Gyromagnetic Ratio of the Proton

The weak-field NPL apparatus for determining the gyromagnetic ratio of the proton, and for checking the ampere as maintained by the Laboratory standard resistors and Weston cells, is working satisfactorily. The principle of the method is shown in Fig 1. The field-forming coils are vertical, and, when carrying 1.018A, produce at the centre a flux density of about 1.2mT, corresponding to a precessional frequency of about 50 kHz, uniform to 0.5 in 106 over the volume of a sphere 40 mm in diamet er. The current is provided by a 110V battery of large accumulators, and is controlled by a specially made controller of the galvanometer and photo-cell type, so that only very slight hand adjustment, if any, is required to keep the current constant at the value determined by the standard resistor and Weston cell.