642 ADOLF F. VOIGT 



worker are available. The older of these is a chamber made of Bake- 

 lite or other plastic about the size of a fountain pen (Fig. 136) {84,87, 

 92). The inside of the chamber wall is coated with an electrically 

 conducting film. This film and a thin metal rod down the center, but 

 insulated from this coating, constitute the two electrodes. The 

 chamber is charged by plugging it into an a.c.-operated electrometer, 

 which makes contact with the two electrodes. It is read also by 

 means of this electrometer {64)- 



Another type of pen-sized pocket chamber was one developed 

 during the war by O. G. Landsverk and now made by a number of 

 instrument makers. This is truly a pocket electrometer since each 

 chamber contains its own quartz fiber and optical system and oper- 

 ates on the general principle of the Lauritsen electroscope described 

 earlier (Fig. 13a). It is charged by a battery-operated charging box, 

 which also allows one to view the fiber during the charging operation. 

 Its principal advantage is the fact that it can be viewed at any time 

 by merely looking through it at a light source {83,84,92). The sim- 

 pler chamber is somewhat less accurate, less convenient, a little more 

 rugged, and considerably less expensive than the latter. Either 

 should do an adequate job of on-the-spot personnel monitoring for 

 most laboratories, though at least a few pocket electrometers are 

 recommended for medium to high level work since the worker can 

 tell very quickly whether his radiation dose rate is approaching the 

 dangerous level. 



Of equal importance are the nonwearable but still portable survey 

 meters. These are battery operated and usually weigh 5-10 pounds. 

 As usual two types are available: GM tube and ionization chamber 

 survey meters. In the first type the integrated current of the tube 

 pulses or, in the second, the chamber current is amplified and made to 

 operate a direct current meter. Since the dose is dependent on the 

 amount of ionization and not solely on the number of particles, it is 

 expected that the ion chamber meter, which measures the actual 

 ionization, will be more accurate than the GM tube, which merely 

 counts the particles. However, experience favors the GM tube sur- 

 vey meters for their stability, ease of handling and repair, and more 

 rapid response to a change in radiation intensity. The circuits of 

 the ionization chamber survey meters are frequently slow in respond- 

 ing, having time constants of five to twenty seconds. The GM tube 

 survey meter responds more rapidly and is usually equipped with ear 

 phones through which the actual pulses are fed, producing an in- 



