PAPERS OX CHEMISTRY AND PHYSICS 267 



THE EFFECT OF ALKALI VAPOES AXD OTHER 



GASES AT VARIOUS PRESSURES IX 



THERMIONIC DETECTORS 



Hugh A. Beowx and Chaeles T. Kxipp. Lxhtirsity 

 OF Illixois 



IXTBODrCTIOX 



In recent years there lias been put on the market, and 

 used extensively, a class of vacuum tubes knowTi as ''gas 

 content detector tubes". The advantage of using this 

 type of tube as a detector lies in the fact that it does not 

 require a high plate voltage for its oiDcration; in fact, the 

 plat^ voltage is often as low as IS volts, but must be ad- 

 justed carefully to the best value for loudest signal re- 

 sponse. For such tubes the adjustment of filament cur- 

 rent is also critical, and these two characteristics consti- 

 tute a serious disadvantage. In the case of higher vacu- 

 um tubes used as detectors adjustments are not so criti- 

 cal, Avhich of course is a distinct advantage, the only dis- 

 advantage being that higher plate voltages are necessary 

 for good audibility of signal response. During the past 

 year, and recently, considerable work was done by the 

 authors of this i^aper on the effect of variation of pres- 

 sure and nature of gas content upon the efficiency, con- 

 stants, and characteristics of detector tubes. It is not 

 within the scope of this paper to describe the work in de- 

 tail, but the results and conclusions will be reviewed, to- 

 gether with some of the more important curves. 



Several tubes were connected to a condensation pump 

 and vacuum gauge, see diagram A, and for various pres- 

 sures readings were taken of plate voltage for loudest 

 signal reesponse, called the ''operating voltage". Read- 

 ings were also taken of percent signal intensity when the 

 tube was operating as a detector of undamped waves. 

 Tyi^ical results are shown in Fig. 1. It will be noticed 

 that the operating voltage decreases very rapidly with a 

 slight increase of pressure above the high vacuum stage, 

 and that the maximum audibility occurs at rather good 

 vacua, .002 to .004 mm. of mercury, and for operating 

 voltages of from 40 to 50 volts. The percent signal in- 



