Anew superconducting reference device for thermometry below 1000mK

To provide a means for dissemination of a new temperature scale below 0.65 K, a device is being developed consisting of a number of superconducting reference points, the SRD1000. In comparison with the former SRM768 of NIST, the poisonous Be has been omitted, and IrRh alloys are introduced to ll in the gap between 15 mK and 100 mK. At the high temperatures Al and Zn are used to provide overlap with ITS-90. A new detection system for the transitions was developed consisting of planar microcoil systems with dedicated electronics. A prototype of the sensor has been constructed and ten materials have been selected to be included in the sensor. For 8 materials good results have been obtained and transition temperatures can be dened with an accuracy of better than 0.5%