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OCR for page 203
Glossary
ACRONYMS AND ABBREVIATIONS
ATLAS
CEBAF
CERN
DDHF
DOE
eV
fm
Alternating Gradient Synchrotron, Brookhaven
National Laboratory
Argonne Tandem Linear Accelerator System, Argonne
National Laboratory
Continuous Electron Beam Accelerator Facility,
proposed for construction at Newport News, Virginia.
(Formerly called the National Electron Accelerator
Laboratory, NEAL)
CEN Saclay Centre d' etudes Nucleaires (Center for Nuclear
Studies) de Saclay, Gif-sur-Yvette, France
Centre Europeenne pour la Recherche Nucleaire
(European Organization for Nuclear Research; also
called the European Laboratory for Particle Physics),
Geneva, Switzerland
density-dependent Hartree-Fock (method)
Department of Energy
electron volt
fermi (10-~5 m)
Grand Accelerateur National d'Ions Lourds (National
Large Heavy-Ion Accelerator), Caen, France
giga-electron volt (109 eV)
203
OCR for page 204
204 GLOSSAR Y
GSI Gesellschaft fur Schwerionenforschung (Laboratory for
Heavy-Ion Research), Darmstadt, West Germany
HHIRF Holifield Heavy Ion Research Facility, Oak Ridge
National Laboratory
IUCF Indiana University Cyclotron Facility
JACEE Japanese-American Cooperative Emulsion Experiment
JINR Joint Institute for Nuclear Research, Dubna, USSR
KKK Kokuritsu Ko-Enerugii Butsurigaku Kenkyusho
(National High-Energy Physics Laboratory), Tsukuba,
Japan
keV kilo-electron volt (103 eV)
km kilometer
LAMPF Los Alamos Meson Physics Facility, Los Alamos
National Laboratory
LEAR Low-Energy Antiproton Ring at CERN
MeV mega-electron volt (106 eV)
msec millisecond
NSAC Nuclear Science Advisory Committee of the
Department of Energy and the National Science
Foundation
NSCL National Superconducting Cyclotron Laboratory,
Michigan State University
NSF National Science Foundation (United States)
QCD quantum chromodynamics
QED quantum electrodynamics
QHD quantum hadrodynamics
RNC relativistic nuclear collider
SIN Swiss Institute of Nuclear Research, Villigen,
Switzerland
SLAC Stanford Linear Accelerator Center
SURA Southeastern Universities Research Association
TeV tera-electron volt (10'2 eV)
TRIUMF Tri-University Meson Facility, Vancouver, British
Columbia, Canada
TUNL Triangle Universities Nuclear Laboratory, Duke
University
V volt
OCR for page 205
G f OSSAR Y 205
TECHNICAL TERMS
Accelerator. A machine designed to accelerate charged particles to
some energy suitable for bombarding a target and studying the
resulting nuclear reactions. The four major kinds of accelerators are
Van de Graaff electrostatic accelerators, linear accelerators, cyclo-
trons, and synchrotrons.
Allowed process. Any physical process that is allowed by a given
theory; it may or may not have been observed to occur. See also
Forbidden process.
Alpha particle. The nucleus of the helium-4 atom, consisting of two
protons and two neutrons. It is also a product of radioactive decay.
See also Beta particle.
Antimatter. Matter that consists of antiparticles (e.g., positrons and
antinucleons) instead of ordinary particles.
Antiparticle. A particle that is identical to an ordinary particle in
every respect except for having certain opposite elementary proper-
ties, such as electric charge. For every particle, there is an antipar-
ticle; some particles are their own antiparticles.
Asymptotic freedom.
. ~. ,
A phenomenon in which the strength of the
color force between quarks approaches zero when the quarks come
very close together and increases when they move apart. See also
Quark confinement.
Atom. The smallest unit of a chemical element, consisting of a central
nucleus surrounded by orbital electrons. It is held together by the
electromagnetic force.
