STUDIES IN DETECTIXG RADIO-ACTIVE FALL-OUT 



particles which have fallen out of the stratosphere and also out of the 

 atmosphere, as distinct from the particles which have fallen out ol" the 

 stratosphere hut ha\e been collected as airborne particles or as present in 

 rainwater. 



The 16 ft.- roof protecting the cheesecloth was covered witli a sheet of 

 polyvinyl chloride. This presented a fairly smooth surface to collect dust 

 which was subsecjuently washed by rain from the roof into a beaker. The 



Figure 1. Photograph of apparatus 



bottom of the beaker w^as covered with filter paper as it was found that 

 without this, dust adhered to the bottom of the beaker and efficient collection 

 was difficult. 



{3) For the colleclion of material brought down by rain 



The protective roof was sloped to one corner and had a retaining rim 

 1 in. high, around it, so that rain falling on to the roof was collected in a 5-1. 

 beaker. 



{4) For comparison of the gummed-paper method commonly used at monitoring stations 

 A strip of 6 in. wide commercial adhesive tape, exposed length 1 in., 



attached to a brass frame was placed beside the rest of the apparatus. 

 All of the apparatus was situated on the roof of the nurses' home of the 



Peter MacCallum Clinic — a site reasonably unobstructed by other buildings. 

 All counting was carried out with an EHM2S mica end-window Geiger- 



Mtiller tube, with tube and sample shielded on all sides by 1| in. of lead. 



PROCEDURE 



The cheesecloth was changed at weekly intervals. After exposure, it was 

 ashed over a Bunsen burner, the ash was weighed, transferred to an alu- 

 minium planchette and counted for 20 min. This was the airborne material. 



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