Time and frequency activities at NRC

The National Research Council of Canada (NRC) is currently involved in a number of research projects aimed at improving time and frequency realization based on the accurate and precise stabilization of microwave and optical sources on atomic and molecular transitions. Projects described in this summary will focus on the development of a primary standard for the realization of the Si second based on a cesium atomic fountain and a next generation standard based on an optical transition in a single trapped and laser cooled ion of strontium. The cesium fountain is undergoing evaluations of its systematic shifts for an eventual contribution to TAI and for a re-measurement of the absolute frequency of the strontium ion clock transition at the 10(-15) level. The main contribution to the uncertainty budget of the fountain is thought to be caused by the inhomogeneity in the magnitude of the magnetic field in the drift region. The latest measurements of this field are presented. A new strontium ion trap of the endcap design was completed last year. This new system has compensation electrodes and access ports in three orthogonal directions to control the ion position and minimize micromotion. We report preliminary results indicating improved performance of this trap over our previous rf Paul trap. As part of an effort to reduce the systematics shifts to a minimum, the heights of the atomic standards above the geoid were measured with an accuracy of 5 cm, corresponding to a fractional frequency uncertainty of 5 x 10(-18) for the gravitational redshift.