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| [00:06.37]The United States has a new official clock. [00:10.95]The clock began operating late last year in the American city of Boulder,Colorado. [00:18.39]Experts say the new clock is so exact that it will neither gain nor lose so much as one second in the next 20,000,000 years. [00:30.82]Scientists with the National Institute of Standards and Technology developed the new atomic clock. [00:39.47]The agency is part of the United States Department of Commerce. [00:44.72]The new clock was built and tested in less than four years. [00:49.92]It is now being used to measure the official world time, known as Coordinated Universal Time. [00:58.28]The clock measures time by counting the movements of atoms of the element cesium. [01:05.72]The natural rate of movement of cesium atoms has been used to measure time since 1967. [01:13.67]Researchers have found that cesium atoms move back and forth at a rate of almost 9,200,000,000 times in one second. [01:26.02]The new clock is less than two meters tall. [01:30.98]This is how it works. [01:33.31]First, a gas of cesium atoms is released in an empty container. [01:39.55]All other matter has been removed from this vacuum chamber. [01:45.06]Six beams of laser light are directed at the center of the chamber. [01:50.86]The lasers slow the movement of the cesium atoms. [01:55.83]The lasers force the atoms into a cloud of gas shaped like a ball. [02:02.36]Two lasers push the ball of gas upward through a passage filled with microwave energy. [02:10.17]Then,all of the lasers are turned off. [02:13.69]Gravity pulls the ball of cesium atoms back down through the passage. [02:20.23]The microwaves change some of the atoms. [02:24.46]The microwaves cause some of the atoms to move quickly back and forth. [02:30.62]Another laser causes the cesium atoms to produce light. [02:35.48]The light is measured by special observation equipment. [02:40.76]This process is repeated many times while different levels of mierowave energy are used. [02:49.25]The researchers find a level of ehergy that makes the cesium atoms produce the most light. [02:57.24]This is the rate of movement used to define one second. [03:02.36]The new device replaces another atomic clock that has served as the official clock of the United States since 1993. [03:12.21]The new clock is said to be three times more exact than the atomic clock it replaced |
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