Accuracy results from NIST-F1 laser-cooled cesium primary frequency standard

Abstract

Since November 1998, we have performed six frequency evaluations of NIST-F1. The results from the last two of these evaluations have been reported to the BIPM for inclusion in TAI. This fountain is presently one of two cesium fountains in the world used in the generation of TAI. This paper presents an overview of the evaluation process and a brief description of the four systematic biases for which the fountain is corrected: blackbody frequency shift, gravitational redshift, second-order Zeeman shift and spin-exchange shift. A large list of other possible shifts which have been studied and found to be negligible are discussed in less detail.