328 



1S0T0PIC TRACERS AND NUCLEAR RADIATIONS [Chap. 10 



o 



+ +H.V. 



Fig. 80. Neher-Harper quenching circuit. The grid bias voltage is adjusted at R2 so 

 that tube V is normally nonconducting. When the counter tube discharges, the grid is 

 driven positive and the tube conducts, thus producing the necessary voltage drop in 

 resistance R3 to stop the counter discharge. The time constant of the circuit is deter- 

 mined by R3 and C. Approximate values of the constants are Rl = 10 6 — 10 7 ohms, 

 R3 = 10,000 ohms and C = 100 wld. [C. E. Wynn-Williams, Brit. Pat., 421 341 

 (1934); H. V. Neher and W. W. Harper, Phys. Rev., 49, 940 (1936).] 



H.V. C- 



Fig. 81. Multivibrator quenching circuit. The high negative bias, — C makes first section 

 of the multivibrator nonconducting while the second section is normally conducting. A 

 negative pulse from the counter tube initiates one cycle of multivibrator during which the 

 first section conducts momentarily and thus applies a high negative voltage pulse to the 

 counter tube anode to extinguish the discharge. The time constant of the circuit depends 

 primarily on the values of R2 and C2. [/. A. Getting, Phys. Rev., 63, 103 (1938).] 



kind of counter tube since some quenching circuits also serve as a preampli- 

 fier and provide a low-impedance output which permits the use of long con- 

 necting cables to the scaling or the recording circuit. Furthermore it is 

 found in many instances that the quenching circuit can, when properly- 

 adjusted for the counter, improve the pulse shape and duration, particularly 



