LESSON 1
MATTER AND ENERGY
Section I. INTRODUCTION
1-1.
PURPOSE
The primary purpose of this subcourse is to discuss the fundamentals of x-ray
physics that the enlisted x-ray specialist needs to know in order to understand the
nature of the service that he is to perform. The secondary purpose is to acquaint the
1-2.
SCOPE
This subcourse includes a brief history of radiography and a discussion of
fundamentals of physics, including the basic structure of matter and its relationship to
1-3.
HISTORY OF RADIOGRAPHY
a. X-rays were discovered in 1895 by Wilhelm Conrad Roentgen, a German
physicist, but many scientists before him paved the way for his discovery. Many major
discoveries relating to electricity had been made during the three centuries that
preceded the discovery of x-rays, but it was the study of electrical discharges under
high voltage in vacuum tubes that led to the actual discovery of these rays. Scores of
scientists had experimented with electrical discharges through different types of vacuum
tubes and, no doubt, many of them had produced x-rays but had not recognized them
as a new type of ray.
b. Roentgen himself was experimenting with cathode rays when he observed
the presence of this new radiation. He was working with a certain (Hittorf-Crookes)
vacuum tube through which a current under high voltage was being passed. The tube
was entirely enclosed in black paper so as to exclude all the light emanating from it.
During the experiment, Roentgen observed a fluorescence of some barium
platinocyanide crystals coating a piece of cardboard lying nearby. It had been known
for some time that these crystals would fluoresce in the presence of a vacuum tube
activated by high voltage, but it occurred to Roentgen that the fluorescence of the
crystals was due to some type of ray that could pass through the black paper around
the tube. When he picked up the chemically coated cardboard, his fingers came
between it and the tube, and he saw the bones of his hand. He realized that he had
discovered the presence of a ray that would penetrate solid matter. By replacing the
chemically coated cardboard with a photographic plate, he was able to record an image
of the internal structure of his wife's hand. He also noted that the rays could not be
reflected or refracted by the usual means and that they were not affected by electrical
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