Tokai Radioactive Ion Accelerator Complex Research Articles

Spin-polarized radioactive isotope beam produced by tilted-foil technique

The tilted-foil method for producing spin-polarized radioactive isotope beams has been studied using the re-accelerated radioactive 8Li and 123In beams produced at Tokai Radioactive Ion Accelerator Complex (TRIAC) facility. We successfully produced polarization in a 8Li beam of 7.3(5)% using thin polystyrene foils (4.2μg/cm2). The systematic study of the nuclear polarization as a function of the number of foils and beam energy has been performed, confirming the features of the tilted-foil technique experimentally. After the study, a spin-polarized radioactive 123In beam, which is the heaviest ever polarized in its ground state by this method, has been successfully generated by the tilted-foil method, for the nuclear spectroscopy around the doubly magic nucleus 132Sn.

Tilted-foil technique for producing a spin-polarized radioactive isotope beam

The tilted-foil method for producing spin-polarized radioactive isotope beams has been studied for the application to nuclear physics and materials science, using the radioactive nucleus 8Li ( \(\ensuremath I^{\pi}=2^+\) , g = 0.82678(9) , \(\ensuremath T_{1/2}=0.838(6)\) s) produced at the Tokai Radioactive Ion Accelerator Complex (TRIAC). We successfully produced polarization in a 8Li beam of \(\ensuremath 7.3\pm0.5\) % using 15 thin polystyrene foils (4.2 \(\ensuremath \mu \mathrm{g/cm}^2\) fabricated especially for this purpose. A systematic study of the nuclear polarization as a function of the number of foils, beam energy, tilt angle and foil material has been performed, confirming the features of the tilted-foil technique experimentally. The contributions made to the nuclear polarization of 8Li nuclei by the atomic states was investigated.

Low-background prebunching system for heavy-ion beams at the Tokai radioactive ion accelerator complex

A novel beam-bunching technique has been implemented at a heavy-ion linear accelerator facility by installing a compact two-gap prebuncher and a multilayer beam chopper. A pulsed beam of 2 to 4 MHz, having kinetic energy up to $1.1\text{ }\text{ }\mathrm{MeV}/\mathrm{u}$, is realized by bunching a $2\text{ }\text{ }\mathrm{keV}/\mathrm{u}$ continuous beam just upstream of the linac. Around 40% of the continuous beam particles are successively gathered in a single microbunch with a time width of around 15 ns in full width at one-tenth maximum. The number of background beam particles over 250 ns just before the bunched beam is well suppressed to less than ${10}^{\ensuremath{-}4}$ of the number of bunched particles. This technique has been adopted to generate intense $\ensuremath{\alpha}$-particle beams for nuclear astrophysics experiments.

Wall-loss distribution of charge breeding ions in an electron cyclotron resonance ion source

We investigated the ion-loss distribution on the sidewall of an electron cyclotron resonance (ECR) plasma chamber using the 18-GHz ECR charge breeder at the Tokai Radioactive Ion Accelerator Complex (TRIAC). Similarities and differences between the ion-loss distributions (longitudinal and azimuthal) of different ion species (i.e., radioactive (111)In(1+) and (140)Xe(1+) ions that are typical volatile and nonvolatile elements) was qualitatively discussed to understand the element dependence of the charge breeding efficiency. Especially, the similarities represent universal ion loss characteristics in an ECR charge breeder, which are different from the loss patterns of electrons on the ECRIS wall.

Wall-loss distribution of charge breeding ions in an electron cyclotron resonance ion source

The ion loss distribution in an electron cyclotron resonance ion source (ECRIS) was investigated to understand the element dependence of the charge breeding efficiency in an electron cyclotron resonance (ECR) charge breeder. The radioactive (111)In(1+) and (140)Xe(1+) ions (typical nonvolatile and volatile elements, respectively) were injected into the ECR charge breeder at the Tokai Radioactive Ion Accelerator Complex to breed their charge states. Their respective residual activities on the sidewall of the cylindrical plasma chamber of the source were measured after charge breeding as functions of the azimuthal angle and longitudinal position and two-dimensional distributions of ions lost during charge breeding in the ECRIS were obtained. These distributions had different azimuthal symmetries. The origins of these different azimuthal symmetries are qualitatively discussed by analyzing the differences and similarities in the observed wall-loss patterns. The implications for improving the charge breeding efficiencies of nonvolatile elements in ECR charge breeders are described. The similarities represent universal ion loss characteristics in an ECR charge breeder, which are different from the loss patterns of electrons on the ECRIS wall.

