The development of atomic clocks at NIST (now NIST) began in 1945 with the suggestion to use atomic beam magnetic resonance. In 1949, NIST announced the world’s first atomic clock using ammonia molecules. The first accurate measurement of the cesium clock resonance was completed in 1952, and commercial cesium clocks became available in 1956.
The 13th General Conference on Weights and Measures defined the second based on cesium vibrations in 1967. NIST’s work on atomic clocks was cited in the 1989 Nobel Prize in Physics awarded to three researchers. NIST-7, completed in 1993, achieved an uncertainty of 5 x 10-15, while NIST-F1, operational since 1999, has an uncertainty of 1.7 x 10-15, making it one of the most accurate clocks ever made.
Source: https://www.nist.gov/pml/time-and-frequency-division/time-services/brief-history-atomic-clocks-nist
Keywords: cesium, clock, frequency, standard, uncertainty
