184 RADIATION BIOLOGY 



requires the use of a 450- to 600-v power source for 8-ft lamps, and lamp 

 life is considerably below normal. 



The third method involves the high-voltage series operation of "instant- 

 start" lamps. Very satisfactory results have been obtained by using 

 approximately 600 v rms per 96-in. tube in series at currents of 300- 

 600 ma. A bank of 34 tubes operating in series on 20,000 v with a single 

 600-ma power transformer and a separate inductance as a ballast has 

 given excellent performance as to reliability and lumen maintenance over 

 a 6000-hr life (Withrow and Harrison, unpubhshed). The principal 

 advantage of such operation is the almost complete lack of internal 

 wiring and the relatively high efficiency of large transformers and induct- 

 ances. The transformer and choke can be placed at any convenient 

 location, and a single two-conductor high-voltage cable is all that is 

 needed to power the bank. The disadvantage is the personnel hazard 

 involved in handhng such high voltages in a laboratory and the extreme 

 protective measures that must be employed. 



A fourth method employs paper capacitor ballasts on a high-frequency 

 power supply. Campbell and Bedford (1947) have shown that, at high 

 frequencies of 300-600 cps, small and inexpensive ballasts may be used. 

 The power dissipated in the paper capacitor ballast is negligible. For 

 96-in. lamps, however, the power supply must be at least 450 v rms, 

 and preferably 600. The high frequency may be obtained from a high- 

 frequency resonant magnetic converter (Campbell, 1948), which converts 

 the 60-cps power frequency to some higher harmonic, such as the ninth, 

 at 540 cps. A 400-cps motor generator set also may be used. Capacitor 

 ballasts cannot be used at freciuencies much below 400 cps for gaseous 

 discharge lamps. At 60 cps a capacitor ballast leads to very unstable 

 operation and a sharply peaked wave form that is destructive of cathodes. 



SHORT-DURATION SOURCES 



Sources that emit radiation in short pulses of 10"^ to 10^^ sec are used in 

 many types of experimentation for the determination of the kinetics of 

 thermochemical reactions associated with photochemical processes, in 

 photography, and as sources for studying high-speed mechanical systems. 

 Flash tubes have been used in studies of the kinetics of photosynthesis 

 by several investigators. Short-duration sources may be classified as 

 single-flash types, in which the basic element must be replaced after each 

 flash, and as repetitive-flash types, where high speeds of flashing can be 

 maintained for thousands of pulses before the tube must be replaced. 



PHOTOFLASH LAMPS 



This type of lamp is extensively used in photography and is a chemical 

 source in which the radiant energy is produced by the burning of alumi- 



