Redefining the Kilogram: Increasing the Precision of Avogadro's Constant
As technology progressed, the units of length and time have been defined and reviewed strictly. Meanwhile, redefinition of the mass standard based on the prototype kilogram using a fundamental physical constant is being reviewed. AIST is working on redefining the kilogram based on the Avogadro constant by using ultrahigh-precision silicon balls.
The unit of many physical quantities, such as length, frequency, temperature, and voltage, are now being defined using invariants of nature or physical laws. At present, the prototype kilogram made of platinum-iridium alloy is still used to define the unit of mass. However, the prototype is an artifact, raising the problem of instability.
Various research institutes are studying ways to develop a new definition of the kilogram, one of which is the precise measurement of the Avogadro constant being conducted at AIST. This constant refers to the number of atoms and molecules per mol. By using an ultrahigh-precision silicon ball that is currently the most perfect sphere on Earth, AIST successfully measured the Avogadro constant with the greatest precision to date. AIST is continuing to work on redefining the kilogram based on the fundamental physical constant.