterized by Fermi–Dirac statistics. These particles obey the Pauli exclusion principle, fermions include all quarks and leptons, as well as any composite particle made of an odd number of these, such as all baryons and many atoms and nuclei. Fermions differ from bosons, which obey Bose–Einstein statistics, a fermion can be an elementary particle, such as the electron, or it can be a composite particle, such as the proton. According to the theorem in any reasonable relativistic quantum field theory, particles with integer spin are bosons. Besides this spin characteristic, fermions have another specific property, they possess conserved baryon or lepton quantum numbers, therefore, what is usually referred to as the spin statistics relation is in fact a spin statistics-quantum number relation. As a consequence of the Pauli exclusion principle, only one fermion can occupy a quantum state at any given time. If multiple fermions have the same probability distribution, then at least one property of each fermion, such as its spin. Weakly interacting fermions can also display bosonic behavior under extreme conditions, at low temperature fermions show superfluidity for uncharged particles and superconductivity for charged particles. Composite fermions, such as protons and neutrons, are the key building blocks of everyday matter, the Standard Model recognizes two types of elementary fermions, quarks and leptons. In all, the model distinguishes 24 different fermions, there are six quarks, and six leptons, along with the corresponding antiparticle of each of these. Mathematically, fermions come in three types - Weyl fermions, Dirac fermions, and Majorana fermions, most Standard Model fermions are believed to be Dirac fermions, although it is unknown at this time whether the neutrinos are Dirac or Majorana fermions. Dirac fermions can be treated as a combination of two Weyl fermions, in July 2015, Weyl fermions have been experimentally realized in Weyl semimetals. Composite particles can be bosons or fermions depending on their constituents, more precisely, because of the relation between spin and statistics, a particle containing an odd number of fermions is itself a fermion. Examples include the following, A baryon, such as the proton or neutron, the nucleus of a carbon-13 atom contains six protons and seven neutrons and is therefore a fermion. The atom helium-3 is made of two protons, one neutron, and two electrons, and therefore it is a fermion. The number of bosons within a composite made up of simple particles bound with a potential has no effect on whether it is a boson or a fermion. Fermionic or bosonic behavior of a particle is only seen at large distances. At proximity, where spatial structure begins to be important, a composite particle behaves according to its constituent makeup, fermions can exhibit bosonic behavior when they become loosely bound in pairs
7.
Fundamental interaction
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In physics, the fundamental interactions, also known as fundamental forces, are the interactions that do not appear to be reducible to more basic interactions. There are four conventionally accepted fundamental interactions—gravitational, electromagnetic, strong, each one is described mathematically as a field. The gravitational force is modelled as a classical field. The other three, part of the Standard Model of particle physics, are described as discrete quantum fields, and their interactions are carried by a quantum. The strong and weak interactions have short ranges, producing forces at minuscule, subatomic distances, the strong interaction, which is carried by the gluon particle, is responsible for the binding of quarks together to form hadrons, such as protons and neutrons. As a residual effect, it creates the force that binds the latter particles to form atomic nuclei. The weak interaction, which is carried by the W and Z particles, also acts on the nucleus, the other two, electromagnetism and gravity, produce significant forces at macroscopic scales where the effects can be seen directly in everyday life. The electromagnetic force, carried by the photon, creates electric and magnetic fields, Electromagnetic forces tend to cancel each other out when large collections of objects are considered, so over the largest distances, gravity tends to be the dominant force. Other theorists seek to unite the electroweak and strong fields within a Grand Unified Theory, some theories, notably string theory, seek both QG and GUT within one framework, unifying all four fundamental interactions along with mass generation within a theory of everything. A few researchers have interpreted various anomalous observations in physics as evidence for a fifth force, inferring that all objects bearing mass approach at a constant rate, but collide by impact proportional to their masses, Newton inferred that matter exhibits an attractive force. Thus Newtons theory violated the first principle of mechanical philosophy, as stated by Descartes, conversely, during the 1820s, when explaining magnetism, Michael Faraday inferred a field filling space and transmitting that force. Faraday conjectured that ultimately, all unified into one. In the early 1870s, James Clerk Maxwell unified electricity and magnetism as effects of a field whose third consequence was light. The Standard Model of particle physics was developed throughout the half of the 20th century. In the Standard Model, the electromagnetic, strong, and weak interactions associate with elementary particles, for predictive success with QMs probabilistic outcomes, particle physics conventionally models QM events across a field set to special relativity, altogether relativistic quantum field theory. Force particles, called gauge bosons—force carriers or messenger particles of underlying fields—interact with matter particles, everyday matter is atoms, composed of three fermion types, up-quarks and down-quarks constituting, as well as electrons orbiting, the atoms nucleus. The electromagnetic interaction was modelled with the interaction, whose force carriers are W and Z bosons, traversing the minuscule distance. Electroweak interaction would operate at high temperatures as soon after the presumed Big Bang
8.
Gravity
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Gravity, or gravitation, is a natural phenomenon by which all things with mass are brought toward one another, including planets, stars and galaxies. Since energy and mass are equivalent, all forms of energy, including light, on Earth, gravity gives weight to physical objects and causes the ocean tides. Gravity has a range, although its effects become increasingly weaker on farther objects. The most extreme example of this curvature of spacetime is a hole, from which nothing can escape once past its event horizon. More gravity results in time dilation, where time lapses more slowly at a lower gravitational potential. Gravity is the weakest of the four fundamental interactions of nature, the gravitational attraction is approximately 1038 times weaker than the strong force,1036 times weaker than the electromagnetic force and 1029 times weaker than the weak force. As a consequence, gravity has an influence on the behavior of subatomic particles. On the other hand, gravity is the dominant interaction at the macroscopic scale, for this reason, in part, pursuit of a theory of everything, the merging of the general theory of relativity and quantum mechanics into quantum gravity, has become an area of research. While the modern European thinkers are credited with development of gravitational theory, some of the earliest descriptions came from early mathematician-astronomers, such as Aryabhata, who had identified the force of gravity to explain why objects do not fall out when the Earth rotates. Later, the works of Brahmagupta referred to the presence of force, described it as an attractive force. Modern work on gravitational theory began with the work of Galileo Galilei in the late 16th and this was a major departure from Aristotles belief that heavier objects have a higher gravitational acceleration. Galileo postulated air resistance as the reason that objects with less mass may fall slower in an atmosphere, galileos work set the stage for the formulation of Newtons theory of gravity. In 1687, English mathematician Sir Isaac Newton published Principia, which hypothesizes the inverse-square law of universal gravitation. Newtons theory enjoyed its greatest success when it was used to predict the existence of Neptune based on motions of Uranus that could not be accounted for by the actions of the other planets. Calculations by both John Couch Adams and Urbain Le Verrier predicted the position of the planet. A discrepancy in Mercurys orbit pointed out flaws in Newtons theory, the issue was resolved in 1915 by Albert Einsteins new theory of general relativity, which accounted for the small discrepancy in Mercurys orbit. The simplest way to test the equivalence principle is to drop two objects of different masses or compositions in a vacuum and see whether they hit the ground at the same time. Such experiments demonstrate that all objects fall at the rate when other forces are negligible
9.
Electromagnetism
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Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force usually exhibits electromagnetic fields such as fields, magnetic fields. The other three fundamental interactions are the interaction, the weak interaction, and gravitation. The word electromagnetism is a form of two Greek terms, ἤλεκτρον, ēlektron, amber, and μαγνῆτις λίθος magnētis lithos, which means magnesian stone. The electromagnetic force plays a role in determining the internal properties of most objects encountered in daily life. Ordinary matter takes its form as a result of forces between individual atoms and molecules in matter, and is a manifestation of the electromagnetic force. Electrons are bound by the force to atomic nuclei, and their orbital shapes. The electromagnetic force governs the processes involved in chemistry, which arise from interactions between the electrons of neighboring atoms, there are numerous mathematical descriptions of the electromagnetic field. In classical electrodynamics, electric fields are described as electric potential, although electromagnetism is considered one of the four fundamental forces, at high energy the weak force and electromagnetic force are unified as a single electroweak force. In the history of the universe, during the epoch the unified force broke into the two separate forces as the universe cooled. Originally, electricity and magnetism were considered to be two separate forces, Magnetic poles attract or repel one another in a manner similar to positive and negative charges and always exist as pairs, every north pole is yoked to a south pole. An electric current inside a wire creates a corresponding magnetic field outside the wire. Its direction depends on the direction of the current in the wire. A current is induced in a loop of wire when it is moved toward or away from a field, or a magnet is moved towards or away from it. While preparing for a lecture on 21 April 1820, Hans Christian Ørsted made a surprising observation. As he was setting up his materials, he noticed a compass needle deflected away from north when the electric current from the battery he was using was switched on. At the time of discovery, Ørsted did not suggest any explanation of the phenomenon. However, three later he began more intensive investigations
10.
Weak interaction
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In particle physics, the weak interaction is one of the four known fundamental interactions of nature, alongside the strong interaction, electromagnetism, and gravitation. The weak interaction is responsible for radioactive decay, which plays an role in nuclear fission. The theory of the interaction is sometimes called quantum flavourdynamics, in analogy with the terms QCD dealing with the strong interaction. However the term QFD is rarely used because the force is best understood in terms of electro-weak theory. The Standard Model of particle physics, which does not address gravity, provides a framework for understanding how the electromagnetic, weak. An interaction occurs when two particles, typically but not necessarily half-integer spin fermions, exchange integer-spin, force-carrying bosons, the fermions involved in such exchanges can be either elementary or composite, although at the deepest levels, all weak interactions ultimately are between elementary particles. In the case of the interaction, fermions can exchange three distinct types of force carriers known as the W+, W−, and Z bosons. The mass of each of these bosons is far greater than the mass of a proton or neutron, the force is in fact termed weak because its field strength over a given distance is typically several orders of magnitude less than that of the strong nuclear force or electromagnetic force. During the quark epoch of the universe, the electroweak force separated into the electromagnetic. Important examples of the weak interaction include beta decay, and the fusion of hydrogen into deuterium that powers the Suns thermonuclear process, most fermions will decay by a weak interaction over time. Such decay makes radiocarbon dating possible, as carbon-14 decays through the interaction to nitrogen-14. It can also create radioluminescence, commonly used in tritium illumination, quarks, which make up composite particles like neutrons and protons, come in six flavours – up, down, strange, charm, top and bottom – which give those composite particles their properties. The weak interaction is unique in that it allows for quarks to swap their flavour for another, the swapping of those properties is mediated by the force carrier bosons. Also, the interaction is the only fundamental interaction that breaks parity-symmetry, and similarly. In 1933, Enrico Fermi proposed the first theory of the weak interaction and he suggested that beta decay could be explained by a four-fermion interaction, involving a contact force with no range. However, it is described as a non-contact force field having a finite range. The existence of the W and Z bosons was not directly confirmed until 1983, the weak interaction is unique in a number of respects, It is the only interaction capable of changing the flavour of quarks. It is the interaction that violates P or parity-symmetry
11.
