Realization of Temperature Standards for the Low-temperature Region and Development of a 3He JT Cryocooler for Thermometer Calibration

Accurately calibrated thermometers are an indispensable tool for reliable and precise temperature measurements. The International Temperature Scale of 1990 (ITS-90) was adopted by the Comité International des Poids et Mesures, CIPM in 1989 to enable accurate and reliable temperature measurements around the world. We realized a temperature scale for the lowtemperature region in accordance with the ITS-90 and calibrated standard resistance thermometers. We also developed a resistance thermometer calibration apparatus based on a pulse tube / 3He JT cryocooler. The calibration apparatus is intended to operate between 24.5561 K (temperature of the triple point of Ne) and 0.65 K (lowest defied temperature of the ITS-90), and is used for comparison and calibration of standard resistance thermometers. The apparatus can reach 0.5 K in continuous operation mode. The temperature control stability at the thermometer comparison block of the apparatus over the operation temperature is better than 0.07 mK, expressed as standard deviation of the temperature variation measured for 15 min. The vibration at the comparison block was also measured and found to be approximately 0.01 m/s2 at maximum. This level of vibration does not affect the calibration of the standard resistance thermometer.