passes through the medium.
of charged
particles, such as electrons,
protons, or heavy ions, for research in high-energy and nuclear physics,
synchrotron radiation research, medical therapies, and some industrial
applications. The accelerator at SLAC is an electron
accelerator. More Information: Accelerator,
Accelerator
Operations, Copper Structure,
Your
TV is an Accelerator
and providing their motion. More Information: Antiparticles:
Pair Production and Annihilation.
The particles that are common in our universe are defined as matter and
their antiparticles as antimatter. In the particle theory there is almost
no a priori distinction between matter and antimatter. Their
interactions
are almost identical. The asymmetry of the universe between these two classes
of particles is a deep puzzle which is yet to be fully understood. More
Information: Antiparticles, BaBar
Experimental Facility, Accelerator
Positron Beam
or fermion
label has a corresponding antiparticle type. Any particle and its antiparticle
have identical mass and spin but opposite charges.
For example the antiparticle of an electron
is a positron. It has exactly the same mass as an electron but positive
charge.
number and lepton
number are further types of "charges" that are reversed for particle and
antiparticle. Thus an electron
and an electron neutrino both have electron number +1 while their antiparticles
the positron and the anti-electron-neutrino have electron number -1. More
Information: Antiparticles
of radiation upon passage through a medium. The attenuation is caused by
absorption
and scattering..
to the required degree. A secondary barrier attenuates stray radiation
to the required degree.
made from a basic structure of three quarks. The proton
and the neutron are both baryon.
The antiproton and the antineutron are antibaryons. More Information:
Hadrons:
Baryons, Color Charge
of all interactions
are bosons. Mesons are also bosons. More
Information: Weak Interactions,
Weak
Interactions Carrier Particles,
Electroweak
Interactions, The Standard Model
of quark (in order of increasing mass), with electric charge
-1/3. More Information: Quarks
in a atom is bound because of its electrical attraction to the nucleus,
which makes the mass of the atom slightly less than the sum of the masses
of the electron plus the rest of the atom without the electron.
particle (such as an electron) is decelerated by passing through matter.
The word bremsstrahlung is German for "braking radiation".
particle. After each beam pulse a photographic record is made of the chamber
and then it is depressurized to clear the bubbles. More Information:
End
Station A Experiment
associated with quantum excitations of the force field corresponding to
some interaction.
Gluons
are carrier particles for strong interactions (color force fields), photons
are carrier particles of electromagnetic
interactions,
and the W and Z bosons are carrier particles for weak interactions. More
Information: Weak Interactions, Strong
Interactions, Electromagnetic Interactions
tube containing an anode and a cathode that generates cathode rays (electrons)
when operated at a high voltage. The cathode rays produce an image on a
screen when they strike phosphors on the screen, causing them to glow.
particle emits Cerenkov radiation (light) in a cone around its direction
of travel when it travels through any medium faster than the speed of light
through that medium. (Cerenkov - is the name of the scientist who first
recognized the nature of this effect and its possible use for distinguishing
particle types.) Although the speed of light in a vacuum is the fastest
speed that any particle or light can have, in a medium of any type light
travels more slowly because of its interactions with the electric
fields
of the atoms in the medium and so it is possible for a high energy particle
to be faster than light in some material . The blue light in the pools
of water you may have seen in pictures of nuclear power plants is Cerenkov
radiation from particles produced in the reactor. More Information:
Cerenkov
Detector, Hadron Tracking: Cerenkov
Detectors
process. A particle with electric charge has electrical interactions; one
with strong charge (or color charge)
has strong interactions, etc. More Information: Force
and Interaction"
of quarks. Also known as the C quark. More Information: Quarks
models used in cancer treatment and stereotactic radiosurgery..
When they "wiggle" up and down together (in phase) they are said to be
coherent. A laser is a good example of coherent light. An ordinary light
bulb produces incoherent light much like the random waves produced when
many raindrops hit a puddle. Electromagnetic radiation is coherent when
the photons are produced in such a way that they are in phase with one
another and incoherent when the phases of the photons are random. Partial
coherence is an intermediate situation where there a significant fraction
of the photons have related phase, but not all of them.
of radiation can be directed at a well-defined part of a target material.
to reduce the size of the beam. Collimators are also useful for removing
stray radiation.
associated with strong interactions.
