290 



ISOTOPIC TRACERS AND NUCLEAR RADIATIONS 



[Chap. 9 



stability, adaptability to routine analyses of gases and vapors, and the small 

 energy spread of the ions it produces. 



The general scheme of this type of source is illustrated by the example 

 shown in Fig. 69. The sample material is admitted to a small closed ioniza- 



FiG. 67. Spark discharge ion source. Ions formed in the discharge between the end of the 

 anode A and the wall of the cathode C are accelerated and focused through slit S. [A . E. 

 Stow and W. Rail, Atomic Energy Commission Report, MDDC-45 (1946).] 



tion chamber whose dimensions are of the order of a centimeter. Ionization 

 is produced by a stream of electrons which enter through a collimating slot 

 at one end and traverse the chamber to be collected at the opposite side by an 

 anode. A fraction of the ions that are produced diffuse out through a slit 



Fig. 68. High-voltage gas-discharge ion source. Ions are formed in the gas discharge 

 maintained between the anode A and hollow cathode C. Those ions passing through the 

 cathode are then collimated by slit 5 before entering the analyzing fields. Material to be 

 analyzed may be introduced as a gas, or if solid, may be deposited on the cathode. [A'. T. 

 Bainbridge and E. B. Jordan, Phys. Rev., 50, 282 (1936).] 



in one side of the chamber and are then accelerated in an electric field main- 

 tained by an appropriate slit or electrode system. 



The filament may be made of tungsten or tantalum and used in the form 

 of a helix or a short thin ribbon, usually about 0.001 in. thick. Heating 

 current for filament cross sections commonly used is about 5 amp, alternating 



