Sec. 5-1] 



RA DIA TION TRANSDUCERS 



245 



and sound reproduction where their slight nonlinearity and lower 

 output at high frequencies play a minor role. In physical structure 

 they resemble corresponding vacuum phototubes. 



12 



"D 



10 



u 



0.2 0.4 



0.6 0.8 1.0 

 Time, msec 



1.4 



1.6 



Fig. (5-1)11. Time-response characteristic of a gas-filled 

 photoelectric cell for different plate voltages [from W. S. 

 Huxford and R. W. Engstrom, Rev. Sci. Instr., 8, 385 

 (1937); by permission]. 





100 



en 

 o 



90 



-80 t 



-70 



10 20 50 100 200 500 2,000 



Frequency, cps 



5,000 



20,000 



Fig. (5-1)12. Response of a gas-filled photoelectric tube to light 

 modulated at different frequencies: (A) phototube having S-l or »S'-3 

 response, Fig. (5-1)3; (B) phototube having S-l response, Fig. (5-1)4 

 (from RCA Tube Manual; by permission). 



c. Photomultipliers . A schematic diagram of a photomultiplier 

 is shown in Fig. (5-1)13. Light strikes a photocathode C and liberates 

 electrons; the electrons are accelerated by a voltage E x and focused 



