. The American journal of roentgenology, radium therapy and nuclear medicine . here is adefinite lower limit in the wave-length (onthe blue end of the spectrum) determinedby the maximum voltage. Above this lower limit (towards the red end) every wave-length is present with some amount of ener-gy, but this energy is not evenly distributed,and it will be noticed that some regions havemore energy (represented by an elevation ofthe line) than those on either side. Thesepeaks or elevations are found to be charac-teristic of the metal in the target, and if theregions of extraordinary energy be repre
. The American journal of roentgenology, radium therapy and nuclear medicine . here is adefinite lower limit in the wave-length (onthe blue end of the spectrum) determinedby the maximum voltage. Above this lower limit (towards the red end) every wave-length is present with some amount of ener-gy, but this energy is not evenly distributed,and it will be noticed that some regions havemore energy (represented by an elevation ofthe line) than those on either side. Thesepeaks or elevations are found to be charac-teristic of the metal in the target, and if theregions of extraordinary energy be represen-ted by a central line passing through thepeak, the characteristic spectrum of theemitting metal is obtained. M. Sommerfeldhas mapped the characteristic spectra ofpractically all the metals. If the corresponding lines of these char-acteristic spectra are designated by the con-ventional letters used by Sommerfeld as inFigure 5, certain remarkable relations arefound to exist between them. I. The same lines appear in practically thesame order in the spectrum of every Fig. 4. X-ray spectrum and light intensity measuredvertically, wave length horizontally. (By courtesyof Dr. Hull.) 2. The wave-length of any particular linegrows shorter as the atomic number (andthe atomic weight )of the element increases. 3. If the number of waves per centimeter(i/A) be used instead of the wave-length,then the difference between various pairs oflines in the same spectrum is the same; as— i^ — L = L — L = L — L — fff 5 7 j8 d 0 p ^^^ 396 X-Ray Spectra and Structure of Matter This ability on the part of the radiatingatom to emit its energy in certain definitelyrelated frequencies gives a clue to the struc-ture of the atom itself. On the basis of factssuch as these, Bohr, Kossel, and Sommer-feld have developed a hypothetical atomwhich should theoretically emit and absorbenergy exactly as actual atoms do. Figure 6is the representation of such an atom. It consists of a positive nucleu
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