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OCR for page 142
Glossary of Physical Terms
Absolute zero. The temperature of -273.16°C, or -459.69°F, or zero
kelvin (O K), thought to be the temperature at which molecular
motion is at a minimum and a body has no heat energy.
Alpha particle. A positively charged particle consisting of two pro-
tons and two neutrons, identical with the nucleus of the helium atom;
emitted by several radioactive substances.
Angstrom. A unit of length equal to one ten-billionth of a meter (10-'°
m).
Anisotropy. The characteristic of a substance for which a physical
property varies in value with the direction in or along which the
measurement is made.
Antimatter. Material consisting of atoms that are composed of
positrons, antiprotons, and antineutrons.
Antineutron. The antiparticle to the neutron; a strongly interacting
baryon that has no charge, mass of 939.6 MeV, spin 1/2, and mean
life of almost 103 seconds.
Antinucleon. An antineutron or antiproton, that is, a particle having
the same mass as its nucleon counterpart but opposite charge or
opposite magnetic moment.
· · . ~ · .. . . .... .
Antiparticle. A counterpart to a particle, having mass, lifetime, and
spin identical to the particle but with charge and magnetic moment
. .
reverser in sign.
Antiproton. The antiparticle of the proton, a strongly interacting
142
OCR for page 143
GLOSSAR Y OF PHYSICAL TERMS 143
baryon that is stable, carries unit negative charge, has the same mass
as the proton (983.3 MeV), and has spin 1/2.
Astrophysics. The study of such physical properties of celestial
bodies as luminosity, size, mass, density, temperature, and chemical
composition; the study of the origin and evolution of these bodies.
Asymptotic freedom. In some particle-physics theories, the binding
force between two quarks decreases as their relative momentum
increases; equivalently, as two quarks approach, the force between
them disappears.
Atom. The individual structure that constitutes the basic unit of any
chemical element.
Atomic number. The number of protons in an atomic nucleus.
Atomic physics. The science concerned with the structure of the
atom. The characteristics of the elementary particles of which the
atom is composed and the processes involved in the interactions of
radiant energy with matter.
Atomic spectrum. The spectrum of radiations due to transitions
between energy levels in an atom, either absorption or emission.
Aurora. The most intense of the several lights emitted by the Earth's
upper atmosphere, seen most often along the outer realms of the
Arctic and Antarctic, where it is called the aurora borealis and
aurora australis, respectively; excited by charged particles from
space.
Baryon. A particle that can be transformed into a nucleon and some
number of mesons and lighter particles; any of a group of hadrons (as
nucleons) that undergo strong interactions and are held to be a
combination of three quarks.
Beta decay. Radioactive transformation of a nuclide in which the
atomic number increases or decreases by unity with no change in
mass number; the nucleus emits a beta particle.
Beta particle. An electron or positron emitted from a nucleus during
beta decay.
Big bang. A theory in astronomy, according to which the universe
originated billions of years ago from the explosion of a single mass of
material, so that the pieces are still hying apart.
Biophysics. The hybrid science involving the application of physical
principles and methods to study and explain the structures of living
organisms and the mechanics of life processes.
Black hole. A star with radius just outside the Schwarzschild radius;
it is invisible but can capture matter and light from the outside.
Boson. A particle (as a photon, meson, or alpha particle) whose spin
is zero or an integral number.
OCR for page 144
144 GLOSSARY OF PHYSICAL TERMS
"Breathing" mode. The vibrational state in which a nucleus under-
goes spherically symmetric radial expansion and contraction.
Charged particle. A particle whose charge is not zero; the charge of
a particle is added to its designation as a superscript with particles of
~ 1 and -1 (in terms of the charge of the proton) denoted by ~ arid
-, respectively.
Coherent anti-Stokes Raman scattering. Nonlinear spectroscopy
where laser light scattered from a sample undergoes an increase in
frequency (anti-Stokes behavior), derived from vibrational states of
the atoms or molecules in the sample.
Condensed matter ¢physics). The physics of the solid and liquid
states.
Cosmic rays. Electrons, muons, the nuclei of atoms, and photons
that impinge upon the Earth from all directions of space with nearly
the speed of light.
Cosmology. The study of the overall structure of the physical uni-
verse.
Crystallography. The branch of science that deals with the geometric
description of crystals and their internal arrangement.
