Argon ion impact desorption cross sections of chlorine and carbon from molybdenum

Total desorption cross sections have been measured for Cl (σ_Cl) and C(σ_C) on molybdenum by argon ion bombardment for an incidence angle of 60° from the surface normal. For the bombardment an ion gun with low current density (i₀ ~ 1 × 10 ^?7 A cm^?2) at low system pressure (~10^?9 Torr) was used. The detection was performed by AES and the data were sensitivity factor corrected. The AES analysis of the surface after adsorption showed that Mo, C and Cl contributed to more than 94% of the atomic composition. With known i₀, it is possible to obtain σ from the adsorbate signal vs ion bombardment time curve. For ion energies between 0.2 keV to 1.0 keV the measured value for σ_Cl and σ_C are 0.5?3 × 10^?15 cm² and 0.2?4 × 10^?15 cm², respectively. The possible effects of the surface roughness due to prebombardment are discussed.     

Microstructural evolution in irradiated uranium-bearing delta-phase oxides A6U1O12 (A = Y, Gd, Ho, Yb, and Lu)

Irradiation-induced microstructural evolution in uranium-bearing delta-phase oxides of A₆U₁O₁₂ (A = rare earth cations) were characterized using grazing incidence X-ray diffraction and transmission electron microscopy. Polycrystalline Y₆U₁O₁₂, Gd₆U₁O₁₂, Ho₆U₁O₁₂, Yb₆U₁O₁₂, and Lu₆U₁O₁₂ samples were irradiated with 300 keV Kr⁺⁺ to a fluence of 2 × 10²⁰ ions/m² at cryogenic temperature (∼100 K). The crystal structure of these compounds was determined to be an ordered, fluorite derivative structure, known as the delta-phase, a rhombohedral symmetry belonging to space group . Experimental results indicate that all these compounds are resistant to amorphization to a displacement damage dose of ∼60 displacements per atom. In these experiments, we sometimes observed an irradiation-induced order-to-disorder phase transformation, from an ordered rhombohedral to a disordered fluorite structure.     

Heliotron E Results and Large Helical Project

Heliotron E(H-E) experiment was started in 1980. Until 1987 high power heating experiments for improving plasma parameters have almost finished. H-E firstly demonstrated that ECR heated plasmas are usable for target plasmas of NBI or ICRF heating to obtain high density and high temperature currentless plasmas. The highest electron temperature is 1.5keV and ion temperature is 1.6keV and both are realized in the low density regime of <n> (average density) ≤10¹³cm^?3.

H-E also showed that the currentless plasmas have no major disruption and quasi-steady plasmas are confined with controlling impurity ions by titanium gettering and carbon coating.

H-E also obtained <β> (average β) –2%, which is the highest value realized in helical systems, with <n–8×l0¹³cm^?3 and Te(0)–T_i(0)–350 eV at B₀ (magnetic field at the magnetic axis) =0.94 T. In the high β experiments pressure-driven instabilities were observed for peaked pressure profiles and sometimes relaxation oscillations similar to the tokamak internal disruptions were observed.

In the ECRH plasmas neoclassical transport is dominant in the region inside the half radius. However, global confinement time τ_E follows the scaling law τ_E ∝<n>^0.66P_heat ^?0.53 which is different from the neoclassical scaling law. Here P_heat denotes the net heating power.

Based on the H-E results, a new large helical system design study has started in 1986. The plasma parameters entering the regime of <n>τ_E<T> (2–3)× 10¹⁹m^?3?S?keV is investigated, which is about one tenth of fusion plasma condition. From the transport code studies and empirical scaling law based on the H-E results, R=(4×5)m, ā=(50–60)cm and B_o=4T are required to satisfy the above condition with P_heat=20MW. The design study to fix the magnetic field configuration is progressing. Expected one is l=2 and m=10 with additional poloidal coils, where m is a toroidal period number. The magnetic field is produced by superconducting coil and long pulse operation will be tested, if continuous heating is available.     

The disordering of Zr3Al by 1 MeV electron irradiation

The effect of 1 MeV electron radiation on the L1₂ ordered intermetallic compound, Zr₃Al, has been studied over the temperature range 130–775 K, using a high voltage electron microscope. At temperatures in the range 130–375 K, complete disorder was produced by irradiation to a dose of approximately one displacement per atom (dpa), independent of damage rate over the range 5 × 10^?4 to 5 × 10^?3 dpa/s. After irradiation to a few dpa at higher temperatures, 575–775 K, a steady-state was established which was characterized in part by an intermediate degree of long-range order which increased with irradiation temperature. By comparison with published results from ion irradiation experiments, it appears that the number of atomic displacements to cause complete disordering at low temperatures is independent of the nature of the damage events. At the higher temperatures, neither dislocation loops, dislocation networks nor voids were observed. Generally, the crystalline perfection was markedly reduced at all temperatures by irradiation to doses exceeding a few dpa.     

