X-rays are electromagnetic waves
of short wavelength, capable of penetrating some thickness of matter. Medical
x-rays are produced by letting a stream of fast electrons come to a sudden
stop at a metal plate; it is believed that X-rays emitted by the Sun or
stars also come from fast electrons. Both light and radio waves belong
to the electromagnetic spectrum, the range containing all different electromagnetic
waves. Over the years scientists and engineers have created EM waves of
other frequencies--microwaves and various IR bands whose waves are longer
than those of visible light (between radio and the visible), and UV, EUV,
X-rays and g-rays (gamma rays) with shorter wavelengths. The electromagnetic
nature of x-rays became evident when it was found that crystals bent their
path in the same way as gratings bent visible light: the orderly rows of
atoms in the crystal acted like the grooves of a grating.
Wilhelm Röntgen (Roentgen)
On 8 Nov, 1895, Wilhelm Conrad
Röntgen (accidentally) discovered an image cast from his cathode
ray generator, projected far beyond the possible range of the cathode rays
(now known as an electron beam). Further investigation showed that the
rays were generated at the point of contact of the cathode ray beam on
the interior of the vacuum tube, that they were not deflected by magnetic
fields, and they penetrated many kinds of matter.
Mrs. Röntgen's hand, the first X-ray picture of the human body ever
A week after his discovery,
Rontgen took an X-ray photograph of his wife's hand which clearly revealed
her wedding ring and her bones. The photograph electrified the general
public and aroused great scientific interest in the new form of radiation.
Röntgen named the new form of radiation X-radiation (X standing for
"Unknown"). Hence the term X-rays (also referred as Röntgen rays,
though this term is unusual outside of Germany).
The images produced by X-rays are
due to the different absorption rates of different tissues. Calcium in
bones absorbs X-rays the most, so bones look white on a film recording
of the X-ray image , called a radiograph. Fat and other soft tissues absorb
less, and look gray. Air absorbs the least, so lungs look black on a radiograph.
and all photos courtesy of NASA
of the X-Ray
An historical overview of the discovery
of the X-Ray.
patent drawing of the first CAT-scan
Robert S. Ledley - CAT-Scans
X-Ray Systems - CAT-Scans
Robert S. Ledley was granted patent
#3,922,552 on November 25th in 1975 for a "diagnostic X-ray systems" also
known as CAT-Scans.
A computed tomography scan
(CAT-scan) uses X-rays to create images of the body. However a radiograph
(x-ray) and a CAT-scan show different types of information. An x-ray is
a two-dimensional picture and a CAT-scan is three-dimensional. By imaging
and looking at several three-dimensional slices of a body (like slices
of bread) a doctor could not only tell if a tumor is present, but roughly
how deep it is in the body. These slices are no less than 3-5 mm apart.
The newer spiral (also called helical) CAT-scan takes continuous pictures
of the body in a spiral motion, so that there are no gaps in the pictures
A CAT-scan can be three dimensional
because the information about how much of the X-rays are passing through
a body is collected not just on a flat piece of film, but on a computer.
The data from a CAT-scan can then be computer-enhanced to be more sensitive
than a plain radiograph.
William D. Coolidge invented the
X-ray tube - popularly called the 'Coolidge tube.'
William D. Coolidge invented the
X-ray tube - Invention Dimension.
Other inventions of Coolidge: invention
of ductile tungsten
A breakthrough in tungsten
applications was made by W. D. Coolidge in 1903. Coolidge succeeded in
preparing a ductile tungsten wire by doping tungsten oxide before reduction.
The resulting metal powder was pressed, sintered and forged to thin rods.
Very thin wire was then drawn from these rods. This was the beginning of
tungsten powder metallurgy, which was instrumental in the rapid development
of the lamp industry - International Tungsten Industry Association (ITIA)
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