How the U.S. Built the World’s Most Ridiculously Accurate Atomic Clock | Science | WIRED: Both NIST-F2 and the standard it replaces, NIST-F1, are known as cesium-based atomic fountain clocks...
The previous generation of atomic clock was already quite good at figuring out the length of a second but had a few small sources of error. NIST-F1 operates at room temperature and so the walls of the chamber in which the cesium atom ball is tossed heat up, emitting a small amount of radiation. This interferes with the atoms, causing them to shift ever so slightly in their energy levels. By cooling NIST-F2 with liquid nitrogen, the new timepiece reaches temperatures of – 316 degrees Fahrenheit, virtually eliminating this excess radiation and reducing the shifting 100-fold.
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