Atomic number, Z. The number of protons in an atomic nucleus.
Bag model. The model of hadron structure that views the hadron as
an impenetrable bag from which its constituent quarks cannot escape
under any ordinary conditions. See also Quark confinement.
Baryon. One of the two classes of hadrons, consisting of three quarks
or three antiquarks confined in a bag. All baryons are fermions; the
three principal kinds are nucleons, hyperons, and baryon reso-
nances. See also Meson.
Baryon resonance. An excited state of a baryon, having a greater
mass and an extremely short lifetime. The most common baryon
resonances are the nucleon resonances and delta resonances.
Beta particle. A synonym for an electron or a positron when it is
emitted in the process of beta radioactivity, or beta decay. See also
Alpha particle.
Binding energy. A measure of the strength with which a given
OCR for page 206
206 G. f OSSAR Y
physical system is bound; it is the amount of energy needed to break
the bond in question and separate the particles.
Boson. Any particle or group of particles (such as a nucleus) having
an integral value of spin. Among the bosons, in addition to the
elementary vector bosons, are the mesons. The Pauli exclusion
principle does not apply to bosons.
Central collision. A head-on collision of two particles, with near-
maximum overlap of their cross-sectional areas; the impact param-
eter is near zero.
Collective model. Any model of nuclear structure in which the
nucleons are viewed as moving in concert under the influence of
some force. See also Liquid-drop model.
Colliding-beam accelerator. An accelerator in which the projectile
particles in two counterdirectional beams collide in flight.
Color. The name for a property ascribed to quarks and gluons,
somewhat analogous to electric charge. There are three such colors.
Color force. The force through which quarks and gluons interact, by
the exchange of gluons. It is the basis for quantum chromodynamics.
See also Strong force.
Compound nucleus. A heavy nucleus formed by the collision of two
lighter nuclei. See also Fusion.
Conservation law. A law stating that in every conceivable interaction
the total amount of a certain quantity (e.g., electric charge or
mass-energy) cannot change, i.e., the quantity is conserved.
Coulomb barrier. The repulsive Coulomb force between a positively
charged target nucleus and any positively charged projectile, inhib-
iting their close contact.
Coulomb force. The force of electrical attraction or repulsion be-
tween particles of unlike charge or like charge, respectively.
Cross section. A measure of the probability that an interaction of a
given kind will occur; it is expressed in units of area and is one of the
most commonly measured quantities in nuclear physics.
Current. See Exchange current.
Cyclotron. A circular accelerator in which the charged particles spiral
outward from the center of the machine as they are given repeated
energy boosts from an alternating electric field in a fixed magnetic
field.
Decay. Any process in which a radioactive nuclide or an unstable
particle or system changes to another, lower-energy form by emitting
one or more particles or gamma rays.
Deep-inelastic scattering. A noncentral collision in which a great deal
of the collision energy is converted to internal energy of the nuclei.
OCR for page 207
GLOSSAR Y 207
Delta resonance. A baryon resonance; delta resonances differ in
isospin from the nucleon resonances.
Detector. Any device that can detect the presence of a particle or
nuclear fragment produced in a nuclear reaction and measure one or
more of its physical properties.
Deuteron. The nucleus of deuterium (hydrogen-2), consisting of one
proton and one neutron.
Electromagnetic force. A component of the unified electroweak
force, responsible for holding atoms together and for many other
phenomena. It is experienced by all particles with an electric charge
or magnetic moment, through the exchange of photons. See also
Weak force.
Electron. A light, negatively charged lepton with a mass of 0.511
MeV, about 1/1840 that of a nucleon. See also Beta particle,
Positron, Muon, and Tauon.
Electron volt (eV). The amount of energy acquired by any particle
with unit electric charge when it is accelerated through a potential
difference of 1 volt. In various multiples, such as keV, MeV, or GeV,
it is used as a measure of beam energy, of rest mass, and of
temperature.
