In the Beginning


by Gwen Myslinski

Some of the best ideas and inventions are discovered when a person, who knows a subject well, stops thinking about the issue at hand, and lets his/her mind rest. (When do you get your "ah-ha" moments? In the shower or maybe right before you fall asleep?) The same was true when two physicists accidently discovered x-rays and radiation. In fact, they almost didn't believe their own discoveries.

The "Handy" X-Ray

Wilhelm Röntgen was a physicist who, like many others of his time, had been experimenting with Hittorf-Crookes tubes. It just so happens he had been using the tube to study cathode rays (electrons). On November 8, 1895, he decided to completely wrap the tube with black paper. Several feet away there was a small screen that was covered with barium-platinum cyanide, and in a darkened room, much to his surprise, mysterious rays penetrated the black paper and appeared on the screen. He began investigating. He turned the screen so the side without the barium-platinum cyanide faced the tube, and still the screen fluoresced. It didn't work when he placed objects between the tube and the screen. Then he placed his hand in front of the tube. Much to Röntgen's astonishment, he saw his own bones appear on the screen — he had discovered the x-ray. "… a momentous event that instantly revolutionized the fields of physics and medicine," according to the American Nuclear Society.


After learning of Röntgen's discovery, Henri Becquerel thought other fluorescing materials would emit x-rays too, and began his experiments. He tested several phosphorescent and fluorescent substances unsuccessfully, until he tried a uranium salt, uranyl potassium sulfate. He exposed the substances to sunlight and placed them on photographic plates that were wrapped in black paper. After developing the plates, he saw the silhouette of the phosphorescent substance in black on the negative. He tried again, and the experiment was delayed because the skies were cloudy, thereby forcing Becquerel to place the plates in a drawer for a few days. When he retrieved the plates, he expected only faint images. To his surprise, the images were clear and strong, meaning the uranium emitted radiation without an external source of energy such as the sun. Becquerel had discovered radioactivity, but only investigated the rays emitted by uranium. It was Marie and Pierre Curie who experimented with other elements, including polonium and radium, and later gained the full understanding of the process of radioactive decay.

Classroom Discussion

  • How has radiation changed the world, and what are some everyday applications?
  • What are some of the benefits of radiation?