A radioactive beam facility based on projectile fragmentation, RIPS, has been constructed at RIKEN to enable radioactive-beam experiments. The facility is characterized by the production of high-intensity beams and spin-polarized beams. Since the beginning of 1990, experiments on exotic nuclei have been extensively performed exploiting these useful features. The characteristics and the present status of the RIPS are described.

The RIKEN radioactive beam facility

Presented are features of the in-flight radioactive isotope (RI) beam separators in Japan as well as of a next-generation separator BigRIPS being built at RIKEN for the RI-beam factory project. Characteristic features and present status of the existing separators are reviewed for the RIPS at RIKEN, the Secondary Beam Line at RCNP, the Secondary Beam Course at NIRS, the CRIB at CNS and the RMS at JAERI. Design features are outlined for the BigRIPS, which is characterized by two major features: large acceptances and a tandem (or two-stage) separator scheme. The large acceptances allow one to produce RI beams efficiently by using in-flight fission of uranium ions, being achieved by using superconducting quadrupoles with a large aperture. The tandem separator scheme allows one to deliver tagged RI beam. The integrated capability of the BigRIPS and the accelerators of the project can significantly enlarge the scope of future RI-beam experiments. A low-energy course following the BigRIPS can provide energy-degraded and -bunched RI beams to be applied for a gas catcher system with an RF ion guide, aiming at realizing a projectile fragmentation based ISOL system.

In-flight RI beam separator BigRIPS at RIKEN and elsewhere in Japan

The BigRIPS in-flight separator, which became operational in March 2007 at the RI Beam
Factory (RIBF) at RIKEN Nishina Center, has been used to produce a variety of rare-isotope
(RI) beams by using in-flight fission as well as projectile fragmentation. Its major features are
large ion-optical acceptances and two-stage structure. Excellent performance in particle identification
is also an important feature. Efficient RI-beam production based on the in-flight scheme
has been made possible by these features of the BigRIPS separator, allowing us to greatly expand
the accessible region of exotic nuclei. An RI-beam delivery line following the BigRIPS separator
is designed to work as a forward spectrometer, called ZeroDegree. As a major experimental
device at RIBF, the ZeroDegree spectrometer has been used for a variety of reaction studies with
RI beams. In this paper, we present an overview of the BigRIPS separator and the ZeroDegree
spectrometer, emphasizing the capability and potential of the new-generation RI beam facility,
RIBF.

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BigRIPS separator and ZeroDegree spectrometer at RIKEN RI Beam Factory

The achromatic spectrometer LISE installed at GANIL is used for the production and identification of either very neutron- or proton-rich nuclei obtained in the fragmentation of intermediate-energy heavy-ion beams at 0°. The characteristics and advantages of the system are described.

The achromatic spectrometer LISE at GANIL

Energy levels of light nuclei A = 12

The isotopic separation of intermediate-energy (30 to 100 MeV per nucleon) heavy-ion projectile fragments is theoretically and experimentally investigated. Physical separation of nuclides is achieved through magnetic analysis (AZ sensitivity) and differential stopping-power effects (Z−2 sensitivity). Depending on the specific case, a complete mass and charge separation may be achieved or a few nuclides may be selected simultaneously. The projectile fragments isotopic separation method described allows us to obtain an experimental mass separation AΔA ≈ 100. Simple formulae are given to determine the optimum factors for the best separation and transmission of the device. First applications to the spectroscopy of exotic nuclei lead to the new observation of the beta decay of 37P at GANIL and 15B at CERN.

Projectile fragments isotopic separation: Application to the lise spectrometer at GANIL

The new beta-delayed neutron emitter15B has been observed. The measured half-life is 11 ms ±1 ms and limits have been set on other decay channels: P0n<5%, P2n<1.5%. The beta emitter12Be has been separated, unambiguously identified, and its half-life has been measured to be 24±1 ms.

Beta-delayed neutron radioactivity of 15 B

The possibility of producing radioactive secondary beams through interactions of 84 A· MeV 18 O ions with thick aluminum targets (400–1500 mg cm 2 ) has been investigated at the CERN synchrocyclotron. The projectile fragments emitted at 0° have been analyzed by the beam line dipoles and transported over more than 20 m into the experimental area. Conversion ratios (intensity of the secondary beam divided by the intensity of the primary one) have been found equal to 5 × 10 −5 for 17 N and 7 × 10 −6 for 16 C.

Production of 17N and 16C secondary beams via projectile nuclear fragmentation

Target residue cross sections and recoil energies from the reaction of 1760 MeV 40Ar with medium and heavy targets

Radioactive studies of light neutron rich exotic nuclei from C to 40 S have been performed on the LISE line at GANIL. These isotopes were produced via projectile fragmentation of 60 MeV/nucleon Ar on Be. The adjunction of an energy degrader with appropriate shape is shown to allow the use of the LISE spectrometer for a projectile fragment isotopic separation. At least 9 nuclei were observed for the first time through g-y coincidence measurements. The predictive power of different models for 6 decay properties is examined.

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C. Poinot

Papers

Projectile fragments isotopic separation: Application to the lise spectrometer at GANIL

Beta-delayed neutron radioactivity of 15 B

Production of 17N and 16C secondary beams via projectile nuclear fragmentation

Target residue cross sections and recoil energies from the reaction of 1760 MeV 40Ar with medium and heavy targets

Studies of new radioactive nuclei at ganil energies