Electrostatic accelerator. See Van de Grauff electrostatic accelera-
tor.
Electrostatic force. See Coulomb force.
Electroweak force. One of the three fundamental forces, comprising
the actions of both the electromagnetic and weak forces, whose
unification revealed them to be two very different aspects of one
underlying force. See also Gravitation and Strong force.
Elementary particle. A particle that, as far as is known, has no
internal structure. The elementary particles are the leptons, quarks,
and elementary vector bosons. Hadrons are not elementary parti-
cles.
Elementary vector boson. One of the three classes of elementary
particles, consisting of photons, gluons, and the intermediate vector
bosons; these particles are the carriers of the fundamental forces.
See also Lepton and Quark.
Equation of state. A mathematical equation that describes the behav-
ior of a physical system over a wide range of conditions, on the basis
of a few measurable quantities called state variables.
Exchange current. The current, either charged or neutral, arising
from the exchange of charged or neutral virtual particles as carriers
of a force between two particles.
OCR for page 208
208 GLOSSAR Y
Exchange particle. Any virtual particle that acts as the carrier of a
force between two particles.
Excited state. Any energy level of a bound system of particles, such
as a nucleus, above the ground state.
Exclusion principle. See Pauli exclusion principle.
Fermi. The common name for the femtometer (10-~5 meter), the
characteristic dimension of nuclear and particle physics. The diam-
eter of a nucleon is about 1 fermi.
Fermion. Any particle or group of particles (such as a nucleus) having
a half-integral value of spin. All leptons, quarks, and baryons are
fermions. The Pauli exclusion principle applies only to fermions.
Fission. The process-either spontaneous or induced in which a
nucleus of a heavy element, such as uranium, splits into two lighter
nuclei, with the release of energy. See also Fusion.
Flavor. The name for the property that distinguishes the six basic
kinds of quarks: up, down, strange, charm, bottom, and top. Each
flavor can have any of the three different quark colors.
Forbidden process. Any physical process that is forbidden by a given
theory and that typically has never been observed to occur. If it is
observed, the theory is compromised. See also Allowed process.
Fusion. The process in which two nuclei of light elements, such as
hydrogen or helium, fuse to form one heavier nucleus, with the
release of energy. Also, the process in which two heavier nuclei fuse
to form a compound nucleus, which may or may not quickly split
apart. See also Fission.
Gamma ray. An extremely energetic photon, emitted in many nu-
clear reactions and in the decay of many radioactive nuclides and
unstable particles.
Gluon. Any of eight massless, colored particles that are the carriers
of the color force. They are elementary vector bosons and are
confined within hadron bags.
Grand Unified Theory. A mathematical formalism that seeks to unite
the strong and electroweak forces into a single underlying force at a
deeper level, in the same way that electromagnetism and the weak
force were unified into the electroweak force.
Gravitation. One of the three fundamental forces, responsible for the
large-scale structure of the universe. It is experienced by all particles
but is so extremely weak that its effect on any but macroscopic
objects is negligible. See also Electroweak force and Strong force.
Ground state. The lowest (normal) energy level of a bound system of
particles, such as a nucleus. See also Excited state.
OCR for page 209
GLOSSAR Y 209
Hadron. Any particle that experiences the strong force. The two
classes of hadrons are baryons and mesons.
Hadronic matter. A state of nuclear matter encompassing normal
nuclei as well as baryon resonances and other nonnucleonic baryons.
Half-life. The time it takes for half of all the nuclei in a radioactive
sample to decay to some other form; each type of radionuclide has a
characteristic half-life.
Heavy ion. Any ion with a mass number greater than about 40; this
definition is arbitrary but convenient.
Heisenberg uncertainty principle. A fundamental quantum-
mechanical law, stating that it is impossible to measure simulta-
neously both the position and momentum of a particle with arbi-
trarily great precision; the structure of quantum mechanics leads to
an analogous statement for energy and time. It plays an important
role in nuclear processes.
