The Four Circle Diffractometer TRICS


The four circle diffractometer TRICS is used for the study of dynamic and magentic structures by neutron diffraction at single crystals. TRICS can be operated in two modes: 1.) with a single counter very much like a traditional four circle diffractometer and 2.) with three position sensitive detectors operating like a oscillation camera as used by protein crystallographers. This manual describes the operation of TRICS using the SICS software.

TRICS is situated at one of the beamlines for thermal neutrons at the spallation source SINQ at PSI, Switzerland. The incident white neutron beam first hits a monochromator crystal. The selected wavelength is not variable. A monochromator lift with two monochromators and the possiblity to select different reflections peaks however make it possible to select between a few different neutron wavelength. The sample is held in a standard eulerian cradle with the usual angles omega, chi and phi. Up to three position sensitive detectors are held on detector holders at different angles in gamma and nu. Or a single detector is fixed to this setup. The three position sensitive detectors may be moved up and down on a sphere around the sample. This allows to access different lattice planes when the eulerian cradle has been replaced by some cryostat or other sample environment devices to heavy to be used in conjunction with an eulerian cradle.

The control of a four circle diffractometer requires a tight integration between measurement procedures and specialized data anlaysis software. For the actual control of the instrument, its movements and the actual measurement of reflections the SICS software is provided. Preliminary data analysis and special four circle calculations are done with a set of F77 programs. These are mostly programs which originate from the ILL, France.

Given this setup the rest of this manual logically has to have three parts:

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