44 



RADIATION BIOLOGY 



currents. The magnetic effects increase in proportion to the speed of the 

 particles. 



Magnetic effects are generally obscured by the accompanying effects of electric 

 forces in the processes we have been considering unless the particles move with 

 velocities approaching the speed of light. The study of processes involving high- 

 speed particles requires a detailed treatment of magnetic as well as of electric 

 effects. 



Besides the magnetic effects due to the bodily motion of charged particles, 

 those due to internal currents inherent in the structure of the particles must also 

 be considered. Magnetic effects of this nature are exhibited not only by complex 

 particles such as nuclei but also by the so-called "elementary particles," such as 

 electrons, protons, and neutrons. (Notice that neutrons show evidence of 

 internal currents even though they bear no electric charge.) The magnetic 

 effects are particularly conspicuous in the interaction of neutrons with other 

 particles just because neutrons do not exert any electric action. 



Table 1-2. Elementary Processes Resulting from Interaction of Incident 

 Radiations with "Free" Atomic Particles 



2-2e. Effect of Nuclear Forces. The "nuclear forces" which act among 

 protons and neutrons and hold a nucleus together also act upon any 

 neutron or proton which happens to get close to a nucleus. These forces 

 are exceedingly strong (much stronger than electric forces between two 

 protons at comparable distances) but they act only among particles 

 separated by no more than a few times 10~^^ cm. 



Nuclear forces have secondary importance in the collision of protons 

 with nuclei unless the incident proton has sufficient energy to overcome 

 the electric repulsion and get close to a nucleus. No such force resists 

 the approach of incident neutrons. In fact the travel of neutrons is 

 affected almost exclusively by close range coUisions with nuclei. 



