Ion beam microanalysis of individual aerosol particles originating from Saharan dust episodes observed in Debrecen,Hungary

Approximately 50 episodes of Saharan dust intrusion have been observed by PIXE in the atmosphere of Debrecen, Hungary since 1991 [I. Borbély-Kiss, Á.Z. Kiss, E Koltay, Gy. Szabó, L. Bozó, J. Aerosol Sci. 35 (2004) 1205]. In order to separate dust particles of Saharan origin from local sources, and to follow the formation, ageing and evolution of particles originating from long range transport processes, individual dust particle analysis was carried out on the Debrecen ion microprobe.The samples were collected on polycarbonate filters at a rural site 50 km from Debrecen during the Saharan sand plume in November 1996.Quantitative elemental concentrations for elements Z ? 6 were determined using PIXE–PIXE and STIM analytical methods. Saharan dust particles were selected on the base of characteristic elemental ratios like Ti/Ca, Ti/Fe and Al/Ca. Major and trace element content and possible chemical composition of the selected particles were determined.Single particle analysis of Saharan dust particles will lead to a better understanding of their formation process during transport.     

Erbium environment on Er-doped silica and alumino-silicate glass films: An EXAFS study

Er-doped dielectric films are characterized by the emission of a photoluminescence signal at λ = 1.54 μm, the main used in the optical telecommunications. The efficiency of the radiative emission is strongly related to the characteristics of the Er³⁺ environment. Er-doped SiO₂ films (synthesized by rf-magnetron co-sputtering) and 87SiO₂:10Al₂O₃:3Na₂O silicate glass films doped with 0.5 mol% of Er (prepared by sol–gel route and subsequently doped with silver by Ag⁺ ? Na⁺ field-assisted solid-state ion exchange) were studied by extended X-ray absorption fine structure spectroscopy performed at Er L_III-edge (Italian beamline GILDA of the ESRF). In the silica samples the Er coordinates about 4.5 O atoms at a short distance (R = 2.07–2.13 Å), similar to the one observed in Er-doped glasses when the preparation conditions are far from the thermodynamical equilibrium. In alumino-silicate samples the first shell of atoms is formed of 5.5–7.5 O atoms at a distance of about 2.31 Å, showing a local structure similar to other Er-doped sol–gel glasses and glass–ceramics. A comparison between the first shell structure around Er ions and the different intensity of the photoluminescence emission suggests that the increase of the radiative emission upon thermal annealing is mainly related to the decrease of the defects number in the glass structure as a consequence of the annealing.     

10Be in desert sands,falling dust and loess in China

Cosmogenic ¹⁰Be is produced in the atmosphere, and deposits onto the surface of the earth mainly through wet precipitation and dust. Based on the analysis of ¹⁰Be in Chinese loess, we believe that ¹⁰Be in loess is composed of two components: locally precipitated atmospheric ¹⁰Be, and windblown ¹⁰Be adsorbed on the surface of silt grains. On the Loess Plateau, ¹⁰Be concentrations in loess and paleosol range from (1.4 to 2.8) × 10⁸ atoms/g and (2.7 to 4.5) × 10⁸ atoms/g, respectively. To investigate the sources of ¹⁰Be in loess, we measured ¹⁰Be in sand grains from deserts in western China and falling dust from the deposition regions. The results show that the ¹⁰Be concentrations in sand and dust are (1.1–5.1) × 10⁷ atoms/g and (1.3–2.8) × 10⁸ atoms/g, respectively. Loess and paleosol on the Loess Plateau both contain inherited ¹⁰Be adsorbed on silt grains from dust; most of the windblown deposited loess materials do not directly come from the Gobi and other sand deserts, but mainly from the loess–desert transitional zones, which are characterized by silt and dust holding areas.     

Effect of Li3+ irradiation on the transport properties of La0.7Pb0.3MnO3 type CMR material

We report the low temperature (below the metal–insulator transition temperature T_im) resistivity and magnetoresistance (MR) behavior of 50 MeV Li³⁺ beam irradiated La_0.7Pb_0.3MnO₃ for three different fluences. Ion beam irradiation causes a decrease of T_im leading to the increase of insulating regime. Resistivity data of the unirradiated as well as irradiated samples fitted well with an equation of the form ρ = ρ₀ + ρ_2.5T^2.5 which indicates predominant contribution from the electron–magnon interaction (second term). The temperature dependent MR data of samples irradiated with different ion fluences follow the simple relation [MR = a + b/(T + C)] showing appreciable effect of radiation on the parameters a, b and C. The physical significance of the radiation effect on these parameters is not yet very clear.     

