Takasaki Ion Accelerators For Advanced Radiation Application Research Articles

Mechanical properties of self-ion irradiated pure tungsten using nano-indentation test and micro-tensile test

The existing nano-indentation method and developmental micro-tensile testing method are more attractive in accurately defining the irradiation effect on the mechanical behavior and adopted in this study to identify the detailed irradiation behavior of pure tungsten. The pure tungsten (A.L.M.T. Corp., Japan) produced by the powder metallurgy and hot-rolling process has a purity of 99.99 wt%. The irradiation was conducted to a maximum of 18.0 dpa by the TIARA (Takasaki Ion Accelerators for Advanced Radiation Application) at 500 and 800 ℃. The micro-tensile specimens with the gauge section of about 0.8 µm (width) × 0.8 µm (thickness) × 10 µm (length) were machined by a focused ion beam device. The nano-indentation results showed the saturation of irradiation hardening and its irradiation temperature dependence. In the case of 500℃, the indentation hardness of pure tungsten irradiated in TIARA increased with increasing dose, and it reached 6.5 GPa after irradiation to 1.0 dpa. Beyond 1.0 dpa, indentation hardness approached a constant. In the case of 800℃, indentation hardness reached 8.1 GPa by irradiation to 3.0 dpa with an irradiation hardening saturation.Moreover, with the stress vs. strain curve by the micro-tensile tests, we found a similar tendency to the nano-indentation results. Additionally, tungsten micro specimens showed a ductile fracture at all conditions in these tests. The total elongation was independent of irradiation dose and irradiation temperature.

Changes of Oxygen Adsorption State of Pt Nanoparticle Catalyst on the Carbon Support By the Ion Irradiation

Pt nanoparticles (NPs) on an Ar+-irradiated glassy carbon (GC) substrate were recently found to show a higher oxygen reduction reaction (ORR) activity than those on the non-irradiated one [1]. This finding suggests that the Pt nanoparticles would be electronically modified by vacancy introduction due to the irradiation into GC. Our theoretical research revealed that vacancies in graphite would lower a d-band center of the Pt nanoparticles [2]. The downshift of d-band center of Pt 5d electrons leads to higher ORR activity because the downshift causes the downshift of the antibonding orbital level of the oxygen adsorbed states of Pt (Pt-O) closing to Fermi level and then results in weaker Pt-O bond [3]. However, it has not been revealed whether the Pt-O antibonding level of Pt NPs is downshifted by the ion irradiation into the carbon support. Therefore, we performed in situ x-ray absorption fine structure (XAFS) measurements, which can observe the unoccupied states of the Pt 5d orbital binding with the adsorbed oxygen, of Pt NPs on the irradiated GC and derived the oxygen adsorbed surface states.The GC substrates were irradiated with 380 keV Ar+ at the fluences of 7.5×1015 ions/cm2 in the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) facility of the Takasaki Advanced Radiation Research Institute. The Pt nanoparticles were then deposited by RF magnetron sputtering. The Pt deposition was also done on the non-irradiated GC substrates for comparison. The XAFS spectra were measured at BL14B1 in SPring-8. We first measured the XAFS spectra of the irradiated and non-irradiated samples reduced by 1 atm. 100 °C H2 (10%) + He (90%) gas flowing at 100 ml/min for 10min. Then the samples were exposed under mixed gas with O2 + He gas flowing at 100 ml/min at room temperature to adsorb the oxygen to Pt nanoparticles and were measured XAFS spectra. In order to observe the oxygen adsorbed surface states of Pt NPs, we derived the Dm spectra by the subtraction from the XANES spectra after the reduction from the those during the oxygen exposure.Figure 1 shows the Dμ spectra for the Pt/GC and Pt/irradiated GC together with the results of peak fitting. In the non-irradiated sample, we could fit using one peak at around 11562 eV (denoted as peak 1), whereas needed peak 1 in addition to peak 2 on the higher energy side. Since the Dμ spectra represent the change of the electronic state in Pt by oxygen adsorption, the convex peak means that new electronic states are formed at the energy position by the oxygen adsorption. The main peak (peak 1) is the antibonding level of the oxygen adsorbed Pt (Pt-O). On the other hand, the peak 2 is considered to be an oxide species that is more strongly bind to oxygen than Pt-O. It needs future study to elucidate its origin.Comparing the peak 1 of the non-irradiated and the irradiated sample, we found that the peak position for the irradiated sample is 0.7 eV lower than that for the non-irradiated one. This indicates that the Pt-O antibonding level shifts toward low energy and gets close to the Fermi level. Thus, the shift leads to easy electron filling to the antibonding level and thus to a weaker Pt-O bond. In this presentation, we will discuss the change of electronic structure of Pt nanoparticles by the ion irradiation in detail.

