Friday is here, and with it the weekly "A Taste of Physics" column — number 39.
This week: a truly one-of-a-kind metal, and its surprising connections to atomic clocks and nuclear weapons.
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The metal you see in the video is cesium.
Cesium has atomic properties that make it a remarkable phenomenon — exceptionally useful, and also exceptionally dangerous.
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Cesium ionizes (becomes electrically charged) faster than any other metal, because it loses electrons with extraordinary ease and is left with a positive charge.
This property stems from its atomic structure — it contains 55 electrons arranged across 6 shells around the nucleus.
The electrons in the outermost shell are attracted to the nucleus with relatively little force, and therefore detach from it easily.
Cesium also melts into a liquid at an unusually low temperature — 28.5 degrees Celsius — due to the weak bonds between its atoms.
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Cesium is an exceptionally precise natural timekeeper, and the entire modern timekeeping system rests upon it.
The international timekeeping system is based on atomic clocks — clocks that deviate by just one second every 100 million years.
This level of precision is essential for critical systems to function, such as satellite navigation and online commerce.
At the heart of the atomic clock sits cesium, because its electrons oscillate between two energy levels exactly 9,192,631,770 times per second.
Although modern atomic clocks are based on strontium, the oscillation frequency of electrons in the cesium atom remains the reference standard for them as well.
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The fact that cesium ionizes so readily causes it to shed electrons in a chemical reaction upon contact with water.
This reaction is exothermic — it releases energy into the surroundings as it occurs — and so contact between cesium and water produces a violent explosion.
Even exposure to air can cause cesium to burst into flames.
For this reason, it is stored in capsules sealed against both air and water.
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Cesium has a radioactive isotope: cesium-137.
This isotope is almost never found in nature; it is produced primarily by human-made nuclear reactions.
Traces of this isotope can still be detected in the atmosphere today, as a result of the nuclear tests and disasters that took place around the world during the last century.
The half-life of this isotope is 30 years.
This means that every 30 years, half of the remaining cesium-137 decays.
As a result, it serves as a kind of historical clock, and analyzing it allows scientists to date various materials and events.
It is also useful in radioactive applications, such as destroying cancerous tumors and as a highly effective sterilization agent.
Shabbat Shalom 😊
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