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Page 6
X-rays
Over a century ago in 1895, Roentgen discovered the first example of
ionizing radiation, x-rays. The key to Roentgens discovery was a device
called a Crooke’s tube, which was a glass envelope under high vacuum,
with a wire element at one end forming the cathode, and a heavy copper target
at the other end forming the anode. When a high voltage was applied to the
electrodes, electrons formed at the cathode would be pulled towards the
anode and strike the copper with very high energy. Roentgen discovered that
very penetrating radiations were produced from the anode, which he called
x rays.
X-ray production occurs whenever electrons of high energy strike a heavy
metal target, like tungsten or copper. When electrons hit this material,
some of the electrons will approach the nucleus of the metal atoms where
they are deflected because of their opposite charges (electrons are negative
and the nucleus is positive, so the electrons are attracted to the nucleus).
This deflection causes the energy of the electron to decrease, and this
decrease in energy then results in forming an x ray.
Medical x-ray machines in hospitals use the same principle as the Crooke’s
Tube to produce x rays. The most common x-ray machines use tungsten as their
cathode, and have very precise electronics so the amount and energy of the
x-ray produced is optimum for making images of bones and tissues in the
body.
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