11 



maximum concentration occurs certainly depends upon K as we see from 

 Eq.(14) and (15). As a matter of fact K is essentially a measure of the 



rate of spreading of tlie material from the source , in the sense that 



2 



do- /dt = 2K where <j is the standard deviation of the distribution of 



C. about tiie source at time t . 

 1 



The maximum relative concentration of radioactivity , C / C , for a 

 given isotope as a function of relative distance from the source is shown in 

 Fig. 4. Curve (1) corresponds to Eq. (16) and curve (2) to Eq. (17), the 

 latter applying to the special case of D/a = 100 (i.e. , D = 36m for a = 36 cm). 

 For any r/a , the curve with the greatest C/C governs ; thus curve (1) 

 governs for r/a < 100 , curve (2) for 100 < r/a < 2000. For r/a > 2000 

 (r> O.Sn.mi.) other considerations enter in establishing the maximum con- 

 centration which might occur at large distance from the individual source . 



137 

 If we suppose that M. =0.01 curie for isotope Cs for a single package 



source (C . =54 |jic/kg) , then the maximum radioactivity by tliis isotope is 



about .0015 |j.c/kg at 10m from tlie source, 3x10' ^J.c/kg at 100m and 



-8 

 4 X 10 (J-c/kg at 1 km. It must be remembered however, that these values 



137 

 apply to but one package (assuming M. = .01 curie for Cs ) ; the total con- 

 centration of radioactivity at a given position is the sum of the effects from all 

 packages and all isotopes in the source area. 



At a distance of about 1 km from an instantaneous paclcage source 



-10 

 C/C is about 8 x 10 . If the sum total of all packages for a year were 