Antiparticle
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Corresponding to most kinds of particles, there is an associated antiparticle with the same mass and opposite charge. For example, the antiparticle of the electron is the positron, the opposite is also true, the antiparticle of the positron is the electron. Some particles, such as the photon, are their own antiparticle, otherwise, for each pair of antiparticle partners, one is designated as normal matter, and the other as antimatter. Particle–antiparticle pairs can annihilate each other, producing photons, since the charges of the particle and antiparticle are opposite, for example, the positrons produced in natural radioactive decay quickly annihilate themselves with electrons, producing pairs of gamma rays, a process exploited in positron emission tomography. The laws of nature are very nearly symmetrical with respect to particles and antiparticles, for example, an antiproton and a positron can form an antihydrogen atom, which is believed to have the same properties as a hydrogen atom. The discovery of Charge Parity violation helped to shed light on this problem by showing that this symmetry, antiparticles are produced naturally in beta decay, and in the interaction of cosmic rays in the Earths atmosphere. Because charge is conserved, it is not possible to create an antiparticle without either destroying a particle of the charge or by creating a particle of the opposite charge. The latter is seen in many processes in both a particle and its antiparticle are created simultaneously, as in particle accelerators. This is the inverse of the annihilation process. Although particles and their antiparticles have opposite charges, electrically neutral particles need not be identical to their antiparticles. The neutron, for example, is out of quarks, the antineutron from antiquarks. However, other particles are their own antiparticles, such as photons, hypothetical gravitons. The electric charge-to-mass ratio of a particle can be measured by observing the radius of curling of its track in a magnetic field. Positrons, because of the direction that their paths curled, were at first mistaken for electrons travelling in the opposite direction, the antiproton and antineutron were found by Emilio Segrè and Owen Chamberlain in 1955 at the University of California, Berkeley. Since then, the antiparticles of many subatomic particles have been created in particle accelerator experiments. In recent years, complete atoms of antimatter have been assembled out of antiprotons and positrons, solutions of the Dirac equation contained negative energy quantum states. As a result, an electron could always radiate energy and fall into an energy state. Even worse, it could keep radiating infinite amounts of energy because there were many negative energy states available
12.
Electron
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The electron is a subatomic particle, symbol e− or β−, with a negative elementary electric charge. Electrons belong to the first generation of the lepton particle family, the electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the include a intrinsic angular momentum of a half-integer value, expressed in units of the reduced Planck constant. As it is a fermion, no two electrons can occupy the same state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of particles and waves, they can collide with other particles and can be diffracted like light. Since an electron has charge, it has an electric field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law, electrons radiate or absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields, special telescopes can detect electron plasma in outer space. Electrons are involved in applications such as electronics, welding, cathode ray tubes, electron microscopes, radiation therapy, lasers, gaseous ionization detectors. Interactions involving electrons with other particles are of interest in fields such as chemistry. The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms, ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of a quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge electron in 1891, electrons can also participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of isotopes and in high-energy collisions. The antiparticle of the electron is called the positron, it is identical to the electron except that it carries electrical, when an electron collides with a positron, both particles can be totally annihilated, producing gamma ray photons. The ancient Greeks noticed that amber attracted small objects when rubbed with fur, along with lightning, this phenomenon is one of humanitys earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electricus, both electric and electricity are derived from the Latin ēlectrum, which came from the Greek word for amber, ἤλεκτρον
13.
Paul Dirac
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Paul Adrien Maurice Dirac OM FRS was an English theoretical physicist who made fundamental contributions to the early development of both quantum mechanics and quantum electrodynamics. Among other discoveries, he formulated the Dirac equation which describes the behaviour of fermions, Dirac shared the 1933 Nobel Prize in Physics with Erwin Schrödinger for the discovery of new productive forms of atomic theory. He also made significant contributions to the reconciliation of general relativity with quantum mechanics and he was regarded by his friends and colleagues as unusual in character. Albert Einstein said of him This balancing on the path between genius and madness is awful. He is regarded as one of the most significant physicists of the 20th century, Paul Adrien Maurice Dirac was born at his parents home in Bristol, England, on 8 August 1902, and grew up in the Bishopston area of the city. His father, Charles Adrien Ladislas Dirac, was an immigrant from Saint-Maurice, Switzerland and his mother, Florence Hannah Dirac, née Holten, the daughter of a ships captain, was born in Cornwall, England, and worked as a librarian at the Bristol Central Library. Paul had a sister, Béatrice Isabelle Marguerite, known as Betty, and an older brother, Reginald Charles Félix, known as Felix. Dirac later recalled, My parents were terribly distressed, I didnt know they cared so much I never knew that parents were supposed to care for their children, but from then on I knew. Charles and the children were officially Swiss nationals until they became naturalised on 22 October 1919, Diracs father was strict and authoritarian, although he disapproved of corporal punishment. Dirac had a relationship with his father, so much so that after his fathers death, Dirac wrote, I feel much freer now. Charles forced his children to speak to him only in French, when Dirac found that he could not express what he wanted to say in French, he chose to remain silent. Dirac was educated first at Bishop Road Primary School and then at the all-boys Merchant Venturers Technical College, the school was an institution attached to the University of Bristol, which shared grounds and staff. It emphasised technical subjects like bricklaying, shoemaking and metal work and this was unusual at a time when secondary education in Britain was still dedicated largely to the classics, and something for which Dirac would later express his gratitude. Dirac studied electrical engineering on a City of Bristol University Scholarship at the University of Bristols engineering faculty, shortly before he completed his degree in 1921, he sat the entrance examination for St Johns College, Cambridge. He passed, and was awarded a £70 scholarship, but this short of the amount of money required to live. Instead he took up an offer to study for a Bachelor of Arts degree in mathematics at the University of Bristol free of charge and he was permitted to skip the first year of the course owing to his engineering degree. In 1923, Dirac graduated, once again with first class honours, along with his £70 scholarship from St Johns College, this was enough to live at Cambridge. From 1925 to 1928 he held an 1851 Research Fellowship from the Royal Commission for the Exhibition of 1851 and he completed his PhD in June 1926 with the first thesis on quantum mechanics to be submitted anywhere
14.
Invariant mass
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More precisely, it is a characteristic of the systems total energy and momentum that is the same in all frames of reference related by Lorentz transformations. If a center of momentum frame exists for the system, then the invariant mass of a system is equal to its mass in that rest frame. In other reference frames, where the momentum is nonzero, the total mass of the system is greater than the invariant mass. Due to mass-energy equivalence, the rest energy of the system is simply the invariant mass times the speed of light squared, similarly, the total energy of the system is its total mass times the speed of light squared. Systems whose four-momentum is a null vector have zero invariant mass, a physical object or particle moving faster than the speed of light would have space-like four-momenta, and these do not appear to exist. Any time-like four-momentum possesses a frame where the momentum is zero. In this case, invariant mass is positive and is referred to as the rest mass, if objects within a system are in relative motion, then the invariant mass of the whole system will differ from the sum of the objects rest masses. This is also equal to the energy of the system divided by c2. See mass–energy equivalence for a discussion of definitions of mass, for example, a scale would measure the kinetic energy of the molecules in a bottle of gas to be part of invariant mass of the bottle, and thus also its rest mass. The same is true for massless particles in such system, which add invariant mass and also rest mass to systems, for an isolated massive system, the center of mass of the system moves in a straight line with a steady sub-luminal velocity. Thus, an observer can always be placed to move along with it. In this frame, which is the center of momentum frame, the momentum is zero. In this frame, which exists under these assumptions, the invariant mass of the system is equal to the system energy divided by c2. This total energy in the center of momentum frame, is the energy which the system may be observed to have. Note that for reasons above, such a rest frame does not exist for single photons, when two or more photons move in different directions, however, a center of mass frame exists. Thus, the mass of a system of several photons moving in different directions is positive, for example, rest mass and invariant mass are zero for individual photons even though they may add mass to the invariant mass of systems. For this reason, invariant mass is in not an additive quantity. Consider the simple case of system, where object A is moving towards another object B which is initially at rest
15.
