334 



ISOTOPIC TRACERS AND NUCLEAR RADIATIONS [Chap. 10 



With more complicated circuits, pulses lying within a desired voltage 

 range can be passed, whereas pulses smaller and larger are rejected. With 

 several such units, pulses produced by electrons, protons, alpha particles, 

 and fission fragments may be distinguished and recorded separately. 



10.24. Recording Circuits. The recording or register-driving circuit is 

 essentially a power output stage delivering sufficient power at each pulse to 



A OUTPUT 



Fig. 89. Rossi coincidence circuit. A threefold coincidence arrangement is shown 

 but may be extended to an TV-fold circuit by placing N identical input stages in parallel 

 with the tube plates connected to a common resistance R as shown. All tubes are 

 normally conducting. Any fraction of the coincidence set may be made nonconducting 

 by negative input pulses without altering appreciably the voltage at A provided at least 

 one tube remains conducting. If, however, all N tubes are cut off simultaneously, 

 their combined resistance becomes high and a large pulse is produced at the output A. 

 [B. Rossi, Nature, 125, 636 (1930).] 



actuate a mechanical register. For most registers available for counter 

 circuits the output pulse should be 200 to 300 volts at 16 to 50 ma. The ideal 

 output pulse shape is rectangular with a width of the order of 0.01 sec. This 

 can usually be achieved by preforming the pulse before it enters the final 

 power output stage. 



Registers commonly used in counter circuits consist of a light moving 

 armature actuated by the magnetic field of an inductance placed in the plate 

 circuit of the output stage. Through a ratchet mechanism connected to the 

 armature, each pulse is indicated by unit movement on some kind of dial 

 used as an indicating device. 



The maximum counting rate of a register depends on the inertia of the 

 mechanism and the driving power. Although some registers will indicate as 



