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LXIII. Precision-measurements in the X-Iiay Spectra. 

 Part II. By Dr. Manne Siegbahn *. 



The X-ray Spectrum of Tungsten. 



THE X-ray spectrum of Tungsten has often formed the 

 subject of investigation because of its importance 

 for practical use in X-ray tubes, as these are nowadays 

 mostly furnished with anticathodes of tungsten. Never- 

 theless it must be remembered that the line-spectrum of 

 tungsten is only of importance with very high potentials 

 (75 kv. and higher) in the tube where the K-series of 

 the spectrum is produced. Up to date the K-series of 

 tungsten has not been proved to occur in ordinary gas- 

 filled tubes. With (Joolidge-tubes there are no difficulties 

 in producing it. Likewise Lilienfeld and Seemann have 

 shown that with tubes of the Lilienfeld design the 

 somewhat harder K-series of Platinum can readily he 

 produced. There are also reasons for believing that some 

 of the special "therapeutic''' tubes of later design will 

 be able to produce these hard line-spectra. On the other 

 hand, the L-series of tungsten, which is always produced 

 in the tube, is very strongly absorbed in the glass wall 

 of the tube and is therefore of little importance for technical 

 purposes. 



Besides the above-mentioned interest of the tungsten 

 spectrum, it is worthy of a complete investigation from 

 the fact that with this element all the three series K, L, M 

 can be readily studied. It is the purpose of this paper 

 to give the results of an investigation of the K- and L- 

 series, whereas the M-series, which has also been measured 

 with the same spectroscopical apparatus, will be published 

 bv Mr. Wilhelm Stenstroin in his dissertation at Lund. 



The IZ-series. 



For the study of the K-series a spectrograph was used 

 which has been built especially for investigations of Aery 

 hard rays. Its construction is seen in figs. 2 & 3. The 

 essential features of the instrument are shown in fig. 1 . 



* Communicated bv the Author. Tart I., Phil. Mag. Juhq 1919,. 

 pp. 601-612. 