Cyclotron. An accelerator in which charged particles are succes-
sively accelerated by a constant-frequency alternating electric field
that is synchronized with movement of the particles on spiral paths
in a constant magnetic field normal to their path.
Deuteron. The nucleus of the deuterium atom consisting of one
proton and one neutron.
Diabatic. A change in which the environment of a system alters too
rapidly for the system to read just continuously.
Diamagnetic. Having a magnetic permeability less than that of a
vacuum; slightly repelled by a magnet.
Dirac electron theory. Theory that accounts for spin angular momen-
tum of the electron and gives its magnetic moment and its behavior
in an electromagnetic field.
Doppler elect. The change in the observed frequency of a wave due
to relative motion of source and observer.
Electromagnetic theory.
Theory according to which light is an elec-
tromagnetic wave whose electric and magnetic fields obey Maxwell's
equations.
Electromagnetism. Magnetism produced by an electric current rather
than by a permanent magnet.
Electron. An elementary particle consisting of a charge of negative
electricity equal to about 1.602 x 10-~9 coulomb and having a mass
when at rest of about 9.109534 x 10-28 gram (or about 1/1836 that of
a proton).
OCR for page 145
GLOSSARY OF PHYSICAL TERMS 145
Electron accelerator.
energies.
Electron charge. The charge carried by an electron, equal to about
-1.602 x 10-~9 coulomb, or -4.803 x 10-~° statcoulomb.
Elementary particle. A particle that, in the present state of knowl-
edge, cannot be described as compound and is thus one of the
fundamental constituents of all matter.
Entropy. The degradation of the matter and energy in the universe to
an ultimate state of inert uniformity.
Epitaxy. Growth of one crystal on the surface of another crystal, in
which the growth of the deposited crystal is oriented by the lattice
structure of the substrate.
Equivalence Principle. In general relativity, the principle that the
observable local effects of a gravitational field are indistinguishable
from those arising from acceleration of the frame of reference.
Far-ultraviolet radiation. Ultraviolet radiation in the wavelength of
200 to 300 nanometers; germicidal effects are greatest in this range.
Femto-. Prefix meaning one quadrillionth (lo-~5) part of.
Fermion. A particle (as an electron, proton, or neutron) whose spin
quantum number is an odd multiple of l/2.
Ferromagnet. A substance with an abnormally high magnetic perme-
ability, a definite saturation point, and appreciable residual magne-
tism and hysteresis.
Fission. The division of an atomic nucleus into parts of comparable
mass; usually restricted to heavier nuclei such as isotopes of
uranium, plutonium, and thorium.
Fluorescence. Emission of, or the property of emitting, electromag-
netic radiation (usually as visible light) resulting from and occurring
only during absorption of radiation from some other source.
Free-electron laser. A laser in which beams of unbound electrons
interact with a strong magnetic field to produce tunable laser light.
Free radical. An atom or a diatomic or polyatomic molecule that
possesses at least one unpaired electron.
Fusion. Combination of two light nuclei to form a heavier nucleus
(and perhaps other reaction products) with release of some binding
A device that accelerates electrons to high
energy.
Galaxy. A large-scale aggregate of stars, gas, and dust. The aggregate
is a separate system of stars covering a mass range from 107 to 10~2
solar masses and ranging in diameter from 1500 to 300,000 light-
years.
Gamma ray. A high-energy photon, especially as emitted by a
nucleus in a transition between two energy levels.
General relativity. The theory of Einstein that generalizes special
OCR for page 146
146 GLOSSARY OF PHYSICAL TERMS
relativity to noninertial frames of reference and incorporates gravi-
tation and in which events take place in a curved space.
Geophysics. The physics of the Earth and its environment, i.e.,
earth, air, and (by extension) space.
Glass. A hard, amorphous, inorganic, usually transparent, brittle
substance made by fusing silicates, sometimes berates and phos-
phates, with certain basic oxides and then rapidly cooling to prevent
crystallization (NB: not the sense in which the term is used in the
term spin glass).
Gluon. A hypothetical, neutral, massless particle believed to bind
together quarks to form hadrons.
Gluon string. A particle-physics theoretical model to account for the
binding force between quarks that increases monotonically as they
are separated.
Gravitation. The mutual attraction among all masses in the universe.
Gravitational force. The force on a particle due to its gravitational
attraction to other particles.
Gravitational radiation. A propagating gravitational field predicted
by general relativity, which is produced by some change in the
distribution of matter; it travels at the speed of light, exerting forces
on masses in its path.
