The technical origins of nuclear technology and nuclear physics can be traced to several key discoveries at the end of the nineteenth century, especially the discovery of radioactivity. The first important step involved the discovery of a very penetrating new form of radiation, X-rays. In late November 1895, the German physicist Wilhelm Conrad Roentgen (1854–1923) was experimenting with the luminescence produced by cathode rays—the stream of electrons emitted from the negative electrode (cathode) in a Crookes (vacuum) tube. Around 1875, the British scientist Sir William Crookes (1832–1919) had invented the device that bears his name. It consisted of an evacuated glass tube containing two electrodes— a cathode and an anode. In these early discharge tubes, electrons emitted by the cathode often missed the anode and struck the glass wall of the tube, causing it to glow or fluoresce. Roentgen was fascinated by the Crookes tube and the interesting effects it produced. He placed one inside a black cardboard box and darkened the room. He noticed that when he operated the tube it caused a specially coated sheet of paper across the room to luminesce. Roentgen immediately concluded that the phenomenon causing the sheet to glow was a penetrating form of radiation originating in the discharge tube. He called this unknown radiation X-rays. Roentgen soon recognized the immense value of his discovery, when he took the first X-ray photographs of a hand and saw that these mysterious, penetrating rays could reveal the internal structure of opaque objects. Although the precise physical nature of the X-ray as a very short wavelength, high-energy photon of electromagnetic radiation was not recognized until about 1912, other physicists and the medical profession immediately embraced Roentgen’s discovery. For example, in 1896 the American inventor Thomas A. Edison (1847–1931) developed the first practical fluoroscope—a noninvasive device that uses X-rays to allow a physician to observe how internal organs of the body function in 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.
From Dalton to Einstein: Making of Nuclear Sciences
