B W Petley

The Role of the Fundamental Constants of Physics in Metrology

The paper discusses the recent measurements of the fundamental physical constants whose various combinations serve to provide the natural units of measurement in physics and the evaluation of their recommended values by the CODATA Task Group on Fundamental Constants. It emphasizes the strong involvement of the SI units with the present evaluations and shows how the fundamental physical constants play an increasing role in defining and maintaining many of the SI units of today and in sustaining the integrity of our measurement system. The present situation is reviewed and the evolving role of the fundamental physical constants in science and technology is discussed.

The atomic units, the kilogram and the other proposed changes to the SI

The close relationship between the SI units incorporating the proposed changes of Mills et al and the atomic system of units is discussed. It is shown that when the definition of the second is taken into account, a definition of the kilogram in terms of the mass of a photon of specified frequency results in a kilogram that implicitly depends on α4me and other dimensionless constants, where α is the fine structure constant and me is the electron rest mass. Thus the choice of definitions proposed by Mills et al implicitly yields a kilogram that depends either essentially on α4me or on the unified atomic mass unit, mu. Consequently, the kilogram could be regarded as implicitly retaining its present status as an independently defined SI base unit with either definition. The α-dependence of the kilogram and many other SI quantities would, of course, be affected by future changes in the definition of the second.

A Brief History of the Electrical Units to 1964

This paper charts the history of the electrical units up to 1964: from conception through the CGS to the SI via the MKSA system. It incorporates a shortened version of IEC Publication 164 which was published in 1964.

A Measurement of 2e/h by the ac Josephson Effect

2 e/h has been measured using the ac Josephson effect at 36 GHz and the solder-drop type of junction. The final result is that 2 e/h is 483.5941 ± 0.0010 (2.2 in 106) MHz/μ VNPL 1969. If the 1967 differences between the BIPM, NBS and NPL volts are maintained then the value is 483.5938 ± 0.0011 (2.3 in 106) MHz/μ VBIPM 1969 and is 0.6 ± 3.3 in 106 higher than the value of Parker et al.

Progress towards a precision measurement of the helion magnetic moment in Bohr magnetons

We describe progress on a measurement of the magnetic moment of the helion in units of the Bohr magneton. An apparatus has been constructed which allows the exchange of helium-3 for atomic hydrogen in situ. Both helium-3 NMR and hydrogen atom ESR have been observed at a flux density of 0.6 T.

Optically pumped /sup 3/He NMR and atomic hydrogen ESR at 0.6 T

We report the successful observation of high-fields optically pumped nuclear magnetic resonance (NMR) of helium-3 and electron spin resonance (ESR) of atomic hydrogen, both at 0.6 T. Also described are our findings on the relative optical pumping efficiencies of the various components of the 1083 nm line in helium-3. These are a precursor to a measurement of the magnetic moment of the helion in Bohr magnetons. For this measurement the two signal frequencies must be measured sucessively in the same apparatus. This work is aimed at overcoming the limitations for high-accuracy magnetometry of using water as an NMR substance.

A New NPL Determination of 2e/h

The lastest NPL determinations of 2e/h using the ac Josephson effect are reported, with emphasis on the improvements made over earlier measurements. The precision of the experiment is such that it should be regarded as a means of monitoring the national maintained voltage standard. The value of 2e/h obtained most recently, in April 1972, is 483,594.00 (±0.10) GHz/VNPL.

Electrical Units - the Last Thirty Years

The paper discusses the changes in the definitions, the accuracy of realization of the electrical units during the last thirty years, and some problems of usage.

A Proposed Method of Measuring γ́p in Terms of the Quantum of Magnetic Flux: A Route to α

The paper discusses a method for measuring the gyromagnetic ratio of protons in a spherical water sample in terms of the quantum of magnetic flux. Combining this quantity with more accurately determined constants: the proton magnetic moment in terms of the Bohr magneton, and the Rydberg constant, as well as the velocity of light, would yield an improved experimental value for the fine-structure constant.

The magnetic moment of the helion in Bohr magnetons

We have previously described an experiment to measure the magnetic moment of the helion in Bohr magnetons. We now have preliminary results using the first of two proposed methods, an irreversible seal-breaking method. Improvements obtainable with the second method are discussed.