Powder Diffractometer (POWGEN)

Powder Diffractometer at SNS Click image for a larger version.

First neutrons received! Commissioning is under way.

POWGEN will be an extremely flexible and versatile general purpose diffractometer useful for a wide range of structural studies. It can cover d-spacings from ~.5 Å or less to well over 10 Å in a single measurement, and is capable of collecting typical Rietveld statistics in ~20 minutes from a 0.6 cm 3 sample with a <0.1% resolution at short d-spacings and <1% resolution for nearly all d-spacings of interest. Alternatively, much of this resolution can be traded for intensity, making it possible to make measurements in << 20 minutes with still quite good resolution. The adjustable bandwidth-limiting choppers allow large variations in the incident wavelengths and pulse repetition rate. Insertable guide sections and the ability to trade resolution for intensity at the analysis stage allow users great latitude to optimize the data range, resolution, and statistical precision for each particular experiment.

Previous TOF diffractometers used detector "banks" at a few angles, along with a broad wavelength range to produce a limited number of data sets of intensity vs. wavelength at these few effective scattering angles. A new idea due to Paolo Radaelli proposed the use of wide angular coverage and full 60-Hz operation to collect a single data set of intensity vs. angle and time-of-flight. This data can then be combined "appropriately" after-the-fact to produce a single data set with intensity as a function of d-spacing to be used in Rietveld refinement.

This new data collection/analysis concept can be applied to any detector geometry. However, it appears optimally suited to a continuous detector locus, with this locus chosen to optimize the resolution as a function of d-spacing.

The following documents contain more detailed information about the expected performance and design of the diffractometer:
POWGEN Conceptual Design Study (PDF 483K)
Instrument data sheets (PDF)