An Overview of XRF Basics
2. Instrumentation
2.2 Sequential Spectrometers
The heart of the SRS 3x00 and S4 sequential spectrometers is a high-precision goniometer with two independent stepper motors for separate θ/2θ drive.
Several microprocessors control and monitor the functions and processes inside the spectrometer. A master processor coordinates the internal flow of information and communicates with the external analysis computer. Having its own service interface allows the master processor to be remotely diagnosed by Bruker AXS Service Engineers, without their being able to access proprietary data in the analysis computer. This concept enables rapid location and diagnosis of operational issues.
The various measuring parameters are set exclusively via the analysis computer's software and provide the user with great flexibility.
Besides extending the adjustment parameters of the primary beam filter, the crystal and collimator changer beyond those possible on the SRS 303, the detector high-voltages, too, are set via the analysis computer.
The separate θ/2θ goniometer drive with two independent stepper motors allows precise θ/2θ-angle alignment via the analysis computer's software.
The flow counter is situated inside the spectrometer chamber and has an angle range of 2° to 148°. Located behind the flow counter and outside the chamber, separated by a 0.1 mm Al foil, is the scintillation counter with an angle range of 2° to 110°. Both detectors can be used individually or in tandem. In tandem operation, the intensity in the flow counter is measured as well as the radiation that passes through the flow counter and the radiation that is absorbed by the scintillation counter.
Tandem operation was excluded from the S4 EXPLORER and the S4 PIONEER sequential spectrometers to save space. In addition, the scintillation counter is located in the spectrometer chamber next to the proportional counting tube.
Integrating temperature measurement points allows this stability-relevant factor to be checked in the instrument. Furthermore, the temperature of the water in the internal deionized cooling system is kept constant.
An optional protractable/retractable foil screen can be installed between the sample chamber and the spectrometer chamber for measuring, for example, liquids in a He atmosphere.
Fig. 24 shows the beam path and adjustable parameters of the S4 EXPLORER, S4 PIONEER and S8 TIGER.
A flexible, modifiable sample changer with a robot arm that moves in the directions X and Y allows fully automatic transport of samples to the instrument's entry position, including:
- sample cups with a grab
- bare samples with a suction unit
- steel rings with a magnetic holder
The SRS 3000 was the first X-ray spectrometer with an X-Y sample magazine, thereby setting the standard for all subsequent developments. An internal 2-sample changer enables rapid processing of samples in stack operation without time loss through transporting samples. While one sample is being measured, the next is being inserted into the pre-vacuum chamber.
Fig. 24 Beam path in the S4 EXPLORER, S4 PIONEER and S8 TIGER
Problem-free docking onto a conveyor belt allows easy integration of sequential spectrometers into an automated environment.
The function and possible settings for the various parameters will now be described in the order they are encountered by the beam propagating from the tube to the scintillation counter.