A. Drouart

No enhancement of fusion probability by the neutron halo of 6He

Quantum tunnelling through a potential barrier (such as occurs in nuclear fusion) is very sensitive to the detailed structure of the system and its intrinsic degrees of freedom. A strong increase of the fusion probability has been observed for heavy deformed nuclei. In light exotic nuclei such as 6He, 11Li and 11Be (termed ‘halo’ nuclei), the neutron matter extends much further than the usual nuclear interaction scale. However, understanding the effect of the neutron halo on fusion has been controversial—it could induce a large enhancement of fusion, but alternatively the weak binding energy of the nuclei could inhibit the process. Other reaction channels known as direct processes (usually negligible for ordinary nuclei) are also important: for example, a fragment of the halo nucleus could transfer to the target nucleus through a diminished potential barrier. Here we study the reactions of the halo nucleus 6He with a 238U target, at energies near the fusion barrier. Most of these reactions lead to fission of the system, which we use as an experimental signature to identify the contribution of the fusion and transfer channels to the total cross-section. At energies below the fusion barrier, we find no evidence for a substantial enhancement of fusion. Rather, the (large) fission yield is due to a two-neutron transfer reaction, with other direct processes possibly also involved.

S3: The Super Separator Spectrometer for SPIRAL2 stable beams

S3 (Super Separator Spectrometer) is a device designed for experiments with the very high intensity stable beams of LINAG, the superconducting linear accelerator of GANIL, which will be built in the framework of SPIRAL2. These beams, which will provide ions with A/Q = 3 in SPIRAL2 phase one, can reach intensities up to 1mA for light ions, A<50. These unprecedented intensities open new opportunities in several physics domains, e.g. super‐heavy and very‐heavy nuclei, spectroscopy at and beyond the drip line, isomers and ground state properties, multi‐nucleon transfer and deep‐inelastic reactions. An international collaboration has been formed to propose physics experiments and develop technical solutions for this new instrument.

SUPER SEPARATOR SPECTROMETER FOR THE LINAG HEAVY ION BEAMS

The Super Separator Spectrometer (S3) will receive the very high intensity heavy ion beams from the LINAG accelerator of SPIRAL2. Its privileged fields of physics are the delayed study of rare nuclei and secondary reactions with exotic nuclei. The project is presently in a phase of conceptual design. It includes a rotating target to sustain the high energy deposit, a two stages separator (momentum achromat) and spectrometer (mass spectrometer). Various detection set-ups are foreseen, especially a delayed α, γ, and electron spectroscopy array and a gas catcher coupled to a low energy branch. We present here the current status of the project and its main features.

Production of superheavy elements at GANIL

A long-term new experimental program has begun at GANIL, i.e. search for new super heavy nuclei and their structure. The first part consists in studying the structure of the 273110 isotope which involves the development of high intensity Se beam. In parallel, reactions involving Inverse Kinematics will be studied allowing to have a versatileness set-up. By adding germanium and electron detectors, spectroscopic studies could be made on trans-fermium elements. Preliminary results showed that the Wien Filter has a suppression of the incident beam with a 1010 factor, which is comparable with results elsewhere. We show recent results with the present set-up at GANIL in producing Fr isotopes in the Kr+Sb reaction. We present also the result of our Kr+Pb experiment, which tried to reproduce the Berkeley result of the element 118.

A review on SHE research at GANIL

This report summarizes the experiments relative to Super‐Heavy Element studies done at GANIL — CEA — CNRS since 1999. It also gives an overview of future experiments and opportunities offered by SPIRAL 2 and LINAG beams in a medium term..

Structure of light exotic nuclei 6,8He and 10,11C from (p,p′) reactions

Abstract The structure of the light unstable nuclei 10,11 C and 6,8 He is investigated by means of (p,p′) reactions. The experiments were performed at GANIL using the MUST detector, an array of Si and SiLi telescopes. The (p,p′) are analyzed within the framework of the microscopic JLM potential, allowing to test the densities predicted by structure models. Preliminary data from the 8 He(p,o′) reaction performed at the SPIRAL facility at 15.6 MeV/nucleon are discussed.

S3: the Super Separator Spectrometer for LINAG

S3 (Super Separator Spectrometer) is a device proposed for experiments with the very high intensity stable beams of LINAG, the superconducting linear accelerator of GANIL, which will be built in the framework of SPIRAL2. These beams, which will provide in a first phase of SPIRAL2 ions with A/q = 3, can reach intensities exceeding 100pμA for lighter ions (A < 40 – 50) depending on the final choice of the ECR (Electron Cyclotron Resonance) ion source. These unprecedented intensities open new opportunities in several physics domains, e.g. super‐heavy and very‐heavy nuclei, spectroscopy at and beyond the dripline, muld‐nucleon transfer and deep‐inelastic reactions, isomers and ground state properties and nuclear molecular resonances. An international collaboration interested in the aforementioned physics has been formed for developing technical solutions for this new instrument.

Elements discrimination in the study of super-heavy elements using an ionization chamber

Abstract Dedicated ionization chamber (IC) was built and installed to measure the energy loss of very heavy nuclei at 2.7 MeV / u produced in fusion reactions in inverse kinematics (beam of 208 Pb ). After going through the IC, products of reactions on 12 C , 18 O targets are implanted in a Si detector. Their identification through their α-decay chain is ambiguous when their half-life is short. After calibration with Pb and Th nuclei, the IC signal allowed us to resolve these ambiguities. In the search for rare super-heavy nuclei produced in fusion reactions in inverse or symmetric kinematics, such a chamber will provide direct information on the nuclear charge of each implanted nucleus.

SIRIUS project (spectroscopy & identification of rare isotopes using S3)

SIRIUS is a state-of-the-art detector system for nuclear decay spectroscopy that will be mounted at the focal plane of S3 (Super Separator Spectrometer), which is part of the new SPIRAL2 facility at GANIL, Caen in France. Such a system requires high performance as it is dedicated to the study of very exotic nuclei. It is the result of collaboration between GANIL CSNSM, IRFU, and IPHC It is composed of a succession of detectors (Trackers, Silicon detector DSSD and Tunnel plus an array of five clover Germanium detectors). This set-up is mounted in a compact geometry. The energy measurement varies from 50 keV to over 500 MeV with high precision (2 × 10−3) at low energies and 1 % for the detection of heavy ions. A major challenge has been the development of new electronics with a very large dynamic range maintaining an adequate energy resolution for the measured particles (with energies from a few hundred keV up to 500 MeV).

Development of a Tracking System of Exotic Nuclear Beams for FAIR

New accelerators like SPIRAL2 (GANIL, France) or FAIR (GSI, Germany) will be soon constructed, and they will be able to produce radioactive ion beams (RIB) with high intensities of current (⩾106 pps). These beams, at low energy, lower than 20 MeV/n, usually have high emittance, which imposes the use of tracking detectors before the target in order to reconstruct the trajectory of the ions. The group of Nuclear Physics at CNA (Centro Nacional de Aceleradores), is in charge of developing a tracking system for the low energy branch of FAIR (the HISPEC/DESPEC project). A collaboration with CEA‐SACLAY was established, with the aim of developing, building and testing low pressure Secondary electron Detectors (SeD). Within this proposal we have projected and constructed a new Nuclear Physics Line in the CNA in order to be able to receive any kind of detector tests and the associated nuclear instruments.