Why Did Wilhelm Rontgen Discover the X-Ray?
Most people know the term "X-ray" as the image a doctor takes of a bone when he suspects a break or fracture. In fact, an X-ray is actually the radiation used to enable the capture of that picture. By projecting a stream of special high-energy photons at an area, and image is generated. Every element has its own X-ray which allows differentiation between skin, muscle and bone. These X-rays were discovered by accident by a German physicist working in his lab late one night.
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The Discovery
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German physicist Wilhelm Röntgen was the first to systematically study the X-ray in 1895. He was initially interested in experiments utilizing Crookes tubes which used ionization to free electrons. He was so fascinated that he stayed late one night working on an experiment long after his assistants had gone home. It was the unique combination of the dark environment and a screen of fluorescent material left behind on a table a few feet away that produced the familiar green glow of radiation on the table in front of the apparatus. Rontgen was amazed and repeated the experiment numerous times to confirm his findings. He named the radiations "X-rays" for lack of a better definition. For years after their discovery, they were called Rontgen rays in his honor.
Progression
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Once the properties of the Crookes tubes became apparent, special cold cathode tubes known as the Crookes X-ray tubes were created and used until 1920. These tubes were very unreliable and difficult to control but their usefulness was undeniable. It was no surprise that a host of scientists continued work on improving the ability of the x-ray, even while the Crookes tubes were still being used.
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Advancement
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With the invention of the thermionic diode valve by John Ambrose Fleming in 1904, a different type of cathode tube --- called a hot cathode --- was applied to the X-ray concept. These hot tubes allowed current to continue to flow in a vacuum which increased the level of control. These tubes replaced the Crookes tubes around 1920. In 1917 Charles Barkla was awarded the Nobel Prize in Physics for his contributions to the X-ray. He discovered that every element had a characteristic X-ray, and those rays could be scattered by gasses. Continued research by additional scientists proved that the rays could be further diffracted by crystals. This research led to the creation of the Coolidge tube which allowed a continuous production of X-rays. The Coolidge tube is still used today, offering a clear, reliable image.
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References
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