| The sourcesA thoria coated filament is used to emit electrons which are accelerated onto the water-cooled anode by a potential of up to 15 kV. The twin anode version has two target regions (usually Al and Mg), each having an independent filament. The high power version has a single conical target region, surrounded by a circular filament. Both anodes are silver-tipped copper, the use of a silver tip removes any chance of CuLa breakthrough. The X-ray exit aperture contains a 1 mm aluminium foil window which shields the specimen from the high voltage on the anode, and reduces Bremsstrahlung irradiation and cross-contamination of the sample. The window also allows the source to be differentially pumped if required.The standard version of the source (XR3) has a 300W Mg/400W Al twin anode featuring easy switching between sources, yet minimal cross contamination - other materials are available on request. Comparison of spectra from Al and Mg sources allows XPS and Auger peaks to be distinguished.
Anode coatingIn the standard configuration the anode is coated on one side with aluminium giving an X-ray Ka line at 1486.6 eV and magnesium on the other side giving a Ka line 1253.6 eV. Other anode coatings are available by request.A current passes through one of two selectable thoria coated tape filaments which are near earth potential. Electrons are emitted from the filament and strike one of the sides of the coated anode which is at a potential of up to +15 kV. This generates X-ray radiation. The electron emission is controlled by the filament current.
Minimal crosstalkThe anode and filament design minimises the possibility of cross talk between each coating. The copper anode is silver tipped preventing any copper x-ray lines being generated. A thin Aluminium foil window over the end of the X-ray prevents the anode potential affecting electrons in the analyses region. It also acts as a partial filter for other X-ray lines in particular oxygen and allows the source to be differentially pumped if required.The anode is water cooled and the power supply is interlocked to the flow rate. Interlocking is also present for the source cover and earth connections. A spare interlock is available for example it could be a system pressure interlock. It is also possible to shut down the X-ray from the data system at the end of an experiment.
Mechanical featuresAn optional 25 mm linear drive minimises working distance when in use and allows retraction for multi-techique flexibility.The source also features a specially profiled nose piece to avoid mechanical clashes.
Operating conditionsNormal operating currents, voltages and water flow. Anode energy 0 to +15kV Filament current 0 to 5 A Filament emission 0 to 26 mA Water flow rate 3.0 l/min minimum Mains power 240V A.C. 5 A maximum
Vacuum requirementsThe X-ray source should be run at all times at a vacuum level of 1 x 10-7 mbar or better. The source can be safely baked at 250o C. A special collar and T-piece can be provided which allow the source to be differentially pumped if the chamber pressure is high or the analyses area hostile (reactive gasses etc.) |