Quarks and gluons
have color charge and consequently participate in strong interactions.
Leptons,
photons and W and Z bosons
do not have color charge and therefore do not participate in strong interactions.
More Information: Color Charge, Strong
Interactions, The Standard Model.
More
Information: Detectors.
to the left or right by placing one pole above and the other below the
beam pipe. More Information: Magnet
Basics, More About Magnets,
Research
Using Synchrotron Radiation
of radiation, this means determining the absorbed dose rate at a calibrated
point in the beam under a specified set of conditions. Normally, such a
determination is carried out with a number of beams under different specified
conditions.
upon living organisms. For radiation protection purposes, the quantity
of the effective irradiation incurred by exposed persons, measured on a
common scale in sievert (SI) or rem (non-SI).
path of radiation to dose.
of quark (in order of increasing mass), with electric charge
-1/3. More Information: Quarks
placed at rest at any point in space will feel. Electric charges cause
electric fields around them, which then apply a force to any other electric
charge placed in the field. The electric field E has both
a magnitude and a direction at each point in space, and the magnitude and
direction of the resulting force on a charge q at that point is given by
F=
qE. When you get a shock from a door handle after scuffing your
feet on a carpet you feel the effect of an electric field accelerating
electrons.
More
Information: Electrons are Accelerated
in a Copper Structure
when it moves through a potential difference of one volt. By definition
an eV is equivalent to 1.6 x 10-19 joules. This is a very small
amount of energy and the more commonly used multiples are MeV
(million eV), GeV (billion eV or giga-electronvolt)
and TeV (trillion eV).| Electromagnetic waves make up the electromagnetic spectrum.Visible
light, ultraviolet, infrared, radio and TV signals are all examples of
"everyday" em waves. X-rays, microwaves and high energy photons
or gamma rays
are also electromagnetic waves. (See a movie
about the em spectrum!) More Information: Electrons
are Accelerated in a Copper Structure, Electromagnetic
Interactions, Waveguide |
due to electric charge;
this includes magnetic effects that have to do with moving electric charges.
More
Information: Electromagnetic Interactions
particle, therefore absolutely stable. It is the most common lepton
with charge -1. An electron is one of the fundamental
particles
in nature. Fundamental means that, as far as we know, an electron cannot
be broken down into smaller particles. (This concept is one of the things
SLAC physicists always challenge by looking for other particles.) Electrons
are responsible for many of the phenomena that we observe in everyday life.
Mutual repulsion between electrons in the atoms of the floor and those
within your shoes keeps you from sinking and disappearing into the floor!!!
Electrons carry electrical current and successful manipulation of electrons
allows electronic devices, such as the one you are using, to function.
More
Information: Fundamental Particles
and successful manipulation of electronsallows
electronic devices to function. The picture and text on the video terminal
in front of you is caused by electrons being accelerated and focused onto
the inside of the screen, where a phosphor absorbs
the electrons and light is produced. A television screen is a simple, low-energy
example of an electron accelerator. A typical medical electron accelerator
used in medical radiation therapy is about
1000 times more powerful than a color television set, while the electron
accelerator at SLAC is about 2,000,000 times more powerful than a color
TV. One example of an electron accelerator used in radiotherapy is the
Clinac,
manufactured by Varian Associates in Palo Alto, CA..
Primarily used for lesions situated at or near the surface.
and their antiparticles,
which have no known substructure. Gluons,
photons and W and Z bosons
are also fundamental particles. All other particles are composite, that
is made from combinations of fundamental
particles.
More
Information: Fundamental Particles.
Particle
theories predict the probabilities of various events occurring when many
similar collisions or decays are studied. They cannot predict the outcome
for a single collision or decay. More Information: What
is an Event, Event Pictures
and baryons
are all fermions. More Information: Spin
types. The six flavors of quarks are up, down, strange, charm, bottom,
top, in increasing order of mass. The flavors of charged
leptons are electrons,
muon and tau, again in increasing order of mass. For each charged
lepton flavor there is a corresponding neutrino flavor. More
Information: Quarks, Leptons
are the strong, electromagnetic, weak and gravitational
interaction.
