76 



BIOLOGICAL EFFECTS OF RADIATION 



can-made instruments of this type require little or no scale correction, 

 although this should be assured by test for each instrument. 



The condenser type (19, 37, 38) of thimble chamber has definite fields 

 of application in that the thimble chamber can be disconnected from the 

 electrometer while being exposed to X-rays. To use, the chamber is 

 attached to the electroscope and charged in the usual manner as indicated 

 on the scale; it is then removed from the electroscope, the exposed lead 

 covered with a metal cap for shielding, and exposed to X-rays, thereby 

 discharging it; finally, it is replaced on the electroscope which now indi- 

 cates its loss of charge and hence the strength of the X-ray beam. 



"Scale to read olefJecHon of sf ring 

 ■■'Microscope 



~i'. 



',^ 



; .-Focus acjjusfment 

 "ij Lead case--^. 



"'Amber charging disc 



Tliimble ionizafion chamber. 



^ ^^)^mm^^:.t^ ^ 



-j'fj.ii,/A\MM'fVr,C 



yj^/^wv<vvy^V l ■«MHtfv>y44^^■l|jSW I jV'^»yT 



— Coniacf 



,Lamp swifch 



Condenser (Amber) 



Fig. 19. — Condenser roentgenometer. (Glasser-Seitz.) 



These chambers have also been made of the shape and size of radium 

 needles (Fig. 18) thus permitting their direct insertion into tissue for the 

 measurement of radium and X-ray depth dosage. 



Figure 19 shows a condenser type of roentgenometer extensively used 

 in this country. The ionization chamber and short section of the con- 

 necting lead, as a single unit, are inserted into the tube connected to the 

 electroscope. The entire insulated system is then charged by means of 

 the small bakelite electrostatic charging disk which is connected to the 

 insulated system by the switch, S, during the charging operation. The 

 potential of the system is indicated by the deflection of the conducting 

 quartz fiber, illuminated by a 3-volt lamp, and viewed with a low-power 

 microscope having a suitable ocular scale. When fully charged, the 

 chamber is removed and placed in the X-ray beam, after which it is 

 again inserted into the fully charged electroscope. The loss of charge 



