The new D2B high resolution powder diffractometer

E. Suard, A. Hewat, C. Ritter

Institut Laue Langevin, 6 rue Jules Horowitz, BP146X, 38042 Grenoble CEDEX, France.

A new 2D detector was installed on D2B. This is a new type of pseudo-2D high-resolution position sensitive detector, covering 160 degrees horizontally by 14 degrees vertically. In the horizontal plane, high-resolution is obtained by scanning a bank of 128 fine 5-minute collimators. In the vertical plane lower resolution is obtained using vertical linear-wire position sensitive detectors. Since the height of the detectors is 300 mm, vertical resolution is needed to correct for the curvature of the diffraction cones. Initial problems with background and calibration were resolved, and the normal user program restarted while data reduction routines were further developed. The efficiency is about an order of magnitude greater than with the "old" detector. In the high intensity mode a pattern with good statistics can be collected in a few minutes.

A powder pattern measured on the new D2B detector, showing how the curvature of the diffraction cones depends on the scattering angle is shown below. A computer routine "straightens" and integrates these curves to produce a standard intensity vs. 2theta diffraction pattern.

A 30 mg sample of CeO2 was measured at room temperature on D2B. A special vanadium container with very thin walls was used. The data acquisition last 17 hours and the pattern obtained is perfectly refinable. Such a measurement was possible because of the high quality of the new D2B detector as well as the work done on the instrument zone to reduce the neutron background as much as possible.

We have no doubt that it should be possible to measure even smaller samples if longer counting times can be scientifically justified.