Accuracy evaluation of a cesium fountain primary frequency standard at NIST

A new laser-cooled Cs fountain primary frequency standard has been constructed at the National Institute of Standards and Technology (NIST) in Boulder, CO. The new standard, NIST-F1, is described here, including details of systematic frequency biases for which frequency corrections are made. We have submitted two evaluations to the Bureau International des Poids et Mesures (BIPM), which have Type A (statistical) uncertainties less than 1.5/spl times/10/sup -15/ and Type B (systematic) uncertainties less than 0.9/spl times/10/sup -15/.