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The Realization of the SI Second and Generation of UTC(NIST) at the Time and Frequency Division of the National Institute of Standards and Technology (NIST)

Published

Author(s)

Thomas P. Heavner, Steven R. Jefferts

Abstract

The Time and Frequency Division of the National Institute of Standards and Technology (NIST) maintains the laser-cooled Cesium primary fountain frequency standard NIST-F1. NIST-F1 is used to accurately realize the SI second, defined as 9,192,631,770 periods of the radiation of the ground state hyperfine transition in Cesium. Since its completion in 1998, NIST-F1 has undergone 19 formal accuracy evaluations which have been submitted to the BIPM. NIST-F1 has been continuously improved over the years and presently has a fractional frequency inaccuracy of {Δ}f/f {approximately equal} 5 X 10-16. The low atomic temperatures (2 longer than that achieved in thermal beam frequency standards. Since the frequency stability as well as the magnitudes of many systematic biases scale with the Ramsey time, atomic fountains easily outperform thermal beam devices. Presently, the accuracy of NIST-F1 is limited by the blackbody radiation shift. NIST-F2, the second-generation atomic fountain standard under construction at NIST, will operate at 77 K, thus reducing the blackbody shift to a negligible level. Located on the NIST premises is also a continuously operating timescale, comprised of 5 hydrogen masers and several commercial Cesium beam atomic standards. The clocks are continuously inter-compared and their rates calibrated against the SI second whenever NIST-F1 is evaluated. A modified, weighted averaging algorithm is used to generate Universal Coordinated Time at NIST, or UTC(NIST). Frequency measurements from NIST-F1 as well as the rate of UTC(NIST) are compared with clocks and timescales located at other national standards laboratories using time-transfer techniques such as common-view GPS and two-way satellite time-transfer.
Proceedings Title
Proc. 2007 NCSLI Conf.

Keywords

ces, gen, time

Citation

Heavner, T. and Jefferts, S. (2007), The Realization of the SI Second and Generation of UTC(NIST) at the Time and Frequency Division of the National Institute of Standards and Technology (NIST), Proc. 2007 NCSLI Conf., [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=50533 (Accessed June 20, 2024)

Issues

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Created August 2, 2007, Updated February 17, 2017