XVII. RADIOACTIVE TRACERS 



613 



arrangement, and a drying agent to improve the performance in 

 humid weather. The latter can cause serious interference since the 

 backgi-ound in a humid atmosphere can vary as much as tenfold. 

 The chamber to be described can be machined in any instrument shop 

 from a 3-3M iii- ciil^e of aluminum (see Fig. 4). A 2-23^ in. square 

 hole is machined through this cube in what will be its vertical direc- 

 tion. This produces a square shell with about 3^ in. walls that can 



assembled 



A ^^ . ^<; ^^Plate 



Slots for shelves. 

 Additional ones 

 not shown 



Fig. 4. Cubical cast aluiuinuui ionization chamber for LauritHeu electroscope. 



also be cast directly if casting facilities are available. At right angles 

 to this hole are machined a circular hole with the diameter of the elec- 

 troscope head so that a snug fit is obtained over this head, and oppo- 

 site to this a }/2 ill- hole over which a piece of etched glass is cemented 

 as a window for the light source. Through the remaining two walls 

 two 1 in. holes are drilled and tapped with fairly large threads. Lugs 

 to fit these holes are made of brass oi- other metal tubing. In these 



