552 



BIOLOGICAL EFFECTS OF RADIATION 



L1-L2 have been reduced to the point of connecting directly from one 

 tube base to the other. The circuit elements then remaining for the 

 production of high-frequency currents consist of the grid-to-plate capaci- 

 tance of the two tubes (in series) combined, and the inductance of the 

 leads connecting these elements. Naturally, when such a point is 

 reached, it becomes difficult to take power from the tube circuit, owing 



^7- 



C3 







+ <- 



Li 



A 



1-3 



Fig. 1. 



to the limited magnetic coupling possible. Therefore, the practical 

 fundamental frequency possible when using commercial tubes is that 

 frequency which is generated when some external inductance in the form 

 of a loop remains for coupling to an experimental circuit where the energy 

 will be used. Such a circuit is indicated in Fig. 1 as L3-C3. The physical 



details of this circuit as well as that of 

 Fig. 2 will be discussed later. 



The voltage distribution in the 

 circuit shown in Fig. 1 is such that it 

 is maximum at the grid and plate ends 

 of the two inductance loops and zero 

 at the point where the plate voltage and 

 grid resistor are connected. It is 

 necessary then to couple L3 and CS to 

 the oscillator circuit so as to provide a 

 region for exposing biological material. 

 This is provided between the plates of 

 condenser C3 in the exposure circuit. 

 It is necessary to provide also a means 

 of resonating the exposure circuit to 

 the frequency of the oscillator circuit 

 and this is usually accomplished by 

 varying the size of loop L3 after the biological material has been placed 

 between the condenser plates in the exposure circuit. The amount of 

 high-frequency voltage available across the plates of the condenser C3 

 is controlled by varying the magnetic coupling factor between LI and L3, 

 or by fixing the magnetic coupling and varying the voltage applied to the 

 oscillator tubes. All of these items have a variable elTect upon the 

 frequency of the oscillations generated, but it has been found that within 



Ct 



Fig. 



