Roentgen, Wilhelm Conrad (1845-1923), German physicist, discoverer of X rays, and winner of the first Nobel Prize in physics. Roentgen's discovery of X rays was a momentous advance for physics and medicine and earned him the 1901 Nobel Prize in physics.
Roentgen was born in Lennep, Germany, and grew up in the Netherlands. He earned a mechanical engineering degree at the Federal Institute of Technology in Zürich, Switzerland, in 1868 and a Ph.D. degree in physics at the University of Zürich in 1869. Roentgen worked as a laboratory assistant at the University of Würzburg in Germany from 1868 to 1872 and at the University of Strasbourg in Germany from 1872 to 1874. He began teaching physics in 1874, starting at the University of Strasbourg, then moving to the Agricultural Academy in Hohenheim, Germany, in 1875, and back to Strasbourg in 1876. In 1879 he became a professor of physics at the University of Giessen in Germany, where he remained until 1888, when he became professor of physics and director of the Physical Institute at the University of Würzburg. He accepted a position as professor of physics and director of the Physical Science Institute at the University of Munich in 1899 and taught there until his retirement in 1920.
Roentgen made an accidental discovery November 8, 1895, while investigating emissions from a Crookes tube (a glass vacuum tube with electrodes at either end). The emissions Roentgen was looking for are called cathode rays, composed of high-speed electrons that come off the negative electrode when voltage is applied to the electrodes of a Crookes tube. Cathode rays cause the vacuum tube to glow when the vacuum is strong enough and enough voltage is applied; it was this glow Roentgen was watching when he made his discovery. Cathode rays are weak—they cannot pass through glass (scientists use aluminum windows in a vacuum tube when they want to study cathode rays outside the tube) or an ordinary piece of cardboard—but they do excite barium platinocyanide molecules and cause surfaces painted with barium platinocyanide to glow.
Roentgen was using a Crookes tube without an aluminum window and he had surrounded the tube in black cardboard to better see the tube glow. Therefore, when he noticed a glow coming from a screen painted with barium platinocyanide that was some distance away, he knew cathode rays could not be the cause, because cathode rays could not have gone through either the glass of the tube or the cardboard. Roentgen did more tests to verify that the Crookes tube was the source of the emissions that made the screen glow. He inferred that these emissions were present in all experiments like his, but that he was the first to notice them because no one else had set up conditions like his experiment: a nearby barium platinocyanide-painted screen and an arrangement that suppressed the known emissions.
Roentgen called the newly discovered emissions X rays (x is the symbol for the unknown in mathematics) and worked to document them further. He found a photographic plate in a drawer of a desk in the same room as the Crookes tube and noticed it had been exposed. When he developed it and found an image of a key that had been on the desk top, he realized the X rays had passed easily through the wood of the desk, but to a lesser degree through the metal of the key. Using a barium platinocyanide-treated screen and a Crookes tube, Roentgen produced an image of a lead disk—and the bones of his fingers holding the disk.
His experiments showed that X rays pass through different materials to different degrees. Release of his findings caused worldwide excitement and speculation about X rays, also called Roentgen rays. Medical applications in diagnosis began immediately. The hazard of burns from prolonged exposure soon became evident; the risk of cancer was realized later. X rays came to be used in medical treatment, dental examinations, industrial inspections of metal work, and many other areas.
Roentgen was born in Lennep, Germany, and grew up in the Netherlands. He earned a mechanical engineering degree at the Federal Institute of Technology in Zürich, Switzerland, in 1868 and a Ph.D. degree in physics at the University of Zürich in 1869. Roentgen worked as a laboratory assistant at the University of Würzburg in Germany from 1868 to 1872 and at the University of Strasbourg in Germany from 1872 to 1874. He began teaching physics in 1874, starting at the University of Strasbourg, then moving to the Agricultural Academy in Hohenheim, Germany, in 1875, and back to Strasbourg in 1876. In 1879 he became a professor of physics at the University of Giessen in Germany, where he remained until 1888, when he became professor of physics and director of the Physical Institute at the University of Würzburg. He accepted a position as professor of physics and director of the Physical Science Institute at the University of Munich in 1899 and taught there until his retirement in 1920.
Roentgen made an accidental discovery November 8, 1895, while investigating emissions from a Crookes tube (a glass vacuum tube with electrodes at either end). The emissions Roentgen was looking for are called cathode rays, composed of high-speed electrons that come off the negative electrode when voltage is applied to the electrodes of a Crookes tube. Cathode rays cause the vacuum tube to glow when the vacuum is strong enough and enough voltage is applied; it was this glow Roentgen was watching when he made his discovery. Cathode rays are weak—they cannot pass through glass (scientists use aluminum windows in a vacuum tube when they want to study cathode rays outside the tube) or an ordinary piece of cardboard—but they do excite barium platinocyanide molecules and cause surfaces painted with barium platinocyanide to glow.
Roentgen was using a Crookes tube without an aluminum window and he had surrounded the tube in black cardboard to better see the tube glow. Therefore, when he noticed a glow coming from a screen painted with barium platinocyanide that was some distance away, he knew cathode rays could not be the cause, because cathode rays could not have gone through either the glass of the tube or the cardboard. Roentgen did more tests to verify that the Crookes tube was the source of the emissions that made the screen glow. He inferred that these emissions were present in all experiments like his, but that he was the first to notice them because no one else had set up conditions like his experiment: a nearby barium platinocyanide-painted screen and an arrangement that suppressed the known emissions.
Roentgen called the newly discovered emissions X rays (x is the symbol for the unknown in mathematics) and worked to document them further. He found a photographic plate in a drawer of a desk in the same room as the Crookes tube and noticed it had been exposed. When he developed it and found an image of a key that had been on the desk top, he realized the X rays had passed easily through the wood of the desk, but to a lesser degree through the metal of the key. Using a barium platinocyanide-treated screen and a Crookes tube, Roentgen produced an image of a lead disk—and the bones of his fingers holding the disk.
His experiments showed that X rays pass through different materials to different degrees. Release of his findings caused worldwide excitement and speculation about X rays, also called Roentgen rays. Medical applications in diagnosis began immediately. The hazard of burns from prolonged exposure soon became evident; the risk of cancer was realized later. X rays came to be used in medical treatment, dental examinations, industrial inspections of metal work, and many other areas.
