Nuclear structure of Th-229,Th-231 studied with the Th-230,Th-232(d, t) reactions

摘要

Detailed angular distributions for the Th-230,Th-232(d. t)Th-229,Th-231 reactions were measured with 17 MeV deuterons, using a magnetic spectrograph to analyze the reaction products. Comparisons with distorted wave Born approximation predictions were used to determine e-values and spectroscopic strengths for many levels in both nuclides. These results reconfirm previous assignments for the 3/2(+)vertical bar 631 vertical bar band in Th-229, with its bandhead unresolved from the 5/2(+)vertical bar 633 vertical bar ground state, providing support for the existence of the much-sought "3.5 eV" isomer (for which the latest reported energy is 7.6 +/- 0.5 eV). Although Th-231 was previously well studied, many new spin-parity assignments have been made and some changes to adopted model assignments are proposed. There is evidence in both isotopes for appreciable mixing of single-particle orbitals with other configurations, as predicted by the Quasiparticle Phonon Model. Single-nucleon transfer strengths are described Much better with earlier values for the Nilsson model parameters K and It than later values that have been widely used. An earlier Th-232(d, t) study concluded that serious errors could result in the commonly-used method of predicting cross sections by combining distorted wave Born approximation calculations using spherical form factors with Nilsson wave functions for a deformed potential, but the present work shows this conclusion is not valid because it was based on inadequate knowledge of the Th-231 nuclear structure.