Influence of Illumination from Outside on an A-Hg Discharge Tube

Abstract

It has been discovered by the author that a faint illumination of ultra-violet ray or a visible light from a light source thrown on the discharge space of low pressure A-Hg discharge tubes increases the starting potential to a remarkable extent. This effect only takes place when there exist relatively high wall temperature of 40∼90°C (i.e. high density of Hg atoms) and relatively high pressure of argon gas (a few mm Hg). When the intensity of illumination exceeds a certain value, the starting potential shows a somewhat saturated constant voltage. This effect is sensitive to radiations of any wave-length widely ranging from ultra-violent to visible light. An addition of a small quantity of H₂ gas suppresses this effect. The part of the tube that is sensitive to radiation is found on the anode side. According to the hypothesis by the author, under such condition that both the pressure of A gas and the density of Hg atoms are adequate, there seems to exist a region where metastable molecules of mercury are indispensable for starting a glow discharge as a principal source of ions. In the strength of the assumptions based on the hypothesis by the author, most of the experimental results can be explained fairly well.