One-neutron removal from 29Ne: Defining the lower limits of the island of inversion.

Background: Very neutron-rich isotopes, including 30-32Ne, in the vicinity of N = 20 are known to exhibit ground states dominated by fp-shell intruder configurations: the "island of inversion. "Systematics for the Ne-isotopic chain suggest that such configurations may be in strong competition with normal shell-model configurations in the ground state of 29Ne. Purpose: A determination of the structure of 29Ne is thus important to delineate the extent of the island of inversion and better understand structural evolution in neutron-rich Ne isotopes. This is accomplished here through a combined investigation of nuclear and Coulomb-induced one-neutron removal reactions. Method: Cross sections for one-neutron removal on carbon and lead targets and the parallel momentum distribution of the 28Ne residues from the carbon target are measured at around 240 MeV/nucleon. The measurements are compared with reaction calculations combined with spectroscopic information from SDPF-M shell-model wave functions. Results: The deduced width of the inclusive parallel momentum distribution, 98(12) MeV/c (FWHM), suggests that the ground state of 29Ne has a spin parity of 3/2-. Detailed comparisons of the measured inclusive and partial cross sections of the two targets and the parallel momentum distribution of the carbon target with reaction calculations, combined with spectroscopic information from large-scale shell-model calculations, are all consistent with a 3/2- spin-parity assignment. Conclusions: The results indicate that 29Ne lies within the island of inversion and that the ground state of 29Ne is dominated by a 28Ne(01+) ⊗ 2p3/2 neutron configuration. Combined with recently measured interaction cross sections, it is concluded that 29Ne may exhibit a moderately developed halo-like distribution. [ABSTRACT FROM AUTHOR]