U.S. time now flows from atom fountain

4:57pm, June 21, 2002

Just days before the new year began, the United States followed through on a resolution to keep better track of time in the years ahead. On Dec. 29, the National Institute of Standards and Technology (NIST) in Boulder, Colo., switched to a new type of timekeeping technology—the atomic fountain clock—as the nation's primary time standard (SN: 8/7/99, p. 92).

Stunning developments in atom cooling and trapping since the 1980s led to the new clock type (SN: 10/25/97, p. 263). The NIST F-1 fountain clock that went into service last month uses lasers to congeal cesium atoms into a cold ball.

As its name suggests, the fountain clock tosses the ball upward, like a water droplet spurted upward from a spout. As the ball rises a meter and then falls under gravity, the instrument adjusts its microwave frequency to maximize the cesium's excitation. Doing so, it tunes itself to the atoms' resonant frequency, which defines the second.

This article is available only to subscribing members. Join SSP today or Log in.

More from Science News