134 



MICROSCOPIC TECHNIQUES 



unit was designed to develop 1.5 kilowatts at 50 kilovolts or 4.5 

 kilowatts at 15 kilovolts. The evacuation of the roentgen tubes was 

 accomplished by a three-stage mercury diffusion pump connected to 

 a two-stage mechanical forepump. A cooled trap was placed between 

 the tubes and the pumps. 



Roentgen Tube for Primary Excitation. In order to obtain a 

 line spectrum of great intensity it is best to solder the element whose 

 line spectrum is desired to the anode. This cannot always be done, 

 but for elements which lend themselves to this procedure, the anode 

 is made with six surfaces having a different element or suitable alloy 

 of it on each surface. A diagram of the tube is shown in Figure 22. 

 The forged brass body (A) has four openings and bored channels 

 for cooling. The water-cooled cathode (F) with filament E is sepa- 



Fig. 23. Roentgen tube for secondary excitation. 

 From Engslrom (1946) 



rated from A by rubber packing. The anode (B) is insulated from 

 A, which is grounded, by the porcelain tube C. A rubber packing 

 separates the cone (D) from C. The anode may be turned to present 

 its different surfaces to the cathode without breaking the vacuum 

 by virtue of an Apiezon grease packing between it and D. The 

 anode is water-cooled. The roentgen beam is passed through slit G 

 which is covered with an aluminum foil (9 /a thick) fastened on 

 with Apiezon grease. The flexible tube H connects to the vacuum 

 apparatus. The filament (E) consists of a 0.25 mm. platinum wire 

 winding which is coated with an oxide layer (made by burning off 

 sealing wax) . 