Bulk-compositional changes of Ni2Al3 and NiAl3 during ion etching

Bulk-compositional changes of Ni₂Al₃ and NiAl₃ in a Ni-50 wt% Al alloy during ion etching have been investigated by transmission electron microscopy and energy dispersive X-ray spectroscopic analyses. After etching with 7, 5 and 3 keV Ar⁺ ions for 15, 24 and 100 h nickel contents in both Ni₂Al₃ and NiAl₃ exceeded greatly those in the initial compounds and increased with the decrement of the sputtering energy. After 100 h etching with 3 keV Ar⁺ ions the compositions of these two compounds reached a similar value, about Ni_80-83Al_12-15Fe_3-4Cr_1-2 (at%). A synergistic action of preferential sputtering, radiation-induced segregation and radiation-enhanced diffusion enables the altered-layers at the top and bottom of the film extend through the whole film. The bulk-compositional changes are proposed to occur in the unsteady-state sputtering regime of ion etching and caused by an insufficient supply of matter in a thin film.     

Investigation on Space Dependence of C/E Values for Control Rod Worths and Reaction Rate Distributions in ZPPR-10A and -10D Assemblies

In order to investigate the redox equilibrium of uranium ions in molten NaCL-2CsCL, UV-Vis absorption spectrophotometry measurements were performed for U⁴⁺ and U³⁺ in molten NaCL-2CsCL at 923 K under simultaneous electrolytic control of their ratio. Prominent absorption bands at 480 and 570 nm were assigned to U³⁺, and their molar absorptivities were determined to be 1,260±42 and 963±32 mol^?1.l.cm^?1 respectively. From the dependence of the rest potential of the melt on the spectrophotometrically determined ratio of [U⁴⁺]/[U³⁺], the standard redox potential of the couple U⁴⁺/U³⁺ at 923K was determined to be ?1.481±0.004 V vs. Cl₂/Cl^?. Cyclic voltammetry measurements were carried out for the couple U⁴⁺/U³⁺, and the results agreed well with this standard redox potential value. By the results of cyclic voltammetry, a temperature dependence of the standard redox potential was found to be ?2.094+6.639×10^?4 T (T=823-923 K).     

Oxidation of Uranium Dioxide

The oxidation of UO₂ was studied by thermogravimetry and X-ray diffraction. It was clarified that the thermal history covering the first stage of the oxidation from UO₂ to U₃O UO₇ significantly influenced the rate of the oxidation of the second stage from U₃O₇ to U₃ O₈.

The entire oxidation reaction proceeded in what to all appearances, was a single stage when the specimen temperature was raised rapidly, whereas at slower rates of heating up, two distinct stages of oxidation were observed, separated by an intermediate induction period. These findings suggest the existence of a close connection between the rate of formation of the U₃O₇ phase and the rate of the subsequent oxidation of this phase: A slow formation of U₃O₇ would tend to prolong the induction period preceding the second stage of the oxidation. A similar effect was observed also with annealing of the intermediate U₃O₇ at 200°C: The increase of annealing time prolonged the induction stage.

The rate of the second stage oxidation was fairly well expressed by Johnson & Mehl's equation, log (1/(1-y/)=(1/2.303)kⁿtⁿ . The time exponent n in this equation varied in the range of 1.0~2.5, and the rate constant k of 1.15×10^?4~2.04 ×10^?1 min^?1, depending on the experimental conditions.     

Light particle irradiation effects in Si nanocrystals

Si nanocrystals, formed by Si ion implantation into SiO₂ layers and subsequent annealing at 1150°C, were irradiated at room temperature either with He⁺ions at energies of 30 or 130 keV, or with 400 keV electrons. Transmission electron microscopy (TEM) and photoluminescence (PL) studies were performed. TEM experiments revealed that the Si nanocrystals were ultimately amorphized (for example at ion doses ∼10¹⁶ He cm⁻²) and could not be recrystallized by annealing up to 775°C. This contrasts with previous results on bulk Si, in which electron- and very light ion-irradiation never led to amorphization. Visible photoluminescence, usually ascribed to quantum-size effects in the Si nanocrystals, was found to decrease and vanish after He⁺ ion doses as low as 3 × 10¹²–3 × 10¹³ He cm⁻² (which produce about 1 displacement per nanocrystal). This PL decrease is due to defect-induced non-radiative recombination centers, possibly situated at the Si nanocrystal/SiO₂ interface, and the pre-irradiation PL is restored by a 600°C anneal.     

