Sec. 10.2] 



GEIGER-MULLER COUNTERS 



305 



maintain itself and the counter tube is said to be non-self-quenching or 

 "slow." Following the generally accepted qualitative description of the 

 processes given by Montgomery and Montgomery [3] and other writers [4], 

 the presence of the residual slow-moving positive ion sheath greatly modifies 



B 



^ €> 



^. 



^ 



^^ 



B- 



Fig. 73. Typical counter-tube designs. 



A. Bell counter. Wire anode, thin mica window, and chemically deposited silver cathode 

 (beta particles). 



B. Point counter. Ball anode, thin mica window, and alternative inserted copper cylinder 

 cathode (beta particles). 



C. Thin glass window counter (beta particles). 



D. Immersion counter. Thin glass wall, deposited silver cathode. Shown immersed in 

 sample liquid (beta particles). 



E. Cylindrical counter. Thin glass wall and deposited silver cathode for beta particles. 

 Heavy wall and copper mesh cathode for gamma rays. 



the electrostatic field gradient surrounding the anode, thus quenching the 

 avalanche by preventing the remaining free electrons from acquiring suffi- 

 cient energy between collisions to cause further ionization. The positive 

 ions then drift to the cathode in a time of the order of 10 -4 sec. At the 



