The Nuclear Spin and Magnetic Moment ofK40

Abstract

The molecular beam magnetic resonance method has been employed to observe the nuclear spin and the h.f.s. $\Delta \nu$ of ${\mathrm{K}}^{40}$. The apparatus and procedures of this experiment are different from those previously employed in the magnetic resonance method because of the small natural abundance of ${\mathrm{K}}^{40}$ and because both the nuclear spin and h.f.s. $\Delta \nu$ were previously unknown. The spin is shown to be 4 and the h.f.s. $\Delta \nu =1285.70\mathrm{}\pm 0.1$ megacycles per second. The doublet is inverted. By comparison with the known nuclear moment of ${\mathrm{K}}^{39}$, the nuclear moment of ${\mathrm{K}}^{40}$ is taken to be - 1.290 nuclear magnetons.