A novel low-temperature X-ray goniometer with closed-cycle cooling to about 18 K

Abstract

A unique low-temperature, full-circle goniometer for single-crystal X-ray diffraction has been constructed with the novel adaptation of a closed-cycle refrigerator in such a manner that the cold finger remains stationary during the q~ and Y. rotations. This has been made possible through the development of a flexible heattransfer link between the top of the ~p shaft and the cold station. The new design concept incorporates several important features: (1) the vacuum shroud and radiation shields also remain stationary so as to reduce the X-ray windows to narrow slots; (2) the sample crystal is enclosed in a black, nearly isothermal cavity (Hohlraum); and (3) the q~ shaft is mechanically decoupled from the thermal contraction of the cold finger and other parts. The new system has considerable advantages over presently existing low-temperature adaptations for X-ray diffraction: (1) the goniometer operates between 300 and 18 K without expenditure of liquid cryogen and with minimal attendance; (2) the system is capable of operating for long periods of time with minimal risk of interruption of the cooling cycle; (3) absorption of X-rays by the windows is minimal and independent of the Bragg angle; and (4) data collection at any temperature down to its present lowest limit of 18 K is virtually as easy as with any conventional roomtemperature diffractometer. At the time of writing the instrument has been in use for over 10 000 h and has measured over 100000 X-ray reflections from single crystals.

Macromolecular Cryocrystallography

“…Albertsson, Oskarson & Sffthl, 1979) or by heat conduction through the crystal mount and heattransfer links (e.g. Samson, Goldish & Dick, 1980;Adlhart & Huber, 1982). Such closed-cycle cryostats have only rarely been used in macromolecular crystallography owing to their technical complexity (Hartmann, Parak, Steigemann, Petsko, Ringe-Ponzi & Frauenfelder, 1982;Hartmann, Zinser, Komninos, Schneider, Nienhaus & Parak, 1996).…”

High pressure neutron and X-ray diffraction at low temperatures

“…The axial symmetry ensures that the background data has minimised orientation dependence. Despite these devices being somewhat more cumbersome than the cryostream with the need to accommodate the gas lines between the CCR and the compressor during the rotation of the CCR on the goniometer, weighing typically 5 kg, there are examples of implementation with single crystal desktop diffractometers [25][26][27][28]. The serious disadvantage for the use of these cryostats for X-ray studies is the need to include a 'window' for the beam.…”

A Test of the Suitability of CCD Area Detectors for Accurate Electron-Density Studies

“…A colourless crystal (0.450 × 0.450 × 0.125 mm) of LR-B/081 (orthorhombic, space group Pbca, Z = 8) was mounted on a glass fibre on a Syntex P]-diffractometer modified for low-temperature (LT) measurements (Samson et al, 1980); the cryosystem is a closed-cycle helium refrigerator, with no consumption of gas [for a detailed description of the instrument see Destro (1988)]. Graphite-monochromated Mo Ka radiation (~.…”