As tungsten is heated, electrons in the tungsten atom’s orbits spin faster, moving farther from the nucleus.
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The electron cloud is called a space charge and is the source of free (in air) electrons for x-ray production.įIG. This process is called thermionic emission. Electrons in the outermost orbital shells move so far from the nucleus that they are no longer held in orbit but are flung out of the atom, forming an “electron cloud” around the filament ( Fig. As explained in Chapter 4, heat speeds up the movement of the electrons in their orbits and increases their distance from the nucleus. An advantage of using tungsten is that it has a high melting point, which enables it to last through thousands of exposures. An electric current flows through the filament to heat it. Tungsten (chemical symbol W) is a metal element it is a large atom with 74 electrons in orbit around its nucleus. The filament consists of a small coil of tungsten wire. The source of electrons is a filament at one end of the tube. The tube is fitted on both ends with connections for the electric supply. The air is removed from the glass envelope to form a near-perfect vacuum so that gas molecules will not interfere with the process of x-ray production. It is made of strong, heat-resistant glass and contains both the source of electrons and the target. The cathode is the negative end of the tube the filament is part of the cathode.Ī Pyrex glass envelope forms the basic structure of the x-ray tube. The anode is the positive end of the tube the target is part of the anode. 5-2), a “hot cathode tube” that was the prototype for modern x-ray tubes.įIG. In 1913, the General Electric Company introduced the Coolidge tube ( Fig. These tubes were used in physics laboratories in the late nineteenth century for the investigation of electricity. 5-1), a cathode ray tube that was the forerunner of the fluorescent tube and the neon light. Roentgen discovered x-rays while working with a Crookes tube (Fig. When this material is taken in small bites and reviewed as needed, the entire process of creating and controlling x-rays will gradually come into focus. Do not attempt to assimilate it all at once. Although it is all interrelated and is presented in a logical order, you may feel a bit overwhelmed if you try to comprehend it too quickly. Chapters 4 and 5 contain a tremendous amount of detail, and most of it is probably unfamiliar to you. The electric factors that control x-ray production are introduced in this chapter. This chapter is about x-ray tube structure and function and how these factors affect the primary x-ray beam.
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