Nuclear structure of Th231 from neutron capture and (d,p) reaction measurements

The nuclide Th231 was investigated with the reactions Th230(n,) 231Th, Th230(n,e)231Th, and Th230(d,p)231Th. Gamma rays from average resonance capture were measured, in addition to the usual thermal neutron capture spectroscopy. From these data, 70 excited levels in Th231 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 (5/2)+[622], (7/2)+[624], (3/2)-[761], (1/2)-[770], (1/2)+[640], and (5/2)-[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 Th231. The neutron binding energy was determined to be 5118.130.20 keV.