Y. Ishida

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.

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.

Hyperfine structure and isotope shift measurements of long-lived La isotopes by collinear laser spectroscopy

The La isotopes (Z = 57) are in a region of rapid transition from nuclei with nearly spherical shape (the singly magic 139La) to nuclei that are soft towards deformation, presenting a good opportunity to test various nuclear models. There exist two naturally occurring La isotopes: the stable 139La and the long-lived 138La (T 1/2 = 1.05 × 1011 y). The natural abundance of 138La is very low (0.090%). So far, there is no measurement of the hyperfine structure (HFS) and the isotope shift (IS) of 138LaII. In order to extract changes in mean-square nuclear charge radii from IS data on LaII, a detailed knowledge of the ionic structure of La is essential. Therefore, for future measurements of short-lived isotopes, we have measured the HFS and IS of several transitions in 138,139LaII with collinear laser ion-beam spectroscopy. In addition to these naturally occurring nuclides, measurements for accelerator produced 137La (6 × 104 y) were also made.

Development of an RF Ion Guide for Trapping Energetic Radioactive Nuclear Ions

Although the projectile fragment separator (RIPS) at the RIKEN accelerator facility (RARF) provides wide variety of energetic radioactive beams, it is not adequate for low energy beam experiments such as precision spectroscopy of trapped ions. Aiming for an efficient deceleration and cooling of energetic radioactive ions, the development of an rf ion guide system which comprises a large He gas cell and an rf funnel structure in the cell is under progress. A proof of the principle (pop) machine has been successfully tested on-line for collection of 70-MeV/u 8Li ions. A compact gas cell of 70 cm in length and 10 cm in diameter with a He gas pressure of 30 Torr was placed after a variable wedge shaped energy degrader. The ions were stopped in the gas and were transported by a superposition of dc and rf electric field toward a small exit hole. The overall efficiency was 10−4 which can be separated into a gas stopping efficiency of 0.43% and an ion-guide efficiency of 2.4%. The former is limited by the volume ...

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.