Abnormal Li diffusion in β-LiGa by the formation of defect complex

The diffusion coefficients of Li in the NaTl-type Li intermetallic compound of β-LiGa have been measured by using a short-lived radioactive diffusion tracer. As the tracer, the α-emitting radioisotope of 8Li delivered as the energetic and pulsed beam from Tokai Radioactive Ion Accelerator Complex (TRIAC) was implanted into the β-LiGa compounds with the composition in the range of about 43 to 54 at.% Li. By analyzing the time-dependent yields of the α-particles measured according to the repetition cycle of the beam, the tracer diffusion coefficients were extracted over the wide range of Li composition. Abnormal composition-dependence of Li diffusion coefficients in β-LiGa was observed; the stoichiometric β-LiGa showed the highest diffusivity of Li. By referring to the composition-dependent diffusivity of Li in the iso-structural β-LiAl and β-LiIn, we could identify the abnormal diffusion of Li in very Li-poor composition of β-LiGa. The anomaly has been discussed qualitatively in terms of the formation of defect complex and the interaction between the constitutional defects.

KEKCB-18 GHz ECR charge breeder at TRIAC

The KEKCB is an electron cyclotron resonance ion source (ECRIS) operating at the microwave frequency of 18GHz and has successfully operated as the charge breeder at Tokai Radioactive Ion Accelerator Complex (TRIAC). Following an overview of the TRIAC, the recent operating results of the KEKCB have been demonstrated. Special attention was paid on the element-dependent charge breeding efficiency and the beam impurity originating from the ECR plasma of the KEKCB.

Ion source development for the on-line isotope separator at JAEA

A forced electron beam induced arc discharge (FEBIAD-B2) type ion source and a surface ionization type one with a uranium target have been developed for the JAEA-ISOL. The ion sources were utilized to produce medium-heavy neutron-rich radioactive ion beams for acceleration with Tokai radioactive ion accelerator complex (TRIAC). In the FEBIAD-B2 type ion source, a target container containing about 1g/cm2 of 238UCx target is directly attached to a plasma chamber. While the surface ionization type one, 238UCx target is located inside the ion source as an internal target. With both ion sources, about 100 isotopes produced in the proton-induced fission of uranium with separation efficiencies of 0.1–30% have been mass-separated.

KEKCB electron cyclotron resonance charge breeder at TRIAC

The KEKCB is an electron cyclotron resonance (ECR) ion source for converting singly charged ions to multicharged ones at Tokai Radioactive Ion Accelerator Complex. By using the KEKCB, singly charged gaseous and nongaseous ions were converted to multicharged ones of A/q approximately 7 with efficiencies of 7% and 2%, respectively. The conversion efficiency was found to be independent of the lifetime of the radioactive nuclei having lifetimes of the order of one second. Three collimators located at the entrance and the exit of the KEKCB defined the beam axis and facilitated beam injection. Grinding and washing the surfaces of aluminum electrode and plasma chamber dramatically reduced impurities originating from the ECR plasma of the KEKCB.

Diffusion of <sup>8</sup>Li Short-Lived Radiotracer in Li Ionic Conductors of NaTl-Type Intermetallic Compounds

Non-destructive and on-line Li diffusion experiments in Li ionic conductors are conducted using the short-lived !-emitting radiotracer of 8Li. The radiotracers produced as an energetic and pulsed ion beam from TRIAC (Tokai Radioactive Ion Accelerator Complex) are implanted into a structural defect mediated Li ionic conductor of NaTl-type intermetallic compounds ("-LiGa and "-LiIn). The experimental time spectra of the yields of !-particles are compared with simulated results and Li diffusion coefficients in the intermetallic compounds are extracted with an accuracy of ±10%. The diffusion coefficients obtained for "-LiGa with Li content of 43-54 at.% are discussed in terms of the interaction between Li-ion and the structural defects in the specimen, compared with the cases of "-LiAl and "-LiIn. The nonlinear Li-content dependency of Li diffusion coefficients for "-LiGa suggests that the Li diffusion with the Li-deficient region is obstructed by the defect complex composed of vacancies at the Li sites.

Tokai Radioactive Ion Accelerator Complex (TRIAC)

An ISOL-based radioactive nuclear beam (RNB) facility, Tokai Radioactive Ion Accelerator Complex (TRIAC), has been jointly developed by High Energy Accelerator Research Organization (KEK) and Japan Atomic Energy Agency (JAEA). The facility started to supply RNBs for experiments in 2005 and RNBs including fission fragments with energies up to 1.1MeV/A are available in the present. Several experimental studies were performed successfully using 8Li beams with various energies.

