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fashion, a particular isotope can be distinguished from a mixture or a 

 noisy background. 



Scintillation counters can be made with arbitrary shape and size. 



Central . Conductor 



Gas Mixture 



High Potential 



7 



Outer Cylinder 



T 



Figure 2. Side and end views of a Geiger-Mueller tube. The 

 diameter of the tubes used varies from a few millimeters to 

 25 cm. The length varies from one to 50 cm. 



The efficiency of the geometry used can be easily computed. The 

 proportionality between pulse height and particle energy is more precise 

 than it is for a proportional counter of the type illustrated in Figures 

 2 and 3. The use of liquid scintillation counters allows the immersion 



1,000 



Potential Difference, V (volts) 



Figure 3. Current-voltage relationship for a G-M tube. 

 The current per pulse is plotted as a function of potential for 

 a G-M tube excited by monochromatic y rays. 



of weak samples or low-energy emitters, so that radiations in all directions 

 may be used. Scintillation counters are more efficient than Geiger tubes 

 for gamma ray detection. However, for certain applications G-M 



