[Show abstract][Hide abstract] ABSTRACT: Hydrogen (H)- and water (H2O)-storage and desorption characteristics of 25 nm thick Pt films onLi2ZrO3composite materials, exposed to normal air at room temperature, have been investigated by means of elastic recoil detection (ERD), Rutherford backscattering spectrometry (RBS), weight gain measurement (WGM), and thermal desorption spectroscopy (TDS) techniques. It was found by the ERD and TDS that H and H2O were absorbed into the Pt-coated Li2ZrO3 in air at room temperature and desorbed from it in vacuum at much low temperatures of approximately 317 and 309 K, respectively. In addition, the WGM and TDS spectra revealed that the absorption and desorption characters ofsome gases such as CH4, CO, and CO2including H as well as H2Ointo the Li2ZrO3 bulk were improved by Pt deposition.
[Show abstract][Hide abstract] ABSTRACT: This paper describes the results of the experiments performed on Tandem Mirror device GAMMA 10/PDX mainly using a new “divertor simulation experimental module (D-module)” installed on one of the end mirror exits which is specially designed to investigate the physics of plasma detachment. The additional ICRF heating in the anchor-cells, connected to both ends of the central-cell, significantly increases the density in the both cells, which attained the generation of the highest particle flux up to 1023 particles/s m2 at the end-mirror exit. H2 and noble gas injection to enhance the radiation cooling in D-module was performed and a remarkable reduction of the electron temperature (from few tens eV to <3 eV) on the target plate were successfully achieved associated with the strong reduction of particle and heat flux. A significant effect of simultaneous injection with hydrogen and noble gases for detached plasma formation was recognized for the first time.
[Show abstract][Hide abstract] ABSTRACT: This study demonstrates the formation of uniform barrier-type anodic films on magnetron-sputtered magnesium films at high current efficiency in ethylene glycol electrolytes containing 0.1 mol dm−3 NH4F and various concentrations (0.1–28 mol dm−3) of H2O. The anodic films containing a crystalline MgF2 phase develop both at the metal/film and film/electrolyte interfaces due to simultaneous migrations of anions inwards and cations outwards, respectively. When a Mg −1.2 at% Au/Mg bilayer film is anodized, initial prior oxidation of magnesium proceeds with gold atoms accumulating in a thin layer beneath the anodic film. The accumulated gold atoms are incorporated into the anodic film as a band when the alloy layer is completely anodized. Fluoride-containing gold species are formed by the incorporation and the gold species migrate outwards at a rate of 0.4 times the rate of Mg2+ ions. The addition of phosphate in the electrolyte results in the formation of an amorphous anodic film, and the phosphate incorporated into the anodic film is distributed throughout the film thickness. The transport number of cations is also influenced by the phosphate incorporation.
[Show abstract][Hide abstract] ABSTRACT: Ultra-long-pulse helium discharge with ion and electron cyclotron heating (ICH + ECH) in the Large Helical Device (LHD) was achieved in a 48 min plasma (ne ∼ 1.2 × 1019 m−3, Ti,e ∼ 2 keV) with an average heating power of 1.2 MW. The temperature of the first-wall surface during discharges remained at nearly room temperature. However, even in ultra-long-pulse helium discharge, the discharge conditions cannot be said to be in a steady-state, because of two major issues interrupting the steady-state condition. One is the “dynamic change of the wall pumping rate” and the other is the “termination of the discharge with the exfoliation of the mixed-material deposition layers.” Microscopic modifications, such as helium radiation damage and the formation of the mixed-material deposition layers composed of C (∼98%) and Fe (∼2%), on the plasma facing components (PFMs) were clarified to possibly influence the major issues.
[Show abstract][Hide abstract] ABSTRACT: Retention and release of ion implanted deuterium (D) and helium (He) in silicon carbide (SiC) were studied with respect to damage accumulation and annealing behavior using ion beam analysis techniques. α-SiC single crystals were irradiated by 10 keV D2+ and He+ at 300 and 770 K, and depth profiles of retained atoms and lattice disorder were measured during the implantation and successive heat treatments. For the sample pre-irradiated with He at a fluence of 1.0 × 1021 ions/m2, the thermal release of D atoms was completed at an annealing temperature of 1370 K, while the retained D atoms still remained in the sample without pre-irradiation. In contrast to the facilitated thermal release of D by He pre-irradiation, the He release temperature increased in the sample followed by D ion implantation. No significant difference of He retention and damage accumulation behavior was observed between the samples implanted at 300 and 770 K. The D retention and D-ion-induced disorder for 770 K implantation, was reduced to approximately 1/2 comparing to that of the sample implanted at 300 K. The D retention at 770 K was not affected by the He pre-implantation induced damage.
