Neutron capture cross sections of ${}^{178}\mathrm{Hf}$ leading to ${}^{179}\mathrm{Hf}^{m_2}$

Cross sections for radiative neutron capture have been measured for the formation of 25-d ${}^{179}\mathrm{Hf}^{m_2}$ ($J^{\pi }=25/2^{+}$) using targets of enriched ${}^{178}\mathrm{Hf}$. Based on irradiations using pure epithermal neutrons as well as mixed thermal + epithermal neutrons, the thermal cross section has been determined to be $\sigma =6\left(5\right)\mu \mathrm{b}$ and the resonance integral $I=1.63\left(5\right)\mathrm{mb}$. To enhance the determination of the cross sections, the energies and intensities of the $\gamma$ rays from the decay of ${}^{179}\mathrm{Hf}^{m_2}$ have been re-determined with improved precision. The half-life of ${}^{179}\mathrm{Hf}^{m_2}$ has been measured to be 24.91(27) d, in agreement with the previously accepted value. The analysis of the ${}^{179}\mathrm{Hf}^{m_2}$ decay required more precise spectrometry on competing $\gamma$ rays from the decay of ${}^{181}\mathrm{Hf}$, whose results are presented (along with that of the decay of ${}^{175}\mathrm{Hf}$) from irradiation of a source of natural Hf. The measured cross sections are compared with those of other high-spin neutron captures.

Figure 1

Gamma-ray spectrum from irradiated enriched ${}^{178}\mathrm{Hf}$ sample, showing not only lines from ${}^{179}\mathrm{Hf}^{m_2}$ but also those from ${}^{175,181}\mathrm{Hf}$ and ${}^{192}\mathrm{Ir}$.

Figure 2

Expanded version of Fig. 1, showing on a linear scale the lines from ${}^{179}\mathrm{Hf}^{m_2}$.

Figure 3

Level scheme of ${}^{179}\mathrm{Hf}$ from the decay of ${}^{179}\mathrm{Hf}^{m_2}$.

Figure 4

Decay with time of 453-keV line from ${}^{179}\mathrm{Hf}^{m_2}$.

Figure 5

Gamma-ray spectrum of irradiated natural Hf. Peaks labeled above the spectrum are from the decay of ${}^{181}\mathrm{Hf}$, and those labeled below are from ${}^{175}\mathrm{Hf}$.

Figure 6

Coincidence summing in the 615.2- and 619.0-keV lines in the ${}^{181}\mathrm{Hf}$ decay. The error bars are smaller than the plotted points. The $y$ intercept gives the singles intensity in the absence of summing.

Figure 7

Coincidence summing in the 269-keV line from the enriched and natural Hf samples. The counting rates have different normalization lines: 453 keV for the enriched sample and 482 keV for the natural sample.