A Method for Measuring Radon Seeds

Abstract

The method and the instrument about to be described have been in constant use during a period of several months and have proved to be such a rapid, safe and reliable means of measuring radon seeds that it has seemed worth while to describe them in some detail. The instrument used is a simple string electroscope, shown in Fig. 1. AB is very fine, platinum-coated quartz fiber (Diam. 2 to 5 microns) suspended at A with a fine U-shaped piece of quartz, which acts as an insulator as well as a spring to provide the proper tensions in the quartz fiber. A screw arrangement at C is provided for raising and lowering A. B is connected at the mid point of a 100,000 ohm wire wound resistance whose ends are connected to two plates E and E'. E is insulated from the case G with good bakelite and is also mounted on a screw so that it may be moved toward or away from E'. This provides a method for electrically balancing the electroscope. The resistance is also mounted on bakelite. The ion collecting grid H in the ionization chamber I, and E', are carefully insulated with amber. A contacting key J, having silver contacts, makes or breaks electrical connection with E' by releasing or pressing a key some distance from the instrument. K is a 90-volt Radio B battery and supplies the potential for both the electroscope and ionization chamber.