Download No 7 Glossary

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.
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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.
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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.
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antiproton
The antiparticle of the proton. It has the same mass as the proton, but opposite electric charge.
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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.
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-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.
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charge (electric charge)
Property of a particle which determines its participation in the electromagnetic interaction.
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C.E.R.N. (European Council for Nuclear Research)
The Center, one of the most advanced for nuclear research, is located near Geneva,
Switzerland.
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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.
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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).
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-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.
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-Eelectric field
The field associated with electric force. It is united with the magnetic field in the electromagnetic
field.
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electromagnetic field
The field associated with electromagnetic force. This unites the electric and magnetic field.
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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.
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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!
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electron microscope
A microscope that uses an electron beam instead of light (photons), for lighting.
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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).
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-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.
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field
Region of space where a measurable physical greatness is measurable.
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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).
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-Ggamma
High energy photons emitted, for example, in the decay of atomic nuclei or in collisions between
particles.
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gluon
The carrier particle of the strong interaction.
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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.
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graviton
The hypothetical carrier particle of the gravitational interaction. Not yet directly observed.
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-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.
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-Mmagnetic field
The field associated with magnetic force. It unites with the electric field in the electromagnetic
field.
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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.
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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+.
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-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.
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neutron
A neutral particle. It is made up of three quarks. Neutrons together with protons make the atomic
nuclei.
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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.
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-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.
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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).
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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.
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-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.
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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.
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-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.
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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.
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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.
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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.
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-T-U-V-WW+, W-, Z0 boson
Carrier particles of the weak interactions.
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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.
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