[Show abstract][Hide abstract] ABSTRACT: In situ measurements of the volume electrical conductivities of chemical-vapor-deposited silicon carbide (CVD-SiC) samples were carried out under irradiation by 2.5- and 14-MeV fast-neutron beams in air at room temperature. A slight radiation-induced conductivity (RIC) was detected under fast-neutron irradiation. A radiation-induced electrical degradation (RIED)-like behavior was observed in the form of degradation of the base conductivity in the absence of irradiation with increase in the fast-neutron fluence. The SEM micrograph images and XPS analysis of the surface of the fast-neutron-irradiated CVD-SiC samples revealed that the dissociation of carbon from existing SiOxC3-x compositions did not only occur via displacement damage, but also via ionizing effects (radiolysis), thereby leading to the observed RIED-like behavior as well as RIC in the electrical properties of the CVD-SiC samples.
[Show abstract][Hide abstract] ABSTRACT: Magnetron-sputtered iron films were potentiodynamically anodized at two different sweep rates to 50 V in an ethylene glycol electrolyte containing ammonium fluoride and water. At a high sweep rate of 1.0 V s−1, a barrier-type anodic film was formed even though the current efficiency was as low as ∼50%. In contrast, a nanoporous anodic film developed at a low sweep rate of 0.05 V s−1, and the film-formation efficiency reduced to 37%. The main part of the anodic films consists of iron (III) hydroxyfluoride with a thin inner layer composed of FeF3. The inner fluoride layer is formed owing to the faster inward migration of fluoride ions compared to that of the oxygen species. During immersion or re-anodizing of the iron specimen with an approximately 100-nm-thick, barrier-type anodic film at and below 15 V, thinning of the anodic film proceeded uniformly and film dissolution was enhanced by applying an electric field. The impact of the electric field on film formation and dissolution is discussed.
[Show abstract][Hide abstract] ABSTRACT: An electrochemical analysis was conducted with respect to a hydrogen membrane fuel cell (HMFC) comprising proton-conducting, amorphous zirconium phosphate, a-ZrP2.5O8.9H1.3, thin film electrolyte supported on a dense Pd anode. The HMFC gave rise to an OCV of 1.0 V, but the maximum power density was limited and was about 1 mW cm(-2) at 400 degrees C. The impedance spectroscopy revealed that the interfacial polarizations were decreased by two orders of magnitude when the cell configuration was changed from the fuel cell setup to the hydrogen concentration cell with an anode symmetric configuration. These results indicated that the polarization losses at the solid-solid anode interface are not a main contribution to the voltage loss of the HMFC. The large cathode polarization might be attributed to the lessened conductivity of amorphous zirconium phosphate electrolyte thin film formed on a precious metal electrode.
[Show abstract][Hide abstract] ABSTRACT: The present study reports, for the first time, the highly efficient formation of barrier-type anodic films, with flat and parallel metal/film and film/electrolyte interfaces, on magnesium in ethylene glycol electrolytes containing ammonium fluoride and water. The anodizing voltage increases linearly with time during galvanostatic anodizing at 10 A m− 2 up to 350 V. The anodic film formed to 200 V is 247 nm thick, containing a crystalline MgF2 phase. Analysis by Rutherford backscattering spectroscopy discloses the film composition of MgF1.8O0.1 and Pilling–Bedworth ratio (PBR) of 1.67. The PBR value greater than unity and the formation of chemically stable fluoride-based films may contribute to the film growth at high current efficiency.