Gravitational redshift. A displacement of spectral lines toward the
red when the gravitational potential at the observer of the light is
greater than at its source.
Gyrotron. A device for producing microwave energy. Also called an
electron cyclotron maser.
Hadron. Any of the particles that take part in the strong interaction.
Hall conductivity. The reciprocal of the electrical resistivity associ-
ated with the Hall current.
Hall current. When an electric current in a conductor is placed in a
magnetic field that is perpendicular to the current a transverse
electric field is created, which in turn can support a transverse
current.
Heavy-ion linear accelerator. A linear accelerator that produces a
beam of heavy particles of high intensity and sharp energy; used to
produce transuranic elements and short-lived isotopes and to study
nuclear reactions, nuclear spectroscopy, and the absorption of heavy
. .
tons In matter.
Helicity. The component of the spin of a particle along its momen-
tum.
Hydrogen maser. A maser in which hydrogen gas is the basis for
providing an output signal with a high degree of stability and spectral
purity.
OCR for page 147
GLOSSAR Y OF PHYSICAL TERMS 147
Hypercharge. A quantum number conserved by strong interactions,
equal to twice the average of the changes of the numbers of an
isospin multiplet.
Hypernucleus. A nucleus containing one or more hyperons in addi-
tion to the nucleons.
Hyperon. A hadron that has baryon number B = + 1, i.e., that can be
transformed into a nucleon and some number of mesons or lighter
particles and that has a nonzero strangeness number.
Ionicity. The state of being characterized by, relating to, or existing
as ions.
Isospin multiplet. A collection of hadrons that have approximately
the same mass and the same quantum numbers except for charge.
Isotropy. The quality of a property that does not depend on the
direction along which it is measured or of a medium or entity whose
properties do not depend on the direction along which they are
measured.
Joule. Unit of energy, work, or quantity of heat equal to one
newton-meter.
JO particle. An unstable, neutral meson that has a mass about 3
times the mass of the photon.
K meson. See kaon.
Kaon. Collective name for four pseudoscalar mesons having masses
of about 495 MeV and decaying via weak interactions; an unstable
meson produced in high-energy particle collisions with its electri-
cally charged forms being 966.3 times more massive than the
electron; also known as K meson.
Lamb shift. A small shift in the energy levels of a hydrogen atom, and
of hydrogenlike ions, from those predicted by the Dirac electron
theory, in accord with principles of quantum electrodynamics.
Lambda hyperon (A). A quasi-stable baryon, forming an isotopic
singlet, having zero charge and hypercharge, a spin of 1/2, positive
parity, and mass of 1115.5 MeV.
Laser. A device that uses the maser principle of amplification of
electromagnetic waves by stimulated emission of radiation and
operates in the optical or infrared region. Derived from light
amplification by stimulated emission of radiation.
Laser interferometer. An interferometer that uses a laser as a light
source; because of the monochromaticity and high intrinsic brilliance
of laser light, it can operate with path differences in the interfering
beams of hundreds of meters, in contrast to a maximum of about 20
centimeters for classical interferometers.
Laser light. Coherent, nearly single-frequency, highly directional
OCR for page 148
148 GLOSSAR Y OF PHYSICAL TERMS
electromagnetic radiation emitted in the range from infrared to
ultraviolet and x-ray wavelengths.
Laser optics. Optical systems utilizing the properties of laser light.
Laser spectroscopy. A branch of spectroscopy in which a laser is
used as an intense, monochromatic light source; in particular, it
includes saturation spectroscopy, as well as the application of laser
sources to Raman spectroscopy and other techniques.
Lepton. Any of a family of particles (as electrons, muons, and
neutrinos) that have spin quantum number 1/2 and that experience no
strong interactions; a fermion having a mass smaller than the proton
mass.
Light. Electromagnetic radiation with wavelengths capable of caus-
ing the sensation of vision, ranging approximately from 4000 (ex-
treme violet) to 7700 angstroms (extreme red); more generally,
electromagnetic radiation of any wavelength.
Light-year. A unit of measurement of astronomical distance; it is the
distance light travels in one sidereal year and is equivalent to 9.461
x 10~2 kilometers or 5.879 x 10~2 miles.
Luminosity. In optics, a measure of the brightness of a light source;
in colliding-beam accelerators, a measure of the rate of collisions of
the particles in the colliding beams.
