One second equals exactly 9,192,631,770 oscillations of a cesium-133 atom. That's not a joke — it's the official definition of the second in the International System of Units since 1967. Cesium atomic clocks are the most accurate on the planet: a drift of 1 second in 100 million years.
Cesium is the most reactive non-radioactive metal. It explodes on contact with water even at −116°C. It melts at 28.5°C — the warmth of your palm would turn it liquid. One of only three metals (along with gallium and mercury) that can be liquid at room temperature.
Cesium-137 is one of the most dangerous products of nuclear accidents. After Chernobyl, it contaminated thousands of square kilometers. Half-life — 30 years. The body absorbs it like potassium, so it accumulates in muscles.
But peaceful cesium is needed too. Cesium formate is used in drilling fluids for ultra-deep wells. And cesium photocells respond best to infrared light — that's why they're used in night cameras and automatic doors.
Cesium is the most dangerous alkali metal on contact with air and water. It instantly forms caustic CsOH and can cause an explosion. Stored in sealed ampoules under argon or vacuum. Cesium-137 is a powerful gamma radiation source: requires lead or concrete shielding. After Chernobyl, Cs-137 is one of the main contaminants.
Second = 9,192,631,770 oscillations of a cesium-133 atom. That's the official definition since 1967. Cesium clocks drift by 1 s in 100 million years.
Cesium is the most reactive non-radioactive metal. It explodes on contact with water even at −116°C. Even ice is dangerous for it.
Melts at 28.5°C — body warmth is enough. One of three metals (with gallium and mercury) that can be liquid at room temperature.
In spectroscopy, cesium gives a blue flame. That's why it was named from Latin 'caesius' — sky blue.
The cesium atom has the largest radius (265 pm) among all stable elements. Its outer electron is the farthest from the nucleus.
| Isotope | Mass (u) | Abundance | Half-life | Decay |
|---|---|---|---|---|
133Cs | 132.905452 | 100.00% | stable | — |
137Cs☢ | 136.907090 | synthetic | 30.17 years | β− |
Spectroscopic analysis of mineral water