Japanese

 

Research Highlights, Contribution to Determining the Planck Constant Used as the New Definition for the Unit of Mass, “kilogram”

Kenichi Fujii, Naoki Kuramoto, Shigeki Mizushima Research Institute for Engineering Measurement, Lulu Zhang Research Institute for Material and Chemical Measurement

Point

We have measured the Planck constant, one of the fundamental physical constants, with the world’s highest accuracy, and contributed to the redefinition of the kilogram.

Photo: Silicon single-crystal sphere
Silicon single-crystal sphere
Photo: Vacuum balance for measuring mass of silicon single-crystal sphere with high accuracy
Vacuum balance for measuring mass of silicon single-crystal sphere with high accuracy
Photo: Laser interferometer developed by AIST that measures shape of silicon single-crystal sphere with high accuracy
Laser interferometer developed by AIST that measures shape of silicon single-crystal sphere with high accuracy
Photo: X-ray photoelectron spectrometer for evaluating thickness and mass of surface layers of silicon single-crystal sphere
X-ray photoelectron spectrometer for evaluating thickness and mass of surface layers of silicon single-crystal sphere

Background

The unit of mass, the kilogram, is currently defined as the mass of the International Prototype of the Kilogram (IPK), the world’s only one weight. However, it has been recognized that the mass of IPK varies, due to  surface contamination, in the long term. For this reason, to revise the current definition to a definition based on universal, fundamental physical constants, research for determining fundamental physical constants with higher accuracy than the long-term stability of the mass of IPK has been conducted in various countries.

Outcomes and Methods

We have developed an ultrahigh-precision laser interferometer, a surface analysis system, etc. to measure the shape of a silicon single-crystal sphere having a diameter of approximately 94 mm with an accuracy of better than 1 nm. Then, we have measured the Planck constant with the world’s highest accuracy. In addition, on the basis of the highly accurate measurement results of the Planck constant obtained by AIST and multiple overseas research institutes, the Committee on Data for Science and Technology (CODATA) has determined the value of the Planck constant to be used for the new definition of the kilogram.

Future Plan

In 2018, a discussion will be made on whether or not to redefine the kilogram based on the Planck constant. This is the first time that Japan will be directly involved in determining the definition of the base unit in the International System of Units (SI), and it can be said to be a historic achievement, contributing to revising the definition of the kilogram, which was defined  approximately 130 years ago.

Contact

Photo:Kenichi Fujii   Photo:Naoki Kuramoto   Photo:Shigeki Mizushima  
Research Institute for Engineering Measurement

Kenichi Fujii, Prime Senior Researcher (left)
Naoki Kuramoto, Leader, Mass Standards Group (center)
Shigeki Mizushima, Senior Researcher, Mass Standards Group (right)


AIST Tsukuba Central 3, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563 Japan
TEL: +81-29-861-4346
FAX: +81-29-861-4152
Web: https://unit.aist.go.jp/riem/en/intro/index.html


Photo:Lulu Zhang
Surface and Nano Analysis Research Group, Research Institute for Material and Chemical Measurement

Lulu Zhang, Senior Researcher


AIST Tsukuba Central 3, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563 Japan
TEL: +81-29-861-4346
FAX: +81-29-861-4099
WEB: https://unit.aist.go.jp/mcml/en/intro/index.html


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