TUNGSTEN X-RAY SPECTRUM 191 



THE TUNGSTEN X-RAY SPECTRUM. 



ELMER DERSHEM. 



Some work has recently been done in this Laboratory In the 

 analysis of the molecular arrangement in certain crystals by 

 means of the reflection of X-rays from these crystals. To carry 

 out this work it was first necessary to determine the wave 

 lengths of the characteristic lines of the tungsten X-ray spec- 

 trum because tungsten is the material of the anticathode of the 

 Coolidge X-ray tube, the most satisfactory tube for this kind 

 of work. 



The method of obtaining the X-ray spectra was essentially the 

 same as that used by many other X-ray investigators. A crystal 

 was mounted inside a lead box in such a way that it would be 

 slowly and uniformly rotated by means of the rising of a float 

 in a tank into which water from a constant head source was 

 allowed to flow. A cleavage face of the crystal was placed in 

 the vertical axis of rotation and X-rays coming through a nar- 

 row vertical slit in the lead shield between the crystal and the 

 tube were reflected from the crystal whenever the angle made 

 by the crystal planes with the incident rays satisfied the condi- 

 tion given by the formula n x =2dsin €3 in which n is a whole 

 number, the order of the spectrum. x is the wave length, d is 

 the distance between planes parallel to the face in question 

 and €3 the angle between these planes and the incident rays. 

 A photographic plate was placed inside the lead box and with 

 its plane perpendicular to the line joining the crystal and the 

 source of X-rays. In this position it would receive and register 

 a vertical line, or image of the slit, whenever the angle of the 

 crystal was such as to accommodate, according to the above 

 formula, any wave length existing in the X-ray spectrum of 

 tungsten. The distance along the plate from the center to the 

 position of any one of the lines and the distance from the axis 

 of rotation of the crystal to the plate being known it is easy 

 to determine the angle of reflection since the ratio of these dis- 

 tances gives the tangeni of twice this angle. 



