A study of the time-lag in a photoelectric, gas amplified discharge for parallel electrodes as a function of gas pressure, plate separation, and amplification has demonstrated that diffusion of metastable argon atoms is the source of the lag and that these atoms striking the activated caesium cathode are highly efficient in liberating secondary electrons. The Townsend ionization coefficients, a and 7, have been determined in the usual manner over an extended range of values of E/p 0 . Analysis of the time-lag function has made possible the separation of the number of secondary electrons released at the cathode into those due to positive ions and those produced by metastable argon atoms. A factor representing the fraction of electron energy gained in the field which is used to excite atoms to the metastable level has been determined as a function of E/po. The coefficient of diffusion of metastable argon atoms in argon has been computed and shown to be that expected for a metastable atom having a diameter effectively 1.74 that of the normal atom.
A study has been made of the photoelectric emission obtained at room temperature from the equipotential oxide cathodes commonly employed in radio receiving tubes. With a double monochromator, long-wave limits were determined by plotting the currents as a function of the wave-length of the incident radiation. The threshold frequencies decreased with increase in the accelerating potential according to the relation, in which VQ is the "zero-field" threshold and E the electric field at the cathode surface. It is shown that the observed lack of saturation in the photo-currents may be ascribed to a decrease of work function with increase of applied field. The tendency to nonsaturation is greatest for light of longest wave-length. Calculations show that the photoelectric equation of Houston satisfactorily represents the variation in numbers of emitted electrons with color of illumination, and with change of threshold. Some comparisons are made of the photo-emission and the thermionic currents obtained from the same cathode surface. There is a change in photoelectric threshold with activation. Preliminary measurements of thermionic work functions confirm the theory that in both cases the emission of electrons takes place from the outermost layers of the oxide coating.
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