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Download No 7 Glossary
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Glossary (Story of the young girl-electron going to a party) [A B C D E F G H I J K L M N O P Q R S T U V W X Y Z ] (Note - Greek letters are written out by name - alpha, beta etc.) -Aaccelerator A machine used to accelerate particles (for example, electrons or protons) to high speeds, and thus high energy (compared to their rest mass energy). Then particles are usually driven to collide with other particles. In this way Scientists can study the reactions which take place, and therefore obtain information on particles and forces. [close the glossary] annihilation Process in which a particle meets its corresponding antiparticle, and then the two particles destroy each other. The total energy of the initial couple changes into the rest mass of other particles and antiparticles and their kinetic energy. [close the glossary] antiparticle It has the same mass as the particle, but opposite electric charge and other properties. Every particle has a corresponding antiparticle. Example: the antiproton, antineutron and antielectron (or positron) are the antiparticle of the proton, neutron and electron respectively. When a particle meets its antiparticle the two particles annihilate. [close the glossary] antiproton The antiparticle of the proton. It has the same mass as the proton, but opposite electric charge. [close the glossary] atom The smallest part of a simple substance (or element), which maintains unaltered the properties of the simple substance. It is usually imagined like a miniature solar system with a positive nucleus surrounded by electrons. [close the glossary] -B-Ccarrier particle In particle processes, the forces are described as due to the exchange of fundamental particles, called "force carriers"; each type of force is associated with a different type of carrier particle. The carrier particles are what, on a microscopic level, transmit (or, as we say, "mediate") an interaction. Example: the photon is the carrier particle of the electromagnetic interaction. [close the glossary] charge (electric charge) Property of a particle which determines its participation in the electromagnetic interaction. [close the glossary] C.E.R.N. (European Council for Nuclear Research) The Center, one of the most advanced for nuclear research, is located near Geneva, Switzerland. [close the glossary] collider An accelerator in which beams of particles (such as protons and antiprotons or elettrons and positrons), travelling in opposite directions, are driven to collide frontally together. [close the glossary] conduction electron Electron that can move inside a conductor. When a electric field is applied to the conductor, the electron movement gives rise to the known phenomenon of electric conduction (passage of current through a metal). In the story: an electron is struck by a photon, thus absorbs energy and leaves the metal (Photoelectric effect). [close the glossary] -Ddecay Every process in which a particle disappears and another particle takes its place. The sum of the masses of the produced particles is lower than the mass of the initial particle. Examples: a neutron, isolated and at rest, decays after about 15 minutes into a proton, an electron and an electronic antineutrino. Instead, the negative muon (mu-) decays, in two millionths of a second, into an electron, a muonic neutrino and an electronic antineutrino. [close the glossary] -Eelectric field The field associated with electric force. It is united with the magnetic field in the electromagnetic field. [close the glossary] electromagnetic field The field associated with electromagnetic force. This unites the electric and magnetic field. [close the glossary] electromagnetic interaction A fundamental interaction of Nature. It unites the electric and magnetic interactions. The interaction originates from the electric charges and is mediated by the photons. The electromagnetic interaction binds electrons and nucleus to make an atom. The force, which binds atoms to make the molecules, is a "residual" electromagnetic force shielded by the atomic electrons. [close the glossary] electron A fundamental particle, negatively charged. It is a last constituent of matter and a stable particle. Note: in the story the terms "young", "old", "girl-electron", "woman-electron" and so on, attributed to the electrons, are pure fantasy! In Nature there is only one stable particle, called an electron! [close the glossary] electron microscope A microscope that uses an electron beam instead of light (photons), for lighting. [close the glossary] elementary particle The term usually denotes the last constituents (e.g. quarks and electrons), the carrier particles (e.g. photons and gluons), and also the "composite" particles (e.g. protons and neutrons). [close the glossary] -Fforce In dynamics, the physical agent capable of altering the state of motionless or motion of a body. Nella dinamica, è l'agente fisico capace di alterare lo stato di quiete o di moto di un corpo. [close the glossary] field Region of space where a measurable physical greatness is measurable. [close the glossary] fundamental interactions They are the electromagnetic, strong, weak and gravitational interactions. The forces (the interactions) between two particles are transmitted (or, as we say, mediated) by means of the exchange of a third virtual particle (virtual, since it cannot be revealed). Each of the four interactions has its own virtual particle or quantum. The quantum of the electromagnetic interaction is the photons. The strong interaction is mediated by