B(E1) Strengths from Coulomb Excitation of 11Be

The $B$(E1;$1/2^+\to1/2^-$) strength for $^{11}$Be has been extracted from intermediate energy Coulomb excitation measurements, over a range of beam energies using a new reaction model, the extended continuum discretized coupled channels (XCDCC) method. In addition, a measurement of the excitation cross section for $^{11}$Be+$^{208}$Pb at 38.6 MeV/nucleon is reported. The $B$(E1) strength of 0.105(12) e$^2$fm$^2$ derived from this measurement is consistent with those made previously at 60 and 64 MeV/nucleon, i n contrast to an anomalously low result obtained at 43 MeV/nucleon. By coupling a multi-configuration description of the projectile structure with realistic reaction theory, the XCDCC model provides for the first time a fully quantum mechanical description of Coulomb excitation. The XCDCC calculations reveal that the excitation process involves significant contributions from nuclear, continuum, and higher-order effects. An analysis of the present and two earlier intermediate energy measurements yields a combined B(E1) strength of 0.105(7) e$^2$fm$^2$. This value is in good agreement with the value deduced independently from the lifetime of the $1/2^-$ state in $^{11}$Be, and has a comparable p recision.Comment: 5 pages, 2 figures, accepted for publication in Phys. Lett.

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

The GUINEVERE Project for Accelerator Driven System Physics

paper 9414International audienceThe GUINEVERE project is part of the EUROTRANS Integrated Project of the 6th EURATOM Framework Programme. It is mainly devoted to ADS on-line reactivity monitoring validation, sub-criticality determination and operational procedures (loading, start-up, shut-down, ...) as a follow-up of the MUSE experiments. The project consists in coupling a fast lead core, set-up in the VENUS reactor at SCK*CEN Mol (B), with a GENEPI neutron source under construction by CNRS. To accommodate the accelerator in a vertical coupling configuration, the VENUS building is being heightened. The fast core will be loaded with enriched Uranium and will be moderated and reflected with solid lead (zero power experiment). For the purpose of the experimental programme, the neutron source has to be operated not only in pulsed mode but also in continuous mode to investigate the current-to-flux reactivity indicator in representative conditions of a powerful ADS. In this latter mode it is also required to make short beam interruptions to have access to the neutron population decrease as a function of time: from this spectrum it will be possible to apply different analysis techniques such as "prompt decay" fitting techniques and "source jerk" techniques. Beam interruptions will be repeated at a programmable frequency to improve time spectra statistics. Different sub-criticality levels (keff=0.99, 0.97, 0.95, ...) will be investigated in order to obtain a full set of data points for the final overall validation of the methodology. This paper describes the status of the experimental facility assembling, and the foreseen experimental programme to be started

The GUINEVERE project at the VENUS facility

Proc. on CD Rom log315International audienceThe GUINEVERE project is an international project in the framework of IP-EUROTRANS, the FP6 program which aims at addressing the main issues for ADS development in the framework of partitioning and transmutation for nuclear waste volume and radiotoxicity reduction. The GUINEVERE project is carried out in the context of domain 2 of IP-EUROTRANS, ECATS, devoted to specific experiments for the coupling of an accelerator, a target and a subcritical core. These experiments should provide an answer to the questions of online reactivity monitoring, sub-criticality determination and operational procedures (loading, start-up, shutdown, …) in an ADS by 2009-2010. The project has the objective to couple a fast lead core, within the VENUS building operated by the SCK•CEN, with a neutron generator able to work in three different modes: pulsed, continuous and continuous with beam interruptions at the millisecond scale. In order to achieve this goal, the VENUS facility has to be adapted and a modified GENEPI-3C accelerator has to be designed and constructed. The paper describes the main modifications to the reactor core and facility and to the accelerator, which will be executed during the years 2008 and 2009, and the experimental programme which will start in 2009

A telescope for monitoring fast neutron sources

In the framework of nuclear waste management, highly radiotoxic long-lived fission products and minor actinides are planned to be transmuted in a sub-critical reactor coupled with an intense external neutron source. The latter source would be created by a high-energy proton beam hitting a high atomic number target. Such a new system, termed an accelerator-driven system (ADS), requires on-line and robust reactivity monitoring. The ratio between the beam current delivered by the accelerator and the reactor power level, or core neutron flux, is the basis of one method which could give access to a core reactivity change. In order to test reactivity measurement technique, some experimental programs use 14-MeV neutrons originating from the interaction of a deuteron beam with a tritium target as an external neutron source. In this case, the target tritium consumption over time precludes use of the beam current for reactivity monitoring and the external neutron source intensity must be monitored directly. A range telescope has been developed for this purpose, consisting of the assembly of a hydrogenous neutron converter and three silicon stages where the recoiling protons are detected. In this article, the pergormances of such a telescope are presented and compared to Monte-Carlo simulations