Photoluminescence induced by Si implantation into Si3N4 matrix

Up to the present, photoluminescence (PL) was obtained from near stoichiometric or amorphous Si nitride films (SiN_x) after annealing at high temperatures. As a consequence, the existence of PL bands has been reported in the 400–900 nm range. In the present contribution, we report the first PL results obtained by Si implantation into a stoichiometric 380 nm Si₃N₄ film. The Si excess is obtained by a 170 keV Si implantation at different temperatures with a fluence of Φ = 10¹⁷ Si/cm². Further, we have annealed the samples in a temperature range between 350 and 900 °C in order to form the Si precipitates. PL measurements were done using an Ar laser as an excitation source, and a broad PL band basically centered at 910 nm was obtained. We show that the best annealing condition is obtained at T_a = 475 °C for the samples implanted at 200 °C, with a PL yield 20% higher than the obtained at room temperature implantation. Finally, we have varied the implantation fluence and, consequently, the Si nanocrystals size. However, no variation was observed nor in the position neither in the intensity of the PL band. We concluded that the PL emission is due to radiative states at the matrix and the Si nanocrystals interface, as previously suggested in the literature.     

Er+ medium energy ion implantation into lithium niobate

Erbium-doped lithium niobate (Er:LiNbO₃) is a prospective photonics component, operating at 1.5 μm, which could find its use chiefly as an optical amplifier or waveguide laser. In this study, we have focused on the properties of the optically active Er:LiNbO₃ layers, which are fabricated by medium energy ion implantation under various experimental conditions. Erbium ions were implanted at energies of 330 and 500 keV with fluences of 1.0 × 10¹⁵, 2.5 × 10¹⁵ and 1.0 × 10¹⁶ cm^?2 into LiNbO₃ single-crystalline cuts of various orientations. The as-implanted samples were annealed in air at 350 °C for 5 h. The depth distribution and diffusion profiles of the implanted Er were measured by Rutherford Backscattering Spectroscopy (RBS) using 2 MeV He⁺ ions. The projected range R_P and projected range straggling ΔR_P were calculated employing the SRIM code. The damage distribution and structural changes were described using the RBS/channelling method. Changes of the lithium concentration depth distribution were studied by Neutron Depth Profiling (NDP). The photoluminescence spectra of the samples were measured to determine whether the emission was in the desired region of 1.5 μm. The obtained data made it possible to reveal the relations between the structural changes of erbium-implanted lithium niobate and its luminescence properties important for photonics applications.     

Fabrication and characterization of (U,Am)O2−x transmutation targets

A novel dust-free route for the preparation of (U, Am)O_2?x targets has been demonstrated using a combined sol–gel and single- or double Am-infiltration process at the Minor Actinide Laboratory (MALAB) of the Institute for Transuranium Elements (ITU). Samples with 10 and 20 mol% of Am were prepared. For both Am concentrations, a single cubic phase material with a fluorite structure was observed by X-ray diffraction. X-ray absorption spectroscopy was carried out to characterize the chemical state of the metal atoms and their local crystallographic environment. The U(IV) and Am(III) valence states are predominant and the O/Am ratio is ～1.6 for both Am contents. For the 20 mol% Am, EXAFS reveals an expansion of the Am–O (2.43 Å) bond length beyond the metal–oxygen bond length in both AmO₂ (2.31 Å) and UO₂ (2.35 Å).     

Er+ implantation in SnO2:SiO2 layers: Structure changes and light emission

Structure changes and light emission behavior in Er⁺ implanted SnO₂:SiO₂ layers are studied, using transmission electron microscopy (TEM), Rutherford backscattering (RBS) and cathodoluminescence (CL). SnO₂:SiO₂ layers of different composition deposited with RF magnetron sputtering on Si wafers were implanted with 200 keV Er⁺ to a fluence of 3 × 10¹⁵ cm^?2 at room temperature. The implanted structures were then annealed at 600–1000 °C for 30 min, resulting in the formation of crystalline SnO₂ nanoclusters. Cross-section TEM revealed a strong reduction of the SnO₂ crystallite size down to several nanometers in the implanted area of the SnO₂:SiO₂ layer as compared to the undoped layer. In addition, a very narrow layer of SnO₂ nanocrystals appears at the SiO₂/Si interface. Several narrow CL emission peaks and wide bands were found which could be related to the decay of SnO₂ free excitons, to oxygen deficiency centers in SiO₂ and to transitions between the energy levels in the Er ions, apparently located at nanoclusters. The mechanisms of nanostructuring as well as the emission process are discussed.     

