Investigation of the 6He cluster structures

The 4He+2n and t+t clustering of the 6He ground state were investigated by means of the transfer reaction 6He(p,t)4He at 25 MeV/nucleon. The experiment was performed in inverse kinematics at GANIL with the SPEG spectrometer coupled to the MUST array. Experimental data for the transfer reaction were analyzed by a DWBA calculation including the two neutrons and the triton transfer. The couplings to the 6He --> 4He + 2n breakup channels were taken into account with a polarization potential deduced from a coupled-discretized-continuum channels analysis of the 6He+1H elastic scattering measured at the same time. The influence on the calculations of the 4He+t exit potential and of the triton sequential transfer is discussed. The final calculation gives a spectroscopic factor close to one for the 4He+2n configuration as expected. The spectroscopic factor obtained for the t+t configuration is much smaller than the theoretical predictions.Comment: 10 pages, 11 figures, accepted in PR

6He + 9Be reactions at 16.8 MeV

6 pags.; 6 figs.Reactions of a 16.8 MeV 6He beam with a 9Be target have been investigated using highly segmented detector setup covering a large solid angle. Data on elastic and quasi-free scattering, as well as two-neutron transfer, are reported. The results for elastic scattering are fairly well reproduced by a CDCC calculation, in agreement with the interpretation of a breakup effect already observed for the scattering of 6He on other light targets. Exotic quasi-free scattering of 6He on α-cluster in 9Be is clearly observed. Inclusive and coincident events were used to extract information on the two-neutron transfer reaction 9Be(6He, α)11Be. Sequential decay of the 11Be state at the excitation energy Ex = 10.6 MeV through different channels is discussed. © 2010 SIF, Springer-Verlag Berlin Heidelberg.We would like to thank the technical staff at the RNB facility at the CRC-Louvain-la-Neuve for their valuable contributions to this work.Peer Reviewe

Structure of low-lying states of 10,11^{10,11}C from proton elastic and inelastic scattering

NESTER PTH, expérience GANIL, équipement SISSITo probe the ground state and transition densities, elastic and inelastic scattering on a proton target were measured in inverse kinematics for the unstable $^{10}$C and $^{11}$C nuclei at 45.3 and 40.6 MeV/nucleon, respectively. The detection of the recoil proton was performed by the MUST telescope array, in coincidence with a wall of scintillators for the quasiprojectile. The differential cross sections for elastic and inelastic scattering to the first excited states are compared to the optical model calculations performed within the framework of the microscopic nucleon-nucleus Jeukenne-Lejeune-Mahaux potential. Elastic scattering is sensitive to the matter-root-mean square radius found to be 2.42$\pm$0.1 and 2.33$\pm$0.1 fm, for $^{10,11}$C, respectively. The transition densities from cluster and mean-field models are tested, and the cluster model predicts the correct order of magnitude of cross sections for the transitions of both isotopes. Using the Bohr-Mottelson prescription, a profile for the $^{10}$C transition density from the $0^+$ ground to the $2_1^+$ state is deduced from the data. The corresponding neutron transition matrix element is extracted: Mn=5.51$\pm$1.09 fm$^2$

Low-lying states and structure of the exotic 8^8He via direct reactions on the proton

International audienceThe structure of the light exotic nucleus 8He was investigated using direct reactions of the 8He SPIRAL beam on a proton-rich target. The (p,p') scattering to the Click to view the MathML source state, the (p,d)7He and (p,t)6He transfer reactions, were measured at the energy Elab=15.7 A.MeV. The light charged particles (p,d,t) were detected in the MUST Si-strip telescope array. The excitation spectrum of 8He was extracted from the (p,p') reaction. Above the known Click to view the MathML source excited state at 3.6 MeV, a second resonance was found around 5.4 MeV. The cross sections were analyzed within the coupled-reaction channels framework, using microscopic potentials. It is inferred that the 8He ground state has a more complex neutron-skin structure than suggested by previous α+4n models assuming a pure (1p3/2)4 configuration

Experimental evidence for subshell closure in 8^{8}He and indication of a resonant state in 7^{7}He below 1 MeV

NESTERThe spectroscopy of the unstable $^{8}$He and unbound $^{7}$He nuclei is investigated via the p($^{8}$He, d) transfer reaction with a 15.7A MeV $^{8}$He beam from the SPIRAL facility. The emitted deuterons were detected by the telescope array MUST. The results are analyzed within the coupled-channels Born approximation framework, and a spectroscopic factor $C^2$S=4.4±1.3 for neutron pickup to the $^{7}$He_g.s.$is deduced. This value is consistent with a full p3/2 subshell for$^{8}$He. Tentative evidence for the first excited state of$^{7}$He is found at$E^*$=0.9±0.5 MeV (width$\Gamma$=1.0±0.9 MeV). The second one is observed at a position compatible with previous measurements,$E^*$=2.9±0.1 MeV. Both are in agreement with previous separate measurements. The reproduction of the first excited state below 1 MeV would be a challenge for the most sophisticated nuclear theories

Indication for the disappearance of reactor electron antineutrinos in the Double Chooz experiment

The Double Chooz Experiment presents an indication of reactor electron antineutrino disappearance consistent with neutrino oscillations. A ratio of 0.944 $\pm$ 0.016 (stat) $\pm$ 0.040 (syst) observed to predicted events was obtained in 101 days of running at the Chooz Nuclear Power Plant in France, with two 4.25 GW$_{th}$ reactors. The results were obtained from a single 10 m$^3$ fiducial volume detector located 1050 m from the two reactor cores. The reactor antineutrino flux prediction used the Bugey4 measurement as an anchor point. The deficit can be interpreted as an indication of a non-zero value of the still unmeasured neutrino mixing parameter \sang. Analyzing both the rate of the prompt positrons and their energy spectrum we find \sang = 0.086 $\pm$ 0.041 (stat) $\pm$ 0.030 (syst), or, at 90% CL, 0.015 $<$ \sang $\ <$ 0.16.Comment: 7 pages, 4 figures, (new version after PRL referee's comments