These interactions explain all observed physical processes but do not explain
particle masses. Any force between two objects is due to one or another
of these interactions. All known particle decays
can be understood in terms of these strong, electromagnetic or weak interactions.
More
Information: Forces and Interactions,
photons,
gluons
,W-boson
and Z-bosons are fundamental. All other objects are made from these particles.
More
Information: Fundamental Particles,
Matter
Constituents
or photons emitted from the nucleus (center) of an atom. See also: photon.
More
Information: Electromagnetic Interactions
particles via the ionization
of gas that they cause as they pass through a region. Used to detect the
particles produced in certain forms of radioactivity.
in passing through a potential difference of one billion volts.
of the strong interaction.
More
Information: Strong Interactions,
Forces
and Interactions,
i.e. a meson or a baryon.
All such particles have no strong charge (i.e. are strong charge neutral
objects) but participate in residual strong interactions
due to the strong charges of their constituents. More Information: Hadrons
of the fundamental particles,
such as electrons,
photons, neutrons and protons (and many others than can be created). These
particles are the basic building blocks of everyday matter, making up the
human body as well as the entire universe. This type of physics is called
high-energy
because very powerful machines, such as the Two-Mile Accelerator at SLAC,
are created to make these particles go very fast so that they can probe
deeply into other particles and try to understand what they are made of.
or it responds to a force due to the presence of another particle (as in
a collision). More Information: Decays,
Force
and Interactions, Radiation,
either negative or positive..
from electrically neutral atoms, leaving behind charge
atoms or ions. There are four basic types of ionizing radiation: Alpha
particles (helium nuclei), beta particles (electrons), neutrons, and gamma
rays
(high frequency electromagnetic waves, x-rays, are generally identical
to gamma rays except for their place of origin.) Neutrons are not
themselves ionizing but their collisions with nuclei lead to the ejection
of other charged particles that do cause ionization.event
all traveling in roughly the same direction and carrying a significant
fraction of the energy in the event. The particles in the jet are chiefly
hadrons.
More
Information: Hadrons, Event
Display Picture: Typical Hadronic Event, Event
Display Picture: Multi-Jet Hadronic Eventselectron
tube used as an oscillator or amplifier at microwave frequencies. In the
klystron, an electron beam
is velocity modulated (periodically bunched) to produce large amounts of
power. More Information: Klystron
is a Microwave Generator, Microwaves
- Power Up the Particles
leptons are the electron
(e), the muon (
),
the tau (
) and their
antiparticles.
Neutral leptons are called neutrinos (
). More Information: Leptons
particles are accelerated in a straight line, either by a steady electrical
field or by means of radiofrequency electric
fields.
In the latter variety, the passage of the particle is synchronized with
the phase of the accelerating field. The SLAC Linear Accelerator (linac)
is a two-mile long accelerator, consisting of a cylindrical, disc-loaded,
copper waveguide placed on concrete girders in a tunnel about 25 feet underground.
More
Information: Accelerator Form and Function,
SLAC
Linear Collider, Next Linear Collider
x-ray procedure that creates an image of the breast. The x-ray image is
called a mammogram.
matter particles, and their antiparticles
are then antimatter.
More
Information: Matter Constituents,
Building
Blocks of Matter)
to heal people. Radiation therapy is one
example. CAT scans,
mammography, and other x-ray imaging techniques are
diagnostic techniques that have also been developed by physicists working
in medicine. Another important example is the technology that went into
building the particle accelerator at SLAC, which has been adapted for use
in hospitals to treat cancer patients with beams of electrons
and x-rays. There is more information about Medical
Physicists on the WWW. More Information: EGS
and Medical Physics
with the basic structure of one quark and one antiquark. More Information:
Hadrons
in passing through a potential difference of one million volts.
produce microwaves of 2,856 MHz. More Information: Microwaves
- Power Up the Particles, Klystron
is a Microwave Generator
There
is a gaming aspect to Monte Carlo calculations. Every simulation is based
up events that happen randomly, and so the outcome of a calculation is
not always absolutely predictable. This element of chance reminds one of
gambling and so the originators of the Monte Carlo technique, Ulam and
von Neumann, both respectable scientists, called the technique Monte
Carlo to emphasize its gaming aspect.
