Tetsu Sonoda

Slow RI-beams from projectile fragment separators

Abstract The projectile fragment separator provides a wide variety of short-lived RI-ions with less restrictions on their chemical property or lifetime limit. The beam energy and quality is, however, not adequate for low-energy beam experiments, in particular for trapping experiments. Recently, one has proposed to obtain a low-energy beam from an energetic RI-beam leaving a projectile fragment separator by using a large gas-catcher and an rf ion-guide system. In off-line and in on-line test experiments, the principle of the rf ion-guide was proven. An overall efficiency of 0.2% for 70 MeV/u 8 Li from the RIKEN projectile fragment separator (RIPS) was obtained so far.

Development of a resonant laser ionization gas cell for high-energy, short-lived nuclei

Abstract A new laser ion source configuration based on resonant photoionization in a gas cell has been developed at RIBF RIKEN. This system is intended for the future PArasitic RI-beam production by Laser Ion-Source (PALIS) project which will be installed at RIKEN’s fragment separator, BigRIPS. A novel implementation of differential pumping, in combination with a sextupole ion beam guide (SPIG), has been developed. A few small scroll pumps create a pressure difference from 1000xa0hPa–10−3xa0Pa within a geometry drastically miniaturized compared to conventional systems. This system can utilize a large exit hole for fast evacuation times, minimizing the decay loss for short-lived nuclei during extraction from a buffer gas cell, while sufficient gas cell pressure is maintained for stopping high energy RI-beams. In spite of the motion in a dense pressure gradient, the photo-ionized ions inside the gas cell are ejected with an assisting force gas jet and successfully transported to a high-vacuum region via SPIG followed by a quadrupole mass separator. Observed behaviors agree with the results of gas flow and Monte Carlo simulations.

An rf-carpet electrospray ion source to provide isobaric mass calibrants for trans-uranium elements

Abstract For trans-uranium elements, stable atomic isobars do not exist. In order to provide isobaric reference ions for the mass measurement of trans-uranium elements, an electrospray ion source (ESI) was combined with an rf-carpet to collect molecular ions efficiently. The rf-carpet allows for simplification of the pumping system to transport ions from the ESI to a precision mass analyzer. Molecular ions appropriate for isobaric references of trans-uranium elements were extracted from the rf-carpet and analyzed by a multi-reflection time-of-flight mass spectrograph (MRTOF-MS) with a resolving power of R m xa0≳xa0100, 000.

A novel ion cooling trap for multi-reflection time-of-flight mass spectrograph

Abstract A radiofrequency quadrupole ion trap system for use with a multi-reflection time-of-flight mass spectrograph (MRTOF) for short-lived nuclei has been developed. The trap system consists of two different parts, an asymmetric taper trap and a flat trap. The ions are cooled to a sufficient small bunch for precise mass measurement with MRTOF in only 2xa0ms cooling time in the flat trap, then orthogonally ejected to the MRTOF for mass analysis. A trapping efficiency of ≈ 27 % for 23Na+ and ≈ 5.1 % for 7Li+ has been achieved.

Ionization cross section measurements for autoionizing states of iridium and rhenium

New autoionizing states for neutral iridium and rhenium atoms were observed in the continuum structure near the first ionization limit by using a two-colour two-step laser resonance ionization technique. The saturation curves for the autoionizing states were measured, and the ionization cross sections were experimentally determined by solving the rate equations for the ground, intermediate, and autoionizing state populations. Efficient ionization schemes are expected to be useful for applications such as laser ion sources of unstable nuclei.

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.

High-Spin States in 93Nb

The high-spin states of 93 Nb are studied by the 82 Se( 16 O, p4n) 93 Nb reaction at a beam energy of 100 MeV. The in-beam γ-ray spectroscopic techniques are used. The γt-, γγt-coincidence, γ-ray a...

Performance of Ion Surfing Rf-carpets for High-Energy RI Beam Gas Catcher

High-energy radioactive isotopes have been used in ion trap-based precision experiments after being stopped in a large gas cell. The stopped ions of these isotopes can be extracted from the large gas cell as a low-energy ion beam. To transport and extract these ions quickly and efficiently, electric fields are required to guide them. In this respect, an rf-carpet (RFC) method utilizing a dc potential gradient is a standard technique. However, such a method is restricted to longer half-life isotopes because of the transport time owing to the upper limit on the dc gradient that can be supported before electric discharges occur in the large gas cell. To study short half-life isotopes, an RFC featuring faster transport is required. Recently, a hybrid technique wherein the dc gradient is replaced by a traveling potential wave was proposed, called ion surfing. Recently, we have demonstrated the transport and extraction of K ions using a circular RFC in 20 mbar of He gas pressure. However, in a practical gas cell, the gas pressure is higher by one order of magnitude. In this study, the transport and extraction of K and Cs ions with the ion surfing method were tested in high pressure He gas using a 100 mm cylinder electrode to create a push electric field Epush and a circular RFC of 80 mm diameter. In addition, we compared the effect of an RFC of a fine pitch with one of a rough pitch. The fine pitch RFC consists of 0.08 mm wide ring electrodes with 0.16 mm pitch and 0.32 mm diameter orifice, whereas the rough pitch RFC consists of 0.16 mm wide ring electrodes with 0.32 mm pitch and 0.64 mm diameter orifice.

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.