Radiation Dose in Autoradiography 133 



Discussion 



The varying conditions under which tracer experiments 

 are undertaken make it impossible to draw any conclusions 

 from these calculations which might be applicable to all cases. 

 A few cases may, however, shed some light on the order of 

 magnitude of the radiation dose involved even if they are 

 not applicable to a specific experiment. The following 

 computations were based on the data for stripping film; for 

 X-ray film the doses would be about one twentieth. 



In many applications the tracer element will be distributed 

 through an organ and be subsequently incorporated in various 

 compounds. Mathematically this can be regarded as immedi- 

 ate uptake with a constant concentration for a longer or 

 shorter period. Using equation (17) with b=0 and assuming 

 k(T)=k=l we obtain for stripping film in the case of the 

 organism being killed for the preparation (HA =0-693): — 



d= '^^^fi^ k(e^^-l) = 10Q0 E/k(e^t_i) ^eps (37) 



MA 



Computations of equation (37) shown in Fig. 5, show that 

 where these assumptions are fulfilled autoradiographs can be 

 produced with a fair prospect of escaping radiation damage 

 for the isotopes ^^^I, ^^P and ^^S. 



For medical applications the tracer will usually remain in 

 the body until it is either excreted or decayed. This case 

 can be calculated, again under the assumption that the con- 

 centration reaches a permanent value shortly after application 

 of the tracer. 



Taking equation (18) and inserting b=0, b from equation 

 (14a) and k(T)=k = l:— 



d=-^e^*=1000kE/e^t reps (38) 



A 



Calculated values for various isotopes are shown in Fig. 6. 

 It may be of interest that the minimum exposures are high 