Kilogram
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The kilogram or kilogramme is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype of the Kilogram. The avoirdupois pound, used in both the imperial and US customary systems, is defined as exactly 0.45359237 kg, making one kilogram approximately equal to 2.2046 avoirdupois pounds. Other traditional units of weight and mass around the world are also defined in terms of the kilogram, the gram, 1/1000 of a kilogram, was provisionally defined in 1795 as the mass of one cubic centimeter of water at the melting point of ice. The final kilogram, manufactured as a prototype in 1799 and from which the IPK was derived in 1875, had an equal to the mass of 1 dm3 of water at its maximum density. The kilogram is the only SI base unit with an SI prefix as part of its name and it is also the only SI unit that is still directly defined by an artifact rather than a fundamental physical property that can be reproduced in different laboratories. Three other base units and 17 derived units in the SI system are defined relative to the kilogram, only 8 other units do not require the kilogram in their definition, temperature, time and frequency, length, and angle. At its 2011 meeting, the CGPM agreed in principle that the kilogram should be redefined in terms of the Planck constant, the decision was originally deferred until 2014, in 2014 it was deferred again until the next meeting. There are currently several different proposals for the redefinition, these are described in the Proposed Future Definitions section below, the International Prototype Kilogram is rarely used or handled. In the decree of 1795, the term gramme thus replaced gravet, the French spelling was adopted in the United Kingdom when the word was used for the first time in English in 1797, with the spelling kilogram being adopted in the United States. In the United Kingdom both spellings are used, with kilogram having become by far the more common, UK law regulating the units to be used when trading by weight or measure does not prevent the use of either spelling. In the 19th century the French word kilo, a shortening of kilogramme, was imported into the English language where it has used to mean both kilogram and kilometer. In 1935 this was adopted by the IEC as the Giorgi system, now known as MKS system. In 1948 the CGPM commissioned the CIPM to make recommendations for a practical system of units of measurement. This led to the launch of SI in 1960 and the subsequent publication of the SI Brochure, the kilogram is a unit of mass, a property which corresponds to the common perception of how heavy an object is. Mass is a property, that is, it is related to the tendency of an object at rest to remain at rest, or if in motion to remain in motion at a constant velocity. Accordingly, for astronauts in microgravity, no effort is required to hold objects off the cabin floor, they are weightless. However, since objects in microgravity still retain their mass and inertia, the ratio of the force of gravity on the two objects, measured by the scale, is equal to the ratio of their masses. On April 7,1795, the gram was decreed in France to be the weight of a volume of pure water equal to the cube of the hundredth part of the metre
16.
Electronvolt
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In physics, the electronvolt is a unit of energy equal to approximately 1. 6×10−19 joules. By definition, it is the amount of energy gained by the charge of an electron moving across an electric potential difference of one volt. Thus it is 1 volt multiplied by the elementary charge, therefore, one electronvolt is equal to 6981160217662079999♠1. 6021766208×10−19 J. The electronvolt is not a SI unit, and its definition is empirical, like the elementary charge on which it is based, it is not an independent quantity but is equal to 1 J/C √2hα / μ0c0. It is a unit of energy within physics, widely used in solid state, atomic, nuclear. It is commonly used with the metric prefixes milli-, kilo-, in some older documents, and in the name Bevatron, the symbol BeV is used, which stands for billion electronvolts, it is equivalent to the GeV. By mass–energy equivalence, the electronvolt is also a unit of mass and it is common in particle physics, where units of mass and energy are often interchanged, to express mass in units of eV/c2, where c is the speed of light in vacuum. It is common to express mass in terms of eV as a unit of mass. The mass equivalent of 1 eV/c2 is 1 eV / c 2 = ⋅1 V2 =1.783 ×10 −36 kg. For example, an electron and a positron, each with a mass of 0.511 MeV/c2, the proton has a mass of 0.938 GeV/c2. In general, the masses of all hadrons are of the order of 1 GeV/c2, the unified atomic mass unit,1 gram divided by Avogadros number, is almost the mass of a hydrogen atom, which is mostly the mass of the proton. To convert to megaelectronvolts, use the formula,1 u =931.4941 MeV/c2 =0.9314941 GeV/c2, in high-energy physics, the electronvolt is often used as a unit of momentum. A potential difference of 1 volt causes an electron to gain an amount of energy and this gives rise to usage of eV as units of momentum, for the energy supplied results in acceleration of the particle. The dimensions of units are LMT−1. The dimensions of units are L2MT−2. Then, dividing the units of energy by a constant that has units of velocity. In the field of particle physics, the fundamental velocity unit is the speed of light in vacuum c. Thus, dividing energy in eV by the speed of light, the fundamental velocity constant c is often dropped from the units of momentum by way of defining units of length such that the value of c is unity
17.
Electric charge
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Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two types of charges, positive and negative. Like charges repel and unlike attract, an absence of net charge is referred to as neutral. An object is charged if it has an excess of electrons. The SI derived unit of charge is the coulomb. In electrical engineering, it is common to use the ampere-hour. The symbol Q often denotes charge, early knowledge of how charged substances interact is now called classical electrodynamics, and is still accurate for problems that dont require consideration of quantum effects. The electric charge is a conserved property of some subatomic particles. Electrically charged matter is influenced by, and produces, electromagnetic fields, the interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the four fundamental forces. 602×10−19 coulombs. The proton has a charge of +e, and the electron has a charge of −e, the study of charged particles, and how their interactions are mediated by photons, is called quantum electrodynamics. Charge is the property of forms of matter that exhibit electrostatic attraction or repulsion in the presence of other matter. Electric charge is a property of many subatomic particles. The charges of free-standing particles are integer multiples of the charge e. Michael Faraday, in his electrolysis experiments, was the first to note the discrete nature of electric charge, robert Millikans oil drop experiment demonstrated this fact directly, and measured the elementary charge. By convention, the charge of an electron is −1, while that of a proton is +1, charged particles whose charges have the same sign repel one another, and particles whose charges have different signs attract. The charge of an antiparticle equals that of the corresponding particle, quarks have fractional charges of either −1/3 or +2/3, but free-standing quarks have never been observed. The electric charge of an object is the sum of the electric charges of the particles that make it up. An ion is an atom that has lost one or more electrons, giving it a net charge, or that has gained one or more electrons
18.
Coulomb
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The coulomb is the International System of Units unit of electric charge. 242×1018 protons, and −1 C is equivalent to the charge of approximately 6. 242×1018 electrons. This SI unit is named after Charles-Augustin de Coulomb, 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 SI system defines the coulomb in terms of the ampere and second,1 C =1 A ×1 s. The second is defined in terms of a frequency emitted by caesium atoms. The ampere is defined using Ampères force law, the definition relies in part on the mass of the prototype kilogram. In practice, the balance is used to measure amperes with the highest possible accuracy. One coulomb is the magnitude of charge in 6. 24150934×10^18 protons or electrons. The inverse of this gives the elementary charge of 1. 6021766208×10−19 C. The magnitude of the charge of one mole of elementary charges is known as a faraday unit of charge. In terms of Avogadros number, one coulomb is equal to approximately 1.036 × NA×10−5 elementary charges, one ampere-hour =3600 C,1 mA⋅h =3.6 C. One statcoulomb, the obsolete CGS electrostatic unit of charge, is approximately 3. 3356×10−10 C or about one-third of a nanocoulomb, the elementary charge, the charge of a proton, is approximately 1. 6021766208×10−19 C. In SI, the charge in coulombs is an approximate value. However, in other systems, the elementary charge has an exact value by definition. Specifically, e90 = / C exactly, SI itself may someday change its definitions in a similar way. For example, one possible proposed redefinition is the ampere. is such that the value of the charge e is exactly 1. 602176487×10−19 coulombs. This proposal is not yet accepted as part of the SI, the charges in static electricity from rubbing materials together are typically a few microcoulombs. The amount of charge that travels through a lightning bolt is typically around 15 C, the amount of charge that travels through a typical alkaline AA battery from being fully charged to discharged is about 5 kC =5000 C ≈1400 mA⋅h. The hydraulic analogy uses everyday terms to illustrate movement of charge, the analogy equates charge to a volume of water, and voltage to pressure
19.
Spin (physics)
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In quantum mechanics and particle physics, spin is an intrinsic form of angular momentum carried by elementary particles, composite particles, and atomic nuclei. Spin is one of two types of angular momentum in mechanics, the other being orbital angular momentum. In some ways, spin is like a vector quantity, it has a definite magnitude, all elementary particles of a given kind have the same magnitude of spin angular momentum, which is indicated by assigning the particle a spin quantum number. The SI unit of spin is the or, just as with classical angular momentum, very often, the spin quantum number is simply called spin leaving its meaning as the unitless spin quantum number to be inferred from context. When combined with the theorem, the spin of electrons results in the Pauli exclusion principle. Wolfgang Pauli was the first to propose the concept of spin, in 1925, Ralph Kronig, George Uhlenbeck and Samuel Goudsmit at Leiden University suggested an physical interpretation of particles spinning around their own axis. The mathematical theory was worked out in depth by Pauli in 1927, when Paul Dirac derived his relativistic quantum mechanics in 1928, electron spin was an essential part of it. As the name suggests, spin was originally conceived as the rotation of a particle around some axis and this picture is correct so far as spin obeys the same mathematical laws as quantized angular momenta do. On the other hand, spin has some properties that distinguish it from orbital angular momenta. Although the direction of its spin can be changed, a particle cannot be made to spin faster or slower. The spin of a particle is associated with a magnetic dipole moment with a g-factor differing from 1. This could only occur if the internal charge of the particle were distributed differently from its mass. The conventional definition of the quantum number, s, is s = n/2. Hence the allowed values of s are 0, 1/2,1, 3/2,2, the value of s for an elementary particle depends only on the type of particle, and cannot be altered in any known way. The spin angular momentum, S, of any system is quantized. The allowed values of S are S = ℏ s = h 4 π n, in contrast, orbital angular momentum can only take on integer values of s, i. e. even-numbered values of n. Those particles with half-integer spins, such as 1/2, 3/2, 5/2, are known as fermions, while particles with integer spins. The two families of particles obey different rules and broadly have different roles in the world around us, a key distinction between the two families is that fermions obey the Pauli exclusion principle, that is, there cannot be two identical fermions simultaneously having the same quantum numbers
20.
