336 



ISOTOPIC TRACERS AND NUCLEAR RADIATIONS [Chap. 10 



counter-tube resolving time. Typical coincidence circuits are shown in 

 Figs. 89 and 90. 



If the polarity of the pulses from one or more counter tubes in a circuit is 

 reversed before being mixed with simultaneous pulses from the remainder 



Fig. 91. Anticoincidence circuit. A pulse at input 3 is reversed in polarity in F4 and will 

 cancel pulses at inputs 1 and 2 if they occur simultaneously with a pulse at input 3. VI, V2, 

 and Vi are normally conducting whereas V\ is normally nonconducting. The resistance R 

 is chosen to give the correct total plate current for VI and 72. [G. Herzog, Rev. Sci. Instru- 

 ments, 11, 85 (1940).] 



of the tubes, such counter tubes form an anticoincidence set. Simultaneous 

 discharges in the coincidence and anticoincidence sets cancel in the mixing 

 stage and are therefore not registered as a count. Furthermore, independent 

 discharges of the anticoincidence set are clipped at some stage in the counter 

 circuit, thus permitting only independent discharges of the coincidence set 

 to register as counts. 



Examples of such circuits are shown in Figs. 89, 90, and 91. 



10.26. Counting-rate Meter. The counting-rate meter is a circuit devel- 

 oped for the purpose of providing an output, usually a d-c voltage, which is 



