X-Rays - Another Form of Light
Wilhelm
Roentgen
A new form of radiation was discovered in 1895 by Wilhelm Roentgen, a German physicist. He
called it X-radiation to denote its unknown nature. This mysterious radiation had the
ability to pass through many materials that absorb visible light. X-rays also have the
ability to knock electrons loose from atoms. Over the years these exceptional properties
have made X-rays useful in many fields, such as medicine and research into the nature of
the atom.
Roentgen was working in his laboratory at the Physical Institute of the
University of Würzburg, Germany, experimenting with a Crookes tube.
This tube is a glass bulb with positive and negative electrodes, evacuated of air, which
displays a fluorescent glow when a high voltage current is passed though it. When he
shielded the tube with heavy black cardboard, he found that a greenish fluorescent light
could be seen from a platinobaium screen 9 feet away.
He concluded that a new type of ray emitted from the tube, passed through the covering,
and casted shadows of solid objects. The rays passes through most substances, including
the soft tissues of the body, but left the bones and most metals visible. One of his
earliest photographic plate from his experiments was a film of his wife, Bertha's hand
with a ring, was produced on Friday, November 8, 1895.
On Saturday, December 28, 1895 Roentgen submitted his first "provisorial"
communication, Ueber eine nue Art von Strahlen (On a New Kind of Rays) in the
Proceedings of the Würzburg Phisico-Medical Society. On Thursday, January 23, 1896 he
made his first public presentation before the same society. After the lecture Roentgen
made a plate of the hand a famous anatomist named Kölliker, who proposed that the new
discovery be named Roentgen's Rays.
The news spread rapidly through out the world. As early as February 8, 1896, X-rays
were being used clinically the United States. in Dartmouth, Massachusetts when Edwin Brant
Frost produced a plate of a Colles fracture in a man named Eddie McCarthy for his brother,
Dr. Gilman Dubois Frost.
Eventually, X-rays were found to be another form of light. Light is the by-product of the
constant jiggling, vibrating, hurly-burly of all matter.
Like a frisky puppy, matter cannot be still. The chair you are sitting in may look and
feel motionless. But if you could see down to the atomic level you would see atoms and
molecules vibrating hundreds of trillions of times a second and bumping into each other,
while electrons zip around at speeds of 25,000 miles per hour.
When charged particles collide--or undergo sudden changes in their motion--they produce
bundles of energy called photons that fly away from the scene of the accident at the speed
of light. In fact they are light, or electromagnetic radiation, to use the technical term.
Since electrons are the lightest known charged particle, they are most fidgety, so they
are responsible for most of the photons produced in the universe.
X-rays can be produced by a high-speed collision
between an electron and a proton.
The energy of the photon tells what kind of light it is. Radio waves are composed of low
energy photons. Optical photons--the only photons perceived by the human eye--are a
million times more energetic than the typical radio photon. The energies of X-ray photons
range from hundreds to thousands of times higher than that of optical photons.
The speed of the particles when they collide or vibrate sets a limit on the energy of the
photon. The speed is also a measure of temperature. (On a hot day, the particles in the
air are moving faster than on a cold day.)
Very low temperatures (hundreds of degrees below zero Celsius) produce low energy radio
and microwave photons, whereas cool bodies like ours (about 30 degrees Celsius) produce
infrared radiation. Very high temperatures (millions of degrees Celsius) produce X-rays.
The Electromagnetic Spectrum. The wavelength of radiation produced by
an object is usually related to its temperature.
The photons themselves can also collide with electrons. If the electrons have more energy
than the photons, the collision can boost the energy of the photons. In this way, photons
can be changed from low-energy photons to high-energy photons. This process, called
Compton scattering, is thought to be important around black holes, where matter is dense
and has been heated to many millions of degrees.
The photons collected in space by X-ray telescopes reveal the hot spots in the
universe--regions where particles have been energized or raised to high temperatures by
gigantic explosions or intense gravitational fields.
Synchrotron Radiation
But this is not the whole story. X-ray photons can also be created under different
conditions. When physicists were operating the first particle accelerators, they
discovered that electrons can produce photons without colliding at all. This was possible
because the magnetic field in the accelerators was causing the electrons to move in large
spirals around magnetic field lines of force. This process is called synchrotron
radiation.
In the cosmos particles such as electrons can be accelerated to high energies– near
the speed of light– by electric and magnetic fields. These high-energy particles can
produce synchrotron photons with wavelengths ranging from radio up through x-ray and
gamma-ray energies.
Synchrotron
Radiation: Electrons moving in magnetic field radiate photons.otons.
Synchrotron radiation from cosmic sources has a distinctive spectrum, or distribution
of photons with energy. The radiation falls off with energy less rapidly than does the
spectrum of radiation from a hot gas. When synchrotron radiation is observed in supernova
remnants, cosmic jets, or other sources, it reveals information about the high-energy
electrons and magnetic fields that are present.
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