136 ELEMENTARY CHEMICAL PROCESSES 



basis, not wholly dependent on ionization in gases, for estimation of number of 

 primary physical processes might evolve. Of course, this is in addition to the 

 contribution such knowledge could make to the mechanism of damage. 



Burton : 



Study of the effect of radiation on a mixture of benzene and cyclohexane yields 

 information which is of much general interest and which may also have some 

 bearing on Kornberg's comment. The ionization potential of the benzene 

 molecule is less than 10 ev; that of cyclohexane is somewhat higher. If a mixture 

 of the two compounds is irradiated, the ionization will tend to reside ultimately 

 in the benzene. One might therefore expect that only benzene will be chemically 

 affected: the benzene should protect the cyclohexane. The experimental evi- 

 dence, however, indicates appreciable decomposition of the cyclohexane. It 

 would thus appear that not quite all of the energy is transferred to the benzene; 

 some decomposition has occurred before the energy is transferred. Primarily 

 excited molecules may not transfer their energy like the ions, and it may be such 

 cyclohexane molecules that decompose. Perhaps the chemical data may give 

 some clue as to the relative probabilities of ionization and excitation transfer. 

 However, we should note the comphcating possibility of some transfer of energy 

 from benzene to cyclohexane in a sensitization process. 



Lind: 



Is there transfer of energy in the liquid system? 



Burton: 



I should have stated that the experiments were performed on benzene-cyclo- 

 hexane mixtures in the liquid state. 



Morrison: 



In a field as complex as the one under discussion at this symposium it is both 

 useful and necessary to set up simple models. The target theory is such a model, 

 and during the past two decades much useful experimental work has been based 

 upon this model. It is important that future models should define a situation 

 in an operational way, as the target theory has done. I wonder whether the 

 model set up by Burton defines the situation from this point of view. 



Burton (Communicated) : 



Morrison is correct in implying that the proffered model is an oversimplifi- 

 cation. The purpose of this model, as of any other, is to assist in correlation of 

 results of research. Without question it will be modified as the facts demand. 

 The mathematics of the picture I have suggested is. I believe, the mathematics 

 of the target theory. All that I have done is to define a possible target in the 

 light of our present knowledge of the radiation chemistry of aqueous systems. 

 That target is clearly something different from the biological entity. The model 

 is suggestive of the mechanism of the action of oxygen and of experiments 

 which may be performed to test that mechanism. It also indicates why the 



