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

Relativistic radioactive beams: A new access to nuclear-fission studies

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

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ON THE z3 CORRECTIONS TO ENERGY LOSS AND RANGE

The application of the slowing-down process of relativistic heavy ions in a layer of matter in ion-optical devices is theoretically investigated. The modifications of the phase space of the ion beam due to the dissipative forces and the straggling phenomena are discussed. Methods are developed to study the properties of the momentum-loss achromat, an isotope separator consisting of an achromatic magnetic system with an energy degrader located in the intermediate dispersive focal plane. This device separates projectile fragments with respect to A and Z up to uranium over a wide energy range with an efficiency of the order of 50% and with separation times of several hundred nanoseconds.

K.-H. Schmidt

Papers

The momentum-loss achromat — A new method for the isotopical separation of relativistic heavy ions☆