Abstract
A new technique for evaluating the velocity distribution in cesium-beam frequency standards is presented. It is based on the dependence of the amplitude of the central maximum of the Ramsey resonance on the exciting microwave power level. The second-order Doppler shift, typically Δf/f ≃ 4 × 10-13 for the NRC primary standards, can be evaluated by this method with an uncertainty of about 10-15, five times the precision attainable previously.