Eur. Phys. J. Special Topics 150, 161–163 (2007) c  EDP Sciences, Springer-Verlag 2007 DOI: 10.1140/epjst/e2007-00293-5 T HE EUROPEAN P HYSICAL JOURNAL SPECIAL TOPICS Study of N = 16 for Ne isotopes A. Gillibert 1 , A. Obertelli 1 , N. Alamanos 1 , M. Alvarez 1 , F. Auger 1 , R. Dayras 1 , A. Drouart 1 , G. de France 2 , B. Jurado 2 , N. Keeley 1 , V. Lapoux 1 , W. Mittig 2 , X. Mougeot 1 , L. Nalpas 1 , A. Pakou 3 , N. Patronis 3 , E. Pollacco 1 , F. Rejmund 2 , M. Rejmund 2 , P. Roussel-Chomaz 2 , H. Savajols 2 , F. Skaza 1 , and Ch. Theisen 1 1 DSM/DAPNIA/SPhN, CEA Saclay, 91191 Gif-sur-Yvette, France 2 GANIL, BP. 5027, 14076 Caen Cedex 5, France 3 Department of Physics, The University of Ioannina, 45110 Ioannina, Greece Received: January 31, 2007 Abstract. 27 Ne has been investigated through the one neutron transfer reaction 26 Ne(d,p) 27 Ne in inverse kinematics at 9.7 MeV/nucleon. The results support the existence of a low lying negative parity state in 27 Ne which is a signature of a reduced sd-fp shell gap in the N = 16 neutron rich region, at variance with stable nuclei. PACS. 21.10.-k – 21.10.Pc – 25.45.-z – 27.30.+t 1 Introduction N = 16 has been proposed recently to be a new magic number near the neutron drip line. First indications came from the unbound 26 O and 28 O nuclei [1], mass sur- faces with discontinuities observed at N = 16 for large neutron excesses [2] or a large spectroscopic factor for the 23 O ground state described as a single particle state s 1/2 [3]. Moreover, the first 2 + excited state of 24 O was not observed below the one neutron emission threshold at 3.6MeV [4] which implies a high excitation energy. New calculations [5] suggest an enhancement with isospin of the gap between the s 1/2 and d 3/2 subshells of the sd neutron shell. The attractive interaction between pro- tons in the d 5/2 and neutrons in the d 3/2 subshells seems to be a quite important point. Then, removing protons from 30 Si to 24 O makes the neutron d 3/2 subshell less bound. Consequently, the last bound oxygen isotope 24 O could be a doubly magic nuclei, instead of the un- bound 28 O. More information may be obtained with the N = 17 isotones, since the study of the single particle excita- tions is well suited to determine the spacing between the d 3/2 subshell and the fp shell. The lowest excitation energies of the negative parity states for the most bound N = 17 isotones ( 35 Ar, 33 S and 31 Si) are quite high, around 3.5 MeV, reflecting the N = 20 major shell gap for stable nuclei. They are suddenly lower than 1.5 MeV for 29 Mg [6]. The next N = 17 isotone is 27 Ne for which very little information [7] are available. New Ne beams are now delivered by the SPIRAL facil- ity at GANIL which have been used to study 27 Ne with Ne 26 Ne 27 D 2 MCP TARGET EXOGAM Q1 Q2 DIPOLE PLASTIC IONISATION CHAMBER DRIFT CHAMBERS VAMOS γ Fig. 1. Experimental set-up used for the one neutron transfer 26 Ne(d,p) 27 Ne. the one neutron transfer reaction 26 Ne(d,p) 27 Ne in inverse kinematics. 2 Experimental set-up We used the Spiral beam 26 Ne at 9.7 MeV/nucleon im- pinging on a 1 mm thick solid cryogenic deuterium tar- get developed at GANIL [8]. The ejectiles were detected and identified with the VAMOS magnetic spectrometer [9]. Due to the large momentum acceptance and the in- verse kinematics, not only 27 Ne 10+ was transmitted, but others ejectiles simultaneously observed in the focal plane from others reaction channels like (d,d’) or (d,t). A com- plete identification was obtained with usual combinations of time of flight, energy loss and transverse position in the focal plane. Due to the large target thickness, the recoil- ing protons which are emitted at backward angles in the lab frame from the (d,p) channel were not measured. In