Antimatter
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In particle physics, antimatter is a material composed of the antiparticle partners to the corresponding particles of ordinary matter. A particle and its antiparticle have the mass as one another. For example, a proton has positive charge while an antiproton has negative charge, the consequence of annihilation is a release of energy available for heat or work, proportional to the total matter and antimatter mass, in accord with the mass–energy equivalence equation, E = mc2. Formally, antimatter particles can be defined by their negative baryon number or lepton number and these two classes of particles are the antiparticle partners of one another. Antimatter particles bind with one other to form antimatter, just as ordinary particles bind to form normal matter, for example, a positron and an antiproton can form an antihydrogen atom. Physical principles indicate that complex antimatter atomic nuclei are possible, as well as corresponding to the known chemical elements. There is considerable speculation as to why the universe is composed almost entirely of ordinary matter. This asymmetry of matter and antimatter in the universe is one of the great unsolved problems in physics. The process by which this inequality between matter antimatter particles developed is called baryogenesis, Antimatter in the form of anti-atoms is one of the most difficult materials to produce. Individual antimatter particles, however, are produced by particle accelerators. The nuclei of antihelium have been produced with difficulty. These are the most complex anti-nuclei so far observed, the idea of negative matter appears in past theories of matter that have now been abandoned. Using the once popular theory of gravity, the possibility of matter with negative gravity was discussed by William Hicks in the 1880s. Between the 1880s and the 1890s, Karl Pearson proposed the existence of squirts, the squirts represented normal matter and the sinks represented negative matter. Pearsons theory required a fourth dimension for the aether to flow from, the term antimatter was first used by Arthur Schuster in two rather whimsical letters to Nature in 1898, in which he coined the term. He hypothesized antiatoms, as well as whole antimatter solar systems, schusters ideas were not a serious theoretical proposal, merely speculation, and like the previous ideas, differed from the modern concept of antimatter in that it possessed negative gravity. The modern theory of antimatter began in 1928, with a paper by Paul Dirac, Dirac realised that his relativistic version of the Schrödinger wave equation for electrons predicted the possibility of antielectrons. These were discovered by Carl D. Anderson in 1932 and named positrons, although Dirac did not himself use the term antimatter, its use follows on naturally enough from antielectrons, antiprotons, etc
21.
Annihilation
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The total energy and momentum of the initial pair are conserved in the process, and, more generally are distributed among a set of other particles in the final state. Antiparticles have exactly opposite additive quantum numbers from particles, so the sums of all numbers of such an original pair are zero. Hence, any set of particles may be produced whose total numbers are also zero as long as conservation of energy. During a low-energy annihilation, photon production is favored, since these particles have no mass, however, high-energy particle colliders produce annihilations where a wide variety of exotic heavy particles are created. The word annihilation may also be used informally for the interaction of two particles that are not mutual antiparticles, some quantum numbers may then not sum to zero in the initial state, but must be conserved, with the same totals in the final state. An example is the annihilation of an electron antineutrino with an electron to produce a W−. If the annihilating particles are composite, such as mesons or baryons, if the initial two particles are elementary, then they may combine to produce only a single elementary boson, such as a photon, gluon, Z, or a Higgs boson. If the total energy in the frame is equal to the rest mass of a real boson. Otherwise, the process is understood as the creation of a boson that is virtual. This is called an s-channel process, an example is the annihilation of an electron with a positron to produce a virtual photon, which converts into a muon and anti-muon. If the energy is enough, a Z could replace the photon. Both the annihilating electron and positron particles have a rest energy of about 0.511 million electron volts, if their kinetic energies are relatively negligible, this total rest energy appears as the photon energy of the gamma rays produced. Each of the gamma rays then has an energy of about 0.511 MeV, momentum and energy are both conserved, with 1.022 MeV of gamma rays moving in opposite directions. If one or both charged particles carry a larger amount of energy, various other particles can be produced. The inverse process, pair production by a real photon, is also possible in the electromagnetic field of a third particle. When a proton encounters its antiparticle, the reaction is not as simple as electron-positron annihilation, unlike an electron, a proton is a composite particle consisting of three valence quarks and an indeterminate number of sea quarks bound by gluons. This type of reaction will occur between any baryon and any antibaryon consisting of three antiquarks, one of which corresponds to a quark in the baryon, antiprotons can and do annihilate with neutrons, and likewise antineutrons can annihilate with protons, as discussed below. Reactions in which proton-antiproton annihilation produces as many as nine mesons have been observed, the generated mesons leave the site of the annihilation at moderate fractions of the speed of light, and decay with whatever lifetime is appropriate for their type of meson
22.
Gamma ray
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Gamma ray, denoted by the lower-case Greek letter gamma, is penetrating electromagnetic radiation of a kind arising from the radioactive decay of atomic nuclei. It consists of photons in the highest observed range of photon energy, paul Villard, a French chemist and physicist, discovered gamma radiation in 1900 while studying radiation emitted by radium. In 1903, Ernest Rutherford named this radiation gamma rays, Rutherford had previously discovered two other types of radioactive decay, which he named alpha and beta rays. Gamma rays are able to ionize atoms, and are thus biologically hazardous. The decay of a nucleus from a high energy state to a lower energy state. Natural sources of gamma rays on Earth are observed in the decay of radionuclides. There are rare terrestrial natural sources, such as lightning strikes and terrestrial gamma-ray flashes, However, a large fraction of such astronomical gamma rays are screened by Earths atmosphere and can only be detected by spacecraft. Gamma rays typically have frequencies above 10 exahertz, and therefore have energies above 100 keV and wavelengths less than 10 picometers, However, this is not a strict definition, but rather only a rule-of-thumb description for natural processes. Electromagnetic radiation from radioactive decay of nuclei is referred to as gamma rays no matter its energy. This radiation commonly has energy of a few hundred keV, in astronomy, gamma rays are defined by their energy, and no production process needs to be specified. The energies of gamma rays from astronomical sources range to over 10 TeV, a notable example is the extremely powerful bursts of high-energy radiation referred to as long duration gamma-ray bursts, of energies higher than can be produced by radioactive decay. These bursts of gamma rays are thought to be due to the collapse of stars called hypernovae, the first gamma ray source to be discovered historically was the radioactive decay process called gamma decay. In this type of decay, a nucleus emits a gamma ray almost immediately upon formation. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900, However, Villard did not consider naming them as a different fundamental type. Rutherford also noted that gamma rays were not deflected by a field, another property making them unlike alpha. Gamma rays were first thought to be particles with mass, like alpha, Rutherford initially believed that they might be extremely fast beta particles, but their failure to be deflected by a magnetic field indicated that they had no charge. In 1914, gamma rays were observed to be reflected from crystal surfaces, Rutherford and his coworker Edward Andrade measured the wavelengths of gamma rays from radium, and found that they were similar to X-rays, but with shorter wavelengths and higher frequency. This was eventually recognized as giving them more energy per photon
23.
Photon
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A photon is an elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force. The photon has zero rest mass and is moving at the speed of light. Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a photon may be refracted by a lens and exhibit wave interference with itself. The quanta in a light wave cannot be spatially localized, some defined physical parameters of a photon are listed. The modern concept of the photon was developed gradually by Albert Einstein in the early 20th century to explain experimental observations that did not fit the classical model of light. The benefit of the model was that it accounted for the frequency dependence of lights energy. The photon model accounted for observations, including the properties of black-body radiation. In that model, light was described by Maxwells equations, in 1926 the optical physicist Frithiof Wolfers and the chemist Gilbert N. Lewis coined the name photon for these particles. After Arthur H. Compton won the Nobel Prize in 1927 for his studies, most scientists accepted that light quanta have an independent existence. In the Standard Model of particle physics, photons and other particles are described as a necessary consequence of physical laws having a certain symmetry at every point in spacetime. The intrinsic properties of particles, such as charge, mass and it has been applied to photochemistry, high-resolution microscopy, and measurements of molecular distances. Recently, photons have been studied as elements of quantum computers, in 1900, the German physicist Max Planck was studying black-body radiation and suggested that the energy carried by electromagnetic waves could only be released in packets of energy. In his 1901 article in Annalen der Physik he called these packets energy elements, the word quanta was used before 1900 to mean particles or amounts of different quantities, including electricity. In 1905, Albert Einstein suggested that waves could only exist as discrete wave-packets. He called such a wave-packet the light quantum, the name photon derives from the Greek word for light, φῶς. Arthur Compton used photon in 1928, referring to Gilbert N. Lewis, the name was suggested initially as a unit related to the illumination of the eye and the resulting sensation of light and was used later in a physiological context. Although Wolferss and Lewiss theories were contradicted by many experiments and never accepted, in physics, a photon is usually denoted by the symbol γ
24.
Positron emission
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Positron emission is mediated by the weak force. The positron is a type of particle, the other beta particle being the electron emitted from the β− decay of a nucleus. Positron decay results in nuclear transmutation, changing an atom of one element into an atom of an element with an atomic number that is less by one unit. Positron emission should not be confused with electron emission or beta decay, which occurs when a neutron turns into a proton and the nucleus emits an electron. This was the first example of β+ decay, the Curies termed the phenomenon artificial radioactivity, since 30 15P is a short-lived nuclide which does not exist in nature. The discovery of radioactivity would be cited when the husband. Isotopes which undergo this decay and thereby emit positrons include carbon-11, potassium-40, nitrogen-13, oxygen-15, aluminium-26, sodium-22, fluorine-18, the two most common types of quarks are up quarks, which have a charge of +2/3, and down quarks, with a −1/3 charge. Quarks arrange themselves in sets of three such that they make protons and neutrons, in a proton, whose charge is +1, there are two up quarks and one down quark. Neutrons, with no charge, have one up quark and two down quarks, via the weak interaction, quarks can change flavor from down to up, resulting in electron emission. Positron emission happens when an up quark changes into a down quark, nuclei which decay by positron emission may also decay by electron capture. For low-energy decays, electron capture is energetically favored by 2mec2 =1.022 MeV, as the energy of the decay goes up, so does the branching ratio towards positron emission. However, if the difference is less than 2mec2, then positron emission cannot occur. Certain isotopes are stable in galactic cosmic rays, because the electrons are stripped away, a positron is ejected from the parent nucleus, and the daughter atom must shed an orbital electron to balance charge. Isotopes which increase in mass under the conversion of a proton to a neutron, or which decrease in mass by less than 2me and these isotopes are used in positron emission tomography, a technique used for medical imaging. Note that the energy emitted depends on the isotope that is decaying, the short-lived positron emitting isotopes 11C, 13N, 15O and 18F used for positron emission tomography are typically produced by proton irradiation of natural or enriched targets. The LIVEChart of Nuclides - IAEA with filter on β+ decay
25.
