Accuracy evaluation of a cesium fountain primary frequency standard at NIST

Abstract

Since November of 1998, we have performed five frequency uncertainty evaluations on NIST F-1, our laser-cooled cesium fountain. The results from the latest evaluation have a statistical uncertainty of 1.4/spl times/10/sup -15/ and an uncorrected bias of 0.7/spl times/10/sup -15/. The results have been reported to the BIPM for inclusion in TAI, making this clock one of two cesium fountain clocks used as primary standards in the world. We will present an overview of the evaluations and their uncertainties.