450 



RADIATION INJURY AND LETHALITY 



100,000 - 



10,000 



1000 



0.01 



1 10 



Dose rate, r/day 



1000 



Fig. 3. Relation between dose rate and after-expectation of life in the chronic (low 

 dose rate) range, on a log-log grid. These curves illustrate the way in which survival 

 at low dose rates depends on both sensitivity per se and normal expectation of life. 

 Curve A is for ABC mice with normal after-expectation of 540 days and lethality 

 coefficient k = 0.00017 r"^ (34). Curve C is for mongrel dogs with an estimated 

 after-expectation of 5 years and lethaUty coefficient k = 0.00035 r~^ The curves are 

 calculated from the hyperbolic formula 



Mi = 



Mn 



1 - MnkI 



using the values of Mq and k for each curve as given. Curve B is calculated from 

 the above formula for a hypothetical population with Mo = 14,600 days (40 years) 

 and k = 0.00017 r-^ Curve D is calculated for Mo = 14,600 days and k = 0.00035 

 r~^ The arrows indicate the highest dose rates for which the relation holds experi- 

 mentally. Curve E is calculated on the assumption that injury accumulates for 1000 

 days, using the constants Mo = 14,600, k = 0.00017. It is to be compared with 

 curve B, which is calculated for the same values of Mo and k, but on the assumption 

 that injury accumulates indefinitely. All constants employed here are deduced for the 

 case of short daily exposure to x-rays. For continuous exposure to Ra or Co gamma 

 rays the lethality coefficients are smaller by a factor of approximately 2, independent 

 of species or dose rate (34). 



