Physics · Ch 7 — Dual Nature of Radiation and Matter
X – RAYS
X – RAYS
Wilhelm Roentgen, in 1895, discovered that whenever fast-moving electrons strike certain materials, a highly penetrating form of radiation is given off. Because its origin was completely unknown at the time, Roentgen named this mysterious radiation X-rays -- a name that has stuck ever since. X-rays are now understood to be electromagnetic waves of very short wavelength, ranging from about 0.1 Å to 100 Å, far shorter than visible light. Like all electromagnetic waves, they travel in straight lines at the speed of light and are unaffected by electric and magnetic fields. Because X-ray photons are so energetic (a direct consequence of their very high frequency, or equivalently very short wavelength), they can pass straight through materials -- such as flesh, wood, or thin metal sheets -- that are completely opaque to visible light. The overall quality (penetrating power) of an X-ray beam depends on the speed with which the bombarding electrons strike the target and on the atomic number of the target material, while the intensity of the X-ray beam depends on how many electrons strike the target per second. …
What this figure shows. An evacuated discharge tube is shown with a tungsten filament F at the cathode end, heated by a low-tension (L.T.) battery so that it emits electrons by thermionic emission, which are then accelerated across the tube toward a solid copper anode by a high-tension (H.T.) battery connected between filament and anode. The target material (tungsten or molybdenum) is shown embedded in the face of the anode, with that face tilted at an angle to the electron beam so that the X-rays produced when the fast electrons are suddenly decelerated on impact can leave the tube sideways through the tube's wall rather than bei …