1078 Mr. D. Coster on the Spectra of X-rays 



Part II. 



The New Measurements of the L- series in the X-ray Spectra 

 of the Elements from Rb to Ba*. 



§ 1. As mentioned above, the results indicated by diagram I. 

 have a direct bearing only on elements of atomic number 

 comparable with that of niton. We should expect a change 

 in this diagram for elements with lower atomic number, 

 since the formation of new shells in the outer region of the 

 atom with increasing atomic number must be accompanied 

 by the appearance of new levels in the energy diagram 

 which find their expression in the appearance of new lines. 



My previous work was based on an investigation of the 

 L-series of most of the elements from W to U t> which I 

 carried out in the laboratory of Prof. Siegbahn. In view 

 of a comparison with the theory of atomic structure, it 

 was desirable to extend this investigation to elements of 

 lower atomic number. In continuation of the former work 

 I have therefore undertaken in the same laboratory an 

 examination of the L-series of such elements. Though 

 this work is not yet finished, the results already obtained 

 seem to be sufficiently interesting to justify publication. 

 In the present paper only the results obtained for the 

 elements Rb-Ba will be discussed. 



§ 2. The apparatus used for the experiments consisted of 

 an X-ray vacuum-spectrograph, and the metal X-ray tube 

 of the Coolidge type described by Prof. Siegbahn J. The 

 tube was driven by two similar induction-coils of medium 

 size. The primaries of the coils were connected in series to 

 a source of alternating current of 50 cycles. As the tube 

 itself acts as a current rectifier, no other rectifier was used in 

 the secondary circuit. For most of the work the secondaries 

 of the coils were connected in series. In this way a current 

 of about 30 m.a. with a maximum tension of about 30 k.v, 

 could easily be obtained. This tension is at the same time 

 about the highest which can be sustained by this tube. 



The tension was estimated by an adjustable parallel spark- 

 gap. If the vacuum is not very good, the discharges through 

 the tube give rise to great fluctuations in the tension. Under 

 these circumstances no simple relation exists between the 

 maximum tension measured by the spark-gap and the mean 

 value. For a very high vacuum, which could be obtained 

 easily with the molecular pump, the maximum tension was 



* Part of these experimental results have recently been published in 

 Archives Neerlandaises (Serie III. A, tome vi., l re livraison, p. 76.) 



1 Zeitschr.f. Physik, iv. p. 178 (1921), and Zeitschr. f. Phys. I. and II. 

 X Phil. Mag. xxxvii. p. 601 (1919). 



