LIGHT SOURCES AND DETECTORS 



5: 10 



25 30 



60 80 100 120 125 



Volts per stage 



Figure 28.31 Typical amplification characteristics of 931 A and IP21 photo- 

 multipliers. A average multiplication; B typical residual current values as 



functions of stage voltage 



• ♦ 1500 V 



Figure 28.32 Basic circuit of a feedback 

 densitometer {after Sweet^^) 



ooooo ooo 



O CO CM 03 vj vj 00 



C>J «— ,— 1 1 



Temperature of phototube °C 



Figure 28.33 Effective cathode dark current 

 of a multiplier phototube with antimony- 

 caesium photocathode as function of tem- 

 perature. {By courtesy of the Journal of 

 the Optical Society of America^^) 



364 