Macromolecule. A large molecule in which there is a large number of
-one or several relatively simple structural units, each consisting of
several atoms bonded together.
Magnetic hysteresis. Lagging of changes in the magnetization of a
substance behind changes in the magnetic field as the magnetic field
1S varlec .
Magnetic moment. A vector associated with a magnet, current loop,
particle, or such, whose cross product with the magnetic induction
(or alternatively, the magnetic-field strength) of a magnetic field is
equal to the torque exerted on the system by the field.
Magnetic monopole. A hypothetical particle carrying magnetic
charge; it would be a source for magnetic field in the same way that
a charged particle is a source for electric held.
Magnetic permeability. A factor, characteristic of a material, that is
proportional to the magnetic induction produced in a material
divided by the magnetic-field strength; it is a tensor when these
qualities are not parallel.
Magnetic resonance. A phenomenon exhibited by the magnetic spin
systems of certain atoms whereby the spin systems absorb energy at
specific (resonant) frequencies when subjected to magnetic fields
alternating at frequencies that are in synchronism with natural
frequencies of the system.
OCR for page 149
GLOSSAR Y OF PHYSICA ~ TERMS 149
Maser. A device for coherent amplification or generation of electro-
magnetic waves in which an ensemble of atoms or molecules, raised
to an unstable energy state, is stimulated by an electromagnetic wave
to radiate excess energy at the same frequency and phase as the
stimulating wave.
Mass number. The sum of the numbers of protons and neutrons in the
nucleus of an atom or nuclide.
Matter. The substance composing bodies perceptible to the senses;
includes any entity possessing mass when at rest.
Meson. Any of a group of hadrons (as the pion and Loon) that are
strongly interacting and have zero or an integer number of quantum
units of spin.
Metastability. The property of having only a slight margin of stabil-
ity.
Metrology. The science of weights and measures or of measurement.
Mho. A unit of conductance, admittance, and susceptance equal to
the conductance between two points of a conductor such that a
potential difference of 1 volt between these points produces a current
of 1 ampere; the conductance of a conductor in mhos is the
reciprocal of its resistance in ohms.
Microelectronics. The technology of constructing circuits and de-
vices in extremely small packages by various techniques.
Microemulsion. A homogenous, single-phase, thermodynamically
stable mixture of oil, water, and surfactant.
Million electron volts (Me VJ. A unit of energy commonly used in
nuclear and particle physics, equal to the energy acquired by an
electron in falling through a potential of 106 volts.
Molecular biology.
~ . . . . . .
That nart of biology which attempts to interpret
o~o~og~ca~ events In terms of the physicochemical properties of
molecules in a cell.
Molecular ion. A molecule possessing nonzero net electric charge.
Molecular physics. The study of the behavior and structure of
molecules, including the quantum-mechanical explanation of several
kinds of chemical binding between atoms in a molecule; directed
valence; the polarizability of molecules; the quantization of vibra-
tional' rotational, and electronic motions of molecules; and the
phenomena arising from intermolecular forces.
Molecule. A group of atoms held together by chemical forms; a
molecule is the smallest unit of matter that can exist by itself and
retain all its chemical properties.
Monte Carlo method. A technique that obtains a probabilistic ap-
proximation to the solution of a problem by using statistical sampling
techniques.
OCR for page 150
150 GLOSSAR Y OF PHYSICAL TERMS
Multiphoton spectroscopy. Nonlinear spectroscopy usually involv-
ing intense laser light enabling more than one photon to interact with
an atom within a time frame shorter than the decay time of the
atomic state.
Muon. Collective name for two semistable elementary particles with
positive and negative charge, which are leptons and have a spin of
1/2 and a mass of approximately 105.7 MeV.
Muonium. An atom consisting of an electron bound to a positively
charged muon by their mutual Coulomb attraction, just as an
electron is bound to a proton in the hydrogen atom.
Nano-. Prefix meaning one billionth (lo-9) part of.
Neutrino. A neutral lepton having zero rest mass and spin 1/2.
Neutron. An uncharged hadron that has a mass nearly equal to that
of the proton and is present in all known atomic nuclei except the
hydrogen nucleus.
Newton. The unit of force equal to one kilogram-meter per second
squared (I kg m/s2~.
Nonlinear optics. The study of the interaction of radiation with
matter in which certain variables describing the response of the
matter (such as electric polarization of power absorption) are not
proportional to variables describing the radiation (such as electric-
field strength or energy flux).
