Requirements for Obtaining High Accuracy with Proton Magnetometers Part 2

Gyromagnetic Constant

The gyromagnetic constant relates the precession frequency and the magnetic induction or flux density. It is а real constant, i.e. the precession frequency of protons and the applied magnetic inductions are linearly related. Several institutions have been engaged in determination of the gyromagnetic constant:

NIST (USA) National Institute of Standards and Technology formerly NBS
NPL (UK) National Physical Laboratory
VNIIM (Russia) Mendeleyew Institute of Metrology, St.Pеtеrsburg
NIМ (China) National Institute of Metrology
ASMW (former East Germany) Amt fur Standardisierung
Messwesen and Wonenpufung, Berlin

They came with their own results and accuracies, unfortunately often far apart from each other.

Presently we have gyromagnetic constants (γ) determined in high and low field. They differ by about 1.5ррm (results of different laboratories for higher field gyromagnetic constant differ between themselves by more than 4ррm).

Low field gyromagnetic constants that we may adорt as appropriate and convenient differ for NIST and VNIIM laboratories results by 0.7бррm. (NIST and VNIIM claim uncertainties of 0.11 and 0.36 ppm respectively).

Here is a complete list of reported results:

Low field	NIST	1986-8	267 515 427 (29) s-1/T
	VNIIM	1987	267 515 630 (96) s-1/T

Average value for low field is 267515528 s^-1/T ±0.74рpm γ/2π = 4.25763665 kHz/G

High field	NPL	1973-4	267 515 030 (270) As/kg
	NIM	1988	267 515 410 (230) As/kg
	ASMW	1985	267 514 270 (210) As/kg

Stay tuned for part 3 of this article, “Time Reference Stability and Accuracy”