Primary cesium time and frequency standards

Abstract

Cesium frequency standards are used to determine the atomic second in SI units and to provide a national atomic-time scale at the leading meteorological laboratories of the world. In this paper, the state of cesium and atomic frequency standards are examined and methods of increasing their accuracy are analyzed. High-purity polycrystals of platinum-iridium alloy or high-purity and structurally perfect single crystals of tungsten and molybdenum are used as ionizers in beam detection. Relative frequency instabilities that have been obtained at the various laboratories are presented. The main sources of error in reproducing the unperturbed-transition frequency of cesium atoms are discussed, including the second-order Doppler effect and the Majorana effect. Accuracy estimates for cesium frequency standards of the world's leading meteorological laboratories are shown.