RADIATION DOSE 



smaller than the diameter of the nueleus. The clis.sii)ation ()r21 KeV (3-4 



10-* ergs) in a splicrc 10 microns in diameter represents an energy dissipation 



25 

 of 67 ergs per g, or 0-67 rad. It therefore requires——-, or approximately 



B 



MeV 



7-68 



A m » > ^ i . I, I ^i ^i i ^""^ C 



B 



7-68 





*P|I«I«M^ 



«-*-- 



B 



5-25 



*-*»-4- 



.^..^ 



2-63 



B 



017 



Figure 2. Wilson cloud chamber photographs of a particles 



showing S-rays 

 (Reproduced by kind permission of T. Alper from Z. Phys. 76 [1932) 172) 



36 particles, to produce a dose of 25 rad. If we consider a large number of 

 nuclei exposed to this dose, the number of photo-electrons crossing individual 

 nuclei will be distributed about the mean, in accordance with the Poisson 

 formula, and the standard deviation in the number of particles per nucleus 



4 



