PRINCIPLES OF RADIOLOGICAL PHYSICS 



25 



momentum which was previously possessed by the electrons themselves. X rays 

 of lower frequency are emitted more uniformly in different directions (see Fig. 

 1-17). 



When the voltage applied to an X-ray tube is rather low and the anode material 

 rather light, the intensity of the "characteristic" X rays arising from oscillating 



200 400 600 800 



INTENSITY, arbitrary units 

 Fig. 1-17. Approximate X-ray intensity distribution in different directions for oper- 

 ation at different voltages and with different target materials. (A) Aluminum 

 target, 34 kev (Honerjdger, 1940). (B) Tungsten target, 1.25 Mev (Buechner et al., 

 1948). (C) Tungsten target, 2.00 Mev. (D) Tungsten target, 2.35 Mev. 



10 



30 



40 



20 

 ENERGY, kev 



Fig. 1-18. Approximate spectral distribution of X rays from a molybdenum target 

 tube operated at 35 kv. Notice the two ''lines " of characteristic X rays of the target 

 material. 



currents within the atoms compares with the intensity of the "continuous" spec- 

 trum generated directly by the incident electrons. Figure 1-18 shows a spectrum 

 of the intensity of the X-ray components of different frequencies emitted by a 

 tube with a molybdenum anode operated at 35 kv. 



Monochromatic X rays of wave lengths ranging dowm to less than 



10-1" cm = 0.01 A 



