An aerosol particle size analyzer based on a laser Doppler velocimeter (LDV) has been developed to measure the aerodynamic diameter da of individual particles and droplets in real time. The particles are electrically charged and then passed through a 40-kHz electric field. The phase lag φ of the particle motion with respect to the field is measured by the LDV. A microcomputer determines da from φ and stores the aerodynamic size distribution of the sampled particulates. The analyzer has counted and sized particles at a maximum rate of 200 particles/s in the size range of 0.3–5.0 μm in aerodynamic diameter.
Cold electron sources have been studied with particular emphasis on mass spectrometric application. In these sources a relatively weak current from a primary emitter was amplified by an electron multiplier to provide sufficient electron current to ionize neutral gas molecules. The final designs of the cold sources use tantalum photocathodes powered by simulated sunlight as primary electron sources. The sources are highly efficient, consume negligible power, have minimal outgassing and gettering effects, and exhibit considerably less short-term emission fluctuations than a temperature-limited thermionic emitter. These devices would be well suited to calibration work and space flight instrumentation.
An electron emitting source, which operates at ambient temperature, has been developed for instrumental applications including its use for electron emission in an ion source of a mass spectrometer. By the proper generation of a high resistance micron size gap in an electrically conducting tin oxide film, electrons will be emitted at the region of the gap. When the tin oxide film gap is located at the edge of the inner diameter of a very short length of capillary tubing, electron emission of 100 to 200 μA can be typically achieved with 300 V potential placed across the gap. Power consumption for the operation of this device usually remains below 300 mW. If the capillary tubing is made longer and the electrons are made to traverse the length of the capillary bore, a collimated electron beam will emerge at currents appreciably less than above with a diameter equal to the bore of the capillary. If the gap in the tin oxide film is located down in the bore of the capillary, the application of the operating potential will cause the electrons to emerge at one end while an ion current proportional to the pressure in the system comes out the other end.
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