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FARR ET AL. 



Alio 3 



Fig. 6. Coronal section of gross brain, case 8-00-83 r. at 2 cm from the tip of the 

 frontal lobe across the scar partially seen in Fig. 5. 1 here is no tumor growing in the 

 region of marginal irradiation. 



While in a few instances the capture reaction will result in an atomic trans- 

 formation and a beta particle emission, these are so infrequent that in the 

 aggregate no significant contribution to the total exposure is provided by 

 them. It then becomes of major importance to determine the formulation by 

 which the captiu'c gamma dose is computed. It is here that both the major 

 uncertainty and the major difficulty are encoimtered. Since the neutron 

 exposure is not uniform, precise description of the attenuation becomes 

 paramount. Yet difficulties in measurement and alterations in pattern by 

 geometry or port of entry make this factor one of approximation and not 

 certainty. In similar fashion, the formulation of a suitable integral which can 

 be solved to give the summation of the dose and volume of maximum 

 intensity has developed into a problem which can be handled only by a com- 

 puter, and we have not obtained a final answer, though work is continuing. 

 Therefore, in this discussion we have used the values computed by Robertson 

 for the rad dose derived from capture gamma on the assumption of a imi- 

 form distribution of thermal neutrons at the maximum observed intensity of 

 exposure. It is clear that the dose values given in this paper may be greater 

 than the maximum expected value to be obtained by a more precise estima- 

 tion, but the volume of maximum intensity in the latter case may equal or 

 exceed the approximate value herein reported. Whatever the error and 



