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International Atomic Time. International Atomic Time (abbreviated TAI, from its French name temps atomique international[1]) is a high-precision atomic coordinate time standard based on the notional passage of proper time on Earth's geoid. [2] TAI is a weighted average of the time kept by over 450 atomic clocks in over 80 national laboratories ...
Korea Research Institute of Standards and Science. Daejeon, South Korea. Caesium atomic clocks [25] Cs. National Metrology Centre. Queenstown, Singapore. Five caesium clocks, one passive hydrogen maser, two active hydrogen masers.
An atomic clock is based on a system of atoms which may be in one of two possible energy states. A group of atoms in one state is prepared, then subjected to microwave radiation. If the radiation is of the correct frequency, a number of atoms will transition to the other energy state.
The Hafele–Keating experiment was a test of the theory of relativity. In 1971, [1] Joseph C. Hafele, a physicist, and Richard E. Keating, an astronomer, took four caesium -beam atomic clocks aboard commercial airliners. They flew twice around the world, first eastward, then westward, and compared the clocks in motion to stationary clocks at ...
The unit was redefined in terms of the tropical year at 1900.0 instead of the sidereal year; [12] and the standard second was defined first as 1/31556925.975 of the tropical year at 1900.0, [12] [14] and then as the slightly modified fraction 1/31556925.9747 instead, [15] finally being redefined in 1967/8 in terms of the cesium atomic clock ...
A caesium atomic fountain used as part of an atomic clock. The caesium standard is a primary frequency standard in which the photon absorption by transitions between the two hyperfine ground states of caesium-133 atoms is used to control the output frequency. The first caesium clock was built by Louis Essen in 1955 at the National Physical ...
Although less accurate than existing quartz clocks, it served to prove the concept of an atomic clock. [206] The first accurate atomic clock, a caesium standard based on a certain transition of the caesium-133 atom, was built by the English physicist Louis Essen in 1955 at the National Physical Laboratory in London. [207]
Atomichron. The Atomichron was the world's first commercial atomic clock, built by the National Company, Inc. of Malden, Massachusetts. It was also the first self-contained portable atomic clock and was a caesium standard clock. More than 50 clocks with the trademarked Atomichron name were produced. [1][2][3][4]
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