Oxidation properties of Zr–Nb alloys at 973–1273 K in air

In order to investigate the oxidation behavior of LWR cladding materials under the condition of reactor accidents, e.g. LOCA, Zr–Nb alloys with 1–10 wt%Nb and Zircaloy-4 (0 wt%Nb) were oxidized at 973–1273 K in dry air. The weight gain due to oxidation increased with Nb content at 973 and 1073 K was the smallest for 2.5 wt%Nb at 1173 and 1273 K. The oxidation kinetics obeyed the parabolic rate law without a few cases, e.g. 6–10 wt%Nb and 1273 K. The parabolic rate constant at high temperatures had the somewhat low activation energy compared to that at low temperatures. These results implied that such oxidation behaviors of Zr–Nb alloys related to the lattice structures of oxide films as well as underlying metal during oxidation. Especially at high temperatures, 6ZrO₂–Nb₂O₅ compound might promote the oxidation of Zr–Nb alloys with high content of Nb.     

Point defects induced in ion irradiated 4H–SiC probed by exciton lines

The defects produced in 4H–SiC epitaxial layers by irradiation with a 200 keV H⁺ ion beam in the fluence range 6.5 × 10¹¹–1.8 × 10¹³ ions/cm² are investigated by Low Temperature Photoluminescence (LTPL–40 K).The defects produced by ion beam irradiation induce the formation of some sharp lines called “alphabet lines” in the photoluminescence spectra in the 425–443 nm range, due to the recombination of excitons at structural defects.From the LTPL lines intensity trend, as function of proton fluence, it is possible to single out two groups of peaks: the P₁ lines (e, f, g) and the P₂ lines (a, b, c, d) that exhibit different trends with the ion fluence. The P₁ group normalized yield increases with ion fluence, reaches a maximum at 2.5 × 10¹² ions/cm² and then decreases. The P₂ group normalized yield, instead, exhibits a formation threshold at low fluence, then increases until a maximum value at a fluence of 3.5 × 10¹² ions/cm² and decreases at higher fluence, reaching a value of 50% of the maximum yield.The behaviour of P₁ and P₂ lines, with ion fluence, indicates a production of point defects at low fluence, followed by a subsequent local rearrangement creating complex defects at high fluence.     

Effective atomic and electron numbers of some steels at different energies

The effective atomic numbers (Z_eff) and effective electron density (N_e) for three different steels have been determined via the mass attenuation coefficients (μ/ρ). The mass attenuation coefficients have been calculated at the photon energy range of 1 keV–1 GeV and measured at the photon energies of 662, 1173 and 1332 keV. The measurement has been performed using a gamma spectrometer that contains a NaI(Tl) detector connected to Multi-Channel-Analyzer (MCA). The measured results of effective atomic numbers (Z_eff) and effective electron density (N_e) were found to be in good agreement with the calculations.     

Boron lattice site location in (BGa)As and (BGa)P thin films studied using RBS and NRA with a channeled He+ ion beam

In this study the boron lattice site location in ternary B_xGa_1?xAs and B_xGa_1?xP thin films grown on (0 0 1) GaAs and (0 0 1) GaP, respectively, using low pressure metal-organic vapour-phase epitaxy (MOVPE) with boron concentrations between x = 0.8% and x = 3.2% was investigated with RBS and the ¹⁰B(α,p)¹³C nuclear reaction using a 2.3 MeV He⁺ ion beam. For this purpose, the ion beam was aligned with the [0 0 1], [0 1 1] and [1 1 1] axis and the RBS and proton yield from the nuclear reaction compared with random ion incidence. For comparison, theoretical proton yields which assume boron to be located on substitutional lattice sites only were calculated for each sample/axis combination and compared with the experimental yields. The RBS/channeling measurements show a very good crystal quality of the films with χ_min being in the range of 3–5% for the [0 1 1] axis. The best crystal qualities, i.e. the lowest χ_min values and dechanneling rates, are achieved for low boron concentrations. From NRA/channeling it can be deduced that in the B_xGa_1?xAs films the fraction of interstitial boron is approximately 5% for low boron concentrations of x = 1% and 6–10% for concentrations up to x = 3.2%, whereas the fraction of interstitial boron is less than 3% in the B_xGa_1?xP film studied despite a concentration of x = 2.0%. This indicates that antisite effects of the boron incorporation are more likely in GaAs compared to GaP.     

