Hirohisa Sakurai

Temperature Coefficients of Resistivity of Rh-Fe Thin Films for Cryogenic Thermometer Use

The resistivity and its temperature coefficients were measured on Rh-Fe thin films between 4.2 K and room temperature to estimate their thermometric sensitivity. The films were sputter deposited on sapphire substrates from a Rh-Fe(0.5 atm%) target. The temperature coefficients are close to those of high-purity, well-annealed Rh-Fe(0.5 atm%) wires although the resistivity is higher than that of the wires. Rh-Fe thin film resistors have a high potential for cryogenic thermometers because dilute iron in the films is as effective as that in bulk wires to enhance the temperature coefficients.

New Sealed Cells for Realization of Cryogenic Fixed Points at NMIJ/AIST

New sealed cells have been developed at the National Metrology Institute of Japan (NMIJ), which are used for realization of the cryogenic fixed points of the International Temperature Scale of 1990. A metal O‐ring made of stainless steel is introduced as a sealing device for the sealed cells. The triple point of equilibrium hydrogen (e‐H2) is realized using the new sealed cells containing hydrogen and ferric oxy‐hydroxide as a catalyst for the ortho‐para equilibration. Double anomalous peaks on the heat capacity curves are observed at temperatures just below the triple point, but they are suppressed by reducing the amount of the catalyst. The reduction of the amount of catalyst allows one to obtain more reliable melting curves for e‐H2. The triple‐point temperature of e‐H2 obtained by the new sealed cells is in good agreement with those reported previously in measurements of open cells by assuming that the dependence of the triple‐point temperature on the deuterium content is 5.4 μK per ppm of deuterium i...

Non-uniqueness of the International Temperature Scale of 1990 in the range 14 K to 433 K

The non-uniqueness of the International Temperature Scale of 1990 is estimated using 6 standard capsule type platinum resistance thermometers in the range from 14 K to 302 K and 7 standard long-stem type platinum thermometers in the range 0/spl deg/C to 156/spl deg/C. The non-uniqueness is found to be less than 0.3 mK in almost all ranges, except a few subranges that cover from 14 K to 54 K. The inconsistency between subranges is larger than the expected value. Both must be included in uncertainty sources in resistance thermometry.

Rhodium-iron resistance thermometer with fused-silica coil frame

Abstract The dependences of the thermometric properties of a rhodium - iron (RhFe) (mole fraction 0.5%) wire resistance thermometer on the annealing temperature between 700 and 900°C are investigated using fused-silica coil frames. The thermometers annealed at or above 800°C have similar temperature - resistance characteristics. These thermometers can be calibrated with an accuracy of 0.5 mK over the range 4.2–25 K using a reference temperature - resistance function and three calibration points. RhFe wire thermometers from different origins can be calibrated with an accuracy of the order of 10 mK in the same way. The temperature rise of the present thermometers due to heating by the measuring current is in a reasonable range for thermometry with a millikelvin accuracy.

Precise Determination of Hydrostatic Pressure Correction Coefficient of Triple Point Cell of Water using Cryogenic Current Comparator Bridge

Applying a cryogenic current comparator bridge to resistance thermometry, the temperature distributions along the thermometer wells of two triple point cells of water are precisely measured using a standard platinum resistance thermometer with low measuring currents of about 0.1 mA. The average hydrostatic pressure coefficient of the two cells calculated from the temperature distributions is -0.854(38) mK/m. This value agrees well with the reported value of -0.856 mK/m, but is not consistent with the recommended value of the International Temperature Scale of 1990, -0.73 mK/m.

Calorimetric Realization of the Triple Point of Mercury Using a Pulse‐Tube Refrigerator

The triple point of mercury is realized by a calorimetric method using a pulse‐tube mechanical refrigerator and two small Pyrex glass tube cells 10 mm in outer diameter and 5 cm in length. Each cell is filled with about 0.1 mol of pure mercury and sealed off. The cell is used in the horizontal position to reduce the uncertainty of the hydrostatic effect, and its advantage is confirmed from the experimental results. The heat capacity of mercury is measured in the range 230 K to 236 K within the accuracy of 0.2 %. The reproducibility of the melting curves is better than 0.05 mK, and the melting temperatures of two cells agree within the scatter of measurement.

Interpolating Gas Thermometer for Realizing the ITS‐90 at NMIJ/AIST

A new interpolating constant volume gas thermometer (ICVGT) using 3He is constructed for realizing the International Temperature Scale of 1990 (ITS‐90) below 24 K at NMIJ/AIST. The bulb, made of oxygen‐free high‐conductivity copper, has a spherical internal volume of about 1 L. The gas pressure is measured using a pressure gauge at room temperature through a pressure sensing tube made of stainless steel with an inner diameter of 2.2 mm and a length of about 1.4 m between the bulb and a room temperature anchor. The ICVGT is calibrated against the 4He vapor pressure scale and the triple points of equilibrium hydrogen and neon realized at NMIJ. 3 K or 4.2 K is chosen as the lowest calibration point, and the ITS‐90 is realized preliminarily in the range from 3 K to 16 K. The temperature profile along the sensing tube is measured using eight thin‐film RhFe resistance thermometers to evaluate the corrections for the dead space effect and the aerostatic pressure head. The temperature scale realized with these co...

Calorimetric Realization of Low‐Temperature Fixed Points Using a Cryogen‐Free Refrigerator System

A calorimeter is developed for precise heat capacity measurement and for realization of low temperature fixed points using a cryogen free mechanical refrigerator. The design and structure of the calorimeter is explained with some measurement data including heat capacities and melting curves of temperature fixed points. The validity of the relationship between the melting temperature and the inverse of the fraction of melt is demonstrated using several fixed point samples. The heat capacity anomalies of hydrogen by a catalyst for equilibration of ortho‐para hydrogen and the impurity effect of solid‐solid phase transition of oxygen are shortly discussed.

Realization of the triple points of equilibrium hydrogen and equilibrium deuterium

The triple points of equilibrium hydrogen and equilibrium deuterium have been realized using a calorimetric method and sealed cells, which include hydrogen (or deuterium) and a catalyst for the ortho-para equilibration. Anomalous increases on heat capacity curves of each substance, which markedly disturb melting curves of the triple point, are observed at temperatures just below the triple point. In the case of equilibrium hydrogen, a reduction of the amount of the catalyst suppresses the anomalous increases and allows one to obtain more reliable melting curves of the triple point.

Practical Properties of Rhodium-Iron Thermometers with Fused-Silica Coil Frames Down to 2.3 K

Thermometric properties of the recently proposed rhodium-iron (mole fraction 0.5%) wire resistance thermometers with fused-silica coil frames are investigated down to 2.3 K. The thermometers annealed between 800?C and 900?C are calibrated down to 2.3 K with an accuracy of 1 mK by a simple method using a reference function and three reference temperatures, 4.2 K, 13.8 K and 24.5 K, which are the most convenient calibration points in this temperature region. The stabilities in thermal cycling between 4.2 K and room temperature and the self-heating effects due to the measuring current are reasonable for the same accuracy.