46 NEUTRON EFFECTS ON ANIMALS , 



certain specific amount of energy, as they are to certain specific wave 

 lengths of Hght. 



When neutrons pass through a sufficient layer of paraffin, their initial 

 energy is lost as a result of many collisions with the nuclei present in the 

 heavily hydrogenated compound. By regulating the thickness of a paraffin 

 barrier, therefore, some control might be gained over the average amount 

 of energy possessed by the neutrons striking the cells. A further advantage 

 in the use of wax lay in the strong possibility that a greater number of 

 neutrons might actually be brought to bear on the exposed cells than 

 would have been the case if fast neutrons were used without wax. Finally, 

 slower neutrons are more susceptible to capture by atomic nuclei, and might 

 produce effects of an entirely different ftature from those attainable with 

 higher energy neutrons. 



In order to provide some measure of the intensity of bombardment, use 

 was made of the Victoreen 100 r condenser-type meter. The intensities 

 were expressed as "n" units, by which it should be understood that ioniza- 

 tion equivalent to that produced by a number of Roentgens of X-rays 

 whicb would give the same reading with the meter was brought about 

 within the meter chamber. It must be emphasized that this is not a valid 

 estimate of the number or the energy of the neutrons involved. The 

 neutrons do not produce any ionization themselves, but give rise to other 

 particles which create paths of ionization in the material bombarded. 

 Thus the amount of ionization, the value actually measured, is as much a 

 function of the material bombarded as of the concentration and strength 

 of the neutrons. Moreover, X-rays and gamma rays, both capable of 

 producing ionization, are given off by the cyclotron during the production 

 of the neutrons. The effect of the presence of these rays in the general 

 radiation becomes apparent when "n" readings are taken with and without 

 a barrier of lead or wax to act as a filter. Lead cases with one inch walls 

 were used in some experiments to exclude the unwanted radiation, but the 

 results indicated that the intensity of these rays was too slight to affect 

 the results of our experiments. Samples described as having been bom- 

 barded in air, therefore, have been subjected to the total radiation from 

 the cyclotron. 



Wax Forms. Our first concern was to determine, if possible, the most 

 effective amount of wax shielding. For this purpose the wax form illus- 

 trated in Fig. 1 was constructed. It consists essentially of a cylinder five 

 inches long and ten inches in diameter, capped at either end with a hem- 

 isphei-e of the same diameter. From this melon-shaped figure, a sec- 

 tion was removed as indicated, along planes which bisected one. of the 

 hemispheres and extended from the diameter thus defined to the point 

 on the opposite end of the cylinder where a perpendicular from the middle 



