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The caesium standard is a primary frequency ... meaning that any change to the mass of that object would have resulted in a change to the size of the kilogram ...
Caesium (IUPAC spelling; [9] also spelled cesium in American English) is a chemical element; it has symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of 28.5 °C (83.3 °F; 301.6 K), which makes it one of only five elemental metals that are liquid at or near room temperature .
Rubidium standard clocks are prized for their low cost, small size (commercial standards are as small as 1.7 × 10 5 mm 3) [33] and short-term stability. They are used in many commercial, portable and aerospace applications. Modern rubidium standard tubes last more than ten years, and can cost as little as US$50.
Caesium, 55 Cs; Caesium; Pronunciation / ˈ s iː z i ə m / (SEE-zee-əm) Alternative name: cesium (US) Appearance: pale gold: Standard atomic weight A r °(Cs)
Note: All measurements given are in picometers (pm). For more recent data on covalent radii see Covalent radius.Just as atomic units are given in terms of the atomic mass unit (approximately the proton mass), the physically appropriate unit of length here is the Bohr radius, which is the radius of a hydrogen atom.
The standard to be employed is the transition between the hyperfine levels F=4, M=0 and F=3, M=0 of the ground state / of the caesium 133 atom, unperturbed by external fields, and that the frequency of this transition is assigned the value 9192631770 hertz.
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The atomic radius of a chemical element is a measure of the size of its atom, ... Cs 298 Ba 253 * Lu 217 Hf 208 Ta 200 W 193 Re 188 Os 185 Ir 180 Pt 177 Au 174 Hg 171 Tl