Chapter 3 



FAST NEUTRON IRRADIATION PROCEDURE 



By T. ENNS, H. M. TERRILL, and JAMES M. GARNER, Jr. 



The cyclotron was used as the source of fast neutron radiation. The 

 neutrons were produced by deuteron bombardment of berylHum inside the 

 cyclotron chamber. Location of the cyclotron and target are shown in 

 Fig. 1. The numbered rectangles represent positions for which relative 

 dosage values were determined. 



To obtain simultaneous exposures of animals of high and low level dosage 

 groups, cages were placed in different positions. Cages placed nearer the 

 target received radiation dosage at a higher rate than more distant cages. 



IREIADIATION 



Radiation Cages. The cages, shown in cross section in Fig. 2, were de- 

 signed so that the animals were completely surrounded by one-inch thick- 

 ness of lead, with an additional two inches of lead between them and the 

 target. The cages were lined with sheet copper. In the front wall of the 

 cage was an additional sheet of copper, with many perforations. Provision 

 was made for introducing a stream of fresh air between this sheet and the 

 lining. This air flow was turned on whenever animals occupied the cages. 

 There was one inch of clear space all around between the cage and the 

 overlappmg cover. 



The cage temperature was approximately room temperature. Cyclotron 

 operation produced no temperature rise in the cyclotron room. The great 

 heat capacity of the cage metal as well as the circulating air prevented any 

 great temperature rise in the cages due to the presence of the animals. 



Cages 4, 5 and 6 each held 2 dogs, 4 rabbits or 24 rats at one time. Cage 7 

 was considerably smaller, having a capacity of only one rabbit or ten rats. 



Procedure. Dogs were placed directly in the cages without any separate 

 container. They were faced east and west on alternate days. The space 

 available for each dog was 25" x 8|" x 10". 



Rabbits were placed for irradiation in individual copper boxes measuring 

 5" X 9" X 12j" (Fig. 3). These boxes had a handle on one side for conveni- 

 ence in loading and unloading, and were perforated for ventilation near the 

 end adjacent to the animal's head. The boxes were symmetrical at top 

 and bottom and were turned upside down on alternate days if animals were 

 irradiated on more than one day. They were labeled M W F on one edge 

 and T Th S on the opposite edge. Thus, on Mondays, Wednesdays and 



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