Nuclear structure ofTh231from neutron capture and (d,p) reaction measurements

The nuclide ${}_{}{}^{231}{}_{}{}^{}\mathrm{Th}$ was investigated with the reactions ${}_{}{}^{230}{}_{}{}^{}\mathrm{Th}$(n,γ${)\mathrm{}}^{231}$Th, ${}_{}{}^{230}{}_{}{}^{}\mathrm{Th}$(n,γe${)}^{231}$Th, and ${}_{}{}^{230}{}_{}{}^{}\mathrm{Th}$(d,p${)}^{231}$Th. Gamma rays from average resonance capture were measured, in addition to the usual thermal neutron capture spectroscopy. From these data, 70 excited levels in ${}_{}{}^{231}{}_{}{}^{}\mathrm{Th}$ were identified and, of these, 57 were placed in 18 rotational bands with assigned configurations. Candidates have been proposed for all expected Nilsson states below 750 keV, albeit with varying degrees of confidence, including the ${\mathrm{}(5/2)\mathrm{}}^{+}$[622], ${\mathrm{}(7/2)\mathrm{}}^{+}$[624], ${\mathrm{}(3/2)\mathrm{}}^{\mathrm{-}}$[761], ${\mathrm{}(1/2)\mathrm{}}^{\mathrm{-}}$[770], ${\mathrm{}(1/2)\mathrm{}}^{+}$[640], and ${\mathrm{}(5/2)\mathrm{}}^{\mathrm{-}}$[503] configurations. Several vibrational states have been identified; a special feature of these is the observation of greater fragmentation of single-particle-$0^{+}$ phonon-mixed states than expected theoretically. Assuming degenerate parity doublets indicate the existence of stable octupole deformation, no evidence was found for a tendency toward this phenomenon in ${}_{}{}^{231}{}_{}{}^{}\mathrm{Th}$. The neutron binding energy was determined to be 5118.13±0.20 keV.