48 NEUTRON EFFECTS ON ANIMALS 



values were found to be less than the corresponding reading in air. This 

 Avould seem to indicate that some of the radiation from the neutron source 

 Avas in the form of rays which were screened out by the wax, causing an 

 initial reduction in the amount of ionization recorded by the meter. When 

 the wax used was sufficient to produce a large increase in the ionization 

 attributable to the action of the neutrons, the n to integron ratio rose 

 sharply, finally exceeding the sum of the ionizations produced by the total 

 radiation when wax w^as not present. 



Location of the Samples During Bombardment. As nearly as the dimen- 

 sions of the wax form would permit, the experiments were all made with the 

 organisms placed to receive a maximum of neutron intensity in a given 

 time. The spot chosen was about twenty inches from the neutron source 

 and only a few inches from the line of greatest intensity of high energy 

 neutrons (3). 



EXPERIMENTAL 



Orientational Experiments. As a test of the efficacy of the wax in en- 

 hancing the effect of neutrons on bacteria, organisms were exposed at three 

 points beneath the wedge-shaped section of the large paraffin shield, while 

 controls were exposed at the same time without shielding, and a second 

 set of controls was retained without bombardment. In one experiment, 

 it was possible to expose the organisms to sufficient bombardment to give 

 an average "n" reading of 1000 in the specimen tube. The irradiated 

 controls were placed without shielding of any sort immediately against the 

 wall of the neutron source, where they might be expected to receive a 

 maximum bombardment with fast neutrons. In this position, it is true, 

 they were also exposed to slow neutrons scattered from the wax form. 



The samples were measured out as accurately as possible with a capillary 

 pipette, and aspirated into individual capillary tubes which were then 

 sealed. All samples were prepared simultaneously from the same 48-hour 

 broth culture of E. coli. They were then distributed in groups of six by 

 random choice. One group was placed beneath the thin edge of the wedge, 

 one group in the middle and one at the thick edge within the specimen tube. 

 The exposed control was taped to the wall of the cyclotron. Following 

 bombardment, all capillaries were unsealed and the contents blown out 

 onto the surface of sterile agar plates and streaked. The results are indi- 

 cated in Table I. 



It was extremely unfortunate that this crude experiment could not be 

 thoroughly checked by similar runs with more exact technic. The results 

 gave strong indication, as can be seen, that the slower neutrons, which are 

 capable of producing ionization exceeding that of the total radiation with- 

 out wax, exerted a stimulus to further reproduction of the resting culture. 



