Sec. 5-1] 



RADIATION TRANSDUCERS 



257 



stabilized supply sources is required. For instance, a variation of the 

 supply voltage by 1 per cent can cause a variation of the photo- 

 multiplier output by as much as 10 per cent. 



Numerous methods have been devised to avoid the variation with 

 load of the partial voltages incurred with resistive voltage dividers. 



O) 



o 



+- 



o 

 o 



Q. 



. -O -^ 



1.0 1.5 



Light flux , arbitrary units 



Fig. (5-1)22. Relative response of an RCA 931-A photomultiplier 

 as a function of the light flux in the circuit of Fig. (5-1)21. i b , 

 anode current; i t , voltage divider current for zero light flux 

 [from R. W. Engstrom and E. Fischer, Rev. Sci. Instr., 28, 525 

 (1957); by permission]. 



11111 

 —Supply voltage — 



Fig. (5-1)23. Compensated resistive voltage divider; all 

 resistance values in megohms [from R. W. Engstrom and 

 E. Fischer, Rev. Sci. Instr., 28, 525 (1957); by permission]. 



For pulsed light (e.g., scintillation counters), the insertion of capaci- 

 tors in parallel to the resistors of the dividing network, as shown in 

 Fig. (5-1)24, is frequently satisfactory. Only the last few stages need, 

 in general, such a capacitive bypass. 1 



1 F. H. Marshall, J. W. Coltman, and A. I. Bennett, Rev. Sci. Instr., 19, 

 744 (1948); R. Dehn, Brit. J. Appl. Physics, 7, 144 (1956); J. A. Rajchman 

 and R. L. Snyder, Electronics, 13, 20 (December, 1940). 