[Show abstract][Hide abstract] ABSTRACT: We examined the migration of uranium atoms in uranium glasses after applying the electric field of 5-15kV/mm at RT and at 373K using the technique of Rutherford backscattering (RBS). After applying the electric field of 10kV/mm between the front surface and the back surface of the glasses (1mm in thickness) at 373K for 2 hours, there was neither enhancement nor depression in the concentration of uranium atoms at both surfaces of the negative charge or of the positive charge. In addition, we examined some optical properties such as optical absorption, photoluminescence, photoluminescence excitation and the decay properties of the photoluminescence of the uranium glasses. The optical absorption showed intense absorptions below 345nm and three peaks at 416nm, 482nm and 706nm. The luminescence excited by 416nm light showed four peaks at 512nm, 52Snm, 556nm and 584nm. A decay time determined by the forth harmonic light (266nm) of Nd:YAG laser is about 250 μs.
Journal of Nuclear Science and Technology 08/2014; 39(sup3):497-499. DOI:10.1080/00223131.2002.10875515 · 1.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 1-mol%-Yb-doped Gd3Al2Ga3O12 infra-red scintillator crystal has been studied as a novel implantable radiation monitor in radiation therapy. Powder X-ray diffraction measurement and chemical analysis with a field emission scanning microscope and wavelength dispersive spectrometer determined its garnet structure and average chemical composition of Yb0.03±0.01Gd2.99±0.07Al2.21±0.08Ga2.64±0.09O12.10±0.09. Transmittance measurements reached high values of approximately 70% in the human body transparency region between 650 to 1200 nm. Photoluminescence peaks were detected around 970 and 1030 nm under the 940 nm excitation with a Xe lamp. Infra-red scintillation emissions were clearly observed around 970 and 1030 nm due to Yb3+ 4f–4f transitions under X-ray excitation. Therefore, these results suggest that Yb-doped Gd3Al2Ga3O12 might be used as an infra-red scintillator material.
[Show abstract][Hide abstract] ABSTRACT: The trapping of tritium in silicon carbide (SiC) injected from ceramic
breeding materials was examined via tritium measurements using imaging
plate (IP) techniques. Monolithic SiC in contact with ternary lithium
oxide (lithium titanate and lithium aluminate) as a ceramic breeder was
irradiated in the High Flux Isotope Reactor (HFIR) in Oak Ridge,
Tennessee, USA. The distribution of photo-stimulated luminescence (PSL)
of tritium in SiC was successfully obtained, which separated the
contribution of 14C β-rays to the PSL. The tritium
incident from ceramic breeders was retained in the vicinity of the SiC
surface even after irradiation at 1073 K over the duration of
˜3000 h, while trapping of tritium was not observed in the bulk
region. The PSL intensity near the SiC surface in contact with lithium
titanate was higher than that obtained with lithium aluminate. The
amount of the incident tritium and/or the formation of a
Li2SiO3 phase on SiC due to the reaction with
lithium aluminate under irradiation likely were responsible for this
[Show abstract][Hide abstract] ABSTRACT: Be-seeded, high-flux, deuterium/helium mixture plasma exposure
experiments on tungsten target materials have been performed to simulate
ITER all tungsten divertor erosion/modification and deposition
phenomena. The exposure conditions are kept fixed at a typical
low-ion-energy of 60 eV and a flux of 3-6 ×
1022/m2/s. Sample temperature is 1123 K and plasma
exposure times spanning 1050-10,100 s are explored. The typical ratio of
He/D ions is 0.2 and Be content is 0.2%. A He-induced nanostructure
layer is formed on the exposure surfaces of tungsten materials and the
surface of the nanostructure is covered by a thin layer of Be and O. A
fraction of the re-eroded Be from the target is deposited on a glassy
carbon plate with line of sight to the tungsten target. Rutherford
backscattering spectrometry analyses show that the Be redeposit layer is
in the form of laminae. Small amounts of Mo, W and C are also found in
the redeposited Be layer. Elastic recoil detection analyses show that D,
He and H are also included in the redeposited Be layer.
