Structure of 12Be: intruder d-wave strength at N=8

The breaking of the N=8 shell-model magic number in the 12Be ground state has been determined to include significant occupancy of the intruder d-wave orbital. This is in marked contrast with all other N=8 isotones, both more and less exotic than 12Be. The occupancies of the 0 hbar omega neutron p1/2-orbital and the 1 hbar omega, neutron d5/2 intruder orbital were deduced from a measurement of neutron removal from a high-energy 12Be beam leading to bound and unbound states in 11Be.Comment: 5 pages, 2 figure

Experimental study of high-lying states in ²⁸Mg using the resonant elastic scattering of α particles

International audienceThe excitation function of Mg28 above the α-decay threshold has been measured for the first time using the resonant scattering of α particles with the technique of a thick target in inverse kinematics. Thirteen new states are reported between Ex=15.5 and Ex=20.5 MeV, and suggestions for spin-parity assignments are given for two of these. Calculations of the branching ratio to α decay for these states as well as comparison of the measured cross sections to calculations suggest that α+Neg.s.24 clustering is not dominant in this energy regime

Emergence of the N=16 shell gap in ^(21)O

This is the publisher's version, also available electronically from http://journals.aps.org/prc/abstract/10.1103/PhysRevC.84.011301

Low-lying neutron fp-shell intruder states in Ne-27

This is the publisher's version, also available electronically from http://journals.aps.org/prc/abstract/10.1103/PhysRevC.85.011302

Beyond the neutron drip line: The unbound oxygen isotopes (25)O and (26)O

This is the publisher's version, and is also available electronically from http://journals.aps.org/prc/abstract/10.1103/PhysRevC.88.034313.The very neutron-rich oxygen isotopes 25O and 26O are investigated experimentally and theoretically. The unbound states are populated in an experiment performed at the R3B-LAND setup at GSI via proton-knockout reactions from 26F and 27F at relativistic energies around 442 and 414 MeV/nucleon, respectively. From the kinematically complete measurement of the decay into 24O plus one or two neutrons, the 25O ground-state energy and width are determined, and upper limits for the 26O ground-state energy and lifetime are extracted. In addition, the results provide indications for an excited state in 26O at around 4 MeV. The experimental findings are compared to theoretical shell-model calculations based on chiral two- and three-nucleon (3N) forces, including for the first time residual 3N forces, which are shown to be amplified as valence neutrons are added

Evidence for a 3.8 MeV state in 9Be

The breakup reaction 9Be(4He,3a)n was measured using an array of four double-sided silicon strip detectors at beam energies of 22 and 26 MeV. Excited states in 9Be up to 8 MeV were populated and reconstructed through measurements of the charged reaction products. Evidence is given for a state in 9Be at 3.82-0.09+0.08 MeV with width=1240-90+270 keV. This is consistent with two recent measurements of a state with similar properties in the mirror nucleus 9B. An analysis of the reduced widths (Beg.s.8 channel) of this state along with the proposed mirror state has led to a firm limit of J<=7/2 and a tentative assignment of J^pi=1/2- or 3/2-

The thick target inverse kinematics technique with a large acceptance silicon detector array

An experimental technique for studying elastic scattering using a thick gas target is described, with a measurement of the α(24Ne, α) reaction used as an example. Advantages such as ease, detector efficiency, and the possibility of measuring the cross section at 180° in the centre-of-mass are discussed. It is shown that a resolution of tens of keV is practical at zero degrees, and that the dominant contribution to the resolution for large angles is angular straggling of the beam in the entrance window. The use of helium gas as the target allows direct measurement of a-cluster states

Structure around the island of inversion with single-neutron knockout reactions at GANIL

The nuclear structure of the 31Mg nucleus has been studied with the singleneutron knockout reaction. We report on the preliminary results of an experiment performed with the EXOGAM array coupled, for the first time, to the SPEG spectrometer at GANIL.We present a provisional result for the inclusive single-neutron knockout cross section of σinc= 90(5) mb. Preliminary exclusive cross sections for the measured bound states, including the ground state, are also presented. Finally, preliminary longitudinal momentum distributions for the ground state and first excited state are also shown. These results are compared to Monte Carlo Shell-Model calculations in the sd-pf region