618 



ADOLF F. VOIGT 



type of circuit. When the potential has fallen sufficiently to stop 

 the pulse, the counter voltage again is built up to its maximum and a 

 second pulse can be received. It can be seen that there would be a 

 time during which the counter is not able to receive pulses. The 

 "dead time" is quite important in that, as the number of counts per 

 unit time is increased, the spacing between them decreases and a 

 larger fraction will occur within spacings too short for the counter 

 to have recovered. These counts will be lost and their loss should be 

 corrected for. There is a straightforward way of determining the 

 dead time and using it in making this correction (40) . An empirical 

 correction that has found considerable application for counting rates 



(a) 



{i>) 



50/i/i fd. 



50 fJ-fL fd. 



•^ \^\o^ a 



+ High voltage ^^^ |0®n 



2 xlO il 



,| +High voltage 

 + 45v. 



-4.5 V. 



TYPE 57 



Fig. 7. Geiger counter quenching circuits. (a) Resistance-capacitance 

 coupling, (b) Neher-Harper quenching circuit. 



under 5000 per minute is 1% per thousand (1% at 1000, 2% at 2000, 

 etc.). 



Mention has been made of the type of gas used to fill counters. 

 Almost all the commerically available GM tubes are filled with a 

 self-quenching mixture of about 9 cm. mercury pressure of argon 

 or other rare gas and 1 cm. of an organic vapor (ethyl alcohol, diethyl 

 ether, or an acetate ester). The use of a Neher-Harper circuit is, 

 in general, unnecessary, though counting characteristics may be 

 improved. The disadvantage of the self-quenching type of tube is 

 that the quenching mechanism breaks down the organic molecules. 

 Since a limited number of such molecules can be put into a tube, there 

 will be a limit to tube life, usually given as 10^ to 10^ total counts. 

 A non-self-quenching tube without such a complex vapor does not 

 have this Umited life. 



Several different types of construction are used in GM tubes. 

 One of the sturdiest is the all-glass tube in which the cathode is a 



