Neutron resonance spectroscopy:La139

Results of high resolution neutron time of flight spectroscopy measurements on natural lanthanum (99.9% ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$) are presented. Plots of ${\sigma }_t$ vs $E$ are given to 76 keV. Values of $E_0$ and $g{\Gamma }_n^0$ are presented for all 150 ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ levels observed to 26 keV. About 50 of these levels are probably $p$ levels, based on Bayes' theorem and the minimum $g{\Gamma }_n$ for detection vs $E$. Intermediate structure seems to be present in $S_0\equiv \Sigma \frac{g{\Gamma }_n^0}{\Delta E}$. From 6 to 18 keV, $10{}_{}{}^4{}_{}{}^{}S_0^{}{}_{}{}^{}\approx 0.50$. Two strong levels at 3 and 3.5 keV, and several strong levels in the 18.5 to 26 keV region, boost $S_0$ to a value $10{}_{}{}^4{}_{}{}^{}S_0^{}{}_{}{}^{}=0.76\mathrm{}$ for the full 26 keV range. A standard analysis that ignores intermediate structure and uses a single channel Porter-Thomas fit to the entire $g{\Gamma }_n^0$ population yields $10{}_{}{}^4{}_{}{}^{}S_0^{}{}_{}{}^{}=0.76\mathrm{}\pm 0.13$, $D_0=208\mathrm{}\pm 10$ eV, and $10{}_{}{}^4{}_{}{}^{}S_1^{}{}_{}{}^{}=\left({0.6}_{-0.2\mathrm{}}^{+0.3\mathrm{}}\right)$.