K1 - A Miniaturized Non-Radioactive Electron Emitter Including High Vacuum Pressure Monitoring

11. Dresdner Sensor-Symposium 2013
2013-12-09 - 2013-12-11
Dreikönigskirche - Haus der Kirche Dresden
10. Selbstüberwachung und online Verifizierung von Sensordaten
P. Cochems, M. Bellmann, M. Runge, S. Zimmermann - Leibniz University Hannover/D
405 - 408


We present a miniaturized non-radioactive electron source based on thermo emission with integrated high vacuum pressure monitoring. This electron source generates free electrons at atmospheric pressure to be an alternative to radioactive beta minus sources. Most gas sensor systems based on atmospheric pressure chemical ionization (ACPI), such as ion mobility spectrometers, use radioactive beta minus sources to provide free electrons with high kinetic energy to initiate a chemical gas phase ionization of the analytes to be detected. Instead of the typically used radioactive beta minus sources to provide high energetic electrons, we generate free electrons in vacuum by thermionic emission from an electrically heated tungsten filament. The electrons emitted from the filament are then accelerated towards an electron transparent, but gas tight Si3Ni4-membrane, through which the electrons are transferred from vacuum to atmospheric pressure. An insufficient vacuum in the miniaturized nonradioactive electron source may cause electrical breakdown, which not only produces electromagnetic
interference but can also damage the Si3N4-membrane by decreasing the kinetic energy of the electrons leading to charging effects and extensive energy deposition in the membrane. Therefore, we present a concept to self-monitor the vacuum in the non-radioactive electron source by simply switching the electronics from electron emission to pressure monitoring mode.