Paramagnetic Resonance Hyperfine Structure ofCo56

The microwave paramagnetic resonance hyperfine structure of 72-day ${\mathrm{Co}}^{56}$ has been observed in a magnetically dilute single crystal of cobalt potassium sulfate at 20°K. From the number of hfs components and their spacing relative to ${\mathrm{Co}}^{59}$, the spin $I\left({\mathrm{Co}}^{56}\right)=4\mathrm{}$ and the magnetic moment $\left|\mu \right({\mathrm{Co}}^{56}\left)\right|=3.855\mathrm{}\pm 0.007$ nm are directly determined. These results are discussed in relation to those of nuclear alignment experiments and the nuclear shell model.