The quenching of the N =20 shell gap in neutron-rich nuclei is investigated by studying the singleparticle structure of 27 Ne via neutron transfer using a 26 Ne beam. Two low-lying negative parity intruder states have been observed, the lowest of which is identified as J π = 3/2 − , confirming earlier speculations. A level identified as 7/2 − is observed higher in energy than the 3/2 − , contrary to the ordering at β-stability and at an energy significantly different to the predictions of previous shellmodel calculations. The measured energies and deduced spectroscopic factors are well reproduced in full (0,1)-ω 0s-0p-0d-1s-0f -1p calculations in which there is a significant ad-hoc reduction (∼ 0.7 MeV) in the N =20 shell gap. Neutron-rich nuclei often exhibit structural behaviour significantly different to stable nuclei, with a striking example being the "island of inversion" in the A ≃ 32 region of neutron rich nuclei [1,2]. The nuclei in this "island" are deformed rather than spherical owing to residual interactions and quenching of the N =20 magic number through the migration in energy of the shell-model orbitals [3]. This migration is known to be due, in part, to nucleon-nucleon tensor forces and to three-body N N N forces [4,5]. In adjacent more weakly bound nuclei, the migration may also be affected by the proximity of the continuum [6].The N =20 shell gap seen in nuclei near stability arises from the separation of the 0d 3/2 orbital and the negative parity orbitals (0f 7/2 , 1p 3/2 ,.. [10]. Guided by shell model expectations, the 885 keV level was tentatively identified as the lowest 1/2 + state and the 765 keV level was inferred to have a negative parity of 1/2 − , 3/2 − or 5/2 − . The 1/2 + is weak since it is populated mainly via pair-excited components in the 26 Ne ground state, in single-step transfer. In single-neutron knockout at higher energies, both levels were seen and the angular momentum of the removed nucleon was assigned as ℓ=0 or 1 [11], consistent with the results from the (d,p) reaction study [10]. These two excited states were also observed in the p( 28 Ne, 27 Neγ) reaction at intermediate energy [12] but no further information concerning spins was obtained [37]. No evidence for a 7/2 − state has been reported, despite a clear prediction that it should exist at an energy close to the 3/2 − state [11,15]. The most direct means to probe the evolution of orbital energies is to measure the strength of single-particle states where a neutron is transferred into orbitals that are otherwise empty. The present experiment was designed along these lines to populate the 7/2 − and 3/2 − 0f -1p shell states and any other strong single-particle levels via (d,p) transfer and to determine their properties.A beam of 26 Ne ions (∼100% pure) at 9.8A MeV was provided by the SPIRAL facility at GANIL and

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