Novel Approaches for Intensifying Negative C60 Ion Beams Using Conventional Ion Sources Installed on a Tandem Accelerator

We developed novel methods for producing negative C60 ion beams at the accelerator facility Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) to increase the current intensity of swift C60 ion beams accelerated to the MeV energy region using a tandem accelerator. We produced negative C60 ion beams with an intensity of 1.3 µA, which is several tens of thousands of times greater than the intensity of beams produced using conventional methods based on the Cs sputtering process. These beams were obtained by temporarily adding an ionization function based on electron attachment to an existing ion source that is widely used in tandem accelerators. The high-intensity swift C60 ion beams can be made available relatively easily to institutes that have tandem accelerators and ion sources of the type used at TIARA because there is no need to change existing ion sources or install new ones.

Control of the size of etchable ion tracks in PVDF – Irradiation in an oxygen atmosphere and with fullerene C60

We pursue the possibility of controlling the size of etchable ion tracks of poly(vinylidene-fluoride) (PVDF) films. At first, 330 MeV 40Ar ions were irradiated to a 25-µm-thick PVDF film in oxygen using the uniform-beam formation/irradiation system at Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) cyclotron of National Institutes for Quantum and Radiological Science and Technology (QST, Japan). Compared with the irradiation in a high vacuum, which is the conventional method, it is clear that more oxygen-containing functional groups are formed on the surface, the size of the pores becomes larger and the track-etching rate is accelerated. The result shows that the irradiation in oxygen effectively induces oxidation of ion tracks and the oxidation widens the size of the etchable ion tracks. Next, we attempted the irradiation with 6-MeV fullerene C60+ ions. Compared with the irradiation with 100-keV C+ monatomic ions of the same velocity, the fullerene-ion irradiation induced large sized etchable tracks on the surface of PVDF. The result could represent the effect of local and simultaneous collisions by the aggregated ions. Both of the irradiations showed widening the size of etchable ion tracks and we were able to control the pore diameter by varying the etching time.

Studies on Application of Ion Beam Breeding to Industrial Microorganisms at TIARA

Mutation-breeding technologies are useful tools for the development of new biological resources in plants and microorganisms. In Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) at the National Institutes for Quantum and Radiological Science and Technology, Japan, ion beams were explored as novel mutagens. The mutagenic effects of various ion beams on eukaryotic and prokaryotic microorganisms were described and their application in breeding technology for industrial microorganisms were discussed. Generally, the relative biological effectiveness (RBE) depended on the liner energy transfer (LET) and the highest RBE values were obtained with 12C5+ ion beams. The highest mutation frequencies were obtained at radiation doses that gave 1%–10% of surviving fraction. By using 12C5+ ion beams in this dose range, many microorganisms have been improved successfully at TIARA. Therefore, ion-beam breeding technology for microorganisms will have applications in many industries, including stable food production, sustainable agriculture, environmental conservation, and development of energy resources in the near future. Moreover, genome analyses of the ion-beam-induced mutants are in progress to clear the differences of mutational functions induced by different LET radiations in microorganisms. Further characterizations of mutations induced by different LET radiations will facilitate more effective use of ion beams in microorganisms breeding.

