Table of contents

It is shown how a particular phenomenon arising from the ac Josephson effect in superconductors can be used to provide a comparatively simple and inexpensive means for (1) checking on the constancy in time of reference standards of electromotive force, and (2) relating the reference standard of one country to that of another country, thereby contributing to a better international assignment of the volt. The results of recent high accuracy (4 ppm) measurements of the phenomenon in question and the relative ease with which the techniques used in these measurements can be extended to the 1 ppm level will be presented as evidence that these two goals can be reached in the near future.

The nuclear quadrupole resonance frequency of ³⁵Cl in KClO₃ has been studied in the temperature range 12 °K - 297 °K. The combined uncertainties in the frequency and temperature measurements correspond to ± 0.001 °K in the range 50 °K - 297 °K, deteriorating to ± 0.004 °K at 30 °K and ± 0.010 °K at 20 °K. Both the nuclear resonance spectrometer and the temperature control apparatus are described. The experimental data are fitted to a theoretical expression in the temperature range 12 °K - 90 °K; at higher temperature the data are fitted to empirical polynomials.

The accuracy of radioactivity measurements is discussed in the context of current efforts to achieve reproducible results among standards laboratories. This is considered essentially a problem of selecting an absolute method of measurement and defining the experimental requirements in sufficient detail for general use. A further analysis of coincidence counting is made in an attempt to define more clearly the conditions under which this method may provide acceptable accuracy.

A detailed description is given of a 1-metre line-standard interferometer which has been constructed at the National Standards Laboratory, Sydney. The results of a recent series of calibrations of standard scales are reported. A precision of 10⁷ has been obtained. The existence of a difference between the optical metre as defined in 1960 and the prototype metre is confirmed, and the optical metre is found to be 0.38 μm shorter than the prototype.

The thermal and spectral radiation characteristics of the cylindrical enclosures used in the primary standard of light are studied in detail. The temperatures at the walls and base of the cylindrical ceramic sight-tubes are calculated on the basis of thermo-dynamic equilibrium. The effect of the spectral emissivity of the ceramic on the apparent spectral emissivity of the base is studied. Changes of about one percent in the luminance of the base can occur with the sight-tubes that have commonly been used. The effect of a temperature gradient in the surrounding ingot is also considered. A practical design is suggested which should permit realization of the primary standard of light with a luminance error, caused by the sight-tube, of not more than 0.1%.