Y(BD4)3, an efficient store of deuterium,and impact of isotope effects on its thermal decomposition

Y(BD₄)₃, which stores as much as 16.6 wt.% and 252 kg/m³ D, has been synthesized via high-energy disk milling. The thermal decomposition of Y(BD₄)₃ has been investigated using thermogravimetric and calorimetric analyses combined with the spectroscopic evolved gas analysis. Two major endothermic events corresponding to thermal decomposition could be distinguished in the DSC profile up to 400 °C at ca. 231 and 285 °C, preceded by a phase transition (at ca. 198 °C) from the low-temperature Pa-3 form to a high-temperature polymorph of Y(BD₄)₃ (F-43c). The high-temperature phase forming at the onset of thermal decomposition may be prepared quantitatively by heating of the low-temperature phase to ca. 216 °C followed by rapid quenching.Effects of isotope H→D substitution on various properties of yttrium borohydride have been analyzed. Y(BD₄)₃ constitutes a very efficient low-temperature source of deuterium gas on the laboratory scale.     

Evaluation of ductile–brittle transition temperature before and after neutron irradiation for RPV steels using small punch tests

Small punch (SP) tests were performed to evaluate the ductile–brittle transition temperature before and after a neutron irradiation of reactor pressure vessel (RPV) steels produced by different manufacturing (refining) processes. The results were compared to the standard transition temperature shifts from the conventional Charpy tests and the Master Curve fracture toughness tests in accordance with the American Society for Testing and Materials (ASTM) standard E1921. Small punch specimens were taken from a 1/4t location of the vessel thickness and machined into a 10 mm × 10 mm × 0.5 mm dimension. The specimens were irradiated in the research reactors at Korea Atomic Energy Research Institute Nuclear Research Institute in the Czech Republic at the different fluence levels of about 290 °C. Small punch tests were performed in the temperature range of RT to −196 °C using a 2.4 mm diameter ball. For the materials before and after irradiation, the small punch transition temperatures (T_SP), which are determined at the middle of the upper small punch energies, showed a linear correlation with the Charpy index temperature, T_41 J. T_SP from the irradiated samples was increased with the fluence levels and was well within the deviation range of the unirradiated data. However, the transition temperature shift from the Charpy test (ΔT_41 J) shows a better correlation with the transition temperature shift (ΔT_SP(E)) when a specific small punch energy level rather than the middle energy level of the small punch curve is used to determine the transition temperature. T_SP also had a correlation with the reference temperature (T₀) from the Master Curve method using a pre-cracked Charpy V-notched (PCVN) specimen.     

Formation of germanium nanoparticles in silica glass studied by optical absorption and X-ray absorption fine structure analysis

We examined the relation between the 3.1 eV emission band and local structure for Ge⁺ implanted silica glass by means of photoluminescence, optical and X-ray absorption spectroscopies. In the 2 × 10¹⁵ cm^?2 implanted sample, a new emission band around 2.7 eV was observed, the origin of which was assigned to the B_2α oxygen deficient center and/or small Si clusters in silica. When the Ge⁺ fluence exceeded 2 × 10¹⁶ cm^?2, a sharp and intense 3.1 eV emission band replaced the 2.7 eV band. We found that the intense 3.1 eV PL occurred by the prolonged X-ray irradiation onto the 2 × 10¹⁵ cm^?2 implanted sample. UV–vis absorption and XAFS spectroscopies suggested that the aggregation of atomically dispersed tetravalent (Ge(IV)) atoms into Ge(0) clusters of ～1 nm exhibit strongly correlation with the generation of the 3.1 eV PL. Such nano- and/or subnano-size Ge(0) clusters formed by the X-ray radiation were oxidized and decomposed again to the isolated Ge(IV) atoms, while those produced by the higher Ge⁺ fluence were stable against the exposure to air.     

