ENERGY LOSS AND BIOLOGICAL EFFECTS 



359 



to be described here was done in association with Zirkle. The author is 

 greatly indebted to Zirkle for many ideas and stimulating discussions. 

 All charged particles transfer energy to substances in essentially the 

 same way, by ionization and excitation. This has already been explained 

 by Morrison, The rate of energy loss has been calculated by Bohr as a 

 function of particle charge and velocity. Neutral radiations exert their 

 effect mostly through their charged secondaries; thus all radiations of 



REL, ev/cm lo'' 2 5 lo' 2 5 10^ 2 5 lO' 2 5 lO'" 2 5 lO'' 



Specific ionization 

 REL/33 



10' 



Electrons 



X-rays 



Neutrons 



(Fission) (D—D) 



Protons 



1 5 ODmev 



Deuterons 



Alpha particles 



12(+ + + + + +) 



Fission 



Fig. 1. Rate of energy loss from the primaries or secondaries of different types of 



radiations. Note that in these x-rays or neutron beams one usually obtains a wide 



distribution in the rate of energy loss; the data apply for water. 



concern to us will be characterized by a definite rate of energy loss or by 

 a more or less calculable range of energy losses. Since experiments have 

 been reported with a wdde variety of radiations, a nomogram correlating 

 different radiations with their rate of energy loss in water is presented 

 here (Fig. 1). In substances other than water the rate of energy loss has 

 to be corrected, using the relative stopping power and the knowledge of 

 the mode of formation of secondaries from neutral radiations. A glance 

 at the nomogram reveals that several kinds of radiations are necessary 

 to cover the entire range of REL. 



