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Elementary Chemical Processes 

 in Radiobiological Reactions * 



MILTON BURTON 



Department of Chemistry 



University of Notre Dame 



Notre Dame, Indiana 



The elementary chemical processes of radiobiology are the elementary chemi- 

 cal effects of high-energy radiation on aqueous solutions containing oxygen, on 

 pure organic matter, and on organic matter suspended in aqueous solution. In 

 the aqueous layer the important primary physical process is ionization; in the 

 organic portion both ionization and excitation must be considered. In biological 

 systems the active entities in the aqueous layer are principally OH and HO2. 

 The presence of the latter radical increases the volume of the effective aqueous 

 layer around the biological particle, f The effectiveness of a hit in the organic 

 material is determined in part by the properties of the surrounding cage and 

 depends, among other factors, on the size of the biological particle. The effect 

 of a hit may be propagated by ionization transfer, by free-radical diffusion, by 

 a chain reaction, or by change in local pH. Furthermore, free H and resultant 

 HO2 are formed in the ambient hquid even when the hit is in the particle itself. 

 In view of these elementary processes the biological particle cannot be uniformly 

 sensitive to radiation over its entire volume, the target of "target theory" is not 

 to be identified wdth the biological particle, a single ionization act is not neces- 

 sarily lethal, and the target dimension is not simjDly related to the true size of the 

 biological particle. 



From the chemical viewpoint the elementary processes of radio- 

 biology are those which can be expected in aqueous systems containing 

 dissolved and suspended organic compounds. For simplicity we may 

 consider first the general nature of the elementary processes which can 

 occur. 



* A contribution from the Radiation Chemistry Project, operated by the Univer- 

 sity of Notre Dame, under Atomic Energy Commission Contract No. AT(ll-l)-38. 



t In this paper the term biological particle refers to the microscopic unit of in- 

 terest in target theory, such as a cell or a virus unit. 



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