Powder diffraction instruments at the ILL 1976-91

Powder diffraction instruments at the ILL 1976-91 D1A, D1B, D2, D2B, D20

The count-angle information remains easy to exploit, hence there remains real value in these data covering a wide number of experimental fields. Important initial results on high temperature superconductors are included in the early data from the ILL.

Initially D1A and D2 diffractometers only had single detectors, surprising many of the scientists joining the ILL post 1973. D2 was installed in the reactor, D1A and D1B were on a thermal guide in the guide hall with considerably more space for cryogenic and other equipment.

D1A

D1A was quickly modified in 1975 (Hewat) with a bank of ten detectors together with fine mylar collimators developed at the Rutherford Laboratory.

With a high monochromator angle D1A became the work-horse high-resolution powder diffractometer for Rietfeld refinements.

D1B

This was conceived as sharing the same monochromator as D1A, though this proved somewhat impracticable, and each was subsequently given independent crystals.
Having a "banana" multidetector from the start D1B was used for many experiments at lower resolution, mapping parameter space in temperature, pressure and composition, and was much used by physical chemists, looking at adsorbed species and dynamic problems which could be quickly measured over the whole angular range. Heavy demand lead to the construction of D20 at the reactor face on H11, with much higher intensity. This was the only diffraction instrument to be moved from the CARINE control system to a Solar 16/40 which severely limited developments in integrating any advanced controls.

D2, D2B

The beam tube H11 complex of D8/D2 was rebuilt with a larger beam tube providing for D19 single cystal with multi-detector, (replacing D8), D20, a new instrument with a banana detector and high intensity, and the new D2B a high take-off angle, high resolution powder diffractometer with a large focusing moochromator and the RAL Mylar collimators in front of a bank of 64 detectors at approximately 2 degree centres. A scan covered 2 degrees in 0.05 degree steps. Data were hence a table (66x50=3300) of 64 count values plus monitor and a user parameter at 50 positions. Installed at a temporary site in the guidehall while the major H11 monochromator installations were undertaken, it was evident that the heavy detector shielding distorted the central axis. A more substantial support replaced the initial wheel and rail. Later the new monochromator had problems of alignment of the components, and the beam profile was not as clean as D1A. When this was finally corrected (Radaelli, 1995) the instrument took over the main tasks of Rietveld refinement work from D1A. Later the tube detectors were replaced by an array of position sensitive tubes.

D20

This instrument has a very high flux at medium resolution, which, combined with a complete multidetector enables a wide range of experiments. To cope with the expected very high count rates special electronics (Epaud) were developed for a new microchannel gas detector (Oed). Initially only one module was available; the completion (Convert) was achieved after the long shutdown, when it could fully take over from D1B.