PHOTOELECTRIC CURRENTS IN LIQUID AR, LIQUID CH4 AND LIQUID N-2 - EFFECT OF ELECTRIC-FIELD STRENGTH AND INJECTION LEVEL

The photoelectric steady-state currents J(L) in liquid Ar, liquid CH4 and liquid N2 were measured, changing the level of injection current. The current level was varied over a wide range using ultra violet light from a deuterium lamp. In liquid Ar and liquid CH4, when the current in vacuum J(v) (which is defined as an injection current) was less than 0.1 nA cm-2. J(L) was proportional to the external field E0 at low fields, while at high fields J(L) was proportional to E0(1/2). However, by increasing J(v) at low fields a space-charge-limited J(L) was observed, with the linear relation between J(L) and E0(1/2) being unchanged at high fields. On the basis of measured curves of J(L) against E0, the distribution of space charge, field strength, and currents of electron and negative ion components within the gap were simulated. The space charge was presumed to appear due to accumulation of negative ions produced through attachment of electrons to oxygen impurities which might be included originally in gas samples. In liquid N2, J(L) was proportional to E0(1.8-2), although it increased proportionally with J(v).