Nonlinear spectroscopy. Spectroscopy usually using laser light and
the nonlinear optical behavior of certain properties of matter; e.g.,
coherent anti-Stokes Raman scattering.
Nova. A star that suddenly becomes explosively bright (the term is a
misnomer because it does not denote a new star but the brightening
of an existing faint star).
Nuclear physics. The study of the characteristics, behavior, and
internal structures of the atomic nucleus.
Nucleon. A collective name for a proton or a neutron; these particles
are the main constituents of atomic nuclei, have approximately the
same mass, have a spin of l/2, and can transform into each other
through the process of beta decay.
Nucleosynthesis. The production of a chemical element from hydro-
gen nuclei (as in stellar evolution).
Nucleus. The central, positively charged, dense portion of an atom.
Nuclide. A species of atom characterized by the number of protons,
number of neutrons, and energy content in the nucleus; to be
regarded as a distinct nuclide, the atom must be capable of existing
for a measurable lifetime, generally greater than 10-~2 second.
Parity. A physical property of a wave function that specifies its three
behavior under an inversion, i.e., under simultaneous reflection of all
OCR for page 151
GLOSSAR Y OF PHYSICAL TERMS 151
three spatial coordinates through the origin; if the wave function is
unchanged by inversion, its parity is 1 (or even); if the function is
changed only in sign, its parity is -1 (or odd).
Particle physics. The branch of physics concerned with understand-
ing the properties and behavior of elementary particles, especially
through study of collisions or decays involving energies of hundreds
of MeV or more.
Pauli Exclusion Principle. The principle that no two fermions of the
same kind may simultaneously occupy the same quantum state.
Phase. A portion of a physical system (liquid, gas, solid) that is
homogeneous throughout, has definable boundaries, and can be
separated physically from other phases; the type of state of a system,
such as solid, liquid, or gas.
Phase transition. A change of a substance from one phase (e.g.,
solid, liquid, or gas) to another.
Phonon. A quantum of an acoustic mode of thermal vibration in a
crystal lattice.
Photoemission. The ejection of electrons from a solid (or less com-
monly, a liquid) by incident electromagnetic radiation.
Photoionization. The removal of one or more electrons from an atom or
molecule by absorption of a photon of visible or ultraviolet light.
Photon. A massless particle, the quantum of the electromagnetic
field, carrying energy, momentum, and angular momentum.
Photovoltaic. Of, relating to, or utilizing the generation of a voltage
when radiant energy falls on the boundary between two dissimilar
substances (as two different semiconductors).
Pion. A short-lived meson that is primarily responsible for the
nuclear force and that exists as a positive or negative particle with
mass 273.2 times the electron mass or as a neutral particle with mass
264.2 times the electron mass.
Planck's constant. A fundamental physical constant, the elementary
quantum of action; the ratio of the energy of a photon to its
frequency, it is equal to 6.62620 + 0.00005 x 10-34 joule-second;
symbolized by h.
Plasma. A collection of charged particles (as in the atmosphere of
stars or in a metal) containing about equal numbers of positive ions
and electrons, exhibiting some properties of a gas but differing from
a gas in being a good conductor of electricity and in being affected by
a magnetic field.
Plasma physics. The study of highly ionized gases.
Plate tectonics. Global tectonics based on a model of the Earth
characterized by a small number (10-25) of semirigid plates that float
on some viscous underlayer in the mantle; each plate moves more or
OCR for page 152
152 GLOSSARY OF PHYSICAL TERMS
less independently and grinds against the others, concentrating more
deformation, volcanism, and seismic activity along the periphery.
Positive energy theorem. A recent theory that shows that in general
relativity theory, any isolated system must have a positive value for
its total energy.
Positron. An elementary particle having mass equal to that of the
electron and having the same spin and statistics as the electron but
a positive charge equal in magnitude to the electron's negative
charge; the antiparticle of the electron.
Positronium. The bound state of an electron and a positron.
Proton. A hadron that is the positively charged constituent of ordi-
nary matter and, together with the neutron, is a building stone of all
atomic nuclei; its mass is approximately 938 MeV.
Proton accelerator. A particle accelerator that accelerates protons to
high energies, as opposed to one that accelerates heavier ions or
electrons.
