192 Applied Biophysics 



The actual energy liberated in 1 gram of the medium may be 

 compared with the energy communicated by one rontgen of X- 

 or gamma radiation to 1 gram of air, which is a definite quantity 

 equal to about 85 ergs ; or it may be compared with the energy 

 communicated by one rontgen of X- or gamma radiation to 

 1 gram of the medium in question, which is not a definite 

 quantity, but depends on the quality of the radiation and the 

 nature of the medium. In view of the heterogeneous nature of 

 "tissue," it is perhaps as well to base the comparison on energy 

 absorption in air.* Thus, to arrive at the dose in equivalent 

 rontgens, it is merely necessary to know the total amount of the 

 radioactive material, the energy emission per distegrating atom, 

 and the total mass through which the material is dispersed, from 

 which is deduced the energy liberated per unit mass of the 

 medium, which is divided by 85. 



References ** 



1 Bragg, W. H. (1912) Studies in Radioactivity, London. 



2Clarkson, J. R. and W. V. Mayneord (1939) Brit. J. Radiol. 12, 168. 



3 Compton, A. H. and S. K. Allison (1935) X-rays in Theory and 



Experiment, New York, 

 4Failla, G. (1937) Amer. J. Roentgenol. 29, 202. 

 5 Farmer, F. T. (1945) Brit. J. Radiol. 18. 148. 

 fiFricke, H. and O. Glasser (1925) Fortschr. Rontgenstr. 33, 239. 

 ^Friedrich, W. (1938) Amer. J. Roentgenol. 40, 69. 



8 Glasser, O. (1944) Medical Physics, Chicago. 



9 Glasser, O., E. H. Quimby, L. S. Taylor and J. L. Weatherwax 



(1944) Physical Foundations of Radiology, New York. 



10 Gray, L. H. (1937) Brit. J. Radiol. 10, 600 and 721. 



11 Gray, L. H. (1944) Proc. Camb. Phil. Soc. 40, 72. 



12 Gray, L. H. and J. Read (1939) Nature, Land. 144, 439. 



13 Holthusen, H. and R. Braun (1933) Grundlagen iind Praxis der 



Rontgenstrahlen-Dosierung, Leipzig. 



14 Jones, D. E. A. and L. H. Clark (1943) Brit. J. Radiol. 16, 166. 



* The energy absorption in water (for hard gamma radiation"), i.e., Cray's 

 energy unit, is in many cases a better basis for comparisons. This "equivalent 

 rontgen" corresponds to about 94 ergs per gram. 



** A comprehensive bibliography of this subject would be out of place here. The 

 selection of references is arbitrary and in no way representative. It merely 

 includes work referred to explicitly in the text and a few random papers which 

 may serv^ as a possible entry point into the literature, 



