Michihiro Oyaizu

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.

Grating monochromator for electron cyclotron resonance ion source operation

Recently, we started to observe optical line spectra from an ECR plasma using a grating monochromator with a photomultiplier. The light intensity of line spectrum from the ECR plasma had a strong correlation with ion beam intensity measured by a magnetic mass analyzer. This correlation is a significant information for beam tuning because it allows the extraction of the desired ion species from the ECR plasma. Separation of ion species of the same charge to mass ratio with an electromagnetic mass analyzer is known to be an exceptionally complex process, but this research gives new insights into its simplification. In this paper, the grating monochromator method for beam tuning of a Hyper-ECR ion source as an injector for RIKEN azimuthal varying field (AVF) cyclotron is described.

Plasma spectroscopy of metal ions for hyper-electron cyclotron resonance ion sourcea)

In this research, the optical line spectra of metal ions from ECR plasma were observed using a grating monochromator with a photomultiplier. The light intensity of line spectrum from the ECR plasma had a strong correlation with ion beam intensity measured by a magnetic mass analyzer. This correlation is a significant information for the beam tuning process, because it allows to conduct the extraction of the desired metal ion species from the ECR plasma. Separation of ion species of the same charge to mass ratio with an electromagnetic mass analyzer is known to be an exceptionally complex process, but this research provides a new approach for its simplification. In this paper the grating monochromator method for metal ion beam tuning such as (40)Ca(12+), (56)Fe(15+), and (85)Rb(20+) of hyper-ECR ion source as an injector for RIKEN Azimuthal Varying Field cyclotron is described.

Fabrication of Boron-Mixed Carbon Stripper and Target Backing Foils for High-Power Accelerators

We have succeeded, for the first time, in making long-lifetime boron-mixed carbon stripper foils for high-power accelerators. Foils of 10–1000 µg/cm2 thickness were made by controlled DC arc discharge. The lifetime of the foils was tested using 3.2 MeV Ne+ DC beams of 2.5 µA, by which a significant amount of energy was deposited in the foils. The maximum lifetime was found to be extremely long, 110 and 450 times longer than those of diamond and commercially available carbon foils, respectively. The foils turned out to be free from any shrinkage, and showed an extremely low thickness reduction rate, even at a high temperature of 1800 K.

Note: An innovative method for 12C4+ suppression in 18O6+ beam production in an electron cyclotron resonance ion source

It is a major and complex task to accelerate an ion which has the same charge to mass ratio with strong contaminant ions, such as 12C4+ in the 18O6+ beam. An innovative method has been developed to suppress the contaminant ions in the Electron Cyclotron Resonance (ECR) ion source by introducing Li vapor. The ion distribution inside the ECR zone was obtained by the optical analysis of ions inside the ECR ion source. The 12C4+ ions were suppressed as much as by a factor of 10, whereas the 18O6+ beam changed little with the use of this technique.

Note: 6Li III light intensity observation for 6Li3+ ion beam operation at Hyper-Electron Cyclotron Resonance ion source

The light intensity of (6)Li III line spectrum at λ = 516.7 nm was observed during (6)Li(3+) beam tuning at the Hyper-Electron Cyclotron Resonance (ECR) ion source. Separation of ion species of the same charge to mass ratio with an electromagnetic mass analyzer is known to be an exceptionally complex process. However, (6)Li III line intensity observation conducted in this study gives new insights into its simplification of this process. The light intensity of (6)Li III line spectrum from the ECR plasma was found to have a strong correlation with the extracted (6)Li(3+) beam intensity from the RIKEN Azimuthal Varying Field cyclotron.

Note: {sup 6}Li III light intensity observation for {sup 6}Li{sup 3+} ion beam operation at Hyper-Electron Cyclotron Resonance ion source

The light intensity of (6)Li III line spectrum at λ = 516.7 nm was observed during (6)Li(3+) beam tuning at the Hyper-Electron Cyclotron Resonance (ECR) ion source. Separation of ion species of the same charge to mass ratio with an electromagnetic mass analyzer is known to be an exceptionally complex process. However, (6)Li III line intensity observation conducted in this study gives new insights into its simplification of this process. The light intensity of (6)Li III line spectrum from the ECR plasma was found to have a strong correlation with the extracted (6)Li(3+) beam intensity from the RIKEN Azimuthal Varying Field cyclotron.

6Li III light intensity observation for 6Li3+ ion beam operation at Hyper-Electron Cyclotron Resonance ion source

The light intensity of (6)Li III line spectrum at λ = 516.7 nm was observed during (6)Li(3+) beam tuning at the Hyper-Electron Cyclotron Resonance (ECR) ion source. Separation of ion species of the same charge to mass ratio with an electromagnetic mass analyzer is known to be an exceptionally complex process. However, (6)Li III line intensity observation conducted in this study gives new insights into its simplification of this process. The light intensity of (6)Li III line spectrum from the ECR plasma was found to have a strong correlation with the extracted (6)Li(3+) beam intensity from the RIKEN Azimuthal Varying Field cyclotron.

Development of long-lived thick carbon stripper foils for high energy heavy ion accelerators by a heavy ion beam sputtering method

In the past decade, we have developed extremely long-lived carbon stripper foils of 1-50 μg/cm2 thickness prepared by a heavy ion beam sputtering method. These foils were mainly used for low energy heavy ion beams. Recently, high energy negative Hydrogen and heavy ion accelerators have started to use carbon stripper foils of over 100 μg/cm2 in thickness. However, the heavy ion beam sputtering method was unsuccessful in production of foils thicker than about 50 μg/cm2 because of the collapse of carbon particle build-up from substrates during the sputtering process. The reproduction probability of the foils was less than 25%, and most of them had surface defects. However, these defects were successfully eliminated by introducing higher beam energies of sputtering ions and a substrate heater during the sputtering process. In this report we describe a highly reproducible method for making thick carbon stripper foils by a heavy ion beam sputtering with a Krypton ion beam.

An Experimental Plan to Study Beta‐decay Properties on N = 126 Waiting‐Point Nuclei in the r‐process

The {beta}-decay properties of the neutron-rich isotopes with neutron number N = 126, out of reach by any reaction well established so far, are very interesting from the astrophysical point of view. We will propose {beta}-decay lifetime measurements with a new isotope separation system, which is supposed to separate a single species of the radioactive nuclei among target-like fragments produced via multi-nucleon transfer reactions in binary heavy ion collisions, by using a gas catcher cell combined with laser resonance ionization technique. The present proposal aims to measure {beta}-decay properties of several nuclei around A{approx}200 with N = 126 and nearby nuclei by using a stable {sup 136}Xe beam on a {sup 198}Pt target.