134 



S. R. Pelc 



and the radiation dose presents a very severe limitation for 

 elements other than ^^S unless a high proportion of the 

 element is excreted or the values for the factors k and f are 

 very favourable. It is obvious that the factor k will remain 



minimum dose to tissue for a.r.g. 

 (organism killed) 



'^-•) REPS. 



f CO -CONST 1 



10^ E^ 



(e 



IQOOO 



lOOO 



1 (REPS) 



lOO 



lO 



aoi 



o-i 



10 



lOO 



lOOO 



DAYS 

 Fig. 5. 



small if labelled precursors of compounds of interest rather 

 than inorganic compounds are used in the first instance, and 

 better knowledge of precursors for various substances will be 

 of great advantage for further work. 



As an example of work with long-lived isotopes, radioactive 

 carbon ^*C may be chosen. For immediate uptake and sub- 

 sequent constant concentration equation (29) can be used 