Pulsar. A celestial radio source, emitting intense short bursts of radio
emission; the periods of known pulsars range between 33 millisec-
onds and 3.75 seconds, and pulse durations range from 2 to about 150
milliseconds, with longer-period pulsars generally having a longer
pulse duration.
Quantize. To restrict an observable quantity, such as energy or
angular momentum, to a discrete set of values, to subdivide (as
energy) into small but measureable increments.
Quantized Hall effect. The appearance of quantum levels in the Hall
conductivity for a two-dimensional conductor in a magnetic field.
Quantum. For certain physical quantities, a unit such that the values
of the quantity are restricted to integral multiples of this unit (e.g.,
the quantum of angular momentum is Planck's constant divided by
2~; an entity resulting from quantization of a field or wave, having
particlelike properties such as energy' mass, momentum, and angu-
lar momentum (e.~., the photon is the quantum of an electromagnetic
field, and the phonon is the quantum of a lattice vibration).
Quantum chromodynamics. The quantum theory that describes the
strong interactions that bind quarks together to form hadrons.
Quantum electrodynamics. The quantum theory of electromagnetic
radiation, synthesizing the wave and corpuscular pictures, and of the
interaction of radiation with electrically charged matter, in particular
with atoms and their constituent electrons.
Quantum mechanics. The modern theory of matter, of electromag-
netic radiation, and of the interaction between matter and radiation;
it differs from classical physics, which it generalizes and supersedes,
mainly in the realm of atomic and subatomic phenomena.
OCR for page 153
GLOSSARY OF PHYSICAL TERMS 153
Quark. Hypothetical elementary particles that have charges whose
magnitudes are 1/3 or 2/3 of the electron charge; quarks are thought
to come in several types (as up, down, strange, charmed, and
bottom) and are held to be a constituent of hadrons.
Quark-gluon model. The particle-physics model of the constituents of
hadrons and the force that binds them; see quantum chromodynam-
iCS.
Radiation pressure. The pressure exerted by electromagnetic radia-
tion on objects on which it impinges.
Radio astronomy. The study of celestial objects by measurement and
analysis of their emitted electromagnetic radiation in the wavelength
range from roughly 1 millimeter to 30 meters.
Raman spectroscopy. Nonlinear spectroscopy named for Sir
Chandrasekhara Venkata Raman (1888-1970), Indian physicist.
Relativistic magnetron. A device to produce microwaves that uses
electrons moving at velocities near the speed of light in a magnetic
field.
Renormalization group approach or theory. A mathematical tech-
nique to avoid infinities that occur in certain classes of physical
theories.
Resistivity. The electrical resistance offered by a material to the flow
of current times the cross-sectional area of current flow and per unit
length of current path; the reciprocal of the conductivity.
Robotics. Technology dealing with the design, construction, and
operation of robots in automation.
Schwarzschild radius. For a given body of matter, a distance equal to
the mass of the body times the gravitational constant divided by the
square of the speed of light.
Second-order Doppler elect. At velocities close to the speed of light,
additional Doppler effects may be detected even in cases where the
source and observer are moving only transversely.
Semiconductor. A solid crystalline material whose electrical conduc-
tivity is intermediate between that of a metal and an insulator,
ranging from about 105 mhos to 10-7 mho per meter, and is usually
strongly temperature dependent.
Semiconductor laser. A laser in which the wavelength of the coher-
ent light beam is determined by a semiconductor compound.
Sidereal year. The time period relative to the stars of one revolution
of the Earth about the Sun; it is about 365.2564 mean solar days.
Sigma-zero (I) particle. An unstable elementary particle of the
baryon family, of neutral charge, with a mass about 1.4 times the
mass of the proton.
OCR for page 154
154 GLOSSARY OF PHYSICAL TERMS
Soft x ray. An x ray having a comparatively long wavelength and
poor penetrating power.
Solar mass. The mass of the Sun, 2 x 103° kg.
Solar physics. The scientific study of all physical phenomena con-
nected with the Sun; it overlaps with geophysics in the consideration
of solar-terrestrial relationships such as the connection between
solar activity and auroras.
Solid. A substance that has a definite volume and shape and resists
forces that tend to alter its volume or shape; a crystalline material,
i.e., one in which the constituent atoms are arranged in a three-di-
mensional lattice, periodic in three independent directions.
SolitonfsJ. Solitary waves (as in a gaseous plasma) that retain their
phase and speed after colliding with each other.
