RADIATION BIOLOGY 



1-1. CORPUSCULAR RADIATIONS 



Material corpuscles (or "particles") are physical entities endowed with 

 a mass. Because of their mass atomic particles behave like macroscopic 

 bodies, at least in so far as their velocity can be varied to a great extent 

 by physical means. Any change of velocity is accompanied by energy 

 transformations. Acceleration of a particle is effected by a force which 

 imparts to the particle a certain amount of energy to be stored in the form 

 of kinetic energy. This energy is returned when the particle slows down 

 owing to the action of a force opposing its motion. The storage of kinetic 



energy constitutes the main mechanism for 

 energy transport by corpuscular radiation. 

 RAYS / (The internal structure of each traveling par- 



ticle may contain additional energy.) 



The deflection of radiation particles is effected 

 by a force perpendicular to their line of motion. 

 Fig. 1-1. Deflection of the ^he observation of such deflections serves to 

 a and ^ rays from a mate- analyze the radiation response to various forces 

 rial located in a magnetic and thereby to analyze the nature of the radia- 

 field perpendicular to the ^Jq^ For example, the a and 13 rays ejected by 

 tuZavl ^"""^ pointing certain radioactive substances turn in opposite 



directions when they traverse a magnetic field 

 (see Fig. 1-1). The deflection indicates that the a rays carry a positive 

 charge, and, in these cases, the ^ rays a negative charge. 



The analysis of corpuscular radiations progresses also through the 

 study of their penetration in various materials (see Sects. 2, 3, and 4). 

 Determination of the nature and velocity of the constituent particles 

 marks the completion of this analysis. 



1-la. Methods of Detection. Corpuscular radiations are detected by the 

 effects produced by their impact on matter. For instance, the electric 

 charge delivered to a body by a radiation, the heat dissipated in the body, 

 the luminescence caused in certain materials, or the blackening of photo- 

 graphic films can be measured. Electrically charged radiation particles 

 are generally easier to detect than electrically neutral ones, because they 

 interact electrically with the atoms of matter even from a considerable 

 distance. 



It is possible to demonstrate directly that a radiation consists of dis- 

 crete particles, for example by detecting the arrival of individual particles 

 upon a luminescent screen. This method of observing "scintillations" 

 served as a basis for the early study of a rays. It has become much 

 more practical since the introduction Of improved luminescent materials 

 and of devices which record the scintillations automatically. 



Two other very effective methods for detecting and studying individual 

 fast charged particles are the Wilson cloud chamber and the Geiger 



