If you have ever had an X-ray as part of a medical checkup, you owe thanks to Wilhelm Roentgen. Medical X-rays have been one of the most powerful, useful, and life-saving diagnostic tools ever developed. X-rays were the first noninvasive technique developed to allow doctors to see inside the body. X-rays led to the more modern MRI and CT technologies.
Chemists have used X-rays to understand and decipher the structure of complex molecules (such as penicillin) and to better understand the electromagnetic spectrum. The discovery of X-rays earned Roentgen the 1901 Nobel Prize in physics.
In 1895 Wilhelm Roentgen was just a 40-something academic professor at the University of Wurzburg, Germany, doing ho-hum research into the effects of passing electricity through gas-filled bottles. In November of that year he began experiments in his home basement lab with a Crookes’ tube (a device that amplified an electrical signal by passing it through a vacuum).
On November 8, he happened to notice that a photographic plate that had been wrapped in black paper and tucked inside a leather case in the bottom drawer of his desk had mysteriously been exposed and imprinted with the image of a key. The only key in the room was an oversized key for a garden gate he had tossed into the desk’s center drawer over a year ago. The image on his photographic plate was of that key.
Even more strange, he found that the key in the center drawer lay along a straight line from his glass Crookes’ tube mounted on the wall to the photographic plate deep in the bottom drawer. But no visible rays emitted from the Crookes’ tube and surely no light could have penetrated through the desk and leather case to the photographic plate. What could have mysteriously flown across the room and passed through wood, leather, and paper to expose the photographic plate? Whatever it was, it could not pass through the metal key, which was why a dark gray image of the key was outlined on his photograph.
Other scientists theorized that rays would be emitted from a Crookes’ tube and had named them cathode rays after the name of one of the metal plates inside the tube. Crookes thought these rays might come from another world. But no one had detected, measured, or studied these unknown rays.
Roentgen suspected that cathode rays had somehow exposed his film. Two weeks later he was able to prove the existence of these mysterious rays, which he named “X-rays” since “X” was used to represent the unknown. By this time, he had seen that X-rays could pass through wood, paper, cardboard, cement, cloth, and even most metals, but not lead.
For this experiment, Roentgen coated a sheet of paper with barium platino-cyanide (a kind of fluorescent salt) and hung it on the far wall of his lab. When he connected power to his Crookes’ tube, the fluorescent sheet glowed a faint green. When he held an iron disk in front of the paper, the paper turned back to black where the iron disk blocked the X-rays.
Roentgen was shocked to also see the outline of every bone in his hand and arm in faint green outlines on the fluorescent paper. When he moved a finger, the bones outlined in glowing green also moved.
On seeing these first X-ray images, Roentgen’s wife shrieked in terror and thought that the rays were evil harbingers of death. Roentgen, however, began six weeks of intensive study before releasing his results on the nature and potential of X-rays.
Within a month Wilhelm Roentgen’s X-rays were the talk of the world. Skeptics called them death rays that would destroy the human race. Eager dreamers called them miracle rays that could make the blind see again and could beam complex charts and diagrams straight into a student’s brain.
Doctors called X-rays the answer to a prayer.
The Z Machine at the Sandia National Laboratories, New Mexico, can, very briefly, produce X-rays with a power output roughly equivalent to 80 times that of all of the world’s electrical generators.
