Physics and programmes
- Study of nuclear matter in its extreme states / exotic nuclei
- Physics for nuclear energy / nuclear data and modelling
Goals of the experiment
Study of the structure of nuclei and of the reaction mechanisms by complete reconstruction of the kinematics with stable as well as radioactive beams.
The R3B experiment will be built within the future FAIR project (Facility for Antiproton and Ion Research, http://www.gsi.de/fair) to be built at GSI (Darmstadt, Germany). The FAIR project gathers different physics around a common facility: exotic nuclei at low and high energy, hadronic physics with proton – antiproton collisions, relativistic heavy-ion collisions (a few 10 GeV per nucleon), plasma physics and atomic physics.
The international collaboration R3B (Reaction studies with Relativistic Radioactive Beams, http://www-land.gsi.de/r3b) has built a scientific programme of experiments devoted to the physics of stable and radioactive beams at energies between 150 MeV and 1.5 GeV per nucleon: nuclear structure, reaction mechanisms, study of the fission of radioactive isotopes, reaction cross-sections of interest for astrophysics, etc. The production of the radioactive beams is done using the in-flight fragmentation: A primary stable beam reacts impinges on a production target and the projectile fragments are selected in mass and charge with a high-resolution magnetic spectrometer and focussed afterwards in order to form a secondary beam of well identified radioactive isotopes.
Among the nuclear physics facilities in Europe and around the world capable of producing exotic beams, GSI (Gesellschaft für SchwerIonenforschung) in Darmstadt, Germany, is at the moment the only accelerator where experiments using stable or radioactive beams at 1 GeV per nucleon can be performed. The use of such an energy domain is important in order to limit the influence of reaction mechanisms on the observables where nuclear-structure information and the reaction mechanisms are mixed. Indeed, the physics R3B will take fully advantage of the experience acquired by the scientific teams already working at GSI.
During the last ten or fifteen years, the reactions of secondary beams of rather high energy on fixed targets have developed their potential as exploratory tools to study the properties of atomic nuclei far from stability. These reactions have permitted, for example, the extraction of detailed spectroscopic data weakly influenced by reaction mechanisms, or to improve our understanding of the nuclear interaction through the study of the nuclear structure far from stability. The energy (around 1 GeV per nucleon) necessary for these reactions as well as the high intensity of the secondary beams which will be available at the future FAIR/R3B facility create the necessity to build new experimental apparatus with improved performances: a central dipole magnet placed behind the reaction target providing a higher bending power and a larger angular aperture, faster detectors providing higher resolutions in the reconstruction of the kinematics at the reaction points.
The spallation group of the Service de Physique Nucléaire (SPhN) is following two scientific goals within the R3B collaboration:
- The study of spallation of heavy nuclei (208Pb, 238U) in inverse kinematics and in coincidence
- The study of the fission of radioactive actinides after their Coulomb excitation in a heavy element target
The R3B hall at FAIR will be the only installation in the world where these experiments will be efficiently feasible.
- Other similar installations
- RIKEN (Japan): exotic beams. This facility is producing radioactive beams already and is in a phase where the experimental equipments are being tested and calibrated. However, the maximum beam energy will be around 350 MeV per nucleon.
- RIA (Radioactive Ion Accelerator): This project is presently under discussion and conceptual design in the United States of America, with maximum beam energies around 500 MeV per nucleon.
The FAIR and R3B projects are in a rather busy international scientific environment. There are two projects of accelerators and facilities which will provide radioactive beams and which are under construction or foreseen in Europe: FAIR and SPIRAL 2. Others are already working but essentially at much lower beam intensities. With respect to SPIRAL-2, it seems rather more appropriate to talk of FAIR more as complementary than as a competitor. In fact, the production mechanisms are very different from one another, with different energy ranges. This means that the available beams in both facilities are rather different. Therefore, the experiments performed in SPIRAL-2 will be different from those to be done at FAIR. In particular, SPIRAL-2 will be specialized in providing beams of fission fragments of 238U.
GSI laboratory, Darmstadt, Germany. The R3B experimental area will be placed, within the FAIR facility, downstream of the Super-FRS fragment separator (Superconducting FRagment Separator) which will provide the secondary beams and identify them. The first experiments are foreseen in 2011 and 2012.
o Within the R3B collaboration, the DAPNIA is working on the construction of the R3B-GLAD magnet and on the study of a multi-track detector to be installed behind GLAD.
o The DAPNIA is totally in charge of these two activities.
- Size of the experiment
o The R3B collaboration gathers around 150 physicists from approximately 50 institutions around the world
o The spokesperson of the collaboration is Tom Aumann (GSI, Germany) and the deputy is Bjorn Jonsson (Chalmers University, Sweden)
- Divisions of the DAPNIA involved in R3B:
o SIS & SEDI for the TPC, SIS & SACM for the dipole magnet. SPhN is involved in both projects.
Scientific leader: Jean-Eric DUCRET