Pair production
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Pair production is the creation of an elementary particle and its antiparticle. Examples include creating an electron and a positron, a muon and an antimuon, or a proton, pair production often refers specifically to a photon creating an electron-positron pair near a nucleus but can more generally refer to any neutral boson creating a particle-antiparticle pair. However, all other conserved quantum numbers of the particles must sum to zero – thus the created particles shall have opposite values of each other. For instance, if one particle has electric charge of +1 the other must have electric charge of −1, the probability of pair production in photon-matter interactions increases with photon energy and also increases approximately as the square of atomic number of the nearby atom. For photons with high energy, pair production is the dominant mode of photon interaction with matter. These interactions were first observed in Patrick Blacketts counter-controlled cloud chamber, the photon must have higher energy than the sum of the rest mass energies of an electron and positron for the production to occur. The photon must be near a nucleus in order to satisfy conservation of momentum, because of this, when pair production occurs, the atomic nucleus receives some recoil. The reverse of this process is electron positron annihilation and these properties can be derived through the kinematics of the interaction. Using four vector notation, the conservation of energy-momentum before and after the interaction gives and we can square the conservation equation,2 =2 However, in most cases the recoil of the nuclei is much smaller compared to the energy of the photon and can be neglected. This derivation is a semi-classical approximation, an exact derivation of the kinematics can be done taking into account the full quantum mechanical scattering of photon and nucleus. Cross sections are tabulated for different materials and energies, in 2008 the Titan laser aimed at a 1-millimeter-thick gold target was used to generate positron–electron pairs in large numbers. Pair production is invoked to predict the existence of hypothetical Hawking radiation, according to quantum mechanics, particle pairs are constantly appearing and disappearing as a quantum foam. In a region of strong tidal forces, the two particles in a pair may sometimes be wrenched apart before they have a chance to mutually annihilate. When this happens in the region around a hole, one particle may escape while its antiparticle partner is captured by the black hole. Supernova SN 2006gy is hypothesized to have been a pair production type supernova, annihilation Electron–positron annihilation Meitner–Hupfeld effect Pair-instability supernova Two-photon physics Dirac equation Matter creation Theory of photon-impact bound-free pair production
26.
Dirac equation
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In particle physics, the Dirac equation is a relativistic wave equation derived by British physicist Paul Dirac in 1928. In its free form, or including electromagnetic interactions, it describes all spin-1/2 massive particles such as electrons and it was validated by accounting for the fine details of the hydrogen spectrum in a completely rigorous way. The equation also implied the existence of a new form of matter, antimatter, previously unsuspected and unobserved, moreover, in the limit of zero mass, the Dirac equation reduces to the Weyl equation. This accomplishment has been described as fully on a par with the works of Newton, Maxwell, in the context of quantum field theory, the Dirac equation is reinterpreted to describe quantum fields corresponding to spin-1/2 particles. The Dirac equation in the originally proposed by Dirac is. The p1, p2, p3 are the components of the momentum, also, c is the speed of light, and ħ is the Planck constant divided by 2π. These fundamental physical constants reflect special relativity and quantum mechanics, respectively, Diracs purpose in casting this equation was to explain the behavior of the relativistically moving electron, and so to allow the atom to be treated in a manner consistent with relativity. His rather modest hope was that the corrections introduced this way might have a bearing on the problem of atomic spectra, the new elements in this equation are the 4 ×4 matrices αk and β, and the four-component wave function ψ. There are four components in ψ because the evaluation of it at any point in configuration space is a bispinor. It is interpreted as a superposition of an electron, a spin-down electron, a spin-up positron. These matrices and the form of the function have a deep mathematical significance. The algebraic structure represented by the matrices had been created some 50 years earlier by the English mathematician W. K. Clifford. In turn, Cliffords ideas had emerged from the work of the German mathematician Hermann Grassmann in his Lineale Ausdehnungslehre. The latter had been regarded as well-nigh incomprehensible by most of his contemporaries, the appearance of something so seemingly abstract, at such a late date, and in such a direct physical manner, is one of the most remarkable chapters in the history of physics. The Dirac equation is similar to the Schrödinger equation for a massive free particle. The left side represents the square of the momentum operator divided by twice the mass, space and time derivatives both enter to second order. This has a consequence for the interpretation of the equation. Because the equation is second order in the derivative, one must specify initial values both of the wave function itself and of its first-time derivative in order to solve definite problems
27.
Special relativity
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In physics, special relativity is the generally accepted and experimentally well-confirmed physical theory regarding the relationship between space and time. In Albert Einsteins original pedagogical treatment, it is based on two postulates, The laws of physics are invariant in all inertial systems, the speed of light in a vacuum is the same for all observers, regardless of the motion of the light source. It was originally proposed in 1905 by Albert Einstein in the paper On the Electrodynamics of Moving Bodies, as of today, special relativity is the most accurate model of motion at any speed. Even so, the Newtonian mechanics model is useful as an approximation at small velocities relative to the speed of light. Not until Einstein developed general relativity, to incorporate general frames of reference, a translation that has often been used is restricted relativity, special really means special case. It has replaced the notion of an absolute universal time with the notion of a time that is dependent on reference frame. Rather than an invariant time interval between two events, there is an invariant spacetime interval, a defining feature of special relativity is the replacement of the Galilean transformations of Newtonian mechanics with the Lorentz transformations. Time and space cannot be defined separately from each other, rather space and time are interwoven into a single continuum known as spacetime. Events that occur at the time for one observer can occur at different times for another. The theory is special in that it applies in the special case where the curvature of spacetime due to gravity is negligible. In order to include gravity, Einstein formulated general relativity in 1915, Special relativity, contrary to some outdated descriptions, is capable of handling accelerations as well as accelerated frames of reference. e. At a sufficiently small scale and in conditions of free fall, a locally Lorentz-invariant frame that abides by special relativity can be defined at sufficiently small scales, even in curved spacetime. Galileo Galilei had already postulated that there is no absolute and well-defined state of rest, Einstein extended this principle so that it accounted for the constant speed of light, a phenomenon that had been recently observed in the Michelson–Morley experiment. He also postulated that it holds for all the laws of physics, Einstein discerned two fundamental propositions that seemed to be the most assured, regardless of the exact validity of the known laws of either mechanics or electrodynamics. These propositions were the constancy of the speed of light and the independence of physical laws from the choice of inertial system, the Principle of Invariant Light Speed –. Light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body. That is, light in vacuum propagates with the c in at least one system of inertial coordinates. Following Einsteins original presentation of special relativity in 1905, many different sets of postulates have been proposed in various alternative derivations, however, the most common set of postulates remains those employed by Einstein in his original paper
28.
Zeeman effect
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The Zeeman effect, named after the Dutch physicist Pieter Zeeman, is the effect of splitting a spectral line into several components in the presence of a static magnetic field. It is analogous to the Stark effect, the splitting of a line into several components in the presence of an electric field. Also similar to the Stark effect, transitions between different components have, in general, different intensities, with some being entirely forbidden, the Zeeman effect is very important in applications such as nuclear magnetic resonance spectroscopy, electron spin resonance spectroscopy, magnetic resonance imaging and Mössbauer spectroscopy. It may also be utilized to improve accuracy in atomic absorption spectroscopy, a theory about the magnetic sense of birds assumes that a protein in the retina is changed due to the Zeeman effect. When the spectral lines are lines, the effect is called inverse Zeeman effect. Historically, one distinguishes between the normal and an anomalous Zeeman effect, the anomalous effect appears on transitions where the net spin of the electrons is an odd half-integer, so that the number of Zeeman sub-levels is even. It was called anomalous because the spin had not yet been discovered. At higher magnetic fields the effect ceases to be linear, at even higher field strength, when the strength of the external field is comparable to the strength of the atoms internal field, electron coupling is disturbed and the spectral lines rearrange. This is called the Paschen-Back effect, in the modern scientific literature, these terms are rarely used, with a tendency to use just the Zeeman effect. The magnetic moment consists of the electronic and nuclear parts, however, therefore, μ → ≈ − μ B g J → ℏ, where μ B is the Bohr magneton, J → is the total electronic angular momentum, and g is the Landé g-factor.0023192. If the interaction term V M is small, it can be treated as a perturbation, in the Paschen-Back effect, described below, V M exceeds the LS coupling significantly. In ultrastrong magnetic fields, the interaction may exceed H0, in which case the atom can no longer exist in its normal meaning. There are, of course, intermediate cases which are more complex than these limit cases. If the spin-orbit interaction dominates over the effect of the magnetic field, L → and S → are not separately conserved. The spin and orbital angular momentum vectors can be thought of as precessing about the angular momentum vector J →. Thus, ⟨ V M ⟩ = μ B ℏ J → ⋅ B →, in the presence of an external magnetic field, the weak-field Zeeman effect splits the 1S1/2 and 2P1/2 levels into 2 states each and the 2P3/2 level into 4 states. Note in particular that the size of the splitting is different for the different orbitals. On the left, fine structure splitting is depicted and this splitting occurs even in the absence of a magnetic field, as it is due to spin-orbit coupling
29.
Hermann Weyl
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Hermann Klaus Hugo Weyl, ForMemRS was a German mathematician, theoretical physicist and philosopher. His research has had significance for theoretical physics as well as purely mathematical disciplines including number theory. He was one of the most influential mathematicians of the century. Weyl published technical and some works on space, time, matter, philosophy, logic, symmetry. He was one of the first to conceive of combining general relativity with the laws of electromagnetism, while no mathematician of his generation aspired to the universalism of Henri Poincaré or Hilbert, Weyl came as close as anyone. Michael Atiyah, in particular, has commented that whenever he examined a mathematical topic, Weyl was born in Elmshorn, a small town near Hamburg, in Germany, and attended the gymnasium Christianeum in Altona. From 1904 to 1908 he studied mathematics and physics in both Göttingen and Munich and his doctorate was awarded at the University of Göttingen under the supervision of David Hilbert whom he greatly admired. In September 1913 in Göttingen, Weyl married Friederike Bertha Helene Joseph who went by the name Helene, Helene was a daughter of Dr. Bruno Joseph, a physician who held the position of Sanitätsrat in Ribnitz-Damgarten, Germany. Helene was a philosopher and also a translator of Spanish literature into German and it was through Helenes close connection with Husserl that Hermann became familiar with Husserls thought. Hermann and Helene had two sons, Fritz Joachim Weyl and Michael Weyl, both of whom were born in Zürich, Switzerland, Helene died in Princeton, New Jersey on September 5,1948. A memorial service in her honor was held in Princeton on September 9,1948, speakers at her memorial service included her son Fritz Joachim Weyl and mathematicians Oswald Veblen and Richard Courant. In 1950 Hermann married sculptress Ellen Bär, who was the widow of professor Richard Josef Bär of Zürich, einstein had a lasting influence on Weyl, who became fascinated by mathematical physics. In 1921 Weyl met Erwin Schrödinger, a theoretical physicist who at the time was a professor at the University of Zürich and they were to become close friends over time. Weyl left Zürich in 1930 to become Hilberts successor at Göttingen, leaving when the Nazis assumed power in 1933, particularly as his wife was Jewish. He had been offered one of the first faculty positions at the new Institute for Advanced Study in Princeton, New Jersey, as the political situation in Germany grew worse, he changed his mind and accepted when offered the position again. He remained there until his retirement in 1951, together with his second wife Ellen, he spent his time in Princeton and Zürich, and died from a heart attack on December 8,1955 while living in Zürich. Hermann Weyl was cremated in Zurich on December 12,1955 and his cremains remained in private hands until 1999, at which time they were interred in an outdoor columbarium vault in the Princeton Cemetery, located at 29 Greenview Avenue, Princeton, New Jersey. The remains of Hermanns son Michael Weyl are interred next to Hermanns ashes in the same columbarium vault in the Princeton Cemetery
30.
