Abstract
The island of inversion for neutron-rich nuclei in the vicinity of N=20 has become the testing ground par excellence for our understanding and modeling of shell evolution with isospin. In this context, the structure of the transitional nucleus ²⁹Mg is critical. The first quantitative measurements of the single-particle structure of ²⁹Mg are reported, using data from the d(²⁸Mg, p γ)²⁹Mg reaction. Two key states carrying significant ℓ=3 (f-wave) strength were identified at 2.40±0.10 (Jπ=5/2¯) and 4.28±0.04 MeV (7/2¯). New state-of-the-art shell-model calculations have been performed and the predictions are compared in detail with the experimental results. While the two lowest 7/2¯ levels are well described, the sharing of single-particle strength disagrees with experiment for both the 3/2¯ and 5/2¯ levels and there appear to be general problems with configurations involving the p3/2 neutron orbital and core-excited components. These conclusions are supported by an analysis of the neutron occupancies in the shell-model calculations.