18 



POLLARD: I think you could take care of that. You could, for in- 

 stance, have glutathione present during irradiation. In other words, if the re- 

 covery system is present any radiation effects will be superimposed on that. 



KAMEN: I am surprised that none of the experts have hopped on this 

 point. You would expect that if you got a positive charge on the carbon, this 

 would stop the "walk". I don't know what the times are. 



POLLARD: I have not had a chance to say what I now realize is the 

 key to everything here. All of these timies are such that no heavy thing can 

 move. This is a key all the way through. It is a key to the very nature of ioni- 

 zation itself. The proton or the nucleus in the ionization process never moves, 

 and it is interesting that in neutron studies with solids, the damage can be re- 

 lated to the number of recoils that actually do cause a motion of a heavy part, 

 the part that is usually unable to move and really is insignificant here. I feel 

 that the times involved are such that there isn't any chance for a free radical to 

 form. If a free radical did occur I would be confident that you would no longer 

 have a specific protein. So, possibly, one of the things to look for is, as Dr. 

 Curtis has said, effects at the end. It might well be that all that is necessary is 

 that something break way from the end and, having broken away, the molecule is 

 then inactivated. 



MAGEE: You have, in addition to this freedom of motion of the positive 

 charge, a competition with the motion of the nuclei, i.e. , vibrations. So when 

 the charge gets into a certain region, you freeze the charge and it no longer 

 moves freely. You freeze the charge into the region because of the excitation of 

 motion of heavy nuclei; some of the energy is transformed into vibrations and 

 the electronic energy is reduced. Then, the charge stays in one vicinity and 

 chemical reaction occurs. I think, in general terms, that this is the explanation 

 for the specificity of the direct action of ionizing radiation. In radiation chemis- 

 try, the fact that there is specificity of effects in certain functional groups of a 

 molecule is known. This has been investigated, I think, rather extensively for 

 decarboxylation of aliphatic acids. I believe that a relatively high fraction of 

 total absorbed energy goes into decarboxylation {12.). 



POLLARD: You mean that it comes to a place where you can transfer 

 from electron excitation to vibrational. It then freezes in position. That suits 

 me fine. 



ALLEN: This may shed some light on why this energy apparently does 

 not migrate from one molecule to another. We know, of course, from the liquid 

 scintillation counters that certain kinds of energy will do this. You can get fair- 

 ly good scintillation out of dilute solutions of some aromatic compounds in nor- 

 mal hexane. This means that the energy absorbed by the normal hexane mole- 

 cule travels from one hexane to another until it reaches the aromatic molecule. 

 This aromatic molecule then fluoresces and produces the light that you see. 



One might ask, why does this not happen with these protein molecules'' 

 Why does the energy not migrate from one to another as it probably does with 

 normal hexane? I think it is because the protein molecule contains groups that 

 have an affinity for hanging onto the positive charges, thereby producing decom- 

 position, and this process is in competition with the transfer of charge from one 

 molecule to the neighboring molecule. The fact that the protein molecules ap- 

 parently do, in general, possess these reactive groups is the reason the energy 

 stays in the same molecule. 



PLATZMAN: May I make a few remarks about the charge migration? 



