Background: Very neutron-rich isotopes, including Ne30-32, 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 Ne-29.
Purpose: A determination of the structure of Ne-29 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 Ne-28 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 Ne-29 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 Ne-29 lies within the island of inversion and that the ground state of Ne-29 is dominated by a Ne-28(0(1)(+)) circle times 2p(3/2) neutron configuration. Combined with recently measured interaction cross sections, it is concluded that Ne-29 may exhibit a moderately developed halo-like distribution.