Development of the high-energy neutron fluence rate standard field in Japan with a peak energy of 45 MeV using the 7Li(p,n)7Be reaction at TIARA

ABSTRACTIn this study, we developed a 45 MeV neutron fluence rate standard of Japan. Quasi-monoenergetic neutrons with a peak energy of 45 MeV in the neutron standard field were produced by the 7Li(p,n)7Be reaction using a 50-MeV proton beam from an azimuthally varying field (AVF) cyclotron of the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA). The neutron energy spectrum was measured using an organic liquid scintillation detector and a 6Li-glass scintillation detector by the time-of-flight method, and using a Bonner sphere spectrometer by the unfolding method. The absolute neutron fluence was determined using a proton recoil telescope (PRT) composed of the liquid scintillation detector and a Si(Li) detector that was newly developed in the present study. The detection efficiency of the PRT was obtained using the MCNPX code. The peak neutron production cross section for the 7Li(p,n)7Be reaction was also derived from the neutron fluence in order to confirm the neutron fluence of the TIARA high-energy neutron field. The peak neutron production cross section obtained in the present study was in good agreement with those of previous studies. The characteristics of the 45-MeV neutron field in TIARA were successfully evaluated in order to calibrate high-energy neutron detectors and high-energy neutron dosimeters.

EFFECTIVENESS OF A COMBINATION OF ML-EM AND STIM-CT IN PIXE-CT FOR BIOLOGICAL SPECIMEN

In this study, we applied ML-EM (maximum likelihood expectation maximization) iterative algorithm and STIM-CT to a three dimension imaging technique of PIXE -CT for cellular analysis using 3 MeV proton microbeam with a diameter of 1 μm at TIARA (Takasaki Ion Accelerators for Advanced Radiation Application). The algorithm had been applied to tomography such as SPECT (Single Photon Emission Computed Tomography). It is also possible and suitable to apply the algorithm to PIXE-CT because the algorithm can be used to project images taking into account errors due to rare events. Energy loss of incident particles and absorption of X-rays, however, affect quantitative values dramatically in the case of PIXE -CT. We estimated those effects from density distribution of major elements measured by STIM-CT in this work. In order to show the appropriateness of this method, X-ray yield and absorption were calculated using density distribution of two-dimensional Shepp phantom. The PIXE-CT experiments were carried out using a dried unicellulate as a test sample placed on an automatic rotation stage, which made a full turn by rotating 360° at each step of 18° in vacuum. The results of those simulation and experiments have proved that this method is effective.

Fluorine analysis of human dentin surrounding resin composite after fluoride application by μ-PIGE/PIXE analysis

The use of fluoride for the prevention of caries is based on the transformation of hydroxylapatite to fluoroapatite in the presence of fluoride ions, thereby strengthening tooth structure. Adhesion of dentin and resin composite (tooth-colored restoration material) requires a dentin bonding system, since resin composite is not able to adhere to dentin directly. Demineralization of dentin by acid etching is an important step in the dentin bonding system, however, demineralization also introduces weaknesses in tooth structure. If the demineralized dentin could be strengthened by the application of fluoride, then the dentin–resin composite bond strength might also improve. To test this hypothesis, the present study evaluated the influence of fluoride applications on the strength of the dentin–resin composite bond by (1) tensile strength testing analyses, (2) SEM analyses of tooth structure, and (3) detection of calcium (Ca) and fluorine (F) distribution patterns by micro proton-induced X-ray emission (μ-PIXE) and micro proton-induced gamma-ray emission (μ-PIGE) analyses conducted at the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) at the Takasaki Advanced Radiation Research Institute (TARRI).In this study, the dentin in extracted human molars was exposed by grinding and the dentin was etched with 35% phosphoric acid. Fluoride was applied at two concentrations, 0.022% (100ppm F) and 2.21% (10,000ppm F) NaF solution, for two time periods, 30 and 60s, prior to bonding the resin composite with the treated dentin. Controls were prepared in the same manner, but without the fluoride application. Bond strength was measured with a micro-tensile testing unit, and the fluorine and calcium distributions at the interface between dentin and resin composite were detected by μ-PIGE and μ-PIXE analysis, respectively.Results indicate that the 10,000ppm F applications resulted in higher bond strengths than observed in either the 100ppm F applications or the control group. In addition, PIGE analyses showed high concentrations of fluorine in the hybrid bonding layer of the 10,000ppm F samples, suggesting that the fluorine contributes to the strength of the dentin–resin composite bond. Detection of fluoroapatite within the hybrid bonding layer suggests that bond strength involves remineralization processes.