Photon energy absorption parameters for composite mixtures with boron compounds

Boron compounds that are used in the manufacturing of a variety of products are introduced to the environment in the form of waste. The radiation shielding measurements of mixtures that contain boron compounds is considered to be a topic of concern. The mass attenuation coefficients of (PbO and K₂B₄O₇⋅4H₂O) and (PbO and H₃BO₃) as functions of their changing contents have been measured in the X-ray energy range from 25.191 to 57.903 keV. These values are used to determine the effective atomic number of mixtures. The γ-rays emitted from an Am²⁴¹ annular source have been sent to secondary sources whose characteristic X-rays have been used for transmission arrangement. The characteristic X-rays of the secondary sources have been counted by a Si(Li) detector with a resolution of 149 eV at 5.9 keV. Also, the total effective atomic number of each mixture was determined by using the mixture rule. The measured values were compared with theoretically calculated values.     

Kinetics of chlorination of uranium–antimony composite oxide for uranium removal from waste catalyst used for acrylonitrile synthesis

For uranium removal from waste catalyst used for acrylonitrile synthesis, kinetics of chlorination of uranium–antimony composite oxide was studied. During the chlorination treatment with hydrogen chloride gas at a partial pressure of 0.6–6.7 kPa and 873–1173 K, the uranium–antimony composite oxide, USb₃O_10, which was contained in the waste catalyst converted to another composite oxide, USbO₅, then changed to uranium oxide. Both reaction rates of the conversions, from USb₃O₁₀ to USbO₅ and from USbO₅ to U₃O₈, were described by a first order function of the fraction of USb₃O₁₀ and USbO₅, and their activation energies under the condition at 1.0 kPa hydrogen chloride gas were almost same values at (8.0 ± 0.4) × 10⁴ J mol^?1.     

Thermophysical properties of U2Mo intermetallic

The current paper has investigated specific heat capacity, coefficient of thermal expansion and phase transition temperatures of U₂Mo intermetallic. The transformation of U₂Mo phase to bcc (γ-uranium) phase occurred at 853 K. The coefficient of thermal expansion has been determined in the temperature range 423–873 K to be 14.65 × 10^?6 K^?1. The specific heat data showed a smooth curve up to 773 K and above it a change in trend to follow a λ-shape was observed. The specific heat values of U₂Mo have been found to be lower than that calculated from the additivity rule. This study provides first time data on U₂Mo. The data obtained from this investigation were compared to available literature on U–Mo alloys.     

Effective atomic numbers of some composite mixtures including borax

Effective atomic numbers for (PbO and Na₂B₄O₇10H₂O) and (UO₂(NO₃)₂, and Na₂B₄O₇10H₂O) mixtures against changing contents of PbO, Na₂B₄O₇10H₂O, and UO₂(NO₃)₂ were measured in the X-ray energy range from 25.0 to 58.0 keV. The gamma rays emitted by a ²⁴¹Am annular source have been sent on the absorbers which emits their characteristic X-rays to be used in transmission arrangement. The X-rays were counted by a Si(Li) detector with a resolution of 146 eV at 5.90 keV. The changing compositions of the compounds were assigned to be 0, 0.167, 0.333, 0.500, 0.666, 0.833 and total masses of the mixtures were adjusted to be identical. Also, the total effective atomic numbers of each mixture were estimated by using the mixture rule. The measured values were compared with estimated values for the mixtures.     

Development of methods for recovering uranium from sludge-like uranium generated in decontamination of metal wastes

Sludge-like uranium wastes (SUWs) have been generated with neutralization of acidic aqueous solutions used for decontamination of metal wastes containing a large amount of iron. We have examined the method for recovering uranium from such SUWs using N-cyclohexyl-2-pyrrolidone (NCP) as a precipitate. As a result, it was found that precipitation ratios (PRs) of uranium in the solutions prepared by dissolving SUWs in HNO₃ increase with increasing an amount of added NCP and are 97.7% at [NCP]/[U(VI)] = 20, and that the PRs of iron, aluminum, fluorine, and sulfate species are less than 1% at [NCP]/[U(VI)] = 3–20. This indicates that uranium species are precipitated selectively. The content ratios of U, Fe, Ca, F, and S in the materials after calcining precipitates obtained at [NCP]/[U(VI)] = 20 were 73, 2.2 × 10^?1, <3 × 10^?3, 2.3 × 10^?2, and 2.2 × 10^?2 wt%, respectively. These values are in accordance with the conditions of uranium ore concentrate defined by ConverDyn Corp and ASTM C967. From these results, it is expected that highly purified uranium can be efficiently recovered from SUWs by using NCP as the precipitant.     

