338 



ISOTOPIC TRACERS AND NUCLEAR RADIATIONS [Chap. 10 



the average pulse rate and, hence, a vacuum-tube voltmeter included in the 

 circuit may be calibrated directly in terms of average counting rate. Alter- 

 natively, automatic recording devices can be inserted when continuous 

 records are desirable. 



! ! ! ' 



■PULSE EQUALIZER 1 INTEGRATING CIRCUIT VOLTMETER 



Fig. 94. Typical counting-rate meter. 



(1947).] 



Rl, RS, RIO = 100,000 ohms 



R2, 124 = 250,000 ohms 



R3, R22 = 300,000 ohms 



R6, R25 = 2,000 ohms 



Rl = 500,000 ohms 



R8 = 3,300 ohms 



R9 = 30,000 ohms 



2211, RU, R13 = 10 megohms 



RU = 50,000 ohms 



R15 = 25,000 ohms 



R\6, R17, #18, R19, R20 = 15,000 ohms 



[A. Kip, et ah, Rev. Sci. Instruments 117, 323 



R21 = 8,500 ohms 

 R23 = 12,000 ohms 

 R2A, R26 = 1,000 ohms 

 CI, C2 = 100 /x M fd 

 C3 =0.5 Mid 

 C4 = 200 MMid 

 C5 = 2 jufd, polystyrene 

 71, V2, V3 = 6SJ7 

 74 = 6AC7 - GT/G 

 Ml = D-C Voltmeter 

 /l = Phone jack for recording milliammeter 



In principle the integrating circuit establishes an equilibrium voltage 

 across the RC tank circuit which is directly proportional to the counting rate. 

 Equilibrium is reached when the charge leakage rate through the high resist- 

 ance of the tank circuit is equal to the rate of charge added by the pulses. 

 In general, equilibrium is established after several decay half-times of the 

 RC circuit. Starting from zero time, equilibrium is reached [27] when 



t = RCm log 2nRC + 0.394) sec 



where n = number of pulses per unit time 