High energy. For the purposes of this report, a projectile energy
(somewhat arbitrarily) of 100 MeV per nucleon to 1 GeV per
nucleon. See also Relativistic energy.
Hypernucleus. Any nucleus in which a nucleon has been replaced by
a hyperon.
Hyperon. Any baryon containing one or more strange quarks; the
most common such baryon is the lambda hyperon.
Impact parameter. A measure of the degree of overlap of the
cross-sectional areas of two particles in a collision; it is zero in an
idealized, perfectly central collision and significantly greater than
zero in peripheral collisions.
Independent-particle model. Any model of nuclear structure in which
the motion of a single nucleon is viewed in terms of an average force
field produced by all the other nucleons. See also Shell model.
Intermediate vector boson. One of three massive, charged or neutral
particles that are the carriers of the weak force. Designated as W+,
W-, and Z°, they are elementary vector bosons, as are photons and
gluons.
Ion. In general, any atom that has lost or gained one or more
electrons. In nuclear physics, especially in connection with acceler-
ators, the term is used as a synonym for nucleus, because frequently
ions with some electrons still bound are accelerated; bare nuclei,
however, are also referred to as ions.
Isospin. A quantum number ascribed to hadrons that permits them to
be grouped in simpler ways, such as a generalized nucleon that in
different isospin states is either a proton or a neutron.
Isotope. Any specific nucleus of a given chemical element. The
OCR for page 210
210 GO OSSARY
isotopes of an element (which is defined by its proton number) differ
from one another in their neutron number. See also Nuclide.
Kaon. A strange meson, i.e., one that contains a strange quark. Like
pions, kaons can be positive, negative, or neutral.
Lepton. One of the three classes of elementary particles, consisting
of electrons, muons, tauons, their associated neutrinos, and the six
corresponding antiparticles. All 12 leptons are fermions; they inter-
act via the weak force but not the strong force. See also Elementary
vector boson and Quark.
Light ion. Any hydrogen ion or helium ion. Lithium ions are some-
times also included in this category.
Linear accelerator. A type of accelerator in which the charged
particles follow a straight path as they are given repeated energy
boosts from a series of electric fields.
Liquid-drop model. A collective model in which the properties of the
nucleus are viewed in terms analogous to those of an ordinary drop
of liquid.
Low energy. For the purposes of this report, a projectile energy
(somewhat arbitrarily) of less than about 10 MeV per nucleon.
Many-body problem. The mathematical problem of describing the
dynamic behavior of any system of three or more mutually interact-
ing particles (such as most nuclei).
Mass-energy equivalence. The principle that mass and energy are
equivalent, interconvertible quantities. In nuclear physics, masses
are customarily expressed in terms of an equivalent energy, usually
in units of MeV.
Mass number, A. The number of protons plus neutrons (A = Z + N)
in an atomic nucleus. Nuclei of different elements can have the same
mass number.
Medium energy. For the purposes of this report, a projectile energy
(somewhat arbitrarily) of 10 to 100 MeV per nucleon.
Medium ion. Any ion from lithium up to a mass number of about 40;
this definition is arbitrary but convenient.
Meson. One of the two classes of hadrons, consising of a quark-
antiquark pair confined in a bag. All mesons are bosons; among the
more common ones are pions and kaons. Mesons are the principal
carriers of the strong force between hadrons. See also Baryon.
Meson-exchange model. A model of nuclear interactions that takes
into account the effects of the exchange of virtual mesons between
nucleons, rather than considering the nuclei to be composed only of
nucleons.
Muon. A moderately massive, negatively charged lepton that appears
~. .
OCR for page 211
GLOSSARY 21 1
to be identical to the electron in every respect except for its greater
mass. See also Tauon.
Neutrino. Any of three kinds of neutral, presumably massless leptons
that are emitted in weak-interaction processes, such as beta decay.
