![]() ![]() Inner-shell electrons are nearer the nucleus than others in an atom and thus feel little net effect from the others. Characteristic x rays are produced when an inner-shell vacancy is filled. How do we calculate energies in a multiple-electron atom? In the case of characteristic x rays, the following approximate calculation is reasonable. This property can be used to identify elements, for example, to find trace (small) amounts of an element in an environmental or biological sample.Ĭalculate the approximate energy of a K α x ray from a tungsten anode in an x-ray tube. The energies of these x rays depend on the energies of electron states in the particular atom and, thus, are characteristic of that element: every element has it own set of x-ray energies. Similarly, when an electron falls into the n = 2 shell from the n = 3 shell, an L α x ray is created. A more energetic K β x ray is produced when an electron falls into an n = 1 shell vacancy from the n = 3 shell that is, an n = 3 to n = 1 transition. The labels K, L, M,… come from the older alphabetical labeling of shells starting with K rather than using the principal quantum numbers 1, 2, 3, …. ![]() X rays created when an electron falls into an n=1 shell vacancy are called K α when they come from the next higher level that is, an n = 2 to n = 1 transition. Figure 2 shows a representative energy-level diagram that illustrates the labeling of characteristic x rays. A characteristic x ray (see Photon Energies and the Electromagnetic Spectrum) is electromagnetic (EM) radiation emitted by an atom when an inner-shell vacancy is filled. The most energetic of these are produced when an inner-shell vacancy is filled-that is, when an n=1 or n=2 shell electron has been excited to a higher level, and another electron falls into the vacant spot. When the anode’s atoms de-excite, they emit characteristic electromagnetic radiation. Part of the energy that they deposit by collision with an atom results in one or more of the atom’s inner electrons being knocked into a higher orbit or the atom being ionized. Some electrons excite atoms in the anode. For example, a 100-kV accelerating voltage produces x-ray photons with a maximum energy of 100 keV. Electric potential energy is converted to kinetic energy and then to photon energy, so that E max = hf max = q eV. Units of electron volts are convenient. Thus the accelerating voltage and the maximum x-ray energy are related by conservation of energy. The highest-energy x ray produced is one for which all of the electron’s energy was converted to photon energy. The broad range of x-ray energies in the bremsstrahlung radiation indicates that an incident electron’s energy is not usually converted entirely into photon energy. The spectrum in Figure 1 is collected over a period of time in which many electrons strike the anode, with a variety of possible outcomes for each hit. The x-ray spectrum in Figure 1 is typical of what is produced by an x-ray tube, showing a broad curve of bremsstrahlung radiation with characteristic x-ray peaks on it. The second process is atomic in nature and produces characteristic x rays, so called because they are characteristic of the anode material. ![]() In one process, the deceleration of electrons produces x rays, and these x rays are called bremsstrahlung, or braking radiation. There are two processes by which x rays are produced in the anode of an x-ray tube. A different anode material would have characteristic x-ray peaks at different frequencies. The smooth part of the spectrum is bremsstrahlung radiation, while the peaks are characteristic of the anode material. X-ray spectrum obtained when energetic electrons strike a material, such as in the anode of a CRT.
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