The SNB diffractometer consists of two coaxial turntables.

The first one (Theta table) is fitted with a 120cm diameter aluminium disk which holds the detector stage.

The second one carries a smaller disk (Omega table) holding an X-Y-table. This table holds again a fast spinning table for averaging where the sample capillary is attached to.

The X-Y table allows also for attaching and aligning a cryostat in order to centre the sample. Both tables con be run independently permitting also Theta/2Theta scans.

The detector stage consists of 6 independent Si-111 analyzer crystals. Each crystal is mounted on a small rotary stage such that all six crystals can be aligned individually.

Furthermore, all these individual rotary stages are again mounted on one support plate which can be turned with the aid of a precision stage in order to change the bragg angle on all analyzer crystals simultaneously.

The design was made as compact as possible in order to reduce the spacing between the crystals to 1.1° only. The analyzers are followed by an array of 6 pen-scintillation counters. A thick scintillator (2mm thick NaI disk, 12mm aperture) was chosen for a high stopping power up to 80keV.

At present the system can run at wavelengths down to 0.37keV. limited by the increasing cross-talk between adjacent channels. All detecters are assembled in a block which is again attached to another turn table in pemitting to follow the change in Bragg angle when the analyzers are set to a different wavelength.

To minimize the cross talk all channels are individually separated by sliding Soller slits which can adapt their length to adapt for the rotary theta/2theta motions of the Bragg and detector stage.

 

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