Y. Higurashi

Quadrupole deformation of 12Be studied by proton inelastic scattering

Abstract Inelastic proton scattering exciting the 2 + 1 states in the neutron-rich beryllium isotopes 10,12 Be has been studied in inverse kinematics. From a coupled-channel analysis, the deformation lengths for the 2 + 1 states in 10 Be and 12 Be were determined to be 1.80±0.25 fm and 2.00±0.23 fm respectively, indicating that a tendency towards strong quadrupole deformation is preserved for these nuclei and that the singly-closed shell structure does not prevail in 12 Be. A quantitative analysis based on shell model calculations supports this picture.

Isomeric 0+ state in 12Be

An isomeric 0+ state at E x = 2.24 MeV in 12Be was found in the projectile fragmentation of 18O at 100 A MeV on a Be target. The excitation energy and the spin assignment were deduced by the measurements of the energies and the angular correlation function of the coincident two γ-rays corresponding to the 0+ → 2+ → 0+ decay, respectively.

First results from the new RIKEN superconducting electron cyclotron resonance ion source (invited)a)

The next generation heavy ion accelerator facility, such as the RIKEN radio isotope (RI) beam factory, requires an intense beam of high charged heavy ions. In the past decade, performance of the electron cyclotron resonance (ECR) ion sources has been dramatically improved with increasing the magnetic field and rf frequency to enhance the density and confinement time of plasma. Furthermore, the effects of the key parameters (magnetic field configuration, gas pressure, etc.) on the ECR plasma have been revealed. Such basic studies give us how to optimize the ion source structure. Based on these studies and modern superconducting (SC) technology, we successfully constructed the new 28 GHz SC-ECRIS, which has a flexible magnetic field configuration to enlarge the ECR zone and to optimize the field gradient at ECR point. Using it, we investigated the effect of ECR zone size, magnetic field configuration, and biased disk on the beam intensity of the highly charged heavy ions with 18 GHz microwaves. In this article, we present the structure of the ion source and first experimental results with 18 GHz microwave in detail.

Intense beam production from RIKEN 18 GHz ECRIS and liquid He free SC-ECRISs

Intense beams of heavy ions with medium charge states (1.3 mA of Ar8+, 200 μA of Xe20+) have been produced from a RIKEN 18 GHz electron cyclotron resonance ion source (ECRIS) using various kinds of techniques, e.g., utilization of an aluminum cylinder and a biased disk, and optimization of the plasma electrode position. Furthermore, we have recently constructed two superconducting ECRISs (operational frequencies of 14 and 18 Hz) which have unique characteristics, i.e., they do not need liquid He to obtain the superconductivity of solenoid coils and utilize the G–M refrigerator instead. These sources are suitable to generate intense beams of heavy ions with very high charge states. We obtained 10 μA of Xe30+, 5 μA of Xe33+, and 1.5 μA of Xe36+ at a radio frequency power of 700 W (14 GHz microwave) without using the gas mixing method. Through various experiments, we confirmed that not only the magnetic field strength and microwave power but also the characteristics of the plasma chamber surface play the ess...

Effect of minimum strength of mirror magnetic field (Bmin) on production of highly charged heavy ions from RIKEN liquid-He-free super conducting electron–cyclotron resonance ion source (RAMSES)

Abstract We measured the beam intensity of highly charged heavy ions (O, Ar and Kr ions) as a function of the minimum strength of mirror magnetic field (Bmin) of the RIKEN liquid-He-free super conducting electron–cyclotron resonance ion source. In this experiment, we found that the optimum value of Bmin exists to maximize the beam intensity of highly charged heavy ions and the value was almost the same ( ∼0.49 T ) for various charge state heavy ions.

Electron cyclotron resonance ion source developments in RIKEN (invited)

We have constructed four high performance electron cyclotron resonance (ECR) ion sources in RIKEN and produced a variety of intense beams of heavy ions (e.g., 2 emA of Ar8+, 0.6 emA of Kr13+, 0.3 emA of Xe20+). During the improvement of their performance, we found that several key parameters play essential role on increasing the beam intensity. The parameters are plasma electrode position, magnetic field configuration, property of the chamber wall material and position of a biased disk. To investigate how the parameters influence on the beam intensity, we made a systematic study using the laser ablation method. In these experiments, we observed that Bmin influences the electron density and confinement time of ECR plasma.

Isobaric analog state of 14Be

The halo structure of the neutron-dripline nucleus 14Be has been investigated by various approaches, such as the interaction cross section measurement, dissociation reaction and 14Be fragmentation. In the recent plausible view, the mixing of s and d-wave components in the halo wave function has been suggested. In the present study, the halo structure of 14Be was investigated by measuring its Isobaric Analog State (IAS). Since the wave function of the IAS is essentially the same as that of its isobaric partner, possible exotic natures of 14Be may be traced in properties of the IAS such as the Coulomb displacement energy (ΔE C) and the width of the IAS. The IAS of the 14Be was excited by the charge-exchange reaction which was successfully applied to the neutron-dripline nucleus 11Li and obtained the halo properties [1, 2]. In the present study, applying this reaction to 14Be, we have measured the 14Be(p,n)14B* reaction in inverse kinematics at E in = 74 A MeV [3].

Effect of magnetic-field configuration on the beam intensity from electron cyclotron resonance ion source and RIKEN superconducting electron cyclotron resonance ion source

We measured the main plasma parameters (density of electron, temperature of electrons, and ion confinement time) as a function of Bmin and Binj with laser ablation technique. We observed that the Bmin mainly affects the temperature and density of electrons and all of the three parameters increase with increasing the Binj. We also observed that the gas pressure of the plasma chamber at the rf injection side became minimum at the optimum value for Bmin at fixed gas flow. This result indicates that the ionization efficiency becomes maximum at optimum value for Bmin. From these results, it is concluded that the plasma production is strongly dependent on the Bmin (plasma generator). We also observed that the Binj affects the ion confinement time, temperature, and density of electrons. All of the three parameters increase with increasing Binj.

New superconducting electron cyclotron resonance ion source for RIKEN RI beam factory project.

For RIKEN radio isotope beam project, we started to construct the new superconducting electron cyclotron resonance ion source (SC-ECRIS), which has an operational frequency of 28 GHz, in 2007. The main feature of this ion source is that we can produce large size of resonance zone with six sets of solenoid coils. Before starting, we intensively studied the effect of several key parameters of ECRIS (magnetic field configuration, microwave power density, negatively biased disk) on the plasma. In this article, we describe the effect of key parameters on the plasma and detailed structure of the new SC-ECRIS.

Results of RIKEN superconducting electron cyclotron resonance ion source with 28 GHza)

We measured the beam intensity of highly charged heavy ions and x-ray heat load for RIKEN superconducting electron cyclotron resonance ion source with 28 GHz microwaves under the various conditions. The beam intensity of Xe(20+) became maximum at B(min) ∼ 0.65 T, which was ∼65% of the magnetic field strength of electron cyclotron resonance (B(ECR)) for 28 GHz microwaves. We observed that the heat load of x-ray increased with decreasing gas pressure and field gradient at resonance zone. It seems that the beam intensity of highly charged heavy ions with 28 GHz is higher than that with 18 GHz at same RF power.