PRINCIPLES OF RADIOLOGICAL PHYSICS 



97 



reason the concentration of particles and photons never attains a value 

 as high as that given by expression (36) l)ut remains some 10 times lower. 

 Wilson (1952) has made numerical calculations of shower development at 



15 20 25 30 35 40 45 50 

 DEPTH, radiation lengths 



Fig. 1-57. Approximate number of particles in showers of different total energies at 

 various depths within a material. Depth is expressed in radiation lengths (see 

 Table 1-9). Shower energy Eo is expressed with reference to the energy e dissipated 

 by a high-energy particle per radiation length. This energy equals 98 Mev for air, 

 52 for aluminum, 25 for iron, and 7 for lead and is about 30 to 40 per cent smaller 

 than lO'/Z ev. Therefore Eo/e is essentially the same as the quantity (36). The 

 number of particles multiplied by e and divided by the radiation length gives the 

 energy dissipation in a layer of 1 cm. (Rossi and Greisen, 1941.) 



moderately high energies, up to 500 Mev, starting from more realistic 

 data on X-ray and pair production than had been done in earUer calcula- 

 tions. The shower maximum is shown to spread over a still broader range 



100 

 50 



z 10 



g 5.0 

 < 





111 



z 



UJ 



1.0 

 0.5 



0.1 

 0.05 



0.01 



50 



200 



250 



100 150 



DEPTH, g/cm^ 

 Fig. 1-58. Energy dissipation at various depths within materials exposed to X rays 

 from a 330-Mev synchrotron. (Blocker et al., 1950.) 



of layers of the material than had been anticipated. Figure 1-58 gives 

 experimental data on the energy dissipation vs. the depth of penetration 

 for showers generated by a synchrotron. 



When the process of shower multiplication subsides, the lower energy 



