Optimizations in angular dispersive neutron powder diffraction using divergent beam geometries

Angular dispersive neutron powder diffractometers are usually built using beam divergencies defined by Soller type collimators. To account for the needs of resolution for crystal structure refinement a good in-pile collimation α1α1, a high take-off angle above 90∘90∘ at the monochromator and a good collimation α3α3 in front of the detector bank are chosen whereas the value of α2α2 for the collimation between monochromator and sample is less crucial.During the last years new strategies were developed at our institute using wide divergent beam geometries defined by fan collimators or slit-type diaphragms which correlate ray direction and wavelength within the beam.Here we present the performance of a newly developed fan collimator, which enables one to adjust the opening of the collimator channels on both sides independently. This fan collimator is positioned in front of the monochromator at the instrument E6 at the Helmholtz Centre Berlin (formerly Hahn-Meitner-Institut Berlin).It will be shown that control of the beam divergency allows optimization of the resolution in a large angular diffraction range. Hence the resolution and intensity can be adapted to the needs of powder diffraction.Monte Carlo simulations using McStas are used to check and prove the optimal setting of the instrument. We obtain a very good agreement between experimental and simulated data and demonstrate the superior outcome of the new instrument configuration with respect to Soller type instruments.