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p. J. LINDOP AND J. EOTBLAT 



constant. However, starting from the second line there appears to be a 

 systematic increase in the LDgg with increasing dose-rate. This impression 

 is strengthened when one compares our results with those obtained by other 

 workers at lower dose-rates. In Fig. 1, in which the dose-rate is plotted on a 



Table I. Effect of dose-rate 



log scale to accommodate the large range of dose-rates, the broken line 

 represents the variation of LDgg with dose-rate obtained by other workers 

 (Corp and Neal, 1959; Lawrey and Fowler, 1959) and normalized to the values 

 obtained by us. It is seen that after an initial rapid decrease of the LD5Q 

 there is a flat minimum at about 1,000 rads/min, followed by a very gradual 

 increase. 



1,600 



1,400 



1,200 



Q 



1,000 



800 



600 



0-25 1 



10 100 1,000 10,000 100,000 



Dose-rate (rad/min) 



Fig. 1. Variation of LDjq with dose-rate. 



In the case of life-shortening the variation with dose-rate foUows the 

 same trend but is much more pronounced (Table I). The results are plotted 

 in Fig. 2, where again the broken line is based on the results of other workers. 

 It is seen that there is a definite maximum of the life-shortening effect at about 

 1,000 rads/min. 



