A variety of circumstances led him to enroll at the polytechnic in Zurich, Switzerland, in 1865. Roentgen graduated in 1868 as a mechanical engineer and then completed his Ph.D. in 1869 at the University of Zurich. Upon graduation, he pursued an academic career. He was a physics professor at various universities in Germany, lecturing and also performing research on piezoelectricity, the heat conduction in crystals, the thermodynamics of gases, and the capillary action of fluids. His affiliations included the universities of Strasbourg (1876–1879), Giessen (1879–1888), Würzburg (1888–1900), and Munich (1900–1920).
His great discovery happened at the University of Würzburg on the evening of November 8, 1895. Roentgen, like many other late nineteenth century physicists, was investigating luminescence phenomena associated with cathode ray tubes. This device—also called a Crookes tube, after its inventor, Sir William Crookes (1832–1919)—consisted of an evacuated glass tube containing two electrodes, a cathode, and an anode. Electrons emitted by the cathode often missed the anode and struck the glass wall of the tube, causing it to glow, or fluoresce. On that particular evening, Roentgen decided to place a partially evacuated discharge tube inside a thick black cardboard carton. As he darkened the room and operated the light-shielded tube, he suddenly noticed that a paper plate covered on one side with barium platinocyanide had begun to fluoresce—even though it was located some two meters from the discharge tube. He concluded that the phenomenon causing the sheet to glow was some new form of penetrating radiation originating within the opaque paper-enshrouded discharge tube. He called this unknown radiation X-rays, because x was the traditional algebraic symbol for an unknown quantity.
During subsequent experiments, Roentgen discovered that objects of different thickness placed in the path of these mysterious X-rays demonstrated variable transparency when he recorded the interaction of the X-rays on a photographic plate. Roentgen even held his wife’s hand steady over a photographic plate and produced the first medical X-ray of the human body. When he developed this particular X-ray-exposed plate, he observed an interior image of the hand. This first “roentgenogram” contained dark shadows cast by the bones within his wife’s hand and by the wedding ring she was wearing. These shadows were surrounded by a less darkened (penumbral) shadow corresponding to the fleshy portions of the hand. Roentgen formally announced this important discovery on December 28, 1895—instantly revolutionizing both the field of physics and the field of medicine.
Although the precise physical nature of X-rays, as very short wavelength, high energy photons of electromagnetic radiation, was not recognized until about 1912, scientists in the field of physics and the medical profession immediately embraced Roentgen’s discovery. Many scientists consider this event as the beginning of modern physics. In 1896, the American inventor Thomas A. Edison (1847–1931), developed the first practical fluoroscope— a noninvasive device that used X-rays to allow a physician to observe how internal organs of the body function within a living patient. At the time, no one recognized the potential health hazards associated with exposure to excessive quantities of X-rays or other forms of ionizing radiation. Roentgen, his assistant, and many early X-ray technicians would eventually exhibit the symptoms of and suffer from acute radiation syndrome.
The German physicist had to endure several bitter personal attacks by jealous rival scientists who had themselves overlooked the very phenomena that Roentgen alertly observed during his experiments. Eventually, Roentgen received numerous honors for his discovery of X-rays, including the first Nobel Prize ever awarded in physics, in 1901. Both a dedicated scientist and a humanitarian, Roentgen elected not to patent his discovery so the world could freely benefit from his work. He even donated the money he received for his Nobel Prize to the University of Würzburg. Roentgen died on February 10, 1923, in Munich, Germany, four years after the death of his wife. The cause of his death was carcinoma of the intestine—a condition most likely promoted by chronic exposure to ionizing radiation resulting from his extensive experimentation with the X-rays he discovered. At the time of his death, the scientist was nearly penniless due to the hyperinflationary economy of post–World War I Germany.
Key Stages in Development of Modern Nuclear Physics