Investigation of hydrogen concentration and hardness of ion irradiated organically modified silicate thin films

A study of the effects of ion irradiation of organically modified silicate thin films on the loss of hydrogen and increase in hardness is presented. NaOH catalyzed SiNa_wO_xC_yH_z thin films were synthesized by sol–gel processing from tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) precursors and spin-coated onto Si substrates. After drying at 300 °C, the films were irradiated with 125 keV H⁺ or 250 keV N²⁺ at fluences ranging from 1 × 10¹⁴ to 2.5 × 10¹⁶ ions/cm². Elastic Recoil Detection (ERD) was used to investigate resulting hydrogen concentration as a function of ion fluence and irradiating species. Nanoindentation was used to measure the hardness of the irradiated films. FT-IR spectroscopy was also used to examine resulting changes in chemical bonding. The resulting hydrogen loss and increase in hardness are compared to similarly processed acid catalyzed silicate thin films.     

Deducing the stress–strain response of anisotropic Zr–2.5%Nb pressure tubing by spherical indentation testing

In this paper we developed a method of analysis by which the average stress–plastic strain flow curve of mechanically anisotropic materials can be deduced from spherical indentation test data. Our analysis is based upon spherical indentation tests performed on the extruded and cold-drawn Zr–2.5%Nb CANDU pressure tube material over the range of temperature from 25 °C to 300 °C. The indentation force and depth data were analyzed and σ_avg and ?_avg were calculated using previously reported equations developed for spherical indentation of isotropic material which were then modified, by incorporating the appropriate Hill’s anisotropy coefficients, to characterize the anisotropic yield stress of the indented material. The resulting flow curves were dependent on indentation direction and correspond closely with flow curves obtained from previously reported conventional uniaxial stress tests performed on the Zr–2.5%Nb material. Indentation tests performed with large, 200 μm, and small, 40 μm, diameter spheres indicate that for small diameter indentations, when the indentation depth is less than several micrometers, the calculated σ_avg is heavily influenced by the depth dependence of the yield strength of the indented material.     

Measurement of thermal neutron cross section and resonance integral for 165Ho(n, γ)166gHo reaction by the activation method

The thermal neutron cross section and the resonance integral of the reaction ¹⁶⁵Ho(n, γ)^166gHo were measured by the activation method using ⁵⁵Mn(n,γ)⁵⁶Mn monitor reaction. The sufficiently diluted MnO₂ and Ho₂O₃ samples with and without a cylindrical Cd case were irradiated in an isotropic neutron field of the ²⁴¹Am–Be neutron sources. The γ-ray spectra from the irradiated samples were measured with a calibrated n-type high purity Ge detector. Thus, the thermal neutron cross section for ¹⁶⁵Ho(n,γ)^166gHo reaction has been determined to be 59.2 ± 2.5 b relative to the reference thermal neutron cross section value of 13.3 ± 0.1 b for the ⁵⁵Mn(n,γ)⁵⁶Mn reaction, and it generally agrees with the recent measurements within about 1 to 12%. The resonance integral has also been measured relative to the reference value of 14.0 ± 0.3 b for the ⁵⁵Mn(n,γ)⁵⁶Mn reaction using an epithermal neutron spectrum of the ²⁴¹Am–Be neutron source. The resonance integral for ¹⁶⁵Ho(n, γ)^166gHo reaction obtained was 667 ± 46 b at a cut-off energy of 0.55 eV for 1 mm Cd thickness. The existing experimental and evaluated data for the resonance integral are distributed from 618 to 752 b. The present resonance integral value agrees with most of the previously reported values obtained by ¹⁹⁷Au standard monitor within the limits of error.     

Determination of differential cross-sections for the natK(p, p0) and 39K(p, α0) reactions in the backscattering geometry

In the present work, new, differential cross-section values are presented for the ^natK(p, p₀) reaction in the energy range E_lab = 3000–5000 keV (with an energy step of 25 keV) and for detector angles between 140° and 170° (with an angular step of 10°). A qualitative discussion of the observed cross-section variations through the influence of strong, closely spaced resonances in the p + ³⁹K system is also presented. Information has also been extracted concerning the ³⁹K(p,α₀) reaction for E_lab = 4000–5000 keV in the same angular range. As a result, more than ～500 data points will soon be available to the scientific community through IBANDL (Ion Beam Analysis Nuclear Data Library – http://www-nds.iaea.org/ibandl/) and could thus be incorporated in widely used IBA algorithms (e.g. SIMNRA, WINDF, etc.) for potassium depth profiling at relatively high proton beam energies.