I. Katayama

Magnetic spectrometer Grand Raiden

Abstract A high-resolution magnetic spectrometer called “Grand Raiden” is operated at the RCNP ring cyclotron facility in Osaka for nuclear physics studies at intermediate energies. This magnetic spectrometer has excellent ion-optical properties. In the design of the spectrometer, the second-order dispersion matching condition has been taken into account, and almost all the aberration terms such as (x|θ 3 ), (x|θφ 2 ), (x|θ 2 δ) and (x|θδ2) in a third-order matrix calculation are optimized. A large magnetic rigidity of the spectrometer ( K = 1400 xa0MeV) gives a great advantage to measure the charge-exchange (3He, t) reactions at 450xa0MeV. The ability of the high-resolution measurement has been demonstrated. Various coincidence measurements are performed to study the nuclear structures of highly excited states through decay properties of nuclear levels following nuclear reactions at intermediate energies.

A new cooling and focusing device for ion guide

Abstract A highly efficient focusing device which uses a RF multipole field (sextupole-ion-beam guide (SPIG)) has been developed for the ion guide isotope separator on-line (IGISOL). The SPIG, placed after the nozzle, consists of six circular rods uniformly distributed on a circle in the plane perpendicular to the axis of symmetry. Under the combined action of the sextupole RF electric field produced by the rods and helium gas flow, well focused ion beams with low energy spread can be transmitted efficiently by use of the SPIG. The experimental results, using a discharge ion source, show that almost nearly 90% of the ions which leave the nozzle can be transported through the SPIG, and that the width of the kinetic energy distribution after the SPIG is about 0.8 eV (FWHM). These experimental results agree with the results of Monte Carlo simulations; the simulation studies also indicate that the size of the spatial distribution in the plane perpendicular to the symmetry axis is less than 1 mm in diameter at the end of the SPIG.

Accumulation of ions from a recoil mass separator in a new type of linear ion trap

Abstract A new type of linear ion trap system in combination with a sextupole ion beam guide (SPIG) has been developed for the accumulation of a continuous ion beam. An axial trapping potential is generated by three cylindrical electrodes mounted outside, but concentric to, the SPIG. The ions in a continuous beam are trapped in the potential well via collisions with He gas. This linear ion trap is called the “SPIG-trap”. The properties of the SPIG-trap were tested off-line with a discharge ion source in a gas cell. Up to 106 ions were trapped and extracted as a bunch with an efficiency of 10% for 10 ms of accumulation. The SPIG-trap system was then connected to a gas filled recoil mass separator (GARIS) and tested with an energetic primary beam from a cyclotron (16O, 107 MeV). The overall efficiency of the SPIG-trap including ion losses in an energy degrader, which was placed in front of the He cell, was measured to be of the order of 10−5 for 10 ms accumulation.

Charge state dependent energy loss of high velocity carbon ions in the charge state non-equilibrium region

Abstract Energy losses of high velocity bare H-like and He-like carbon ions passing through thin carbon foils were measured in the charge state non-equilibrium region. The mean energy losses for each charge state increased proportionally to the foil thickness and a clear charge state dependence was observed.

Charge state dependent energy loss of high velocity oxygen ions in the charge state non-equilibrium region

Mean energy losses of high velocity bare H-like, He-like and Li-like O ions in thin carbon foils were measured in the charge state non-equilibrium region and a clear charge state dependence was observed. The screening effect of bound projectile electrons on energy losses are deduced and compared with theoretical predictions.

Energy loss of high velocity 6Li2+ ions in carbon foils in charge state non-equilibrium region

Abstract Mean energy losses of high velocity H-like Li ions in thin carbon foils were measured in the charge state non-equilibrium region. Owing to the screening effect of the bound electron, the fixed-charge stopping power for 6 Li 2+ was smaller than that for 6 Li 3+ . The projectile atomic number dependence of the fixed-charge stopping powers for H-like ions is discussed including our previous data of He, C and O ions with the same velocity. The present result is also compared with the theoretical prediction.

Simulation Study on the Measurements of Diffusion Coefficients in Solid Materials by Short-lived Radiotracer Beams

We have examined, by a computer simulation, an on-line measurement of diffusion coefficients by using a short-lived alpha particle emitter, 8Li (half life of 0.84 s), as a radiotracer. The energy spectra of alpha particles emitted from diffusing 8Li primarily implanted in the sample of LiAl are simulated as a measure of the diffusion of 8Li in the sample. As a possible time sequence for the measurement, a time cycle of 6 s, i.e. the implantation of 8Li for 1.5 s and subsequent diffusion for 4.5 s, is supposed. The sample is primarily set on a given temperature for the measurement. The time-dependent yields of alpha particles during the time cycle reveal the possibility to measure the diffusion coefficient with an accuracy of 10% if larger than 1×10-9 cm2/s, by the comparison with the experimental spectra measured at the temperature, i.e. at a certain diffusion coefficient.

High resolution study of24Mg(p, d)23Mg for the Ne-E problem

Nuclear levels of23Mg near and above the proton threshold were investigated with high resolution. A new level has been identified at 7.643 MeV (66 keV above the proton threshold) with a possible Jπ=(3/2, 5/2)+. Some other spin-parity and excitation-energy assignments are also made. These results enable the reaction rate estimate of22Na(p,γ)23Mg with much smaller uncertainties, which is critical for the Ne-E problem in nuclear astrophysics.

NUCLEAR LASER SPECTROSCOPY WITH ON-LINE ION TRAPS

The hyperfine structure of atoms informs us various static characteristics of nuclei, particularly for electro-magnetic moments and their distributions. We have been developing an experimental method to perform laser-microwave double-resonance spectroscopy for the hyperfine structure of Be and Ca isotopes, including unstable nuclei. The purpose and the status of the experiments are described.

Charge state dependent energy loss of light ions

Abstract Energy loss measurements for individual charge states of high energy light ions are expected to give us an important clue to investigate some basic physics behind the stopping process, which we cannot obtain from total energy loss measurements. An overview of experimental works concerning the charge state dependent energy loss is presented.