A liquid-helium cryostat for collection of three-dimensional X-ray intensity data down to 20 K. The crystal structure of D (+)-tartaric acid at 35, 105, 160 and 295 K

A Be-walled conduction cooling He(l) cryostat intended for the interval 20–80 K and the κ geometry of the CAD4 X-ray diffractometer is described. Three-dimensional X-ray intensity data can be collected in the interval − 45 < χ < 45° with the temperature stability maintained within ± 1 K. The experimental problems caused by centering an unseen crystal and by the absorption and scattering in the Be walls are discussed. d(+)-tartaric acid, C4H6O6, was chosen as a test compound. Only minor differences occur in its crystal and molecular geometry between 295 and 35 K.