Neutrino oscillation. The postulated phenomenon whereby neutrinos
change periodically from one form (electron neutrino, muon neu-
trino, or tauon neutrino) to another during their flight through space.
Such behavior has not been observed.
Neutron. An uncharged (neutral) baryon with a mass almost identical
to that of the proton.
Neutron number, N. The number of neutrons in an atomic nucleus.
Nuclear matter. Matter that consists primarily of nucleons whether
in atomic nuclei or in an extended state, as in neutron stars.
Nuclear reaction. Any change brought about in the states of two
nuclei as a result of their collision with each other.
Nuclear spectroscopy. The study of the detailed structure of nuclei
their spectrum of energy levels, associated physical properties,
decay modes, and other properties.
Nucleon. A proton or a neutron; nucleons are the least massive, most
stable baryons.
Nucleon resonance. A baryon resonance that is an excited state of a
nucleon; nucleon resonances differ is isospin from the delta reso
nances.
Nucleus. The small, dense, positively charged core of the atom,
consisting primarily of nucleons (protons and neutrons). It is held
together by the strong force, through the exchange of mesons
between the nucleons. See also Ion.
Nuclide. Any specific nucleus, as defined by a unique combination of
proton number and neutron number. See also Isotope.
Parity. A fundamental symmetry principle governing the nature of
physical laws when the spatial coordinates of the system are totally
reflected. The parity principle is obeyed (i.e., nature exhibits no
spatial preference) in the strong and electromagnetic interactions,
but it appears always to be violated in weak interactions, such as
beta decay.
Pauli exclusion principle. A fundamental quantum-mechanical law,
obeyed by fermions but not by bosons, stating that in any system of
particles, such as a nucleus, no two fermions are allowed to coexist
in the identical quantum state. It plays a dominant role in determin-
ing nuclear structures.
Phase transition. A change in the physical state of a system from one
form to a different form (e.g., ice to water).
OCR for page 212
212 GLOSSARY
Photon. A massless, neutral particle that is the quantum of electro-
magnetic radiation and the carrier of the electromagnetic force. It is
one of the elementary vector bosons.
Pion. The most commonly observed meson, existing in any of three
charge states: positive, negative, and neutral. Virtual plans exist in
nuclei and are important for an understanding of nuclear structure.
Positron. The positively charged antiparticle of the electron.
Proton. A positively charged baryon with a mass of 938 MeV, about
1840 times greater than that of the electron.
Proton number, Z. The number of protons in an atomic nucleus.
Quantum. The smallest possible unit of energy associated with any
change in a physical system. The best-known example of a quantum
of energy is the photon.
Quantum chromodynamics (QCD). The quantum field theory of the
color interaction between quarks and gluons. It is also loosely
referred to as the quantum field theory of the strong interaction
which derives from the color interaction.
Quantum electrodynamics (QED'. The quantum field theory of the
electromagnetic interaction between any particles with electric or
magnetic properties.
Quantumfield theory. A mathematical formalism, based on relativity
and quantum mechanics, that describes one of the fundamental
interactions. The two most important such theories are quantum
electrodynamics and quantum chromodynamics.
Quantum hadrodynamics (QHD). A model quantum field theory that
attempts to account for the actions of the strong force in terms of the
hadrons themselves rather than of their constituent quarks and
gluons.
(quantum mechanics. The physical theory that underlies all phenom-
ena at the level of molecules, atoms, nuclei, and elementary parti-
cles.
Quark. One of the three classes of elementary particles. There are six
basic kinds of quarks (quark flavors) and six corresponding antipar-
ticles. All 12 quarks are fermions; they interact via the color force as
well as the weak force. All have a fractional electric charge and are
confined within hadron bags. See also Elementary vector boson and
Lepton.
Quark confinement. The observation that it is apparently impossible,
under any ordinary conditions, for quarks to escape from their
hadron bags and exist as free particles. See also Asymptotic free-
dom.
