Show pageBacklinksCite current pageExport to PDFBack to top This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong. ====== Caesium-133 ====== Caesium-133 is the only stable isotope of [[caesium]]. The SI base unit of time, the second, is defined by a specific caesium-133 transition. Since 1967, the official definition of a second is: The second, symbol s, is defined by taking the fixed numerical value of the caesium frequency ΔνCs, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s−1. ---- caesium-133.txt Last modified: 2024/06/07 02:56by 127.0.0.1