  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 modelling 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 gamma)29Mg reaction. Two key states carrying significant ell=3
(f-wave) strength were identified at 2.40 +/- 0.10 (Jpi = 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. Whilst 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.
