SOME EXPERIMENTS WITH GAS-FILLED Cs–O–Ag PHOTO CELLS

Abstract

The amplification of the cathode emission by argon is much greater for a tube with a photo‐cathode, than for a tube of similar geometry equipped with a thermionic cathode. This difference is attributed to large secondary electron emission by positive ion bombardment of the photo‐cathode. If the anode voltage of one of these argon‐filled tubes is abruptly increased, the time lag in the resulting current change is of the order 5×10⁻⁵ sec. for the thermionic tube, but of the order 10⁻³ sec. for the photo‐tube. This lag is attributed to the life of the positive ion charge on the spongy surface of the photo‐cathode. Measurements of the spontaneous fluctuations in the current through a gas‐filled photo‐tube indicate that the ``noise'' is of low frequency and associated with the gas amplification effect.