gluons. The weak interaction is transmitted by means of the W +, W - and Z0 bosons. The quantum of the gravitational interaction is the graviton (the latter not yet directly observed). [close the glossary] -Ggamma High energy photons emitted, for example, in the decay of atomic nuclei or in collisions between particles. [close the glossary] gluon The carrier particle of the strong interaction. [close the glossary] gravitational interaction The weakest of the four fundamental interactions. It's the interaction between particles due to their mass/energy. The carrier particle of the gravitational interaction is the graviton, not yet experimentally observed. [close the glossary] graviton The hypothetical carrier particle of the gravitational interaction. Not yet directly observed. [close the glossary] -H-I-Llast constituents The particles for which a further subdivision, at present, is not possible. They are the bottom step of the particle scale. For example: quarks and electrons are last constituents. Protons and neutrons are instead particles made of three quarks. [close the glossary] -Mmagnetic field The field associated with magnetic force. It unites with the electric field in the electromagnetic field. [close the glossary] mass (rest mass) The rest mass (m) of a particle is defined as the ratio between the energy E of an isolated (free) particle at rest, divided by the square of the light speed c (m= E/c 2). When Scientists talk about "mass", they always mean the "rest mass" m of the object in question. [close the glossary] muon An elementary particle, negatively charged (mu-). A last constituent of matter. It's like the elettron, but about 200 times heavier. It decays into an electron, a muonic neutrino and an electronic antineutrino. Its mean life is about two millionths of second. The corresponding antiparticle is the mu+. [close the glossary] -Nneutrino A neutral particle, having zero rest mass or very small (at the present time Scientists are still investigating) and zero electric charge. There are three kinds of neutrinos: electronic, muonic and tau. [close the glossary] neutron A neutral particle. It is made up of three quarks. Neutrons together with protons make the atomic nuclei. [close the glossary] nucleus (atomic) The central part of an atom. It is made up of protons and neutrons. It can be consider the "sun" of the atom. In the nucleus is concentrated almost all the mass of the atom. [close the glossary] -O-Pphoton (electromagnetic field quantum) The carrier particle of the electromagnetic interaction. It's electrically neutral. Note: in the story the light is imagined as being made of many balls (!) which represent the photons. [close the glossary] positron The antiparticle of the electron. It has the same mass but opposite charge of the electron. When an electron meets a positron, they annihilate giving rise to, in the simpler case, two energetic photons (gamma). [close the glossary] proton È il nucleo di un atomo di idrogeno. Ha carica elettrica positiva. È costituito da tre quark. Insieme al neutrone forma i nuclei atomici. The nucleus of a hydrogen atom, it has a positive electric charge. It is made up of three quarks. Together with the neutron it forms atomic nuclei. [close the glossary] -Qquantum The smallest discrete amount of any quantity. Examples: photons are the quanta of the electromagnetic field. The electron charge is the quantum of electricity. [close the glossary] quark A last constituents of matter. For example, a proton is formed of three quarks. There are various kinds of quarks called up, down, charm, strange, top and bottom. [close the glossary] -R-SSpecial Relativity Theory developed by Einstein. It is based on two hypotheses: the light speed c in the vacuum is constant, and the laws of Physics are the same for observers in relative motion with constant speed. Special Relativity supplies a new vision of timespace and provides the possibility to convert energy into mass (and, vice versa, mass into energy). Every system, with speed near to that of light, has to be analysed with the formulae of relativistic Mechanics rather than by classic formulae. [close the glossary] stable particle Does not decay. A particle is stable if there are no processes in which the particle disappears and different particles appear in its place. Example: protons and elettrons are stable. Instead, some particles live a short mean life, then decay into other particles. E.g. a neutron, isolated and at rest, decays after about 15 minutes into a proton, an electron and an antineutrino. [close the glossary] strong interaction The strongest of the four fundamental interactions of Nature. It is mediated by the gluons. It joins together quarks to make protons and neutrons, and, as "residual" strong force, unites protons and neutrons to form the atomic nuclei. [close the glossary] subnuclear particle Any particle that is small compared to the size of the atomic nucleus. The microscopic world is very rich in subnuclear particles with strange names. Examples: protons, neutrons, electrons, muons, neutrinos, quarks and so on. [close the glossary] -T-U-V-WW+, W-, Z0 boson Carrier particles of the weak interactions. [close the glossary] weak interaction A fundamental interaction of Nature. It is known above all to be present in decay processes. For example, it operates when a neutron decays into a proton, an electron and an antineutrino. At ordinary energies, the weak interaction is much weaker than the electromagnetic and the strong one. At very high energy, the weak interaction is unified with the electromagnetic one in the socalled electroweak interaction. [close the glossary] -X-Y-Z-