Wilhelm Conrad R?ntgen, the discoverer of X-rays, was born in 1845 in the town of Nippes, Germany. He received his doctorate in philosophy from the University of Zurich in 1869. Over the next nineteen years, R?ntgen worked at a number of different universities, gradually earning a reputation as a brilliant scientist, and in 1888 he was appointed professor of physics and director of the Institute of Physics at the University of Würzburg, where R?ntgen discovered X-rays in 1895.
On this day, September 8, 1895, Roentgen was experimenting with cathode rays. Cathode rays consist of a stream of electrons. A stream of electrons is produced when there is a high voltage between electrodes located at the ends of a closed glass tube in an almost complete vacuum. Cathode rays are not particularly penetrating, and have difficulty passing through even a few centimeters of air. This time R?ntgen covered the cathode rays completely with thick black paper so that the light from the glass tube would not be seen even if a current passed through. But when Roentgen turned on the circuit of the cathode ray tube, he was surprised to find that a fluorescent screen (plated with a fluorescent substance, barium cyanoplatinate) on a nearby bench began to glow, just as if it had been excited by the induction of a lamp. He disconnected the current to the cathode ray tube and the screen stopped glowing. Since the cathode ray tube was completely covered, Roentgen soon realized that when the current was turned on, there must be some kind of invisible radiation emitted from the cathode. Because of the mysterious nature of this radiation, he called it "X-rays" -- X is often used in mathematics to represent an unknown number.
This serendipitous discovery excited Roentgen, who put his other research on hold to concentrate on the nature of X-rays. After weeks of intense work, he discovered the following facts. (1) In addition to causing barium cyanoplatinate to fluoresce, X-rays can cause many other chemicals to fluoresce. (2) X-rays can penetrate many ordinary light can not penetrate the material; in particular, can pass directly through the muscle but can not pass through the bone, roentgen put his hand between the cathode ray tube and fluorescent screen, you can see on the fluorescent screen of his hand bone. (3) X-rays travel in a straight line; unlike charged particles, X-rays are not deflected by magnetic fields.
Roentgen wrote his first paper on X-rays in December 1895, and the publication immediately aroused great interest and excitement. Within a few months hundreds of scientists were working on X-rays, and within a year about a thousand papers were published on the subject! One of the scientists directly inspired by Roentgen's invention was Antoine-Henri Becquerel. Although Becquerel was intentionally working with X-rays, he stumbled upon an even more important radiological phenomenon.
In general, X-rays are produced whenever an object is bombarded with high-energy electrons, which themselves are made not of electrons but of electromagnetic waves. Such rays are therefore essentially similar to visible radiation (i.e., light waves), although their wavelength is much shorter.
Of course the best-known application of X-rays is in medical (including oral) diagnosis. Another application is radiotherapy, in which X-rays are used to destroy or inhibit the growth of malignant tumors, and there are many industrial applications, for example, to measure the thickness of certain substances or to survey for potential defects. x-rays are also used in many fields of scientific research, ranging from biology to astronomy, and in particular have provided scientists with a wealth of information about the structure of atoms and molecules.
The full credit for the discovery of X-rays goes to Roentgen. He studied it alone, his discovery was unanticipated, he followed it up superbly, and his discovery was an important catalyst for Becquerel and other researchers.
However, one should not overestimate the importance of Roentgen; the use of X-rays is certainly beneficial, but it cannot be regarded as having transformed our whole technology in the same way as Faraday's discovery of electromagnetic induction; nor can it be argued that the invention of X-rays has had its really great significance in scientific theory. It has been known for nearly a century that ultraviolet light (which has a shorter wavelength than visible light) is similar to X-rays, but its wavelength is even shorter than that of ultraviolet light, and its existence is entirely consistent with the ideas of classical physics. In short, I think there is every reason to rank Roentgen far behind Becquerel, whose discovery was of far greater significance.
R?ntgen had no children, but he and his wife adopted a daughter, and in 1901 he was awarded the Nobel Prize for Physics, the first person to receive it. He died in Munich, Germany, in 1923.