CHAPTER THREE 



IONIZING RADIATION AND VIRUSES 



Ionization is, to a very large extent, caused by the passage 

 of very fast, charged particles through matter. These particles 

 have atomic dimensions or less {much less in the case of fast 

 protons, deuterons, or alpha particles), and because of their 

 high speed they are relatively unaffected by the vast majority 

 of the atoms near their path. Thus these fast charged particles 

 can readily penetrate into the interior of viruses, and may in- 

 deed produce no effect at all until some internal action is pro- 

 duced. For this reason, fast, charged particles are probes of virus 

 structure. In addition they produce transient excitation effects 

 in the solvent, which carry energy and can produce action on the 

 large molecules of biology. The study of this shovild one day add 

 still more to the knowledge of virus structure. The importance 

 of studying the effect of ionizing radiation on viruses therefore 

 lies in the fact that it is concerned mainly with the internal 

 organization of the virus, something which is not measured by 

 the techniques of the last chapter. 



The basic idea underlying the use of ionizing radiation is 

 that it is a localized, destructive agent. The average energy 

 release, which, as will soon be seen, is confined within a region 

 of 7 A radius (on the average), is 110 electron volts or 2,500,000 

 calories/mole. It is likely that all ionization energy releases 

 exceed 25 ev. This will destroy any sensitive function in its 

 vicinity. So, by bombardment in this way, the loss of certain 

 kinds of viral behavior can be studied. There are many of these, 

 and for each there can be found a volume or an area related to 

 the bombardment. Thus loss of infectivity, serological affinity, 

 hemagglutination ability, bacterial killing power, and ability 

 to adsorb, can each be measured. In the very limited number of 



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