Determination of Spins of Neutron Resonances and the Hyperfine Coupling Constant inHo165

Neutron transmission measurements on targets of polarized holmium nuclei were extended using a holmium single crystal. Owing to the large hyperfine coupling in holmium and the complete magnetization of the single-crystal sample, it was possible to make spin determinations for the compound states corresponding to the neutron resonances at 18.2 eV and 21.3 eV. The spins were both found to be $I-\frac{1}{2}=3\mathrm{}$. The nuclear polarization of the sample was obtained as a function of temperature at the 3.924-eV resonance and the data were fitted to a theoretical curve with the magnetic and electric hyperfine splitting constants as fitting parameters. The results for the magnetic and electric hfs constants are, respectively, $\frac{A}{k}=0.610\mathrm{}\pm 0.005°$K and $\frac{P}{k}=0.002\mathrm{}\pm 0.001°$K. This corresponds to an effective magnetic field at the nucleus of 8.8×${10}^6$ Oe.