(in order of increasing mass), with electric charge
-1. More Information: Leptons,
Cosmic
Rays
capable of registering tracks of charged
particles. The detector is designed so that the only charged particles
that can get out to this layer are muons.
with no electric charge.
Neutrinos participate only in weak (and gravitational) interactions
and therefore are very difficult to detect. There are three known types
of neutrino, all of which have very low or possibly even zero mass. More
Information: Leptons
with electric charge
zero. Its basic structure is two down
quarks
and one up quark. More Information: Hadrons
for each type. All conservation laws are obeyed in these processes.
More
Information: Antiparticles
Pair Production and Annihilation.
of the same type can exist in the same state at the same place and time.
More
Information: Spin
of the electromagnetic interaction.
Depending on its frequency (and therefore its energy) photons can have
different names such as visible light, X rays and gamma
rays.
We describe light in several ways. When we talk about "photons" we generally
think of uncharged particles with out mass that carry energy (but be careful,
there are other particles like this!). Photons of light are known by other
names too, such as gamma rays and x-rays.
Low-energy forms are called ultraviolet rays, infrared rays,
even radio waves! A photon is one of the fundamental
particle
in nature and it plays an important role involving electron interactions.
Photons are the most familiar particles in everyday existence. The light
we see, the radiant heat we feel, microwaves we cook with, are make use
of photons of different energies. An x-ray is simply a name given to the
most energetic of these particles. More Information: Electromagnetic
Interactions
is a beam of particles whose spins are aligned in a particular direction.
The polarization of the beam is the fraction of the particles with
the desired alignment..
More
Information: Leptons, Positron
Electron Project (PEP) Experiment
with electric charge
+1. Protons contain a basic structure of two up quarks and one down
quark
. The nucleus of a hydrogen atom is a proton. A nucleus with atomic number
Z contains Z protons; therefore the number of protons is what distinguishes
the different chemical elements. More Information: Hadrons
come in discrete amounts called quanta. More Information: Quantum
Mechanics
given as an integer multiple of the electron's charge is an example
of a quantum number. More Information: Antiparticles.
Quarks have an electric charge
of either +2/3 (up, charm
and top) or -1/3 (down, strange and bottom) in units where the proton charge
is 1. More Information: Quarks, Strong
Interactionsof
100 ergs in a gram of any material. An "erg" is a unit for quantifying
energy (just like a "mile" is used for measuring distance.).
Radiation is further defined into ionizing and non-ionizing radiation.
from their orbits, causing the atom to become charged
or ionized. Examples are X-rays and electrons...
More information about radiotherapy is available through the National
Cancer Institute at the National Institutes
of Health..
The image is the result of the differential attenuation
of the radiation in its passage through the object being radiographed.,
such as X-rays, gamma rays,
alpha particles, and beta particles.
between objects that do not carry a charge
but that contain constituents that do have a charge. Although some chemical
substances involve electrically-charged ions, much of chemistry is due
to residual electromagnetic interactions
between electrically neutral atoms. The residual strong interaction between
protons and neutrons, due to the strong charges of their quark constituents,
is responsible for the binding of the nucleus.
can create photons by interacting with a medium. In a similar way, photons
can create electrons and their antiparticles,
positrons, by interacting with a medium. So, imagine a very high-energy
electron, of the sort used at SLAC, impinging on some material. The electron
can set photons into motion and these photons can, in turn, set electrons
and positrons into motion, and this process can continue to repeat. One
high-energy electron can set thousands of particles into motion. Albert
Einstein's famous relation governing the equivalence of matter and energy
(E = mc²) governs this process -- namely, matter (electrons
and positrons) can be creased from pure energy and vice versa. The particle
creation process only stops when the energy runs out. More Information:
Liquid
Argon Calorimeter Electromagnetic Shower, Why
was EGS developed?
spin is an intrinsic and inherently quantum property, it cannot be understood
in terms of motions internal to the object. More Information: Spin.
and their interactions.
