Sec. 10.22] 



GEIGER-MULLER COUNTERS 



329 



for old counters. If no quenching or preamplifying circuit is used with a 

 self-quenching counter tube, the lead to the counting circuit should be short 

 and well shielded. Lengths up to several meters usually will not seriously 

 impair the pulse characteristics. 



The most frequently used quenching circuits are shown in Figs. 79 to 82. 



+ 150 v. 



OUTPUT 



Fig. 82. Modified Neher-Pickering quenching circuit. This circuit allows operation of 

 the counter tube with the cathode grounded. It further provides one stage of amplification 

 (V2), stabilization by negative feedback and a cathode follower output (V3). 



Rl, R3 = 1 megohm 

 R2, R6 = 10,000 ohms 

 RA = 240,000 ohms 

 R5 = 5 megohms 



Rl, R\\ = 20,000 ohms 

 RS = 1.1 megohms 

 R9 = 56,000 ohms 

 RIO = 5 megohms 



CI == 50 MMfd 

 C2 = 250 MM fd 

 C3 = 100 w*fd 

 VI = 6AK5 

 V2, V3 = 6J6 



10.22. Scaling Circuits. Scaling circuits must be used whenever the 

 counting rate exceeds that which the mechanical register can follow without 

 loss of counts. For the best registers the limiting rate is about 25 to 50 cps. 

 In practice, however, scaling circuits are normally employed for all but the 

 lowest counting rates. Most counter circuits now available are based on 

 the scale of two, with six such sealing circuits in series to provide a total 

 scale factor of 64. 



The fundamental scale of two circuit consists of a trigger circuit that has 

 two stable states of operation, the first tube conducting and the second 

 nonconducting, or the reverse. The arrival of a pulse flips the trigger cir- 



