Brief History of Atomic Clocks at NIST
1945 Isidor Rabi, a physics
professor at Columbia University, suggests a clock could be made from a
technique he developed in the 1930's called atomic beam magnetic resonance.
1949 Using Rabi’s technique,
NIST (then the National Bureau of Standards) announces the world’s first
atomic clock using the ammonia molecule as the source of vibrations.
1952 NIST announces the first
atomic clock using cesium atoms as the vibration source. This clock is
1954 NBS-1 is moved to NIST’s
new laboratories in Boulder, Colo.
1955 The National Physical
Laboratory in England builds the first cesium-beam clock used as a calibration
1958 Commercial cesium clocks
become available, costing $20,000 each.
1960 NBS-2 is inaugurated
in Boulder; it can run for long periods unattended and is used to calibrate
1963 The search for a clock
with improved accuracy and stability results in NBS-3.
1967 The 13th General Conference
on Weights and Measures defines the second on the basis of vibrations of
the cesium atom; the world’s timekeeping system no longer has an astronomical
1968 NBS-4, the world’s most
stable cesium clock, is completed. This clock was used into the 1990s as
part of the NIST time system.
1972 NBS-5, an advanced cesium
beam device, is completed and serves as the primary standard.
1975 NBS-6 begins operation;
an outgrowth of NBS-5, it is one of the world’s most accurate atomic clocks,
neither gaining nor losing one second in 300,000 years.
1989 The Nobel Prize in Physics
is awarded to three researchers -- Norman Ramsey of Harvard University,
Hans Dehmelt of the University of Washington and Wolfgang Paul of the University
of Bonn -- for their work in the development of atomic clocks. NIST’s work
is cited as advancing their earlier research.
1993 NIST-7 comes on line;
eventually, it achieves an uncertainty of 5 parts in 10 to the 15th power,
or 20 times more accurate than NBS-6.
begins operation with an uncertainty of 1.7 parts in 10 to the 15th power,
or accuracy to about one second in 20 million years, making it the most
accurate clock ever made (a distinction shared with a similar standard
Information and illustrations provided
by the National Institute of Standards and Technology.
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