132 THE UNIVERSITY OF OKLAHOMA 



from the top of the case by means of an amber plug. A spiral 

 spring- at the bottom of the leaf support makes contact with the 

 electrode used. A telescope is rigidly mounted on the case to read 

 the position of the leaf. 



The ionization chamber used is a metal cylinder 6cm. in diam- 

 eter through which the gas flows. The electrode is a metal rod 

 0.5cm. in diameter and 5 cm. long coaxial with the cylinder and 

 suported by a rod at right angles to it around which is cast a 

 sulfur plug. This plug is cast into a brass ring of such a size 

 that the electroscope head fits over it and is held firmly in place. 

 The rod holdino- the electrode comes uo the insulator far enough 

 to make connection with the leaf system through the spiral spring. 

 Tne whole leaf system is thus well insulated from the case. 



Sulfur was used as an insulator principally because of the 

 ease with which it can be worked. The insulator is easily kept 

 clean by scraping the exposed surface occasionally. It is small 

 enough that the so called "soak" of charge is not a serious factor. 

 This effect can be almost entirely corrected if the e'ectroscnpe is 

 left charged for som.e time before it is to be used. It is found that 

 charging an hour at the average potential at which the electro- 

 scope is to be used is sufficient to saturate the insulator. 



Apart from low capacity there is another factor which makes 

 for sensitivity. The gas under examination is constantly flowing 

 through the ionization chamber. In this way a much larger volume 

 can be examined than woula be feasible if the gas were drawn into 

 a chamber and left to stand during examination. Of course most of 

 the r.^.dioactive material (gaseous emanation) is carried rapidly past 

 the electrode. But the emanation, upon disintegrating, leaves a 

 short-lived solid deposit of very active material on the walls of 

 the chamber, (half periods range from 3 minutes to half an hour). 

 The principal effect is expected from these active deposits. The 

 effect is therefore cumulative and due to a much larger vo!ume of 

 gas than could be easily examined by methods now in use. 



There is another facto'" to be considered, namely, that the ga£ 

 will be moist. The insulator must be entirely protected from mois- 

 ture. This is done bv means of a drying tube, at the side and just 

 below the msulator, through which air is forced from a tank out- 

 side. 



Calibration is carried out by passing air over a preparation con- 

 taining a known am.ount of radium. Tlie amount of emanation in 

 the air that goes through the ionization chamber is known. The 

 rate of fall of the electroscope leaf will measure directly the radio- 

 activity. The volume of gas going through the ionization chamber 



