Synchrotron radiation
Synchrotron radiation is the name given to light radiated by an electric
charge following a curved trajectory -for example, a charged particle
under the influence of a magnetic field. Synchrotron radiation is a
natural phenomenon that has existed since the Big Bang. It is in the
starlight that we see at night, generated by charged particles of matter
spiraling through the cosmos.
When charged particles, in particular electrons or positrons, are forced
to move in a circular orbit, photons are emitted. At relativistic
velocities (when the particles are moving at close to the speed of light)
these photons are emitted in a narrow cone in the forward direction, at
a tangent to the orbit. In a high energy electron or positron storage
ring these photons are emitted with energies ranging from infra-red to
energetic (short wavelength) X-rays. This radiation is called
Synchrotron Radiation.
Electromagnetic radiation at all
Light, electricity, and magnetism are manifestations
of the same thing called electromagnetic radiation. The energy you see
coming out of the computer screen you are using to read this page is
made of fluctuating electric and magnetic energy fields. The electric
and magnetic fields oscillate at right angles to each other and the
combined wave moves in a direction perpendicular to both of the electric
and magnetic field oscillations. This energy also comes in many forms
that are not detectable with our eyes such as infrared (IR), radio,
X-rays, ultraviolet (UV), and gamma rays.
We feel infrared light as heat and our radios pick up the messages
encoded in radio waves emitted by radio stations. Ultraviolet light has
high enough energy to damage our skin cells, so our bodies will produce
a darker pigment in our skin to prevent exposure of the deeper skin
cells to the UV (we tan as a defense mechanism). The special bulbs
called ``black lights'' produce a lot of UV and were used by hospitals
to kill bacteria, amoebas, and other micro-organisms. X-rays are
produced by very hot things in space. X-rays have more energy than UV,
so they can pass through skin, muscles, and organs. They are blocked by
bones, so when the doctor takes your X-ray, the picture that results is
the shadow image of the X-rays that passed through your body. Because
X-rays have such high energy, they can damage or kill cells. A few brief
exposures to low-intensity X-rays is okay. The X-ray technician would be
exposed to thousands of X-ray exposures if s/he did not use some sort of
shielding. Gamma rays are the most energetic form of electromagnetic
radiation and are produced in nuclear reactions.
Electromagnetic spectrum
When we look at the world around us we are seeing
visible light waves (or visible radiation). However, there are many
other forms of radiation that we cannot see with our eyes. These types
include gamma rays, x-rays, ultraviolet, infrared, microwaves and radio
waves. Together with visible light, all these types of radiation make up
what we call the electromagnetic spectrum - the complete spectrum of
radiation. Light (or radiation) is made up of vibrating waves of
electrical and magnetic fields. This is where the term electromagnetic
radiation comes from. Electromagnetic radiation travels in waves which
have different wavelengths, energies and frequencies.
Synchrotron radiation
Sychrotron radiation is emitted when a fast electron
interacts with a magnetic field. A magnetic field in an area an electron
is traveling in will cause the electron to change direction by exerting
a force on it perpendicular to the direction the electron is moving. As
a result, the electron will be accelerated, causing it to radiate
electromagnetic energy. This is called magnetic bremsstrahlung or
synchrotron radiation (after radiation observed from particle
accelerators by that name). If the electrons and the magnetic field are
energetic enough, the emitted radiation can be in the form of X-rays.
Characteristics of Synchrotron Radiation
Synchrotron radiation has a number of unique properties:
• High brightness: synchrotron radiation is extremely intense (hundreds
of thousands of times higher than conventional X-ray tubes) and highly
collimated.
• Wide energy spectrum: synchrotron radiation is emitted with a wide
range of energies, allowing a beam of any energy to be produced.
• Synchrotron radiation is highly polarised.
• It is emitted in very short pulses, typically less that a nano-second
(a billionth of a second)
• Some terminology
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