Mass Transfer Model of Purex Process in Mixer-Settlers

The formation rate of ruthenium tetroxide (RuO₄) from nitrosyl ruthenium trinitrate (RuNO(NO₃)₃) was measured at temperatures of 70–115°C in 3–9 mol·dm^?3 nitric acid solutions. The gas-liquid equilibrium ratio was measured at temperatures of 40–80°C in 0.1–9 mol·dm^?3 nitric acid solutions. The gas-liquid equilibrium ratio of RuO₄ ranged about 60–260 under the experimental conditions. The reaction rate increased greatly with acid concentrations above 6 mol·dm^?3. The activation energy of the reaction was about 130 kJ·mol^?1 in 9 mol·dm^?3 nitric acid solution. It was concluded that the rate of RuO₄ formation dominated the distill-out phenomena of Ru in an evaporator as used in nuclear fuel reprocessing plants.     

SIMS depth profiling of multilayer metal-oxide thin films — improved accuracy using a xenon primary ion

Multilayer thin films containing silver and copper, sandwiched in a metal oxide, have been depth profiled by secondary ion mass spectrometry (SIMS) using primary ions of differing mass, energy and chemical reactivity. These results were compared for accuracy with those obtained by Rutherford backscattering spectrometry (RBS). The use of O₂⁺ or O^? as primary ions resulted in severe distortion of the silver ion intensity distribution in the SIMS profile of a ZnO/Ag/ZnO thin film on glass; O₂⁺ bombardment at energies from 3–10 keV resulted in the detection of silver at the glass interface, while the use of O^? caused the silver to be detected closer to the outer surface than expected from RBS results. Primary beams of Ar⁺ and Xe⁺ gave progressively more accurate results for the Zn/Ag/Zn distribution; Xe⁺ at 5.0 keV energy produced profiles that agreed within 10% of RBS-derived values. The same beam conditions, used to profile a double silver layer in ZnO, resulted in some discrepancy in the position of the inner layer, compared to RBS results, and this was attributed to an enhanced sputter rate in the oxide under the outside metal film. Depth profiling of TiO₂/Cu/TiO₂ films with oxygen also resulted in significant distortion of the perceived position of the metal layer, and this was again significantly improved using Xe⁺ primary ions of 6–9 keV energy. The distorting effects of oxygen bombardment can be understood in terms of a migration of metal ions in an electrostatic field created by a charged surface. Ionization of the metallic layer is enhanced by the use of oxygen. By contrast, the use of rare gases reduces the production of ions from the metallic layer which can migrate prior to the onset of sputtering.     

Radiation blistering of Nb Implanted sequentially with helium ions of different energies (3–500 keV)

Cold rolled, polycrystalline niobium samples were irradiated at room temperature with ⁴He⁺ ions sequentially at 14 different energies over an energy range from 3–500 keV. The dose for each energy was chosen to give an approximately uniform concentration of helium between the implant depths corresponding to 3 keV and 500 keV. In one set of experiments the irradiations were started at the Kurchatov Institute with 3-keV ⁴He⁺ ions and extended up to 80 keV in several steps. Subsequently, the same target area was irradiated with ⁴ He⁺ ions at Argonne National Laboratory (ANL) starting at 100 keV and increased to 500 keV in steps of 50 keV. Another set of irradiations was started at ANL with 500-keV ⁴ He⁺ ions and continued with ion energies decreasing to 100 keV. Subsequently, the same area was irradiated at the Kurchatov Institut starting at 80 keV and continued with ion energies decreasing to 3 keV. Both sets of irradiations were completed for two different total doses, 0.5 C cm^?2 and 1.0 C cm^?2.     

