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Chapter Six: X-Rays

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الكلية كلية التربية للعلوم الصرفة     القسم قسم الفيزياء     المرحلة 3
أستاذ المادة فؤاد عطية مجيد       14/12/2016 10:07:25
6.1 Discovery of X-rays
In late 1895, a German physicist, W. C. Roentgen was working with
a cathode ray tube in his laboratory. He was working with tubes similar to our
fluorescent light bulbs. He evacuated the tube of all air, filled it with a special
gas, and passed a high electric voltage through it. When he did this, the tube
would produce a fluorescent glow. Roentgen shielded the tube with heavy
black paper, and found that a green colored fluorescent light could be seen
coming from a screen setting a few feet away from the tube. He realized that
he had produced a previously unknown "invisible light," or ray, that was
being emitted from the tube; a ray that was capable of passing through the
heavy paper covering the tube. Through additional experiments, he also found
that the new ray would pass through most substances casting shadows of solid
objects on pieces of film. He named the new ray X-ray, because in
mathematics "X" is used to indicated the unknown quantity.
In his discovery Roentgen found that the X-ray would pass through the
tissue of humans leaving the bones and metals visible. One of Roentgen’s first
experiments late in 1895 was a film of his wife Bertha s hand with a ring on
her finger. The news of Roentgen’s discovery spread quickly throughout the
world. Scientists everywhere could duplicate his experiment because the
cathode tube was very well known during this period. In early 1896, X-rays
were being utilized clinically in the United States for such things as bone
fractures and gun shot wounds.

6.2 Production of X-rays
An X-ray tube is a vacuum tube designed to produce X-ray photons. The
first X-ray tube was invented by Sir William Crookes. The Crookes tube is
also called a discharge tube or cold cathode tube. A schematic x-ray tube is
shown below.
The glass tube is evacuated to a pressure of air, of about 100 pascals, recall
that atmospheric pressure is 106 pascals. The anode is a thick metallic target;
it is so made in order to quickly dissipate thermal energy that results from
bombardment with the cathode rays. A high voltage, between 30 to 150 kV, is
applied between the electrodes; this induces an ionization of the residual air,
and thus a beam of electrons from the cathode to the anode ensues. When
these electrons hit the target, they are slowed down, producing the X-rays. The
X-ray photon-generating effect is generally called the Bremsstrahlung effect,

المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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