DISCUSSION 



DISCUSSION 



Dr. George : There is one problem that I have had for some time and I should like 

 to ask Professor Titterton if he could clear it up now — in reading references he has 

 mentioned, and I noticed again this morning in his slides, he did give the radiation 

 hazard to the population in terms of the dosage, in milliroentgens, which are quite 

 small, due to the y-rays — I was under the impression that a good proportion of the 

 radiation burden to the population from fall-out arose from the jS activity. Firstly, is 

 this so; secondly, if it is so, how did it compare with the y-ray dose that he has 

 mentioned ? 



Professor Titterton: I am unable to give you the precise numbers. The ^ dose is 

 actually very small, for the simple reason that the range of jS-particles in anything is 

 small, therefore it cannot constitute a whole-body dose; it cannot reach the gonads 

 in either the male or the female. 



Dr. George : What about ingestion ? 



Professor Titterton: Well, yes, but where does it go? We saw this morning 

 (Paper 14), a very large fraction is excreted, and again the range of the particle 

 concerned is very small. The only case to worry about is one where the activity is 

 laid down in a very confined region and can selectively irradiate a very small volume 

 of tissue, and that is the case with '"Sr. The other point is that even if there was a 

 significant contribution to dose here, since we are in the region of a few mREM 

 per 50 years, doubling this or trebling, or multiplying by 10, would not result in any- 

 thing to worry about. 



Mr. Rocke: You stated that there is a suggestion that there is a threshold to the 

 effects of ®"Sr. Is that only for leukaemia or is it for all the radiobiological effects of 

 90Sr? 



Professor Titterton: I would rather this question be addressed to the biologists, 

 but the situation is that there has always been an argument as to whether the dose- 

 effect relationship is linear or shows a threshold, and the prudent thing to do, which 

 is what we have always done, has been to assume that it is linear. There is now a 

 very strong body of opinion in scientific circles swinging to the point of view that 

 there is a threshold. From the discussions I had in the U.S.A. and in the U.K. 

 recently, this applies to leukaemia and bone cancer — but if any biologist here could 

 throw further light on it I would be very glad. 



Dr. Loutit: I think the situation has been identified over the last few days. I did 

 quote some of Dr. Mole's work on experimental leukaemia in the mouse, which 

 stated that if one took the observable leukaemia after irradiation the points fell on a 

 graph, which one can extrapolate to zero, and say that there is a threshold dose, 

 given by the intercept, below which no effects can be observed. One cannot measure 

 biologically with any precision in the low dose region, and this is definitely an extra- 

 polation. A mathematical relationship indicating that there was a sigmoid curve 

 would be equally possible. In this case, as an approximation one can draw a straight 

 line through the lowest experimental point and the origin, and this is the part we 

 are considering when the considerations are for populations rather than experimental 

 groups. It may be that there is a very small contribution of effect, call it leukaemia 

 or carcinoma of bones — which will be there, but which one cannot, in the present 

 state of experimental work, measure. 



Dr. Springell: There has been some concern about the ^^C fall-out in nuclear 

 weapon tests; I wondered whether Professor Titterton would like to comment on this. 



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