WAVELENGTH OF A HETEROGENEOUS X-RAY BEAM 



2.0 



29 



5 10 



Aluminum filter thickness in mm 



Fig. 1-12. Decrease of the per cent transmission with increased filter thickness. 

 From their shape, the solid curves seem to indicate an exponential absorption. Had 

 they followed an exponential law of absorption the broken curves would have been 

 straight lines. Note that at large filter thicknesses the broken curves become linear. 

 (After Taylor and Singer.) 



radiation it is possible to make use of absorption measurements. These 

 measurements determine the comparable wavelength of a homogeneous 

 radiation which would be reduced in intensity by a given filter in the 

 same degree as the heterogeneous radiation. The heterogeneous radia- 

 tion is then designated as having an effective wavelength equal to that 

 of its corresponding homogeneous radiation. This does not imply, 

 however, that the effective wavelength equivalent can produce the same 

 biological results as its comparable heterogeneous beam. 



Illustrations of the method for determining the effective wavelength 

 with its composite absorption coefficient are found in Fig. 1-13, where 

 with increasing thickness of the copper filter the logarithm of the trans- 

 mitted energy is plotted against thickness of filter material. 



Suppose that one were interested in obtaining a beam of radiation 



