Saito Norio
NMIJ International Cooperation Office, National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST).
Igaku Butsuri. 2021;41(1):27-33. doi: 10.11323/jjmp.41.1_27.
The International System of Units (SI) is recommended for the practical system of units of measurement. The decision of redefining the seven base units of the SI (the second, the meter, the kilogram, the ampere, the kelvin, the mole and the candela) was made at the 26th meeting of the General Conference on Weights and Measures on 16 November 2018. This redefinition came into force starting 20 May 2019, and it became a big historic turning point for the metrology society. This is because the kilogram, the unit of mass, was defined only by an artifact as the international prototype of the kilogram, has been kept for 130 years since its determination in 1889, and was finally changed to the new definition by taking the fixed numerical value of the Planck constant on that day.It is easily imagined that the redefinition of the SI base units has a strong impact on our daily life or the field of science. The reason why the SI redefinition had to be adapted is introduced firstly. Then, how the new definitions are applied now after a year from the redefinition and future prospective of the new definitions are discussed. In the last, the impacts of the SI redefinition in the field of the ionizing radiation, especially in the fields of the medical application of the ionizing radiation, are discussed.
国际单位制（SI）被推荐作为实际的测量单位制。2018年11月16日，在第26届国际计量大会上做出了重新定义国际单位制七个基本单位（秒、米、千克、安培、开尔文、摩尔和坎德拉）的决定。这一重新定义于2019年5月20日起生效，成为计量学界一个重大的历史性转折点。这是因为质量单位千克此前仅由一件实物——国际千克原器来定义，自1889年确定以来已沿用了130年，而在那一天终于通过采用普朗克常数的固定数值改为新定义。不难想象，国际单位制基本单位的重新定义对我们的日常生活或科学领域都产生了重大影响。首先介绍了必须采用国际单位制重新定义的原因。然后，讨论了自重新定义一年以来新定义是如何应用的以及新定义的未来前景。最后，讨论了国际单位制重新定义在电离辐射领域，特别是在电离辐射医学应用领域的影响。
