cesium133atoomfrequentie

Cesium-133, or 133Cs, is the only stable isotope of the element cesium (atomic number 55). It has a mass of 133 atomic mass units and a nucleus containing 78 neutrons. In the periodic table, cesium is an alkali metal; 133Cs is a soft, silvery-gold metal that is highly reactive with air and water.

It melts at 28.5 °C and boils at 671 °C. It is stored under mineral oil to prevent oxidation and hydration. Its chemistry is dominated by the +1 oxidation state, with Cs+ as the common ion. The electronic configuration is [Xe] 6s1, giving a single valence electron that is easily removed.

133Cs has nuclear spin I = 7/2. Its ground state is a 6s1/2 electronic state; fine structure yields hyperfine levels F = 3 and F = 4, split by the hyperfine interaction. The transition between these two levels in the ground state underpins the definition of time in atomic clocks.

Since 1967, the hyperfine transition frequency of 133Cs is defined as exactly 9,192,631,770 hertz, forming the basis of the SI second in atomic clocks. Cs-133 clocks are widely used as primary frequency standards and in timekeeping, navigation, and telecommunications.

Natural cesium consists almost entirely of Cs-133; other isotopes exist only in trace or artificial contexts. Cesium is commonly extracted from minerals such as pollucite. Cs-133 is produced and refined for metrology, research, and various precision applications.