The Nuclear Structure (or “Exotiques”) group is active in the investigation of the structure of neutron-rich nuclei using the probes of direct reactions and decay spectroscopy.
In the direct reaction studies, the structure of light (A<50) neutron-rich nuclei, including haloes, clustering and correlations and shell structure, is explored using energetic radioactive beams. Two different approaches are employed : (i) at high energies (>100 MeV/nucleon) and close to the dripline nucleon “knockout”, breakup, inelastic excitation and Coulomb dissociation ; and (ii) at low energies ( 5 – 10 MeV/nucleon) and closer to stability nucleon transfer.
The high-energy reaction studies, which have been the main focus of the group’s reaction studies activities over the course of the last two years, are undertaken at the Radioactive Isotope Beam Factory (RIBF) at RIKEN where beam intensities 3 or 4 orders of magnitude higher than elsewhere, are available for the light near dripline nuclei. At the RIBF experiments are carried out, with radioactive beams delivered by the BigRIPS fragment separator, using the ZDS zero-degree spectrometer coupled to the DALI2 NaI array and, since Spring 2012, the SAMURAI spectrometer plus NEBULA neutron array. One of the goals of the group in the next few years is to upgrade, through a doubling of the number of scintillator walls, the NEBULA array (“NEBULA-Plus”) to enable us to exploit to the maximum the unique beams available at the RIBF and to explore, in particular, multi-neutron decaying systems and the most exotic neutron-rich systems accessible. This project is, at the time of writing, the subject of a grant request – “EXPAND” – made to the ANR.
Our complementary transfer reaction studies – typically neutron addition to the beam via (d,p) in inverse kinematics – at lower energies and closer to stability employ at GANIL-SPIRAL1, the TiaRA Si-strip array coupled to the EXOGAM Ge-array and the VAMOS spectrometer. In the near future experiments will be undertaken employing beams, such as 16C, not available with SPIRAL1, prepared using the LISE3 separator. In the case of our TRIUMF based work, the beams are delivered by the ISAC2 facility (which offers a suite of beams unavailable at SPIRAL1) and the SHARC Si-strip array coupled with the TIGRESS Ge-array is employed for the measurements. Owing to the lack of a suitable spectrometer, zero-degree detection is provided by a thin scintillator plus stopper foil setup developed at LPC. The main priority in the near future at ISAC is the measurement of the d(28Mg,p)29Mg reaction which will complement our earlier work on d(24,26Ne,p)25,27Ne [1,2] and further help map the transition into the island of inversion around N=20.
The second main theme of the group’s research is centred on the investigation of structure through b-decay, and in the context of neutron-rich nuclei, the study of b-delayed neutron emission. Presently this activity is focussed on R&D for a new neutron time-of-flight array which has included extensive neutron beam measurements at CEA/DAM-Arpajon. In addition, a proof of principle experiment is under preparation for ISOLDE aiming at a measurement of the -delayed two-neutron decay of 11Li. Extensive source testing, in particular in terms of investigating neutron-gamma discrimination techniques, digital signal processing and new scintillators, has also been carried out at LPC. This work has benefited greatly from the untiring support of our colleagues at LPC who have developed the FASTER digital acquisition system.