[Show abstract][Hide abstract] ABSTRACT: The paper presents a brief overview of current research activities on
functional ceramic materials for insulating components, tritium breeder
and optical sensing systems, mainly carried out at Institute for
Materials Research (IMR), Tohoku University. Topics include recent
experimental results related to the electrical degradation and optical
changes in typical oxide ceramics (e.g. Al2O3 and
SiO2) concerning radiolytic effects. Hydrogen effects on the
electrical conductivity in the Perovskite-type oxide ceramics and the
interaction between hydrogen and irradiation induced defects in ternary
Li oxides used as breeder materials, were dynamically observed under the
irradiation environment. Further attention is focused on several
challenging qualifications required for an advanced sensing system using
optical characteristics (e.g., thermoluminescence in SiO2
core fiber, neutron-induced long lasting emission from oxides doped with
rare-earth elements, and gasochromic coloration phenomenon of
[Show abstract][Hide abstract] ABSTRACT: The degradation and recovery of the optical emission characteristics of
polyethylene naphthalate (PEN) films were studied during irradiation
with MeV protons and UV photons. The photo-stimulated luminescence (PL)
consisting of two major peaks decreased with the incident energy
fluence, particularly for ion irradiation. At the beginning of
irradiation, the rate of reduction of the PL intensity in the
UV-irradiated film was comparable to that for ion irradiation, but the
residual PL intensity in the UV-irradiated film was considerably larger
at higher fluences. In addition, no change in the PL characteristics of
the UV-irradiated film was observed after stopping the UV irradiation,
indicating that the damage caused by the UV photons was permanent.
However, the PL intensity from the ion irradiated film increased
immediately when the film was exposed to air. The recovery of the
luminescence centers in the ion-irradiated PEN film is attributed to
ion-induced surface modification, which plays a role in the enhancement
of the dissociation of water molecules and the diffusion process for
Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 11/2013; 315:157-160. DOI:10.1016/j.nimb.2013.03.027 · 1.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Toroidal profiles of the microscopic damage and erosion/deposition on
the Large Helical Device (LHD) first-wall (SUS316L) were simultaneously
evaluated. 10 pairs of SUS316L and Si specimens were mounted on 10 sets
of special holders, and were located on the outer side of the first-wall
surface in each 36° toroidal angle section (Nos. 1-10). For separate
determination of the effects of glow discharge cleanings (GDCs) and main
plasma discharges, two types of holders —"floating-potential" and
"ground-potential"— were used in each toroidal section. The former
was electrically insulated from the first wall; therefore, energetic
ions could not be injected into the specimens during GDC. Hence, we
could analyze two cases: with and without GDCs exposure. Sputtering
erosion of the first-wall surfaces was mainly caused by GDCs and not
main plasma discharges, and the erosion depths of each toroidal section
were varied from 50 nm to 1 μm. Characteristics of the deposition
layers and microscopic damages on the SUS316L matrix were different in
each toroidal section.
[Show abstract][Hide abstract] ABSTRACT: In order to examine the basic characteristics of light emission and
damage accumulation in lithium tantalate (LiTaO3),
ion-induced luminescence was measured. A broad peak centered at about
540 nm was observed under ion bombardment. The ion-induced luminescence
was essentially the same as the luminescence under UV photon
irradiation. The initial intensity of the luminescence was proportional
to the projected range of the incident ions and independent of the
electronic energy loss. The shape of the spectra was independent of the
species, energy, and fluence of incident ions. The luminescence
monotonically decreased with an increase in ion fluence. Assuming
first-order kinetics in the annihilation and recovery process of the
luminescent centers, the annihilation rate was proportional to the
nuclear energy stopping power. It was considered that the luminescent
center was mainly damaged by nuclear collisions, and the recovery of the
damaged luminescent center was caused by local heating by the ion beam.
Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 11/2013; 315:149-152. DOI:10.1016/j.nimb.2013.05.066 · 1.12 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper describes the results of characterization of high heat and particle fluxes produced at the end-cell of the large tandem mirror GAMMA 10 and of the initial plasma-irradiation experiments. In the case of ICRF plasmas, the heat flux of 0.8 MW/m(2) and the particle flux of 4 x 10(22)/m(2) s were achieved at the end-mirror exit. The heat flux increases with the ICRF power and has a linear relationship with the stored energy. Direct ion energy analysis clarified that the parallel ion temperature can be controlled from 100 eV to 400 eV by changing the ICRF power. Additional plasma heating using another ICRF system in the anchor-cell significantly increases the particle flux, which gives a clear prospect of generating the higher particle flux by applying additional ICRF heating in the neighboring cells. The initial results of the plasma-gas-material interactions on a new V-shaped tungsten target were also reported.