116 PRIMARY PROCESSES 



atoms may receive an average charge exceeding 4; nevertheless, it is found ex- 

 perimentally that as many as 60-70 per cent of the molecules will not rupture 

 their bonds. According to a simple electrostatic repulsion model, the bromine 

 ion in this case would capture all available electrons, and, as a result, the positive 

 hydrogen and the still positive bromine would repel each other with 100 per cent 

 probabiUty of decomposition. The model obviously fails- for this simple case, 

 and there is no reason to beUeve that it applies in any more compUcated one. 



Morkison: 



Platzman has brought out in interesting detail the role of what he has termed 

 the nuclear coUision in the energy loss of charged particles moving through 

 matter. By this designation he referred to the way in which energy was trans- 

 ferred to the mass motion of the atom as a whole. That is to say, the collision 

 arises from an interaction between the charged particle and the electrostatic 

 field of the nucleus. In other words, the nucleus is here regarded not as a sticky 

 point, but as center of an electrostatic field. This kind of reaction does occur, 

 and it is to be clearly distinguished from the sort of collision discussed by Tobias 

 and Wilson, in which there is a nuclear-force interaction between the nucleus and 

 very high-energy protons or deuterons. It is interesting to compare the two for 

 200-Mev deuteron beams. Most such particles traverse their range without 

 making a single nuclear coUision of the sort I have described, that is, a nuclear- 

 force collision. There is about one chance in three that such a particle will make 

 a nuclear-force collision. Wlien it does, it transfers a considerable amount of its 

 energy, giving rise to a many-pronged star from which several columns of heavy 

 ionization start out in several directions. If any large-scale structure of micron 

 size responsible for racUobiological effects is located in one of these stars of ion- 

 ization, the stars might give rise to biological effects. But the sort of nuclear 

 collision that Platzman has been discussing, that is, the electrostatic field col- 

 hsion, might occur in the order of 100 times, along the deuteron path, while each 

 energy transfer would involve only enough energy to disrupt a few^ molecules. 

 The difference betw^een these two types of characteristic nuclear events is worth 

 mentioning. 