Quark-gluon plasma.
An extreme state of matter in which quarks and
OCR for page 213
GLOSSARY 213
gluons are Reconfined and are free to move about in a much larger
volume than that of a single hadron bag. It has never been observed
on earth.
Radioactivity. Any of several kinds of processes in which a nuclide
changes to another nuclide by the emission of one or more particles.
Relativistic energy. A projectile energy greater than about 1 GeV per
nucleon, i.e., an energy comparable with or greater than the
particle's rest mass.
Relativity. The theory of space and time (special relativity) that
describes the nature of physical laws in terms of postulates regarding
the speed of light and the observation of motion made from moving
frames of reference.
Resonance. A large increase in the amplitude of oscillation of a
physical system when it is acted on by an external driving force that
oscillates at or near a particular frequency, the resonant frequency of
the system. Also, an extremely unstable (short-lived) particle state.
See also Baryon resonance.
Rest mass. The mass of a particle when it is not moving with respect
to some frame of reference (such as the laboratory). The mass of a
moving particle is greater than its rest mass. See also Relativistic
energy.
Shell model. An independent-particle model in which the nucleons
are viewed as occupying a series of shells analogous to those of the
electrons in the theory of atomic structure.
Spin. An intrinsic property of all particles and nuclei, analogous to
rotation about an axis. Spin, however, occurs only in multiples of a
basic quantum mechanical unit of measure. Particles having an
integral value of spin are bosons; particles having a half-integral
value are fermions.
Spontaneousfission. See Fission.
Standard Model. The combined (but not yet unified) theories of the
electroweak interaction and quantum chromodynamics, with which
all known facts of nuclear physics and elementary particle physics
are consistent.
State variable. One of a minimum set of measurable quantities whose
values are sufficient to define the state of a given physical system and
predict its behavior over a wide range of conditions. See also
Equation of state.
Strangeness. The property associated with the strange quark or anv
, . . · ·
_A _ = ~^ ~ ~
particle containing a strange quark.
Strong force. One of the three fundamental forces, responsible for
holding nuclei together. It is experienced by all the hadrons through
OCR for page 214
214 GLOSSARY
the exchange of mesons and is actually a vestige of the much
stronger color force between quarks and gluons. See also
Electroweak force and Gravitation.
Sum rule. A rule that sets an upper limit on the magnitude of some
quantity within the framework of a given model.
Symmetry principle. A fundamental principle governing the nature of
physical laws under the effect of a symmetry transformation of some
kind. Two of the most important symmetry principles in nuclear and
particle physics are parity and time-reversal invariance.
Synchrotron. A ring-shaped accelerator in which the charged parti-
cles follow a fixed circular path as they are given repeated energy
boosts from a radio-frequency field in a time-varying magnetic field.
Tauon. A very massive, negatively charged lepton that appears to be
identical to the electron in every respect except for its much greater
mass. See also Muon.
Time-reversal invariance. A fundamental symmetry principle gov-
erning the nature of physical laws when the direction of the flow of
time is considered to be reversed.
Uncertainty principle. See Heisenberg uncertainty principle.
Van de GraaJf electrostatic accelerator. A type of accelerator in
which the charged particles are given a single energy boost by
passing through a very large electrostatic potential drop.
Vector boson. Any spin-1 boson that acts as the carrier of a force
between two particles. See also Virtual particle.
Virtual particle. A particle, typically a boson, whose ephemeral
existence serves to carry a force between two material particles. The
virtual particle appears spontaneously near one of the two particles
and disappears near the other one. Under certain conditions, a
virtual particle can become a material particle.
Weakforce. A component of the unified electroweak force, respon-
sible for the decay of many radioactive nuclides and unstable
particles and for all neutrino interactions. It is experienced by all
leptons, quarks, and hadrons, through the exchange of intermediate
vector bosons. See also Electromagnetic force.
Representative terms from entire chapter:
elementary vector
