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APPLIED RADIOACTIVITY 



The quantity or intensity of the radiation delivered by a seed is ex- 

 pressed in either of two ways. The fraction of the original activity 

 used is stated in terms of the percentage of millicuries remaining in the 

 seed, or the amount of radon disintegrating during tissue exposure is 

 given as millicurie-hours delivered. Recently, the second notation is 

 being used in America to denote the quantity of radiation delivered 

 interstitially. 



Fig. II-9. Percentage intensity of radiation reaching different distances, from a 

 buried gold seed. (By courtesy of E. Quimby [1928].) 



Intensity of Radiation in the Vicinity of Radon Seed Implants 



Since the radiations from radon must pass through the 0.3-mm gold 

 envelope of the seed, the emitted energy will be composed primarily 

 of gamma radiations, and the curve of Fig. II-9 reproduced from 



