130 



W. ARNOLD 



For the last part of the decay curve, the Chlorclla suspension was 

 transferred after being illuminated into a large glass vessel directly in 

 front of the photomultiplier, and the signal was recorded as a func- 

 tion of the time. The suspension was kept at room temperature by a 

 water jacket. A hand-operated shutter made it possible to check the 

 dark current of the photomultiplier from time to time. 



c 



3 



w 

 O 



w 



2 



w 

 O 



N 



1 = 500.0 



3 4 



TlME(min) 



— r 

 6 



Fig. 3. The reciprocal of the square root of the intensity of the delayed Hght 

 as a function of the time in the dark. Numbers on the curve give the relative 

 intensity of the continuous exciting light. 



For dark times less than a few hundredths of a second, the flowing 

 method is not satisfactory. In order to obtain some information about 

 the beginning of the decay curve a small air-driven high-speed cen- 

 trifuge was converted into a Becquerel Phosphoroscope. This in- 

 strument has two shutters on the same shaft. Each shutter is open 

 a fifth of the time. The two shutters are exactly out of phase. A 

 Chlorella suspension placed between the two shutters and illumi- 



