Hydrogen Maser Wall Shift Experiments at the National Research Council of Canada

Abstract

One of the limiting factors which restrict the hydrogen maser to the role of a secondary frequency standard is the uncertainty in the experimental determination of the wall shift. This paper describes a series of experiments carried out at the National Research Council of Canada, using two hydrogen masers, to investigate the wall shift of five spherical storage bulbs of different diameters, each coated by the same technique with FEP Teflon from the same batch. The theoretically predicted inverse relationship between wall shift and bulb diameter was found to hold experimentally with very small point scatter for all five bulbs. Results showing the dependence of wall shift on bulb diameter and the variation of wall shift with temperature from 23°C to 35°C are given. Measurements made on the largest storage bulb at the beginning and end of the series of experiments allow some estimate to be made of the stability of the wall shift over a period of several months. Measurements indicating a change in wall shift of not more than 2 parts in 1013 over a period of 7 months for a storage bulb transported between Japan and Canada are also discussed. Comparison of the frequency of one of the masers with that of the NRC primary cesium beam frequency standard (Cs III) has given a value of the unperturbed hydrogen hyperfine transition frequency of 1420405751.770 ± 0.003 Hz, which is in satisfactory agreement with the most recent determinations by other workers.