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一、概述1967年第十三届国际计量大会正式定义国际单位制中时间的基本单位——秒为“铯~(133)原子在两个超精细能级间跃迁辐射9192631770个周期所持续的时间。”这个决定的基础是美、英、瑞士和加拿大等铯束时间频率标准十多年
I. Overview The 13th International Conference of Metrology in 1967 formally defined the basic unit of time in the international system of units - second as “cesium ~ (133) atoms in the transition between the two hyperfine energy levels 9192631770 cycles continued Time. ”The decision was based on the Cesium Beam Time Frequency Standard for the United States, Britain, Switzerland and Canada for more than a decade