The Magnetic Moment ofK40and the Hyperfine Structure Anomaly of the Potassium Isotopes

The nuclear magnetic moment and atomic hyperfine splitting of the rare ${\mathrm{K}}^{40}$ isotope have been measured by the atomic beam magnetic resonance technique. Detection of ${\mathrm{K}}^{40}$ atoms, from a source of normal potassium, was achieved by employing a conventional surface ionization detector as the ion source for a mass spectrometer, and by utilizing an electron multiplier to count the ${\mathrm{K}}^{40}$ ions. By measuring the frequencies of appropriate lines in the Zeeman pattern, the nuclear moment was determined to be ${\mu }_I=-1.2964\mathrm{}\pm 0.0004$ nuclear magnetons. The hyperfine splitting in the ground state was redetermined, with higher precision than that of previous measurements, to be $\Delta \nu =1285.790\mathrm{}\pm 0.007$ Mc/sec.