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

Spectroscopy of 26^{26}F

The structure of the weakly-bound $^{26}_{\;\;9}$F$_{17}$ odd-odd nucleus, produced from $^{27,28}$Na nuclei, has been investigated at GANIL by means of the in-beam $\gamma$-ray spectroscopy technique. A single $\gamma$-line is observed at 657(7) keV in $^{26}_{9}$F which has been ascribed to the decay of the excited J=$2^+$ state to the J=1$^+$ ground state. The possible presence of intruder negative parity states in $^{26}$F is also discussed.Comment: 3 pages, 1 figure, accepted for publication in Physical Review

Helium Clustering in Neutron-Rich Be Isotopes

Measurements of the helium-cluster breakup and neutron removal cross sections for neutron-rich Be isotopes A=10-12,14 are presented. These have been studied in the 30 to 42 MeV/u energy range where reaction measurements are proposed to be sensitive to the cluster content of the ground-state wave-function. These measurements provide a comprehensive survey of the decay processes of the Be isotopes by which the valence neutrons are removed revealing the underlying alpha-alpha core-cluster structure. The measurements indicate that clustering in the Be isotopes remains important up to the drip-line nucleus 14^Be and that the dominant helium-cluster structure in the neutron-rich Be isotopes corresponds to alpha-Xn-alpha.Comment: 5 pages, 2 tables and 3 figure

1n- and 2n-transfer with the Borromean nucleus 6^{6}He near the Coulomb barrier

Accepetd for publication in Physical Review LettersAngular distributions for 1n- and 2n-transfer are reported for the 6He + 65Cu system at Elab = 22.6 MeV. For the first time, triple coincidences between particles, neutrons and characteristic rays from the target-like residues were used to separate the contributions arising from 1n- and 2n-transfer. The differential cross sections for these channels, elastic scattering, and fusion were analyzed using a Coupled Reaction Channels approach. The large measured ratio of the 2n/1n cross section and the strong influence of 2n-transfer on other channels indicate that the di-neutron configuration of 6He plays a dominant role in the reaction mechanism

Spectroscopy around 36^{36}Ca

Expérience GANILInternational audienceAn experiment was performed to study excited states in neutron-deficient nuclei around Ca. A one-neutron knockout reaction was used to produce $^{36}$Ca ions from a $^{37}$Ca secondary beam, and in-beam $\gamma$-rays were measured. The $2^+$ energy in $^{36}$Ca is compared to the mirror nucleus $^{36}$S to deduce information on the isospin dependence of the nuclear force near the proton drip line. The energy of the first excited $2^+$ state in $^{36}$Ca and the cross section for the 1-neutron knock-out reaction from $^{37}$Ca at $\sim$ 45 · AMeV were obtained. Furthermore, for two other $T_z$ = −2 nuclei, $^{28}$S and $^{32}$Ar, the de-excitation of the first $2^+$ state has been observed

The electromagnetic calorimeter for the T2K near detector ND280

The T2K experiment studies oscillations of an off-axis muon neutrino beam between the J-PARC accelerator complex and the Super-Kamiokande detector. Special emphasis is placed on measuring the mixing angle θ 13 by observing ν e appearance via the sub-dominant νμ ν e oscillation and searching for CP violation in the lepton sector. The experiment includes a sophisticated, off-axis, near detector, the ND280, situated 280 m downstream of the neutrino production target in order to measure the properties of the neutrino beam and to understand better neutrino interactions at the energy scale below a few GeV. The data collected with the ND280 are used to study charged- and neutral-current neutrino interaction rates and kinematics prior to oscillation, in order to reduce uncertainties in the oscillation measurements by the far detector. A key element of the near detector is the ND280 electromagnetic calorimeter (ECal), consisting of active scintillator bars sandwiched between lead sheets and read out with multi-pixel photon counters (MPPCs). The ECal is vital to the reconstruction of neutral particles, and the identification of charged particle species. The ECal surrounds the Pi-0 detector (PØD) and the tracking region of the ND280, and is enclosed in the former UA1/NOMAD dipole magnet. This paper describes the design, construction and assembly of the ECal, as well as the materials from which it is composed. The electronic and data acquisition (DAQ) systems are discussed, and performance of the ECal modules, as deduced from measurements with particle beams, cosmic rays, the calibration system, and T2K data, is described.© 2013 IOP Publishing Ltd and Sissa Medialab srl.The ECal detector has been built and is operated using funds provided by the Science and Technology Facilities Council U.K. Important support was also provided by the collaborating institutions. Individual researchers have been supported by the Royal Society and the European Research Council

Etude de la decroissance par neutrons retardes de noyaux legers riches en neutrons avec le multidetecteur TONNERRE

A new detection array for beta delayed neutrons was built. It includes up to 32 plastic scintillation counters 180 cm long located at 120 cm from the target. Neutron energy spectra are measured by time-of-flight in the 300 keV-15 MeVrange with good energy resolution. The device was tested with several known nuclei. Its performances are discussed in comparison with Monte Carlo simulations. The very high overall detection efficiency of the TONNERRE arraymade it possible to study one and two neutron emission of nLi. A complete decay scheme was obtained. The 33Mg and 35A1 beta decays were investigated for the first time by neutron and gamma spectroscopy. Complete decay schemes were established and compared to large scale shell-model calculations .Un nouveau détecteur pour l'étude des décroissance bêta-neutron retardé a été construit (TONNERRE). Il se compose de 32 scintillateurs plastiques courbés d'une longueur de 180 cm, positionnés chacun à 120 cm de la cibled'implantation. L'énergie des neutrons est obtenue par la mesure du temps de vol sur cette distance, permettant de-couvrir une gamme de 300 keV à 15 MeV avec une très bonne résolution. Ce dispositif a été testé avec différents noyaux connus. Ses performances sont comparées avec des résultats de simulation Monte Carlo. La grande efficacité de TONNERRE a permis l'étude de l'émission de un et de deux neutrons du uLi. De plus un schéma complet des décroissances |3 du 33Mg et du 35A1 est établi pour la première fois en faisant une spectroscopie (3-n-y. Ce schéma est comparé à des calculs de modèle en couche