Production of High Concentrations of Hydrogen Atoms

Abstract

RECENTLY we wished to produce high concentrations of hydrogen atoms in flowing gas at pressures of about 0.08 mm. of mercury. An electrodeless discharge is the most suitable source at this pressure, but although several attempts were made to use such discharges maintained by microwave radiation, a stable discharge could not be obtained at pressures less than 0.12 mm. of mercury with power inputs of up to 250 W. The discharge was therefore maintained using 9.7 Mc./s. radiation from a 350-W. radio-frequency oscillator, when the method described below proved very satisfactory. About 25 cm. downstream from the discharge, the atomic concentration was 50–60 per cent. This compares favourably with most values quoted in the literature, and using microwave radiation from a ‘Raytheon’ diathermy unit at 0.12 mm. mercury pressure, fewer than 10 per cent atoms were obtained. Atomic concentrations were measured with a Wrede gauge with an orifice of 0.13 mm. diameter, the differential pressure being measured directly with a sensitive differential Pirani bridge.