Preliminary accuracy evaluation of a cesium fountain primary frequency standard at NIST

Abstract

Since November of 1998, we have performed four uncertainty evaluations on NIST F-1, our laser-cooled cesium fountain. The results from the latest evaluation have a statistical uncertainty of 2.6/spl times/10/sup -15/ and an uncorrected bias of 1.1/spl times/10/sup -15/. This paper presents a brief overview of the evaluations and their uncertainties.