Measurements of temperature and humidity are required in all fields, from daily life to industry and science. There is a great demand for the development of the standards, we are dedicated to the realization and development of the standards based on the international temperature scale. Also, several world-leading researches aiming to improve the international temperature scale are currently conducted. In the area of physical properties, our fields of research include thermophysical properties, such as thermal expansion, thermal conductivity, density and viscosity of various substances and materials, and the distribution or mass distribution of particulates in gases and liquids. Research on the evaluation technology of uncertainty of measurement that expresses the reliability of measurement results and the development of "distributed thermophysical property databases" also falls within our scope.    

Our programs in this field cover the R&D of fixed points, platinum resistance thermometers, helium-3 vapor pressure thermometers and gas thermometers, in the range of 0.65 K (-272.5 °C) to 2000 °C, necessary for realizing the International Temperature Scale of 1990 and research on calibration technology of resistance thermometers and thermocouples. The freezing point of copper (1084.62 °C) is an important fixed point for the calibration of high-temperature thermocouples. We have developed an apparatus with excellent reproducibility (±10 mK) to realize the freezing point of copper which is used as the national standard for the calibration of noble metal thermocouples. The triple points of equilibrium hydrogen and other pure materials are used as defining fixed points for calibration in low temperature ranges. We have developed a high-precision measurement method of these triple points using refrigerators and sealed cells. We have designed these cells to prevent contamination and leakage of specimens more securely and easily than before, and have successfully realized the triple points to a high level of accuracy.     [ Thermometry Section ][ Cryogenic Thermometry Section ]

Sensing thermal emission from a substance, a radiation thermometer measures its surface temperature based on the Planck's law. The NMIJ establishes, maintains and disseminates the standards of radiation temperature scales ranging from 0 °C to 2000 °C, to meet the clinical and industrial needs. Fixed-point blackbodies with pure metals, for example, silver, gold and copper, can be used for calibration of radiation thermometers below 1100 °C. To extend the temperature range the NMIJ has been developing high-temperature fixed points using metal-carbon eutectic alloys instead of pure metals. Evaluations of these fixed points have been successfully in progress up to 2900 °C.     [ Radiation Thermometry Section ]

Our standard humidity generator that generates air with a fixed humidity value using water saturation is used as the standard for humidity. Dew point hygrometers are calibrated using this standard. The available range of dew points is from -10 °C to +23 °C, with the best level of uncertainty being 0.03 °C. We are now trying to expand the dew points between -70 °C to +85 °C. Another subject of research is the development of technology to provide standards for trace moisture, required by the semiconductor industry (-100 °C for dew point and 13 n mol/mol for amount-of-substance fraction).     [ Humidity Standards Section ]

A picosecond thermoreflectance system has been developed in order to measure thermal diffusivities of thin films thinner than 1 micrometer. A boundary between a film and a transparent substrate is heated by a picosecond laser pulse. Heat generated by the pump laser pulse diffuses towards the front surface of the thin film. The temperature change on the front surface opposite to the heated area is probed by the reflected intensity of another picosecond laser pulse. The heat diffusion across metal thin films with thickness of 75,120, and 200 nm has been observed successfully for the first time in the world. Based on this technique, we are now developing the thin film thermal diffusivity standard and the reference thin film for thermal diffusivity measurements.     [ Thermophysical Properties Section ]

The Flow Standards Section is researching techniques for calibrating the density of materials based on the solid density determined from the mass and shape of a monocrystal silicon sphere (bottom left photo). The relative uncertainty of silicon solid density standards has so far realized a level of one in 10 million (10^-7), which is the highest precision seen in standards research institutes worldwide. Density standard solutions (690 to 1500 kg/m³) calibrated on the basis of this solid density standard are provided as standard calibration materials. These measurement technologies are used to determine basic physical constants, such as the Avogadro constant or Planck constant; work on defect evaluation techniques using super-precise measurement of density differences among silicon crystals, and measurements of the thermophysical properties of working fluids, and for compiling relevant databases.     [ Fluid Properties Section ]

The Metrological Statistics and Particle Measurement Section is engaged in developing measurement methods of fine particles and powders, and related standard reference materials. The electro-gravitational aerosol balance developed in this section, which makes use of the temporal change in the number of charged particles confined in a closed space under the influence of electrostatic and gravitational forces, is a device for absolute size measurement of monodisperse particles. The uncertainty of 100 nm particle measurement by this device is 0.66 nm in terms of the expanded uncertainty with coverage factor of 2.     [ Metrological Statistics and Particle Measurement Section ]

Research on various "uncertainty" related problems is conducted in the Metrological Statistics and Particle Measurement Section. These problems include the application of the Monte Carlo method to evaluating measurement uncertainties of complex geometrical shape such as gear tooth profiles, and the formulation of uncertainty associated with quantization errors using the Bayesian approach. The table on the right is an example of output from the novel ANOVA (analysis of variance) program that can generate symbolical expressions of the expectations of variances. Also provided is assistance in uncertainty analysis of various measurements conducted within as well as outside of the NMJ.     [ Metrological Statistics and Particle Measurement Section ]