Sec. 10.23] 



GEIGER-M ULLER CO UN TERS 



333 



rejected. This is usually accomplished either with a multigrid tube with a 

 negative grid bias or with a diode, both of which pass only positive pulses. 

 Typical scale of two circuits are shown in Figs. 83 and 84. 



Less frequently used in the past, decade counters and "ring" circuits 

 are now finding more frequent application. An example of a highly efficient 

 decade circuit is shown in Fig. 85. 



TO REGISTER 

 Q 



Fig. 88. Recording circuit from "Model 200" pulse counter. 71 reshapes the pulse into 

 a rectangular form before it enters the power tube V2. The output pulse length is 0.01 sec 

 and delivers sufficient power to operate any register that requires no more than 40 ma and 



300 volts. [W 

 706(1947).] 



Rl 



A. Higinbotham, J. Gallagher, and M. Sands, Rev. Sci. Instruments, 18, 



2 megohms 

 R2 = 200,000 ohms 

 R3 = 1 megohm 

 U4 = 1,500 ohms 

 R5 = 10,000 ohms 

 R6 = 20,000 ohms 

 Rl = 30,000 ohms 

 R% = 100,000 ohms 



CI = 0.05 M fd 

 CI = 0.005 M fd 

 C3 = 20pfd 

 C4 = 8 M fd 

 C5 = 4 M fd 

 C6 = 0.01 ,ufd 

 VI = 6SL7 

 V2 = 6V7 



10.23. Discriminators. Discriminating circuits are often placed before 

 counter circuits for the purpose of rejecting pulses smaller than a predeter- 

 mined peak voltage. Their function is particularly useful for proportional 

 counters where the pulse size depends upon the intensity of ionization pro- 

 duced by the incident particle. Thus, in counting alpha particles the back- 

 ground is effectively reduced by rejecting the smaller pulses initiated by 

 electrons, gamma rays, and protons. 



