X-ray diffraction measurement at 0.20 K

We have developed an X-ray diffraction measurement system for powder samples below I K. We use a dilution refrigerator (D.R.) of Oxford Instr. Kelvinox VT, which was modified for the X-ray measurement (J. Low Temp. Phys. 128 (2002) to be published). After our previous publication, we improved our measuring system. The X-ray beam was reduced approximately 1/12, after passing through the windows of the dilution refrigerator. The windows are consist of four walls of Be 2 mm thick, two Al film 10 mum thick and two aluminized mylar walls. The lowest temperature of the Xray measurement was about 0.20 K. We have studied the temperature gradient between the specimen and the thermometer (RuO2) which was attached to the mixing chamber. The results of our measurement suggest that there is no temperature difference between the RuO2 on the mixing chamber of D.R. and the specimen down to 0.5 K. Below this temperature the gradient was observed to some extent. (C) 2003 Elsevier Science B.V. All rights reserved.