Monitoring of a 14 MeV neutron source

International audienceAccelerator-driven systems (ADS) may allow the transmutation of themost radiotoxic nuclear waste. They consist of the coupling of an intensehigh-energy proton beam, hitting a high atomic number target, and asub-critical reactor core. For safety reasons, an on-line accurate and robustcore reactivity monitoring is mandatory. The beam current delivered by theaccelerator and the power level, or neutron flux, of the reactor core arestrongly correlated through a proportionality relationship which has to beinvestigated, since, among different techniques, it could give access to anyreactivity change.To demonstrate the feasibility of such an on-line reactivity monitoring, anexperimental program is planned at the YALINA facility, in Byelorussia, inthe framework of the EUROTRANS Integrated Project (6th FP). At thissub-critical installation, the incident 14 MeV neutron flux is produced by adeuteron beam impinging on a 3H target. Due to the consumption of the 3Htarget, the deuteron beam current will not remain proportional to the neutronproduction-rate over time. Therefore, in order to monitor the neutronproduction rate, we developed a new detector device. It is composed of athin CH2 foil, followed by three Si detectors. This telescope will be installeda few meters downstream the 3H target, at 0°. The detection method is basedon the conversion of neutrons into recoiling protons, which are thendetected by the three Si. Their thicknesses and thresholds have been chosenso that the most energetic protons, associated with the 14 MeV neutrons, arestopped in the last stage of the telescope. Requiring triple coincidences inthe telescope enable then to select events originating only from neutronsproduced in the d+3H reactions. Doing so, the correlation between a changeof the source intensity and the flux will be kept and the proportionalityconstant can be investigated and determined (via a calibration) and thereforeused to detect any reactivity change of the sub-critical medium.In this contribution, we will present the performances of this new neutronbeam monitoring device. They were studied during a test experiment done atthe GENEPI neutron source of the PEREN installation, in France.Comparisons with simulations will also be presented

Breakup reaction studies of 10Be and 10,11B using a 10Be beam

The structure of 10Be has been investigated by inelastic scattering to states above the breakup threshold using the reaction 12C(10Be,10Be* → 6He+4/He)12C at Ebeam=302 MeV. Excited states in 10Be were observed at 9.6±0.1 and 10.2±0.1 MeV. No evidence was observed for the population of the 4 + member of the ground-state band of 10Be indicating the shell-model-like structure of the ground state. In addition, the decay of 8Be, 10B, and 11B, populated in the two-neutron, proton pickup, breakup and 1p pickup reactions, was reconstructed through the detection of coincident 4He+4He, 4He+6Li, and 4He+7Li particles. Cross sections for the formation of the 8Be, 9Be, 10B, and 11B were also deduced. Contrary to expectations, the two-neutron removal results in the production of 8Be predominantly (80%) in the first excited (2+) state. This suggests that dynamical excitations play an important role in the neutron removal process.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Neutron flux measurements in the TRADE experiment : Critical configuration

The TRiga Accelerator Driven Experiment (TRADE) to be performed in the existing TRIGA reactor of the ENEA Casaccia centre had the objective of coupling a spallation target, a proton accelerator and a sub-critical reactor core. On the way of the transmutation of minor actinides in dedicated facilities, the TRADE experiment represents the intermediate step between the validation of each component of an Accelerator Driven System (ADS), i.e. the spallation target, the high intensity accelerator and the sub-critical core, and the final facility aiming to incinerate radioactive nuclear waste. Measurements have been performed in the TRIGA - RC1 reactor of the ENEA Casaccia centre in the second semester of 2004 to characterize the neutron flux in a critical configuration. Gold and Indium samples were introduced in the core with the help of a "fast rabbit" pneumatic device. Bare samples and samples covered with Cadmium foils were successively irradiated to estimate the thermal and epithermal fluxes. Measurements have been carried out along a traverse of the core. Samples were put inside Aluminium shuttles travelling in stainless steel tubes. Trains composed of five shuttles allowed for simultaneous measurements in five different axial positions. γ spectrometry of the radioactive nuclides has been performed with two HPGe detectors

Breakup reaction studies of 10Be and 10,11B using a 10Be beam

The structure of 10Be has been investigated by inelastic scattering to states above the breakup threshold using the reaction 12C(10Be,10Be* → 6He+4/He)12C at Ebeam=302 MeV. Excited states in 10Be were observed at 9.6±0.1 and 10.2±0.1 MeV. No evidence was observed for the population of the 4 + member of the ground-state band of 10Be indicating the shell-model-like structure of the ground state. In addition, the decay of 8Be, 10B, and 11B, populated in the two-neutron, proton pickup, breakup and 1p pickup reactions, was reconstructed through the detection of coincident 4He+4He, 4He+6Li, and 4He+7Li particles. Cross sections for the formation of the 8Be, 9Be, 10B, and 11B were also deduced. Contrary to expectations, the two-neutron removal results in the production of 8Be predominantly (80%) in the first excited (2+) state. This suggests that dynamical excitations play an important role in the neutron removal process.SCOPUS: ar.jinfo:eu-repo/semantics/publishe