X-RAY SPECTRAL DISTRIBUTION 



9 



At these low kilovoltages a continuous spectrum, as indicated by the 

 smooth curves, is observed outside the glass-jacketed vacuum tube. 

 Compare these data with those represented in Fig. 1-5, and note partic- 

 ularly the sharp peaks which 

 appear in the 110-kv spectrum 

 emitted by a tungsten target. 



The continuous spectrum or 

 " general radiation " begins sud- 

 denly at the minimum wave- 

 length Xq obtainable from 



100 



90 



80 



\ V P = 12,395 



, is the maximum po- 

 across the tube. If a 



where V 

 tential 



rectified alternating potential is 

 used to excite the roentgen 

 tube, then V p is the peak volt- 

 age. 



From X the intensity rises 

 rapidly to a maximum (X max ), 

 from which it gradually declines. 



In the roentgenographic re- 

 gion generally used for diagnos- 

 tic work or superficial therapy, 

 namely, 100 to 50 kv (0.12 to 

 0.25 A), the maximum intensity 

 of the general radiation, to a 

 good approximation, is found at 



70 



.2 60 



'^50 



TO 



a 



40 



30 



20 



10 



1 



KcXya 2 



110-kv tungsten spectrum 

 No filter 



0.28 mm tungsten filter 



0.1 0.2 0.3 o 0.4 



Wavelengths in A 



0.5 



*max 



l.GXo 



Fig. 1-5. These curves show the general 

 x-ray spectrum of tungsten with super- 

 imposed characteristic K series. Note that 

 the 0.28-mm tungsten filter does not change 

 the distribution of the wavelengths. Com- 

 pare these with the curves of Fig. 1-14, 

 where filters other than tungsten were used. 

 (By courtesy of A. W. Hull.) 



These curves are typical examples of the distribution in intensity 

 of a continuous spectrum emitted by a tungsten target excited by the 

 indicated differences of potential. Note particularly that these are 

 general radiation curves with the bright-line spectra of tungsten missing. 

 They show that the continuous spectrum possesses a rapid intensity 

 increase on the short-wavelength side of the curve and that its maximum 

 intensity shifts to longer wavelengths as the exciting voltage is de- 

 creased, and also that the total x-radiant energy, as indicated by the 

 area under each curve, rapidly increases with the increase in exciting 

 potential. This area, when expressed in terms of intensity, is for all 

 practical purposes proportional to the square of. the exciting potential. 



