RADIATION DOSE 



space of the energy deposited within biological materials exposed to ionizing 

 radiation, i cfiTs only to an initial state. New species are formed locally along 

 the track in high concentrations and will move radially outwards and mingle 

 \vith one another, in accordance with the laws of diffusion, in times which 

 have been estimated to be ~ 10~" sec-*. Large electric fields arc suddenly 

 brought into existence by the separation of positive and negative charges'-^. 

 These fields will, at first, influence the movement of electrons and all ionic 

 species, and in a polar medium may break secondary hydrogen bonds and 

 thus lead to disorder in micromolecules and possibly to denaturization of 

 proteins-*-". The rapidity of the changes which we believe to be occurring 

 along the path traversed by an ionizing particle is one added difliculty in the 



0-6^ 



1000 



Figure 7. Efficiency tj as a function of photon energy for a process requiring 

 an energy transfer of amount, 0-5 < < 3-0 ekV 



already complex task of providing a physical basis for the interpretation of 

 the chemical and biological changes which the irradiation provokes. 



REFERENCES 



^ Report of the International Comrriission on Radiobiological Units and Measurements (I. C.R.U.), 



Handbook 62: U.S. Department of Commerce, National Bureau of Standards, 



Washington, 1956 



2 Gray, L. H. Brit. J. Radiol. N.S. 29 (1956) 355 

 ^BoAG, J. W. Communication to the International Symposium on Quantities, Units and 



Measuring Methods of Ionising Radiations, Rome, 1958 — in the press 

 « Wilson, C. T. R. Nobel Lecture, Les Prix Nobel en 1927, p. 6 

 ^Hutchinson, F. Radiation Res. 7 (1957) 473 



'Hutchinson, V., Preston. A. and Vogel, B. Radiation Res. 7 (1957) 465 

 ^Lea, D. E. Actions of Radiations on Living Cells, 2nd edn: Cambridge University 



Press, London, 1955, p. 51 

 sChapiro, a. Radiation Res. 6 (1957) 11 

 "Ghormley, J. A. Radiation Res. 5 (1956) 247 

 loSuTTON, H. C. and Rotblat, J. Nature, Lond. 180 (1957) 1332 



12 



