NEUTRON EFFECTS ON ANIMALS 



49 



The fact that the gradient effect of the wedge was not apparent, and that 

 the exposed control, which presumably was exposed to a smaller number of 

 rebounding slowed neutrons, showed some stimulation, would suggest 

 that the action, if real, is a property of the very slow neutrons which proba- 

 bly are present in the entire length of the specimen tube in equal concen- 

 tration throughout bombardment. 



As it was not possible to make ninnerous repetitions of the experiment, 

 we turned our attention to the elimination of this "fogging" of the gradient 

 which must inevitably occur in a single wax form, due to the tendency of the 

 neutrons to "wander about" from collision to collision within the paraffin 

 before reaching points all along the specimen chamber. Paraffin spheres of 

 various sizes were constructed, ranging in diameter up to that of the melon- 



TABLE I 



Response uf E. coli to Heavy Bombardment Within the Gradient-Producing Paraffin 



Form Illustrated in Figure 1 



Six samples in individual capillaries were exposed in each location. The results 

 express the number of viable organisms found in the capillaries containing the largest 

 number and the smallest number for each group. The average of the six is also in- 

 dicated. 



shaped form itself. The n per integron division values found in the center 

 of these spheres were as follows : 



Diameter of Ball inches 



n/Integron Division 0.85 



m in. 

 0.6S7 



21 in. 

 0.75 



o in. 

 0.79 



10 in. 

 OS 



It will be noticed that the 10-inch ball did not give rise to ionization 

 sufficiently intense to exceed that obtained without wax. It follows that 

 the large volume of wax used in the melon-shaped form was required to 

 produce neutrons with this property, and that hereafter the amount of 

 paraffin as well as the thickness of the shield should be taken into account. 



One-cc. samples of culture were exposed individually to varying amounts 

 of neutron bombardment within these spheres, and accurately measured 

 samples were plated out after appropriate dilution. As a rule, no sig- 

 nificant difference between bombarded specimens and unexposed controls 

 could be found. Occasionally, there appeared to be a certain amount of 

 stimulation, but the observation was not a constant one. 



