Radiative Capture Cross Sections of $^{139}$La(n,$\gamma$) for Thermal Neutrons

A set of partial-production neutron-capture $\gamma$-ray cross sections corresponding to the $^{139}$La$(n,\gamma)$ reaction were measured at the Budapest Research Reactor using a supermirror-guided near-thermal neutron beam. Absolute values for these quantities were obtained through an internal-standardization procedure where the observed $\gamma$-ray intensities were normalized to well-known comparator $^{35}$Cl($n,\gamma$) transitions using a LaCl$_{3} \cdot 7{\rm H}_{2}$O standard. These measurements have been used, together with statistical-model predictions calculated using the Monte Carlo program DICEBOX to simulate the thermal-capture $\gamma$-ray cascade, to evaluate the decay scheme of the compound nucleus $^{140}$La. An independent measurement of the total radiative thermal neutron-capture cross section, $\sigma_{0}$, has also been determined; our preliminary result $\sigma_{0} = 8.51(43)$ b, is consistent with earlier literature. The total mean capture-state width is currently being investigated and may provide further insight into the validity of the Brink hypothesis in $\gamma$ decay.