Stable isotope mass spectrometer

A high precision stable isotope ratio mass spectrometer has been designed, built and its performance evaluated. The mass spectrometer is provided with two ion sources (H, CNOS sources) and ten separate Faraday cups. Its analyzers of 3.7 cm (H) and 13.6-15.1 cm (CNOS) radii and 1800 deflection angle provide first order focusing for ion beams diverging in the radial plane. Trap regulation of a magnetically and electrostatically focused electron beam is used to achieve stable ion production in the ion sources. Ion currents are amplified with low bias-current solid state amplifiers and integrated with voltage to frequency converters and scalers. Mass setting is performed by varying the ion accelerating voltage. A symmetrical dual viscous inlet system has been constructed for measuring the sample and standard gases alternatingly. Pneumatically actuated bakeable gold sealed metal valves exclude cross mixing between sample and standard gases. The instrument, including the inlet system with variable reservoir volumes, is controlled by a microcomputer thus providing automatic and reproducible operation. (author)