Dirac sea
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The Dirac sea is a theoretical model of the vacuum as an infinite sea of particles with negative energy. It was first postulated by the British physicist Paul Dirac in 1930 to explain the anomalous negative-energy quantum states predicted by the Dirac equation for relativistic electrons. The positron, the counterpart of the electron, was originally conceived of as a hole in the Dirac sea. This is a consequence of the relativistic energy-momentum relation E2 = p 2 c 2 + m 2 c 4 upon which the Dirac equation is built. The quantity U is a constant 2 ×1 column vector, the quantity ε is called the time evolution factor, and its interpretation in similar roles in, for example, the plane wave solutions of the Schrödinger equation, is the energy of the wave. This interpretation is not immediately available here since it may acquire negative values, a similar situation prevails for the Klein–Gordon equation. In that case, the value of ε can be interpreted as the energy of the wave since in the canonical formalism. But this is not the case with the Dirac equation, the energy in the canonical formalism associated with negative ε is –Ep. In hole theory, the solutions with negative time evolution factors are reinterpreted as representing the positron, discovered by Carl Anderson. The origins of the Dirac sea lie in the spectrum of the Dirac equation, an extension of the Schrödinger equation that is consistent with special relativity. This is not a big difficulty when an electron is considered, because its energy is conserved. Real electrons clearly do not behave in this way, Diracs solution to this was to turn to the Pauli exclusion principle. Electrons are fermions, and obey the principle, which means that no two electrons can share a single energy state within an atom. Dirac hypothesized that what we think of as the vacuum is actually the state in all the negative-energy states are filled. Therefore, if we want to introduce a single electron we would have to put it in a positive-energy state, furthermore, even if the electron loses energy by emitting photons it would be forbidden from dropping below zero energy. Dirac also pointed out that a situation might exist in all the negative-energy states are occupied except one. This hole in the sea of electrons would respond to electric fields as though it were a positively charged particle. Initially, Dirac identified this hole as a proton, hermann Weyl also noted that a hole should act as though it has the same mass as an electron, whereas the proton is about two thousand times heavier
31.
Proton
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A proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and mass slightly less than that of a neutron. Protons and neutrons, each with masses of one atomic mass unit, are collectively referred to as nucleons. One or more protons are present in the nucleus of every atom, the number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number. Since each element has a number of protons, each element has its own unique atomic number. The word proton is Greek for first, and this name was given to the nucleus by Ernest Rutherford in 1920. In previous years, Rutherford had discovered that the nucleus could be extracted from the nuclei of nitrogen by atomic collisions. Protons were therefore a candidate to be a particle, and hence a building block of nitrogen. In the modern Standard Model of particle physics, protons are hadrons, and like neutrons, although protons were originally considered fundamental or elementary particles, they are now known to be composed of three valence quarks, two up quarks and one down quark. The rest masses of quarks contribute only about 1% of a protons mass, the remainder of a protons mass is due to quantum chromodynamics binding energy, which includes the kinetic energy of the quarks and the energy of the gluon fields that bind the quarks together. At sufficiently low temperatures, free protons will bind to electrons, however, the character of such bound protons does not change, and they remain protons. A fast proton moving through matter will slow by interactions with electrons and nuclei, the result is a protonated atom, which is a chemical compound of hydrogen. In vacuum, when electrons are present, a sufficiently slow proton may pick up a single free electron, becoming a neutral hydrogen atom. Such free hydrogen atoms tend to react chemically with other types of atoms at sufficiently low energies. When free hydrogen atoms react with other, they form neutral hydrogen molecules. Protons are spin-½ fermions and are composed of three quarks, making them baryons. Protons have an exponentially decaying positive charge distribution with a mean square radius of about 0.8 fm. Protons and neutrons are both nucleons, which may be together by the nuclear force to form atomic nuclei. The nucleus of the most common isotope of the atom is a lone proton
32.
J. Robert Oppenheimer
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Julius Robert Oppenheimer was an American theoretical physicist and professor of physics at the University of California, Berkeley. After the war, Oppenheimer became chairman of the influential General Advisory Committee of the newly created United States Atomic Energy Commission and he used that position to lobby for international control of nuclear power to avert nuclear proliferation and a nuclear arms race with the Soviet Union. Nine years later, President John F. Kennedy awarded him with the Enrico Fermi Award as a gesture of political rehabilitation. As a teacher and promoter of science, he is remembered as a father of the American school of theoretical physics that gained world prominence in the 1930s. After World War II, he director of the Institute for Advanced Study in Princeton. Julius came to America with no money, no baccalaureate studies and he got a job in a textile company and within a decade was an executive with the company. The Oppenheimers were non-observant Ashkenazi Jews, in 1912 the family moved to an apartment on the 11th floor of 155 Riverside Drive, near West 88th Street, Manhattan, an area known for luxurious mansions and townhouses. Their art collection included works by Pablo Picasso and Édouard Vuillard, Robert had a younger brother, Frank, who also became a physicist. Oppenheimer was initially educated at Alcuin Preparatory School, and in 1911 he entered the Ethical Culture Society School and this had been founded by Felix Adler to promote a form of ethical training based on the Ethical Culture movement, whose motto was Deed before Creed. His father had been a member of the Society for many years, Oppenheimer was a versatile scholar, interested in English and French literature, and particularly in mineralogy. He completed the third and fourth grades in one year, during his final year, he became interested in chemistry. He entered Harvard College a year late, at age 18, Oppenheimer majored in chemistry, but Harvard required science students to also study history, literature, and philosophy or mathematics. He compensated for his start by taking six courses each term and was admitted to the undergraduate honor society Phi Beta Kappa. He was attracted to physics by a course on thermodynamics that was taught by Percy Bridgman. He graduated summa cum laude in three years, in 1924 Oppenheimer was informed that he had been accepted into Christs College, Cambridge. He wrote to Ernest Rutherford requesting permission to work at the Cavendish Laboratory, Bridgman provided Oppenheimer with a recommendation, which conceded that Oppenheimers clumsiness in the laboratory made it apparent his forte was not experimental but rather theoretical physics. Rutherford was unimpressed, but Oppenheimer went to Cambridge in the hope of landing another offer and he was ultimately accepted by J. J. Thomson on condition that he complete a basic laboratory course. He developed a relationship with his tutor, Patrick Blackett
33.
Richard Feynman
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For his contributions to the development of quantum electrodynamics, Feynman, jointly with Julian Schwinger and Sinichirō Tomonaga, received the Nobel Prize in Physics in 1965. Feynman developed a widely used pictorial representation scheme for the mathematical expressions governing the behavior of subatomic particles, during his lifetime, Feynman became one of the best-known scientists in the world. In a 1999 poll of 130 leading physicists worldwide by the British journal Physics World he was ranked as one of the ten greatest physicists of all time. Along with his work in physics, Feynman has been credited with pioneering the field of quantum computing. Tolman professorship in physics at the California Institute of Technology. They were not religious, and by his youth, Feynman described himself as an avowed atheist, like Albert Einstein and Edward Teller, Feynman was a late talker, and by his third birthday had yet to utter a single word. He retained a Brooklyn accent as an adult and that accent was thick enough to be perceived as an affectation or exaggeration – so much so that his good friends Wolfgang Pauli and Hans Bethe once commented that Feynman spoke like a bum. The young Feynman was heavily influenced by his father, who encouraged him to ask questions to challenge orthodox thinking, from his mother, he gained the sense of humor that he had throughout his life. As a child, he had a talent for engineering, maintained a laboratory in his home. When he was in school, he created a home burglar alarm system while his parents were out for the day running errands. When Richard was five years old, his mother gave birth to a brother, Henry Philips. Four years later, Richards sister Joan was born, and the moved to Far Rockaway. Though separated by nine years, Joan and Richard were close and their mother thought that women did not have the cranial capacity to comprehend such things. Despite their mothers disapproval of Joans desire to study astronomy, Richard encouraged his sister to explore the universe, Joan eventually became an astrophysicist specializing in interactions between the Earth and the solar wind. Feynman attended Far Rockaway High School, a school in Far Rockaway, Queens, upon starting high school, Feynman was quickly promoted into a higher math class. A high-school-administered IQ test estimated his IQ at 125—high, but merely respectable according to biographer James Gleick and his sister Joan did better, allowing her to claim that she was smarter. Years later he declined to join Mensa International, saying that his IQ was too low, physicist Steve Hsu stated of the test, I suspect that this test emphasized verbal, as opposed to mathematical, ability. Feynman received the highest score in the United States by a margin on the notoriously difficult Putnam mathematics competition exam
34.
