20 



BIOPHYSICALLY ACTIVE X-RAYS 



TABLE 1-4 

 Absorption Formulas for Filters 



* Compare blood with hydrogen. After Mayneord [1929], attributed to Kiistner. 



It will be noticed that 1 mm of aluminum allows 36 per cent of the 

 incident energy to be transmitted at 80 kv, 2 mm allows 23 per cent, 

 and 3 mm only 16 per cent to be transmitted. Evidently 3 mm does 

 not transmit one third as much as 1 mm. Neither does the transmission 

 increase linearly with the applied voltage. The absorption governing 

 these phenomena can, however, be represented by the empirical equa- 

 tions shown in Table 1-4, where ju OT is the mass absorption coefficient 

 for the wavelength region designated and p is the filter density 

 (pai = 2.70 grams/cc and p Cu = 8.94 grams/cc). 



Scattering Coefficients 



Next the contribution made to the energy loss of the x-ray beam 

 passing through a filter, by scattering, must be considered. Here, 

 as for absorption, an analogous mass scattering coefficient (<r m ) for the 



