Partial Photoneutron Cross Sections for the Isomeric State ${}^{180}\mathrm{Ta}^m$

Photoneutron cross sections for ${}^{181}\mathrm{Ta}(\gamma ,n){}^{180}\mathrm{Ta}^m$ were determined from simultaneous measurements of total cross sections (${\sigma }^{\mathrm{tot}}$) and ground-state cross sections (${\sigma }^{\mathrm{gs}}$) for ${}^{180}\mathrm{Ta}$ in photodisintegration of ${}^{181}\mathrm{Ta}$ with laser Compton-backscattered $\gamma$ rays. Techniques of direct neutron counting and photoactivation were used for the measurement of ${\sigma }^{\mathrm{tot}}$ and ${\sigma }^{\mathrm{gs}}$, respectively. The partial cross sections for the isomeric state serves as a novel probe of the nuclear level density of ${}^{180}\mathrm{Ta}$. Implications for the $p$- and $s$-process nucleosynthesis of ${}^{180}\mathrm{Ta}^m$ are given.

Figure 1

Typical $K$ x-ray spectrum and the time variation of the $K\alpha$ yield in the photoactivation of the Ta sample.

Figure 2

Comparison between experimental and theoretical cross sections. Open symbols correspond to the total photoreaction [8, 18] and solid symbols to the partial cross section for the isomeric state only. The overall (statistical plus systematic) uncertainty is shown on the partial cross section. The solid (dashed) line is obtained with the combinatorial (statistical) NLD.

Figure 3

Predicted ${}^{179}\mathrm{Ta}(n,\gamma ){}^{180}\mathrm{Ta}^m$ cross sections using the combinatorial (solid line) and statistical (dashed line) NLD. The ratio of the partial cross section to the isomeric state to the total cross section is also shown (line with symbols; right axis).