Homogeneously size distributed Ge nanoclusters embedded in SiO2 layers produced by ion beam synthesis

500 nm SiO₂ layers were implanted with 450 keV (F=3 × 10¹⁶ at./cm²) and 230 keV (F=1.8 × 10¹⁶ at./cm²) Ge ions at room temperature to obtain an almost constant Ge concentration of about 2.5 at.% in the insulating layer. Subsequently, the specimens were annealed at temperatures between 500°C and 1200°C for 30 min in a dry N₂ ambient atmosphere. Cross-sectional TEM analysis reveal homogeneously distributed Ge nanoclusters arranged in a broad band within the SiO₂ layer. Their mean cluster size varies between 2.0 and 6.5 nm depending on the annealing conditions. Cluster-free regions are always observed close to the surface of the specimens independent of the annealing process, whereas a narrow Ge nanocluster band appears at the SiO₂/Si interface at high annealing temperatures, e.g. ⩾1000°C. The atomic Ge redistribution due to the annealing treatment was investigated with a scanning TEM energy dispersive X-ray system and Rutherford back scattering (RBS).     

Ionic Processes of γ-Irradiated Triphenylamine in 3-Methylpentane Glass at 77°K

The ionic processes of γ-irradiated triphenylamine (TPA) in 3-methylpentane glass (3-MP) have been studied. The thermoluminescence curve of the irradiated sample shows two maxima at 77°–83°K and 83°–90°K. The effects of differences in radiation dose and of time elapsed after irradiation at 77°K on the luminescence yield of these two peaks have been examined. The optical absorptions of trapped electrons (e ^? _t ), TPA⁺ and TPA^? are measured as functions of the storage time at 77°K and of the elevation of temperature. The results for IR and UV bleaching and for prolonged storage at 77°K suggest the presence of negative species other than e ^? _t and TPA^?. In the irradiated sample at 77°K in the presence of 10^?4–10^?3 M TPA, positive and negative species other than TPA⁺ and TPA^? exist and these charges are transferred to TPA to form TPA⁺ and TPA^? by warming. These behaviors of the ionic species are discussed.     

Damage creation in α-Al2O3 by MeV fullerene impacts

Single crystals of α-Al₂O₃ were irradiated at room temperature with C₆₀ clusters at normal and grazing incidences. The extent of the induced damage was determined using Rutherford backscattering spectrometry in channeling geometry (RBS-C). A damage cross-section of 3.1 × 10⁻¹² cm² was obtained for the highest electronic stopping power (76.2 keV nm⁻¹). From electron microscopy observations continuous amorphous tracks were evidenced around the projectile trajectory and an electronic stopping power threshold for damage creation of 18 keV nm⁻¹ was also determined. The spatial correlation in depth of the cluster components were deduced from both direct track length measurements and the damage profiles extracted from RBS-C analysis. The maximal correlation length represents about one-third of the projected range (R_p) of a free carbon. Using atomic force microscopy (AFM), conically shaped hillocks corresponding to the out of plane expansion of the latent tracks were observed. These structures characterize nanometric changes of the plastic properties of sapphire induced by high electronic excitations.     

Investigation of plasma exposed W–1% La2O3 tungsten in a high ion flux,low ion energy,low carbon impurity plasma environment for the International Thermonuclear Experimental Reactor

Previous investigations of tungsten for the International Thermonuclear Experimental Reactor (ITER) were focusing on using energetic ion beams whose energies were over 1 keV. This study presents experimental results of exposed W–1% La₂O₃ in high ion flux (10²² m^–2), low ion energies (about 110 eV) steady-state deuterium plasmas at elevated temperatures (873–1250 K). The tungsten samples are floating during plasma exposure. Using a high-pressure gas analyzer, the residual carbon impurities in the plasma are found to be about 0.25%. No carbon film is detected on the surface by the EDX analysis after plasma exposure. An infrared pyrometer is also used as an in situ detector to monitor the surface emissivities of the substrates during plasma exposure. Using the scanning electron microscopy, microscopic pits of sizes ranging from 0.1 to 5 μm are observed on the plasma exposed tungsten surfaces. These pits are believed to be the results of erupted deuterium gas bubbles, which recombine underneath the surface at defect locations and grain boundaries, leading to substrate damage and erosion loss of the substrate material. Low temperature plasma exposure of a tungsten foil indicates that deuterium gas (D₂) is trapped inside the substrate. Macroscopic blisters are observed on the surface. The erosion yield of the W–1% La₂O₃ increases with temperature and seems to saturate at around 1050 K. Scattered networks of bubble sites are found 5 μm below the substrate surface. High temperature plasma exposure appears to reduce the population as well as the size of the pits. The plasma exposed W–1% La₂O₃ substrates, exposed above 850 K, retain about 10¹⁹ D/m², which is two orders of magnitude less than those retained by the tungsten foils exposed at 400 K.