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, $\alpha$ and $\gamma$, have been determined in the usual manner over an extended range of values of $\frac{E}{p_0}$. 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 $\frac{E}{p_0}$. 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.

• Received 30 August 1939

DOI:https://doi.org/10.1103/PhysRev.58.67