Development of the Quasi-monoenergetic Neutron Calibration Fields of Several Tens of MeV at TIARA

Development of three calibration fields for 45, 60 and 75 MeV neutrons has been in progress at Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) of JAEA-Takasaki. Achievement of the neutron calibration fields requires establishment of both measurement of neutron fluence and its monitoring technique. In order to measure the neutron fluence of main energy peak especially at a reference point on low fluence condition, a proton recoil counter telescope with high efficiency has been developed. The design of relatively large telescope components brought a high detection efficiency at the reference point with wide irradiation area at a long distance. Effective and precise measurement of the neutron fluence could be performed with uncertainties less than 6.5 % (standard deviation). For detecting neutrons without scattering near the target, a transmission type neutron fluence monitor has been newly developed to measure the neutron fluence directly at the collimator exit. Its performance such as counting rates was tested for various beam intensities.

Applications of microstructures fabricated by proton beam writing to electric-micro filters

Fabrication of high-aspect-ratio microstructures was performed by proton beam writing (PBW) using a microbeam line at Takasaki Ion Accelerators for Advanced Radiation Application (TIARA), JAEA Takasaki, JAPAN. As one of the applications of the high-aspect-ratio structures micro-machined by PBW, we utilized the high-aspect pillars for electric-micro filters of microbes such as Escherichia coli and Yeast based on the dielectrophoretic force. The filter is equipped with high-aspect pillars with a height of ∼20 μm and a diameter of ∼1 μm on a glass plate. Evaluation of the dielectrophoresis (DEP) device for capturing E. coli and Yeast was made using either observation by optical microscope or photoluminescence (PL) measurements.

Development of the Neutron Calibration Fields using Accelerators at FRS and TIARA of JAEA

The neutron calibration fields using accelerators have been developed at the Facility of Radiation Standards (FRS) of JAEA-Tokai for neutrons below 20 MeV and at Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) of JAEA-Takasaki for those over 20 MeV. At FRS, monoenergetic neutrons are generated by using proton or deuteron beam from a 4 MV Van-de-Graaff (Pelletron) accelerator. Up until the present, developments of the 8, 144, 250, 565 keV, 5.0 and 14.8 MeV fields have been completed. As procedure for the development, measurement of neutron energy spectrum, peak energy and reference fluence, development of monitoring scheme for neutron fluence and establishment of the traceability on neutron fluence to the primary standards were achieved. At TIARA, three neutron fields of 45, 60 and 75 MeV are planned to be established. Quasi-monoenergetic neutrons are generated from 7Li(p,n)7Be reaction by using proton beam from an AVF cyclotron, and led into an irradiation room through a cylindrical collimator, 3 m in thickness. Evaluation of the characteristics of the fields needed for the development as the standard calibration fields is in progress now.

Micro-machining of resists on silicon by proton beam writing

We report micro-machining of resists on silicon by proton beam writing (PBW) at Takasaki Ion Accelerators for Advanced Radiation Application (TIARA), JAEA Takasaki, Japan. We studied the proton beam irradiation effects on typical positive and negative resists such as PMMA and SU-8, respectively, for application of the PBW technique to micro-machining. These resist materials were subjected to the scanning of a focused beam of protons accelerated using the microbeam facility of TIARA. Diameter of the proton beam was focused to about 1 μm. The fluence was varied to examine the irradiation effects on these resists as a function of the beam current and irradiation time. After exposure to proton beam, samples were developed and evaluated by a scanning electron microscope. Attempts to fabricate nickel stamps were also made by electroplating on the structures formed by PBW for application to imprint lithography.

Nano-Structure Controlled Polymer Electrolyte Membranes for Fuel Cell Applications Prepared by Ion Beam Irradiation

Fluoropolymer-based electrolyte membranes for fuel cells were prepared by using heavy ion beams from the cyclotron accelerator of the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA), Japan Atomic Energy Agency (JAEA). The preparation method for these so-called nano-scale structure-controlled membranes involves (i) the swift heavy ion irradiation of polyvinylidene fluoride (PVDF) films and subsequent chemical etching to obtain cylindrical pores with a diameter of 100 nm, and (ii) the filling of proton-conducting polymer chains into the etched pores by gamma-ray-induced graft polymerization. The proton transport only in the thickness direction was observed for the resulting membranes with controlled ion exchange capacities, indicating the formation of one-dimensional straight proton-conducting pathways parallel to the ion-beam incident axis. The membranes exhibited a lower water uptake and reduced methanol permeability compared to commercially-available Nafion probably due to the restricted structures.