Status of JAEA–KEK radioactive ion beam facility, TRIAC

In collaboration with Japan Atomic Energy Agency (JAEA) and High Energy Accelerator Research Organization (KEK), we have been constructed an ISOL-based radioactive ion beam facility, Tokai Radioactive Ion Accelerator Complex (TRIAC), at JAEA – Tokai. This facility consists of a Charge-Breeding 18GHz Electron Cyclotron Resonance Ion-Source (CB-ECRIS), the Split-Coaxial Radio-Frequency Quadrupole (SCRFQ)- and Interdigital-H (IH)-type linacs. An Isotope Separator On-line (JAEA–ISOL) is connected to the CB-ECRIS as the injector of radioactive ions which are produced in proton-induced fission of uranium and heavy-ion reaction. The primary beams are provided from the JAEA Tandem Accelerator. Radioactive singly-charged ions from the JAEA–ISOL are bred to q/A⩾1/7 in the CB-ECRIS and then multi-charged ions are accelerated with the linac-complex from 2keV/u to the energy between 0.14 and 1.1MeV/u. So far, we successfully accelerate 8Li+ and 138Xe20+, the acceleration energy of 1.1MeV/u was achieved. From October 2005, some radioactive ion beams of 1.1MeV/u have become available for users.

Measurement of self-diffusion coefficients in Li ionic conductors by using the short-lived radiotracer of 8Li

For the effective use of short-lived radioactive beams, soon to be available at the Tokai Radioactive Ion Accelerator Complex, the authors have developed a radiotracer method for diffusion studies in solids. The experimental test was performed by the measurement of the diffusion coefficients of Li in a sample of the compound βLiAl using an α-emitting radiotracer of 8Li (T1/2=0.84 s). It was found that the time-dependent yields of the α particles from the diffusing 8Li that was initially implanted in the sample could be used as a measure of the diffusivity of the tracer in a nondestructive way. The method was applied to measure the self-diffusion coefficients of Li in βLiGa, and for investigating how the Li diffusion in the Li ionic conductors is affected by the concentration of atomic defects (i.e., the existence of the atomic vacancies of Li and the defects in Ga sites that are replaced by Li).

Measurement of diffusion coefficients in solids by the short-lived radioactive beam of 8Li

As an effort to effectively use the short-lived radioactive ion beams to be available in near future at Tokai Radioactive Ion Accelerator Complex, we have developed a radiotracer method for diffusion studies in solids. A test experiment has been performed to measure the diffusion coefficients of Li in the sample of LiAl compound, by using the α-emitting radiotracer of 8Li (T1/2=0.84s). The yields of α-particles emitted from diffusing 8Li primarily implanted in the sample have been measured as a function of time under a recurrent time sequence; the implantation of 8Li for 1.5s (beam-on) and subsequent diffusion for 4.5s (beam-off). We have found that the time-dependent yields of the α-particles could be used as a measure of the diffusivity of the tracer in a none-destructive way. By taking into account the experimental conditions, we have simulated the time-dependent α-particle yields for various diffusion coefficients and compared with the experimental ones in order to extract the diffusion coefficients of Li in the sample. The process of the simulations and the comparisons is discussed.

8Li and 18F diffusion experiments in solids - an application of accelerated RNB -

An ISOL based radioactive nuclear beam (RNB) facility in Japan, TRIAC (Tokai Radioactive Ion Accelerator Complex), will be able to provide various short-lived radioactive isotopes for experiments with an energy ranging from 0.1 to 1.1 MeV/nucleon. As an interdisciplinary application of the RNB for materials science, two experiments have been proposed; diffusion studies in super ionic conductors, and β-NMR and PAC studies by implantation of polarized RNB. The present status of the experimental and instrumental development for the experiments is discussed.

Facilities and Methods: KEK-Jaeri Joint RNB Facility, TRIAC

Research and development on an isotope separator on-line (ISOL)-based radioactive nuclear beam (RNB) facility in Japan had mainly been carried out at the Institute for Nuclear Study (INS), University of Tokyo [1]. The first RNB acceleration was realized with the split-coaxial RFQ (SCRFQ) and interdigital-H (IH) type linacs in March 1997. A joint RNB facility, TRIAC (Tokai Radioactive Ion Accelerator Complex) facility, is partly based on the re-installation of the above INS-facility in Tokai site of the Japan Atomic Energy Research Institute (JAERI). It will open up the RNB science with 1.1 MeV/u RNBs from FY2005. The higher energetic (5-8 MeV/u) RNBs will be available in the near future.