Sec. 10.4] 



GEIGER-MULLER COUNTERS 



309 



counting rate for increasing anode voltage. The important characteristic 

 of a Geiger-Muller, or discharge, counter is the existence of a well-defined 

 plateau voltage region over which the counting rate does not increase appre- 

 ciably. Normally this region of the curve should be flat and the counting 

 rate should not increase more than 2 to 5 per cent per 100 volts over an 



Fig. 76. Counter pulse characteristics. [H. G. Slever, Phys. Rev., 61, 38 (1942). 



VOLTAGE 

 Fig. 77. Counting-rate characteristics of counters as a function of anode voltage. 



interval of 100 to 300 volts, although shorter plateaus are satisfactory with 

 well-regulated voltage supplies. 



The following voltages are frequently referred to because they are asso- 

 ciated with characteristic properties of counter tubes at various potentials 

 (see Fig. 77). 



1. Starting voltage. This is the lowest voltage at which counts are 

 observed. It depends largely on the sensitivity of the detecting circuits 

 used. 



2. Proportional threshold voltage. This is the lowest voltage at which pro- 



