High-EnergyγSpectra Resulting from Neutron Capture in Hafnium Isotopes

The $\gamma$ spectra resulting from thermal-neutron capture in targets of natural hafnium, enriched ${\mathrm{Hf}}^{177}$, and enriched ${\mathrm{Hf}}^{179}$ were measured with lithium-drifted germanium detectors. The energies and intensities of 42 gamma lines in the range from about 5.5 to 7.6 MeV were determined and the transitions were identified with the reactions ${\mathrm{Hf}}^{177}(n,\gamma ){\mathrm{Hf}}^{178}$, ${\mathrm{Hf}}^{178}(n,\gamma ){\mathrm{Hf}}^{179}$, ${\mathrm{Hf}}^{179}(n,\gamma ){\mathrm{Hf}}^{180}$, or ${\mathrm{Hf}}^{180}(n,\gamma ){\mathrm{Hf}}^{181}$, The neutron separation energies were determined to be 7623 keV for ${\mathrm{Hf}}^{178}$, 6098 keV for ${\mathrm{Hf}}^{179}$, 7383 keV for ${\mathrm{Hf}}^{180}$, and 5693 keV for ${\mathrm{Hf}}^{181}$, the uncertainty in energy being ±3 keV in each case. The gamma spectrum of each final nucleus was used to identify 28 new levels, and to verify 14 previously known levels. Some of these levels are discussed.