Effects of ion irradiation on hydriding rate of Mm based hydrogen storage alloy

The effect of ion irradiation on the rate of the electrochemical hydrogen absorption by Mm–Ni based alloy was investigated. Since the low-energy ion irradiation is quite useful for surface modification of materials, it is expected that the hydriding properties of Mm samples were improved by ion irradiation. The research, which aimed at the improvement in occlusion ability of Mm alloy using ion irradiation, is the first trial in the world. In this study, the ion irradiation was made with H +, Ar + and K + in the acceleration energy range of 350 keV, up to a dose of 1 × 10 16 cm −2 using Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) in Japan Atomic Energy Research Institute (JAERI). The initial hydrogen absorption rate was increased as the ion dose was increased. These results clearly suggest that the ion irradiation induces a high concentration of vacancies that trap high concentration of hydrogen atoms at the initial stage of the reaction. The induction of a high concentration of vacancies in metal by the ion irradiation is found effective to enhance the initial activation in the electrochemical hydriding process of MmNi 5.

Present status and prospect of microbeams at TIARA

JAERI had made a new research program so-called the advanced radiation technology project in 1987, and conducted microbeam studies in the fields of semiconductor devices, analytical technique and biological application using different type of microbeam systems installed at Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) which is an ion beam irradiation facility for making the promotion of the project. The present status of these microbeam studies is summarized, and the future prospects are discussed.

Vanadium uptake and an effect of vanadium treatment on 18 F-labeled water movement in a cowpea plant by positron emitting tracer imaging system (PETIS)

We present real time vanadate (V5+ ) uptake imaging in acowpea plant by positron emitting tracer imaging system (PETIS). Vanadium-48was produced by bombarding a Sc foil target with 50 MeV α -particlesat Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) AVFcyclotron. Then 48 V was added to the culture solution to investigatethe V distribution in a cowpea plant. The real time uptake of the 48V was monitored by PETIS. We measured the distribution of 48Vin a whole plant after 3, 6 and 20 hours of V treatment by Bio-imaging AnalyzerSystem (BAS). After the 20 hour treatment, vanadate was detected at the up-groundpart of the plant. To know the effect of V uptake on plant activity, 18F-labeled water uptake was analyzed by PETIS. When a cowpea plantwas treated with V for 20 hours before 18 F-labeled water uptakeexperiment, the total amount of 18F-labeled water absorption wasdrastically decreased. Results suggest the inhibition of water uptake wasmainly caused by the vanadate already moved to the up-ground part of the plant.

Isotope Production Cross Section Library for Use of Transmutation Calculation in the IRAC Code System for the TIARA Facility

An isotope production cross-section library for 57 elements and 136 nuclei has been produced by using ALICE-F code based on a Geometry Dependent Hybrid model for incident particles of neutron, proton, deuteron, alpha, C-12, N-14, O-16, Ne-20 and Ar-40. Maximum energy of incident particles for neutron, proton, deuteron and alpha is 150 MeV, and 500 MeV for the other projectile ions. Using the data, a cross-section library, ACSELAhas been prepared for an IRAC code system to calculate product isotopes and induced radioactivity in various radiation environments in the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) facility of Japan Atomic Energy Research Institute (JAERI). The generation scheme of the ACSELA library is presented. Comparisons are shown between the calculated results and experimental data for incident protons and carbon ions as well as evaluations of the Los Alamos 150 MeV library for incident protons.

Fast fluorescence decay of naphthalene induced by Ar ion irradiation

A single photon counting system was constructed for a time resolved fluorescence measurement with pulsed heavy ions from the AVF cyclotron in Takasaki Ion Accelerators for Advanced Radiation Application (TIARA). Fluorescence spectra and decay of naphthalene in poly(vinyl butylal) (PVB) film were observed from the irradiation with Ar ions. Though fluorescence spectra were assigned to the first singlet excited state of naphthalene, the decay with Ar ion irradiation were faster than that excited by UV light. This faster decay results from quenching by the transient species produced. The relative initial concentration of the excited state of naphthalene to that of the radicals increases with increasing energy deposited along the incident ion's trajectory.