We have been investigated and established on DC and low-frequency electrical standards, such as DC voltage including voltage divider, resistance, capacitance, inductive voltage divider, power, AC voltage, AC current and so on. Another area we cover is R&D of high-frequency standards, such as high-frequency power, impedance, attenuation, noise, electromagnetic fields, and antenna standards; and light-related standards, such as laser power, luminous intensity, luminous flux, and illuminance. In the quantum radiation field, we are engaged in R&D of radiation dose standards, such as for X-rays and g-rays, and standards for radiation of nuclides and neutron fluence.    

In the area of direct current and low frequencies, we are already supplying direct current voltage standards, direct current voltage division ratio standards, direct current resistance standards, capacitance standards, and AC/DC difference standards. We plan to further upgrade our impedance standards and begin to provide new electric power standards in the near future.    

The NMIJ has maintained the national standards for voltage, first using Weston cell, since 1948. With the advent of the era of quantum standards, we have started tu use the Josephson effect voltage standard system as the national standard for voltage. The system in use now, shown in the picture, is capable of directly calibrating 10 V and has an uncertainty of 1 × 10^-8 (k=2). The level of uncertainty varies depending on the noise generated by the Zener precision voltage generator, the item being calibrated.     [ Electricity Standards Section 1 ]

NMIJ had been maintained the national standard for resistance with a mercury resistance standard since 1908 and a Manganin resistor since 1948. With the arrival of quantum standards, a quantum Hall resistor has been used as the national standard for resistance since 1990. We manage a group of 1 Ω resistors calibrated and corrected by the quantum Hall resistance device, and provide calibration services at an uncertainty of 1 × 10^-7 (k = 2) based on these resistors.     [ Electricity Standards Section 1 ]

NMIJ established a capacitance standard based on a quantum Hall resistance (with an uncertainty of 1 × 10^-7 (k = 2)) in 2002.
The capacitance standard derived from a DC resistance corrected by the quantum Hall resistance standard into AC resistance, which is further converted to static capacity by means of a quadrature bridge.     [ Electricity Standards Section 1 ]

Antenna measurement of dipole antenna factor is usually made at the Open-Area Test Site (a facility which has a welded metal ground place to cover the ground surface for making ideal specular reflection of EM radiated signal, as shown in the photo) in the AIST north site. The antenna factor is a parameter of antenna sensitivity. A couple of antennas are required to measure the sensitivity. A transmitting antenna generates electromagnetic (EM) field and a receiving antenna receives the field and converts it into guided waves for the measurement in voltage. First, EM fields radiated by a transmitting antenna are received by a reference antenna and the output voltage is measured by a receiver. Then the antenna under test (AUT) is replaced at the same position as the reference antenna. Then the receiver voltage is measured on the AUT. The difference in receiver voltages between these two antennas shows the difference in sensitivity between them. Using our standard antenna as a reference one, the sensitivity of any antenna can be determined in the same way. The type of antenna measured in this system is currently limited to a type of dipole antennas, but the NMIJ plans to expand both of the antenna type and the covered frequency bands in future.     �iRadio Frequency and Fields Section�j

The photo on the right shows a high-precision measuring instrument used for the recently developed laser power standard for the visible and near-infrared light. The measurable wavelength extends from 400 nm to 1600 nm and the measurement power level is 10 mW. Laser power is converted by an absorber into heat, which is then measured by a calorimeter using isothermal control based on DC substitution. For the absorber, NiP alloy, which has a very small reflectivity in this frequency range, is used, realizing flat response characteristics over the entire frequency range and high proximity of substitution characteristics between light and DC power. Evaluation of reflection, equivalence of light power and DC power, non-uniformity of the light absorbing surface, and other factors affecting measurement, control equipment, etc., have resulted in a measurement uncertainty of 0.05%, realizing precision three times better than previous levels. To meet the need for measurement of increasing laser output, we are working on developing high-power standards from 10 W to 1 kW levels.     [ Laser Standards Section ]

The cryogenic electrical substitution radiometer is designed to measure optical power at liquid helium temperature (4.5 K). This achieves lower nonequivalence (less than 0.007 %) in optical-electrical power substitution than that with conventional room-temperature electrical substitution radiometers, resulting in absolute spectral responsivity calibration of detectors with measurement uncertainty of less than 0.05 %. We have improved our photometric units, luminous intensity (cd : candela) and luminous flux (lm : lumen), with the uncertainties of 0.28% and 0.34 %, respectively, using the cryogenic radiometer-based spectral responsivity scale. In the Key Comparisons (1997 to 1999), deviation of our measurement value from the reference value was −0.09 % for luminous intensity and +0.18 % for luminous flux, showing a good agreement within the uncertainty.     [ Optical Radiation Section ]

The quantity of the exposure indicates the intensity of the X- and γ-ray fields. This quantity is defined as ion charges produced in the air by secondary electrons emitted by photons from the unit mass of air. The unit of exposure is C/kg. Free air ionization chambers are used to measure the exposure of X-rays. Corrections for atmospheric pressure and temperature are made in order to determine the mass of air in the ionization volume. Several other corrections are necessary in order to obtain the value of the exposure. For γ-rays, which are higher in energy, graphite cavity ionization chambers (shown below) are used. Correction for the difference between the mass energy absorption coefficients for air and for graphite must be made. Correction factors for attenuation and scattering of γ- rays in the chamber wall can now be obtained by a simulation calculation.     [ Ionizing Radiation Section ][ Quantum Radiation Division ]

The term radioactivity was coined from "radio," a term that means the phenomenon of emission of radiation, and "activity," an index to express its intensity. The unit of Bq (becquerel) indicates the decay number per unit time of a nuclide due to natural phenomena, such as alpha or beta decay. A technique for realizing a primary standard is based on the 4πβ-γ coincidence counting method. lt uses the phenomenon, seen in many nuclides, where the emission of a charged particle is followed by emission of a γ-ray simultaneously, and can calibrate and correct radioactivity independently without resorting to any other information, such as nuclear data. However, not all nuclides emit gamma-radiation upon decay, so we use different measuring equipments (specified primary standards), such as liquid scintillation counter and gas counter, still based on the 4πβ-γ coincidence counting method, to calibrate and correct radioactivity.     [ Radioactivity and Neutron Section ][ Quantum Radiation Division ]

NMIJ has developed precision measuring techniques for neutrons emitted from spontaneous nuclear fission of Cf-252 or (α, n) nuclear reaction of Am-Be mixtures. To be specific, neutron emission rate (s^-1), the unit for the number of neutrons emitted per unit time from a radiation source, and fluence (m^-2), the unit for the number of neutrons passing through a unit area in free space, are adopted as the national standards and provided to related laboratories or radioactivity handling facilities nationwide. We have also established a monochromatic/fast neutron fluence standard that covers a wide range of energies using a Van de Graaf accelerator.     [ Radioactivity and Neutron Section ][ Quantum Radiation Division ]