More
Information: Standard Model, Is
the Standard Model a theory or a model?
of radiation fired from many different directions and all aimed at the
tumor. Machines used include the "gamma-knife," with several hundred small,
high-activity Cobalt-60 sources and conventional medical linear
accelerators
equipped with specially designed sterotactic hardware.
and/or positrons, or protons and/or antiprotons can be circulated
many times and thus "stored". Used to achieve high energy collisions.
Because of the very different masses of protons and electrons a storage
ring must be designed for one or the other type and cannot work for both.
More
Information: The SPEAR Storage Ring,
Circular
Accelerators,
Positron Electron Project
(PEP)
of quark (in order of increasing mass), with electric charge
-1/3. More Information: Quarks
incorporating relativity and quantum mechanics in which the particles are
viewed not as points but as extended objects. String theory is a
possible framework for constructing unified theories which include both
the microscopic forces and gravity.
More
Information: Gravitational Interactions,
An
Additional Force
that makes them combine to form the observed hadrons, such as protons and
neutrons. It also causes forces between hadrons,
such as the strong nuclear force that makes protons and neutrons bind together
to form nuclei. More Information: Strong
Interactions, Forces and Interactions
responsible for binding quarks and gluons
to make hadrons.
Residual strong interactions provide the nuclear binding force. In nuclear
physics the term strong interaction is also used for this residual effect.
(As a parallel, the force between electrically charged
particles is an electromagnetic
interaction,
the force between neutral atoms that leads to the formation of molecules
is a residual electromagnetic effect.) More Information: Strong
Interactions, Forces and Interactions
particle undergoes accelerated motion it radiates electromagnetic energy.
A common example is the emission of radio waves when electrons
move back and forth in a radio antenna. A charged particle traveling in
the arc of a circle is also undergoing acceleration, due to its change
in direction. The radiation emitted by such particles is called synchrotron
radiation and it is particularly intense and very directional when electrons
traveling at close to the speed of light are bent in magnetic fields. More
Information: Stanford Synchrotron Radiation Laboratory
of electrons
to produce x-rays. More Information: End
Station A (ESA), Synchrotron Radiation
Interactions with Matterlepton
(in order of increasing mass), with electric charge -1. More Information:
Leptons
in passing through a potential difference of one trillion volts.
of quark (in order of increasing mass) with electric charge
+2/3. More Information: Quarks.
More
Information: Particle Detectors, Types
of Detector "Tracks", Hadron Tracking
capable of detecting the passage of electrically charged
particles.
In particle physics the standard unit is the unit of energy GeV. One
eV (electron Volt) is the amount of energy that an electron
gains when it moves through a potential difference of 1 Volt (in a vacuum).
G stands for Giga, or 109. Thus a GeV is a billion (in US counting)
electron Volts. The mass-energy of a proton or neutron is approximately
1 GeV. More Information: Units
into other particles.
of quark (in order of increasing mass), with electric charge+2/3.
More
Information: Quarks
rectangular copper tube that provides a path for microwaves to travel along.
They are very carefully designed for a particular wavelength microwave,
so as to transmit as much energy as possible. More Information: Waveguide
of the weak interaction.
More
Information: Weak Interactions,
Weak
Interaction Carrier Particles,
Electroweak
Interactions
responsible for all processes in which flavor
changes; hence for the instability of heavy leptons
and quarks, and particles that contain them. Weak interactions that do
not change flavor have also been observed. More Information: Weak
Interactions, Weak Interaction Carrier
Particles
(photons of light) emitted by energy changes of electrons.
These energy changes are either in the electron orbital shells that surround
an atom or are due to the slowing down (i.e., interaction)
of electrons in matter, such as a "target" in an x-ray machine. More Information:
Electromagnetic
Interactions, Synchrotron Radiation Interactions
with Matter
of weak interactions.
It is involved in weak processes that do not change flavor.
More
Information: Weak Interactions,
Weak
Interaction Carrier Particles,
Electroweak
Interactions