CHAPTER 4 

 PROTONS, DEUTERONS, AND ALPHA PARTICLES 



4.1. Physical Properties. The proton, deuteron, and alpha particle 

 occupy a position of special importance. Aside from their significance as 

 forms of the simplest and most accessible nuclear structures, they are the 

 only charged heavy particles produced in nuclear reactions (except for the 

 few cases in which H 3 and fission fragments are formed) and the only heavy 

 particles normally obtained from high-energy accelerators. Consequently 

 the interaction of these particles with matter is of fundamental importance. 



Table 8. Physical Properties of the Proton, Deuteron, and Alpha Particle 



Property 



Atomic weight (neutral) 



Packing fraction, 10 4 mu 



Charge, 10" 20 abs emu 



Magnetic moment, nuclear magnetons 



Binding energy, mev 



Spin, units of h/2ir 



Statistics 



Proton 



1.008123 

 81.2 

 1 . 60203 

 2 . 7896 



Fermi-Dirac 



Deuteron 



2.014708 

 73.6 

 1 . 60203 

 0.8565 

 2.17 

 1 

 Bose-Einstein 



Alpha particle 



4 . 00390 

 '9.8 

 3 . 20406 



28. 

 

 Bose-Einstein 



Qualitatively the interaction of protons, deuterons, and alpha particles with 

 matter is very nearly the same for all three particles. Quantitatively the 

 differences that exist are due almost entirely to the respective magnitudes of 

 charge and mass of the particles. The following sections, with the exception 

 of alpha decay, therefore, apply in principle equally well to all three particles. 

 Physical theories of the structure of the particles and of their interaction with 

 nuclei are rather involved and at the present time inconclusive because of the 

 uncertainty of the nature of nuclear forces. Reviews of the various theories 

 are to be found in the literature and will not be considered here. 



4.2. Energy Loss of Fast Charged Particles. The mechanism chiefly 

 responsible for the absorption or stopping of charged heavy particles (M ~ 1 

 mass unit) is the interaction of their electric fields with the electrons of the 

 absorbing material. The electrons are regarded, according to the classical 

 theory of the process formulated by Bohr, as harmonic oscillators that are 

 set in motion by the passing particle from which they derive energy. On the 

 basis of this model the rate of energy loss is adequately accounted for by 



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