I RADIATION BIOLOGY 



groups of atoms is also rather well understood. Moreover, an adequate 

 over-all picture of the processes through which the action of radiations 

 becomes distributed over macroscopic portions of matter may be drawn. 



The nature of radiations and their action on small groups of atoms are 

 the subject of the first two sections of this chapter. The over-all picture 

 of the action on sizable amounts of matter constitutes the third section. 

 The fourth section deals with the penetration of radiations to various 

 layers of an irradiated material. Knowledge of this last field is far from 

 satisfactory. 



It should be emphasized from the outset that no detailed information 

 exists regarding the effect of radiations on any but the smallest groups 

 of atoms. Even less is known, of course, regarding the effects on complex 

 biochemical substances or on the far more highly organized biological 

 materials. The present treatment does not attempt to cover these topics 

 which are more properly classed as radiochemistry or radiobiology. 



Nevertheless, the relations between the physical characteristics of a 

 radiation treatment and its eventual biological effects may be analyzed 

 to some extent without any detailed knowledge of the mechanisms of 

 radiobiological actions. The fifth and last section deals with the methods 

 of this analysis. 



1. PROPERTIES AND PRODUCTION OF RADIATIONS 



The term "radiation" usually indicates a physical phenomenon in 

 which energy travels through space, even though that space be empty of 

 matter. 



There are two classes of radiations, namely: 



(1) Corpuscular radiations, consisting of streams of various kinds of 

 atomic or subatomic particles, which can transfer their kinetic energy to 

 anything they strike.^ 



(2) Electromagnetic radiations, consisting of self-propagating electric 

 and magnetic disturbances, which affect the internal structure of matter 

 and thus dissipate their energy. 



Acoustic phenomena depend for their propagation upon the presence of 

 an elastic material medium (e.g., air) and accordingly are not classified as 

 radiations. 



Table 1-1 gives a classification of biologically important radiations 

 with references to the pertinent sections of the following treatment. 

 Corpuscular radiations are classified according to the nature of the con- 

 stituent particles. The classification of electromagnetic radiations has 



2 A stream of macroscopic particles, such as pebbles, fits, strictly speaking, the 

 above definition of radiation, but it is not generally understood to be covered by that 

 name. 



