RELATIVE BIOLOGICAL EFFICIENCY OF FAST 



NEUTRONS AND GAMMA RADIATION FOR 



CHRONIC IRRADIATION OF MICE 



R. H. Mole, R. J. Munson and G. J. Neary 

 Radiobiological Research Unit, Medical Research Council, Harwell 



A GRAPHITE pile at A.E.R.E. Harwell has been used for dally irradiation 

 of mice with fast neutrons substantially free from gamma radiation. 

 Sterilization of male and of female mice and a reducdon in the weight of 

 the testis have provided sensitive indicators of radiation damage. Dose- 

 response curves for fast neutrons and cobalt gamma radiation have been 

 found to be very similar : there has been no evidence so far of any 

 qualitative difference. Relative biological efficiency factors lay between 3 

 and 8 for exposures ranging from 24 hours to 5 months : there are definite 

 differences between different strains of mouse. An experiment to determine 

 the relative biological efficiency for lethal effects of low daily irradiation has 

 been started but no results are yet available. 



DISCUSSION 



L. Ehrenberg : The authors found the relative biological efficiency of neutrons 

 to vary between different mouse races, and the reason for this has been attributed 

 to different sensitivities to gamma rays. I want to point out that this result is similar 

 to those obtained in plant material : several physiological factors have an influence 

 on the sensitivity to sparsely ionizing radiations, but not on the sensitivity to fast 

 neutrons. This difference between the two types of radiations is probably due to a 

 different mechanism of action. 



104 



