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Some Aspects of the Biochemical Effects 

 of Ionizing Radiations 



WALTER M. DALE 



Christie Hospital and Holt Radium Institute 

 Manchester, England 



It is the ultimate aim of research in the field of radiation biology to 

 follow the fate of the absorbed radiation energy through all phases, from 

 the primary physical act to its effect on cells, tissues, and the whole 

 organism. Unfortunately, however, our knowledge of the biochemical 

 processes within the cell, with which this section deals, is the weakest 

 link in the chain of events. It is probably the most inaccessible problem 

 from the point of view of experimental evidence, and we are forced, at 

 least for the time being, to deduce mainly from test-tube experiments 

 what may happen within the intact cell. The conclusions from such 

 experiments are therefore to a certain extent speculative; but, if they 

 carry some core of truth, they may open up possible approaches to the 

 difficult problems to be solved. 



Mode of Action of Ionizing Radiations 



When we consider the developments which have taken place during 

 the past 15-20 years in our views of the mode of action of ionizing 

 radiations, we find as a prominent feature the clear recognition, due to 

 the pioneer work of Risse (1) and Fricke (2), of the fact that these radi- 

 ations act on aqueous systems not only directly, as pointed out by Bur- 

 ton in his paper, by release of energy within the solute molecules but 

 also indirectly by a change of the water molecule, a change which is 

 transmitted to the solute molecule. The mode of this transmission is 

 still not fully understood, but many of the experimental facts can be 

 interpreted in terms of H atoms and OH radicals being formed from 

 the water molecule. Although quite a number of authors are aware that 

 these radicals may originate from excitation as well as from ionization, 

 the accent on ionization is only recently becoming weaker, because for 

 some reactions the number of radical pairs, formed by dissociation or 

 neutralization of charged molecules, is less than the number of solute 



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