Space charge. An electric charge distributed throughout a three-di-
. .
menslona~ . region.
Spectroscopy. The branch of physics concerned with the production,
measurement, and interpretation of electromagnetic spectra arising
from either emission or absorption of radiant energy by various
substances.
Spin. The intrinsic angular momentum of a particle or nucleus, which
exists even when the particle is at rest, as distinguished from orbital
angular momentum.
Spin glass. A state of matter in which the magnetic spins of randomly
located atoms freeze in direction at low temperature; often general-
ized to other systems.
Strong force. See strong interaction.
Strong interaction. One of the fundamental interactions of elemen-
tary particles, primarily responsible for nuclear forces and other
interactions among hadrons.
Substrate. The physical material on which a microcircuit is fabri-
cated.
Superconducting magnet. An electromagnet whose coils are made of
a superconductor with a high transition temperature and extremely
high critical field; it is capable of generating magnetic fields of
100,000 oersteds and more with no steady power dissipation.
Superconductivity. A property of many metals, alloys, and chemical
compounds at temperatures near absolute zero by virtue of which
their electrical resistivity vanishes and they become strongly dia-
magnetic.
Superdense. Densities that are greater than that for an ordinary
nucleus, such as may exist in the core of novae.
OCR for page 155
GLOSSAR Y OF PH YSICA ~ TERMS 1 5 5
Supernova. A star that suddenly bursts into very great brilliance as a
result of its blowing up; it is orders of magnitude brighter than a nova.
Supersymmetry. A particle-physics theory that attempts to unite two
particle classes of fermions and bosons into a unified theory.
Symmetry. The property of remaining invariant under certain
changes (as of orientation in space, of the sign of the electric charge,
of parity, or of the direction of time flow).
Synchrotron. A device for accelerating electrons or protons in closed
orbits in which the frequency of the accelerating voltage is varied (or
held constant in the case of electrons) and the strength of the
magnetic field is varied so as to keep the orbit radius constant.
Tau particle Lor tau lepton (I. A short-lived elementary particle of
the lep ton family that exists in positive and negative charge states
and has a mass about 3500 times heavier than an electron.
Tectonics. A branch of geology concerned with structure, especially
with folding and faulting.
Tera-. Prefix meaning one trillion (10~21.
Tesla. Unit of magnetic flux intensity equal to one weber per square
meter (1 Wb/m2), or one volt second per square meter (1 V s/m21.
Three-degree radiation. The remnant radiation, at microwave fre-
quencies, of the big bang.
Tokamak. A device for confining plasma within a toroidal chamber,
which produces plasma temperatures, densities, and confinement
times greater than those produced by any other such device.
Tomography. A diagnostic technique using x-ray photographs in
which the shadows of structures before and behind the section under
scrutiny do not show.
Toroidal. Of, relating to, or shaped like a torus; doughnut-shaped.
Upsilon particle (Y). Any of a group of unstable electrically neutral
mesons that have a mass about 10 times that of a proton.
Vacuum polarization. A process in which an electromagnetic field
gives rise to virtual electron-positron pairs that effectively alter the
distribution of charges and currents that generated the original
electromagnetic field.
Valley of stability. The region on a chart of the nuclides where the
majority of stable nuclides are found.
W+. A positively charged boson with a mass about 87 times that of
the proton that mediates the weak force.
W-. The negatively charged counterpart to the W+.
Wave. A disturbance that propagates from one point in a medium to
other points without giving the medium as a whole any permanent
displacement.
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156 GLOSSARY OF PHYSICAL TERMS
Weak coupling. The coupling of four fermion fields in the weak
interaction, having a strength many orders of magnitude weaker than
that of the strong or electromagnetic interactions.
Weak force. See weak interaction.
Weak interaction. One of the fundamental interactions among ele-
mentary particles responsible for beta decay of nuclei and for the
decay of particles with lifetimes greater than about 10-~° second,
such as muons, K mesons, and lambda hyperons; it is several orders
of magnitude weaker than the strong and electromagnetic interac-
tions.
X-ray astronomy. The study of x rays mainly from sources outside
the solar system; it includes the study of novae and supernovae in
the Milky Way Galaxy, together with extragalactic radio sources.
X-ray tomography. See tomography.
Z°. A neutral boson with a mass about 100 times that of the proton
that mediates the weak force.
Representative terms from entire chapter:
magnetic field
