A. Takamine

Space-charge effects in the catcher gas cell of a rf ion guide

Slow radioactive ion beams have been produced with an overall efficiency of 4% by thermalizing energetic ions produced by a projectile fragment separator in a He-gas cell and guiding them to a vacuum vessel by dc and rf fields. Space charge was observed to have a limiting effect. Since the ionization of He atoms by energetic ions creates a region of high space charge, many thermalized ions of interest are pushed toward the walls of the gas cell. Such losses have been investigated for different incoming ion intensities.

Restoration of RI‐beams from a projectile fragment separator by Laser Ionization gas Catcher‐PALIS‐

A fragment separator at heavy ion accelerator facilities is a versatile instrument to provide wide variety of radioactive isotope (RI) beams. However, more than 99.99% of precious RI‐ions are simply dumped in the slits or elsewhere in the fragment separator. A novel concept to restore such RI‐ions for parasitic slow RI‐beams is proposed. Installation of a laser ionization gas catcher in the vicinity of the first or second focal point of the fragment separator enables to collect dead isotopes in the slits. The design concept and expected performance are discussed.

Universal Slow RI-Beam Facility at RIKEN RIBF for Laser Spectroscopy of Short-Lived Nuclei

A universal slow RI‐beam facility (SLOWRI) for precision atomic spectroscopy is being built at the RIKEN RI‐beam factory. The facility will provide a wide variety of low‐energy nuclear ions of all elements produced by projectile fragmentation of high‐energy heavy‐ion beams and thermalized by an RF‐carpet ion guide. At prototype SLOWRI, radioactive Be isotope ions produced at 1 GeV were decelerated and cooled in an ion trap down to 1u2009μeV by employing laser cooling. The ground state hyperfine structures of 7Be+ and 11Be+ were measured accurately by laser microwave double resonance spectroscopy. Measurements of the S1/2→P1/2, P3/2 transition frequencies of 7,9,10,11Be+ ions are also in progress aiming at the study of the nuclear charge radii. Other possible experiment at SLOWRI, such as mass spectroscopy, are also discussed.

Precision hyperfine structure spectroscopy of Be isotopes at SLOWRI prototype and prospects of SLOWRI at RIKEN

Precision atomic spectroscopy experiments for Be isotopes have been carried out at the prototype universal slow RI‐beam (SLOWRI) setup at RIKEN. Radioactive Be ions produced at 1 GeV were decelerated and thermlized in an RF‐carpet ion guide. The thermalized ions were transferred to an ion trap where laser cooling was used to reduce the ion energy to the order of 1u2009μeV. Laser microwave double resonance spectroscopy was performed for the hyperfine structure measurements of trapped and laser cooled 7Be+ and 11Be+ ions. Measurements of the S1/2→P1/2,P3/2 transition frequencies of 7,9,10,11Be+ ions are also in progress. These results are briefly discussed. Future prospects for expanding the capability of SLOWRI is also discussed.

Precision Fast Ion Beam Laser Spectroscopy of Ar

Absolute measurements of spectral lines of Ar+ ions using collinear and anticollinear geometries were performed. To provide a precise reference for the laser wavelength, iodine saturation spectroscopy was applied. The precision of this reference is effected by observing the beat node between the spectroscopy laser and the corresponding mode of a femtosecond laser frequency comb. Laser‐induced fluorescence allowed to perform precision frequency measurements of an Ar+ transition in collinear and anticollinear geometries simultaneously; then an exact relativistic formula for the absolute transition frequency V0u2009=u2009VcVa was used. In this geometry the influence of ion source instabilities due to pressure and anode voltage fluctuations was minimized. The result is v0u2009=u2009485,573,619.7(3)u2009MHz, which corresponds to Δv/vu2009=u20096*10−10. This represents an improvement of two orders of magnitude over the previous NIST published value.

A universal slow RI-beam facility at RIKEN RIBF

A next‐generation slow radioactive nuclear ion beam facility (SLOWRI) which provides slow, high‐purity and small emittance ion beams of all elements has been proposed as one of the pricipal experimental facilities at the RIKEN RI‐beam factory (RIBF). High energy radioactive ion beams from the projectile fragment separator BigRIPS are thermalized in a large gas catcher cell. The thermal ions in the gas cell are guided and extracted to vacuum by a combination of DC electric fields and inhomogeneous rf fields in the cell (rf ion guide). In the R&D works at the present RIKEN facility, an overall efficiency of ≈ 5% for ≈ 100A MeV 8Li ion beam from the present projectile fragment separator RIPS was achieved and the dependence of the efficiency on the beam intensity was investigated. A first spectroscopy experiment at the prototype SLOWI was performed on Be isotopes.