Ernst Carl Gerlach Stueckelberg
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Ernst Carl Gerlach Stueckelberg was a Swiss mathematician and physicist, regarded as one of the most eminent physicists of the 20th century. Born into a family in Basel in 1905, Stueckelbergs father was a lawyer. A highly gifted student, Stueckelberg initially began a physics degree at the University of Basel in 1923. While still a student, Stueckelberg was invited by the distinguished quantum theorist Arnold Sommerfeld and he went on to gain a Ph D on cathode physics in 1927. Later that year he went to Princeton University, becoming an assistant professor in 1930 and he returned to Switzerland in 1932, working first at the University of Basel before switching the following year to the University of Zurich. In 1934 he moved again to the University of Geneva, which together with the University of Lausanne became his principal bases for the rest of his career. Stueckelbergs sojourn in Zurich led to contact with leading quantum theorists Wolfgang Pauli and Gregor Wentzel, in 1934 he devised a fully covariant perturbation theory for quantum fields. The approach proposed by Stueckelberg was very powerful, but was not adopted by others at the time, however, besides being explicitly covariant, Stueckelbergs methods avoid vacuum bubbles. Stueckelberg developed the vector boson exchange model as the explanation of the strong nuclear force in 1935. Discussions with Pauli led Stueckelberg to drop the idea, however and it was rediscovered by Hideki Yukawa, who won a Nobel Prize for his work in 1949 — the first of several Nobel Prizes awarded for work which Stueckelberg contributed to, without recognition. In 1938 Stueckelberg recognized that massive electrodynamics contains a hidden scalar and he also proposed the law of conservation of baryon number. The evolution parameter theory he presented in 1941 and 1942 is the basis for recent work in relativistic dynamics, in 1941 he proposed the interpretation of the positron as a positive energy electron traveling backward in time. In 1943 he came up with a program to attack the problems of infinities in quantum electrodynamics. In 1952 he proved the principle of semi-detailed balance for kinetics without microscopic reversibility, in 1953 he and the mathematician André Petermann discovered the renormalization group. In 1976 he was awarded the Max Planck medal and his PhD students included Marcel Guénin. Timeline of atomic and subatomic physics Propagator Relativistic dynamics Stueckelberg action Stueckelberg-Feynman interpretation Cianfrani, F. and Lecian, Stueckelberg, a forerunner of modern physics, Nuovo Cimento 122B, 123-133. Lacki, Jan, Ruegg, H. and Valentine Telegdi The Road to Stueckelbergs Covariant Perturbation Theory as Illustrated by Successive Treatments of Compton Scattering, studies in History and Philosophy of Modern Physics. Schweber, Silvan S. QED and the Men who Made It, the edited PDF files of the physics course of Professor Stueckelberg, openly accessible, with commentary and complete biographical documents
35.
John Archibald Wheeler
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John Archibald Wheeler was an American theoretical physicist. He was largely responsible for reviving interest in general relativity in the United States after World War II, Wheeler also worked with Niels Bohr in explaining the basic principles behind nuclear fission. Together with Gregory Breit, Wheeler developed the concept of Breit–Wheeler process, Wheeler earned his doctorate at Johns Hopkins University under the supervision of Karl Herzfeld, and studied under Breit and Bohr on a National Research Council fellowship. In 1939 he teamed up with Bohr to write a series of using the liquid drop model to explain the mechanism of fission. He returned to Princeton after the war ended, but returned to government service to help design, for most of his career, Wheeler was a professor at Princeton University, which he joined in 1938, remaining until his retirement in 1976. At Princeton he supervised 46 PhDs, more than any other professor in the Princeton physics department, Wheeler was born in Jacksonville, Florida on July 9,1911 to librarians Joseph Lewis Wheeler and Mabel Archibald Wheeler. He was the oldest of four children, having two brothers, Joseph and Robert, and a younger sister, Mary. Joseph earned a Ph. D. from Brown University and a Master of Library Science from Columbia University, Robert earned a Ph. D. in geology from Harvard University and worked as a geologist for oil companies and at colleges. Mary studied library science at the University of Denver and became a librarian and they grew up in Youngstown, Ohio, but spent a year in 1921 to 1922 on a farm in Benson, Vermont, where Wheeler attended a one-room school. After they returned to Youngstown he attended Rayen High School, after graduating from the Baltimore City College high school in 1926, Wheeler entered Johns Hopkins University with a scholarship from the state of Maryland. He published his first scientific paper in 1930, as part of a job at the National Bureau of Standards. He earned his doctorate in 1933 and his dissertation research work, carried out under the supervision of Karl Herzfeld, was on the Theory of the Dispersion and Absorption of Helium. He received a National Research Council fellowship, which he used to study under Gregory Breit at New York University in 1933 and 1934, and then in Copenhagen under Niels Bohr in 1934 and 1935. In a 1934 paper, Breit and Wheeler introduced the Breit–Wheeler process, the University of North Carolina at Chapel Hill made Wheeler an associate professor in 1937, but he wanted to be able work more closely with the experts in particle physics. He turned down an offer in 1938 of a professorship at Johns Hopkins University in favor of an assistant professorship at Princeton University. Although it was a position, he felt that Princeton. He remained a member of the faculty there until 1976, werner Heisenberg subsequently developed the idea of the S-matrix in the 1940s. In doing so he was led to introduce a unitary characteristic S-matrix, Wheeler did not develop the S-matrix, but joined Edward Teller in examining Bohrs liquid drop model of the atomic nucleus
36.
World line
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The world line of an object is the path of that object in 4-dimensional spacetime, tracing the history of its location in space at each instant in time. It is an important concept in physics, and particularly theoretical physics. The idea of world lines originates in physics and was pioneered by Hermann Minkowski, the term is now most often used in relativity theories. In physics, a line of an object is the sequence of spacetime events corresponding to the history of the object. A world line is a type of curve in spacetime. Below an equivalent definition will be explained, A world line is a curve in spacetime. Each point of a line is an event that can be labeled with the time. For example, the orbit of the Earth in space is approximately a circle, a curve in space. However, it there at a different time. The world line of the Earth is helical in spacetime and does not return to the same point, spacetime is the collection of points called events, together with a continuous and smooth coordinate system identifying the events. Each event can be labeled by four numbers, a time coordinate, the mathematical term for spacetime is a four-dimensional manifold. The concept may be applied as well to a higher-dimensional space, for easy visualizations of four dimensions, two space coordinates are often suppressed. The event is represented by a point in a Minkowski diagram, which is a plane usually plotted with the time coordinate, say t, upwards. As expressed by F. R. Harvey A curve M in is called a worldline of a particle if its tangent is future timelike at each point, the arclength parameter is called proper time and usually denoted τ. The length of M is called the time of the worldline or particle. If the worldline M is a segment, then the particle is said to be in free fall. A world line traces out the path of a point in spacetime. A world sheet is the analogous two-dimensional surface traced out by a one-dimensional line traveling through spacetime, the world sheet of an open string is a strip, that of a closed string is a volume
37.
Yoichiro Nambu
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Yoichiro Nambu was a Japanese-born American physicist, a professor at the University of Chicago. Nambu was born in Tokyo, Japan, in 1921, after graduating from the then Fukui Secondary High School in Fukui City, he enrolled in the Imperial University of Tokyo and studied physics. He received his Bachelor of Science in 1942 and Doctorate of Science in 1952, in 1949 he was appointed to associate professor at the Osaka City University and promoted to professorship the next year at the age of 29. In 1952, he was invited by the Institute for Advanced Study in Princeton, New Jersey, United States and he moved to the University of Chicago in 1954 and was promoted to professor in 1958. From 1974 to 1977 he was also Chairman of the Department of Physics and he became a United States citizen in 1970. He was accounted as one of the founders of string theory, after more than fifty years as a professor, he was Henry Pratt Judson Distinguished Service Professor emeritus at the University of Chicagos Department of Physics and Enrico Fermi Institute. The Nambu-Goto action in string theory is named after Nambu and Tetsuo Goto, also, massless bosons arising in field theories with spontaneous symmetry breaking are sometimes referred to as Nambu–Goldstone bosons. Nambu died on 5 July 2015 at the age of 94 in Osaka due to a myocardial infarction. His funeral and memorial services were held among close relatives and he was awarded one-half of the 2008 Nobel Prize in Physics for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics. D. Nambu passing by former student Dr. Madhusree Mukerjee
38.
Particle detector
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Detectors can measure the particle energy and other attributes such as momentum, spin, charge, in addition to merely registering the presence of the particle. Detectors designed for modern accelerators are huge, both in size and in cost, the term counter is often used instead of detector when the detector counts the particles but does not resolve its energy or ionization. Particle detectors can also usually track ionizing radiation, if their main purpose is radiation measurement, they are called radiation detectors, but as photons are also particles, the term particle detector is still correct. A New Classification System for Radiation Detectors, journal of the Optical Society of America. Erratum, The Ultimate Sensitivity of Radiation Detectors, journal of the Optical Society of America. Factors of Merit for Radiation Detectors, journal of the Optical Society of America. AIP Conference Proceedings, Instrumentation in Elementary Particle Physics, VIII, istanbul, Dordrecht, D. Reidel Publishing Co. pp. 3–34
39.
Particle physics
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Particle physics is the branch of physics that studies the nature of the particles that constitute matter and radiation. By our current understanding, these particles are excitations of the quantum fields that also govern their interactions. The currently dominant theory explaining these fundamental particles and fields, along with their dynamics, is called the Standard Model, in more technical terms, they are described by quantum state vectors in a Hilbert space, which is also treated in quantum field theory. All particles and their interactions observed to date can be described almost entirely by a field theory called the Standard Model. The Standard Model, as formulated, has 61 elementary particles. Those elementary particles can combine to form composite particles, accounting for the hundreds of species of particles that have been discovered since the 1960s. The Standard Model has been found to agree with almost all the tests conducted to date. However, most particle physicists believe that it is a description of nature. In recent years, measurements of mass have provided the first experimental deviations from the Standard Model. The idea that all matter is composed of elementary particles dates from at least the 6th century BC, in the 19th century, John Dalton, through his work on stoichiometry, concluded that each element of nature was composed of a single, unique type of particle. Throughout the 1950s and 1960s, a variety of particles were found in collisions of particles from increasingly high-energy beams. It was referred to informally as the particle zoo, the current state of the classification of all elementary particles is explained by the Standard Model. It describes the strong, weak, and electromagnetic fundamental interactions, the species of gauge bosons are the gluons, W−, W+ and Z bosons, and the photons. The Standard Model also contains 24 fundamental particles, which are the constituents of all matter, finally, the Standard Model also predicted the existence of a type of boson known as the Higgs boson. Early in the morning on 4 July 2012, physicists with the Large Hadron Collider at CERN announced they had found a new particle that behaves similarly to what is expected from the Higgs boson, the worlds major particle physics laboratories are, Brookhaven National Laboratory. Its main facility is the Relativistic Heavy Ion Collider, which collides heavy ions such as gold ions and it is the worlds first heavy ion collider, and the worlds only polarized proton collider. Its main projects are now the electron-positron colliders VEPP-2000, operated since 2006 and its main project is now the Large Hadron Collider, which had its first beam circulation on 10 September 2008, and is now the worlds most energetic collider of protons. It also became the most energetic collider of heavy ions after it began colliding lead ions and its main facility is the Hadron Elektron Ring Anlage, which collides electrons and positrons with protons
40.
Muon
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The muon is an elementary particle similar to the electron, with an electric charge of −1 e and a spin of 1/2, but with a much greater mass. It is classified as a lepton, as is the case with other leptons, the muon is not believed to have any sub-structure—that is, it is not thought to be composed of any simpler particles. The muon is a subatomic particle with a mean lifetime of 2.2 µs. Muon decay almost always produces at least three particles, which must include an electron of the charge as the muon and two neutrinos of different types. Like all elementary particles, the muon has a corresponding antiparticle of opposite charge but equal mass and spin, muons are denoted by μ− and antimuons by μ+. Muons were previously called mu mesons, but are not classified as mesons by modern particle physicists, muons have a mass of 105.7 MeV/c2, which is about 207 times that of the electron. Due to their mass, muons are not as sharply accelerated when they encounter electromagnetic fields. As an example, so-called secondary muons, generated by cosmic rays hitting the atmosphere, can penetrate to the Earths surface, because muons have a very large mass and energy compared with the decay energy of radioactivity, they are never produced by radioactive decay. These interactions usually produce pi mesons initially, which most often decay to muons, muons were discovered by Carl D. Anderson and Seth Neddermeyer at Caltech in 1936, while studying cosmic radiation. Anderson noticed particles that curved differently from electrons and other known particles when passed through a magnetic field and they were negatively charged but curved less sharply than electrons, but more sharply than protons, for particles of the same velocity. Thus Anderson initially called the new particle a mesotron, adopting the prefix meso- from the Greek word for mid-, the existence of the muon was confirmed in 1937 by J. C. The transition of a particle from neutron state to proton state is not always accompanied by the emission of light particles. The transition is taken up by another heavy particle. Because of its mass, the mu meson was initially thought to be Yukawas particle, with two particles now known with the intermediate mass, the more general term meson was adopted to refer to any such particle within the correct mass range between electrons and nucleons. The difference, in part, was that mu mesons did not interact with the nuclear force, newer mesons also showed evidence of behaving like the pi meson in nuclear interactions, but not like the mu meson. Also, the mu mesons decay products included both a neutrino and an antineutrino, rather than just one or the other, as was observed in the decay of other charged mesons. In the quark model, a meson was no longer defined by mass, mu mesons, however, had shown themselves to be fundamental particles like electrons, with no quark structure. Thus, mu mesons were not mesons at all, in the new sense and use of the term used with the quark model of particle structure
41.
Kaon
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In particle physics, a kaon /ˈkeɪ. ɒn/, also called a K meson and denoted K, is any of a group of four mesons distinguished by a quantum number called strangeness. In the quark model they are understood to be states of a strange quark. Kaons have proved to be a source of information on the nature of fundamental interactions since their discovery in cosmic rays in 1947. They were essential in establishing the foundations of the Standard Model of particle physics, such as the model of hadrons. Moreover, direct CP violation was discovered in the kaon decays in the early 2000s by the NA48 and KTeV experiments at CERN, the four kaons are, K−, negatively charged has mass 493. 677±0.013 MeV and mean lifetime ×10−8 s. K+ positively charged must have mass and lifetime equal to that of K−, the mass difference is 0. 032±0.090 MeV, consistent with zero. The difference in lifetime is ×10−8 s, K0, neutrally charged has mass 497. 648±0.022 MeV. It has mean squared charge radius of −0. 076±0.01 fm2, K0, neutrally charged has the same mass. It is clear from the quark model assignments that the kaons form two doublets of isospin, that is, they belong to the representation of SU called the 2. One doublet of strangeness +1 contains the K+ and the K0, the antiparticles form the other doublet. No definite lifetime ^ Weak eigenstate, makeup is missing small CP–violating term. ^ The mass of the K0 L and K0 S are given as that of the K0, however, it is known that a difference between the masses of the K0 L and K0 S on the order of 3. 5×10−12 MeV/c2 exists. Although the K0 and its antiparticle K0 are usually produced via the strong force, the short-lived neutral kaon is called the K S, decays primarily into two pions, and has a mean lifetime 8. 958×10−11 s. An experimental observation made in 1964 that K-longs rarely decay into two pions was the discovery of CP violation, main decay modes for K+, Decay modes for the K− are charge conjugates of the ones above. By and large experiments have driven the development, and that major discoveries came unexpectedly or even against expectations expressed by theorists, sanda, CP violation, In 1947, G. D. The estimated mass of the new particles was very rough, about half a protons mass, more examples of these V-particles were slow in coming. The first breakthrough was obtained at Caltech, where a cloud chamber was taken up Mount Wilson, in 1950,30 charged and 4 neutral V-particles were reported. Inspired by this, numerous mountaintop observations were made over the several years, and by 1953
42.
Particle accelerator
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A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to nearly light speed and to contain them in well-defined beams. Large accelerators are used in physics as colliders, or as synchrotron light sources for the study of condensed matter physics. There are currently more than 30,000 accelerators in operation around the world, there are two basic classes of accelerators, electrostatic and electrodynamic accelerators. Electrostatic accelerators use electric fields to accelerate particles. The most common types are the Cockcroft–Walton generator and the Van de Graaff generator, a small-scale example of this class is the cathode ray tube in an ordinary old television set. The achievable kinetic energy for particles in these devices is determined by the accelerating voltage, electrodynamic or electromagnetic accelerators, on the other hand, use changing electromagnetic fields to accelerate particles. Since in these types the particles can pass through the accelerating field multiple times. This class, which was first developed in the 1920s, is the basis for most modern large-scale accelerators, because colliders can give evidence of the structure of the subatomic world, accelerators were commonly referred to as atom smashers in the 20th century. Despite the fact that most accelerators actually propel subatomic particles, the term persists in popular usage when referring to particle accelerators in general. Beams of high-energy particles are useful for both fundamental and applied research in the sciences, and also in many technical and industrial fields unrelated to fundamental research and it has been estimated that there are approximately 30,000 accelerators worldwide. The bar graph shows the breakdown of the number of industrial accelerators according to their applications, for the most basic inquiries into the dynamics and structure of matter, space, and time, physicists seek the simplest kinds of interactions at the highest possible energies. These typically entail particle energies of many GeV, and the interactions of the simplest kinds of particles, leptons and quarks for the matter, the largest and highest energy particle accelerator used for elementary particle physics is the Large Hadron Collider at CERN, operating since 2009. These investigations often involve collisions of heavy nuclei – of atoms like iron or gold – at energies of several GeV per nucleon, the largest such particle accelerator is the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. An example of type of machine is LANSCE at Los Alamos. A large number of light sources exist worldwide. The ESRF in Grenoble, France has been used to extract detailed 3-dimensional images of trapped in amber. Thus there is a demand for electron accelerators of moderate energy. Everyday examples of particle accelerators are cathode ray tubes found in television sets and these low-energy accelerators use a single pair of electrodes with a DC voltage of a few thousand volts between them
43.
Penning trap
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A Penning trap is a device for the storage of charged particles using a homogeneous axial magnetic field and an inhomogeneous quadrupole electric field. This kind of trap is particularly suited to precision measurements of properties of ions. Geonium atoms have been created and studied this way, to measure the magnetic moment. Recently these traps have used in the physical realization of quantum computation. Penning traps are used in laboratories worldwide. For example, at CERN to store antimatter like antiprotons, the Penning trap was named after F. M. Penning by Hans Georg Dehmelt who built the first trap. Dehmelt got inspiration from the vacuum gauge built by F. M. Penning where a current through a tube in a magnetic field is proportional to the pressure. Citing from H. Dehmelts autobiography, I began to focus on the magnetron/Penning discharge geometry, in their 1955 cyclotron resonance work on photoelectrons in vacuum Franken and Liebes had reported undesirable frequency shifts caused by accidental electron trapping. Their analysis made me realize that in an electric quadrupole field the shift would not depend on the location of the electron in the trap. This is an important advantage over many other traps that I decided to exploit. A magnetron trap of this type had been discussed in J. R. Pierces 1949 book, and I developed a simple description of the axial, magnetron. – H. Dehmelt H. Dehmelt shared the Nobel Prize in Physics in 1989 for the development of the ion trap technique, Penning traps use a strong homogeneous axial magnetic field to confine particles radially and a quadrupole electric field to confine the particles axially. The static electric potential can be generated using a set of three electrodes, a ring and two endcaps, in an ideal Penning trap the ring and endcaps are hyperboloids of revolution. For trapping of ions, the endcap electrodes are kept at a positive potential relative to the ring. This potential produces a saddle point in the centre of the trap, the electric field causes ions to oscillate along the trap axis. The magnetic field in combination with the field causes charged particles to move in the radial plane with a motion which traces out an epitrochoid. The orbital motion of ions in the plane is composed of two modes at frequencies which are called the magnetron ω − and the modified cyclotron ω + frequencies. These motions are similar to the deferent and epicycle, respectively, the sum of these two frequencies is the cyclotron frequency, which depends only on the ratio of electric charge to mass and on the strength of the magnetic field
. Bibcode:2008RvMP...80..633M. doi:10.1103/RevModPhys.80.633.
