Nuclear Reaction Analysis Method Research Articles

Changes in the Structure and Microhardness of Rapidly Solidified Foils of Aluminum Alloy 1421 during Their Annealing

In this work, the relationship between the microstructure and microhardness of Al–Mg–Li–Zr–Sc alloy (1421 Al) prepared by ultrafast quenching from the melt has been studied. The following methods are used in studying the rapidly solidified (RS) alloy: scanning electron microscopy integrated with energy dispersive X-ray microanalysis, the method of nuclear reaction analysis, and the measurement of microhardness changes during isochronal annealing. The intercept method is applied to determine the size of secondary phases, their volume fraction, and the specific surface area of the interface boundaries in the samples. It is established that the as-quenched rapidly solidified alloy foils are composed of an aluminum-based supersaturated solid solution. It is found that lithium, the content of which reaches 9.0 at %, is unevenly distributed over the subsurface region of foils. After annealing at 300°C, precipitates of (Sc, Zr)-containing phase are detected in the structure of foils in addition to magnesium-containing phases. Nonmonotonic changes in the microhardness are observed during isochronal annealing of the foils in the temperature ranges of 50–100°C, 150–210°C, 230–340°C, which are associated with the precipitation of metastable and stable phases. It is found that heating of the alloy foils to 340°C leads to an increase in the microhardness by 23%, and a sharp decrease in the microhardness takes place at temperatures above 400°C.

Novel insight into the chemical analysis of light elements in oxycarbides

Pure powders of TiCxO(1-x) solid solution were synthesized through the carbothermal route. The chemical analysis of the light elements in the as-obtained TiCxO(1-x) oxycarbides powders were performed by Instrumented Gas Analysis (IGA). The cell parameters of the samples were determined with an accuracy of about 2% by means of X-ray powder diffraction and the internal standard method. As a result, a model correlating the cell parameters to the chemical composition was established. These reference TiCxO(1-x) oxycarbides powders were then sintered in order to obtain pellets of dense ceramics. After having determined that the sintering process does not change the chemical composition of the starting powder, chemical analysis of the different samples of the solid solution were successfully undertaken by Ion Beam Analysis techniques (IBA). The Nuclear Reaction Analysis (NRA) method - that was used to analyse light elements with very high sensitivity - was coupled with Rutherford Back Scattering (RBS) analysis in order to accurately determine the metallic over light elements ratio and to determine the stoichiometry of the phase on massive samples. Exhaustive simulations of the NRA spectra were performed and demonstrated that discrete compositions of the TiCxO(1-x) can be efficiently measured locally for bulk samples. Compared to IGA results, the relative amounts of carbon and oxygen of bulk materials were determined with a bias lower than 5%. This protocol being implemented for the TiCxO(1-x) system was then tested on HfCxO(1-x)with the same success.

Helium and deuterium irradiation effects in tungsten-based materials with titanium

Pure Tungsten (W) will be used as plasma facing component in fusion devices due to its high melting point, good thermal conductivity and low sputtering yield. However, its structural application as plasma facing component (PFC) is still restricted by its low fracture toughness associated with the high ductile to brittle transition temperature (DBTT).In the present study tungsten‑titanium (W-Ti) samples were produced by Ti implantation at room temperature and 500 °C with a constant fluence of 2 × 1021 at/m2 and an energy of 100 keV. In order to understand the fundamental mechanisms which govern the behavior of defect dynamics in tungsten under reactor conditions, W-Ti materials were implanted at room temperature with 10 keV of He+ with a constant fluence of 5 × 1021 at/m2 and 5 keV of D+ with fluences in the range of 0.1 × 1021–5 × 1021 at/m2. Surface structure and morphology changes were investigated by scanning electron microscopy and X-ray diffraction. Rutherford backscattering spectrometry, nuclear reaction analysis and thermal desorption spectroscopy methods were used to provide information about the distribution of Ti, He and D on W.No changes in the microstructure were observed after Ti implantation in the W plates. NRA analysis showed that D retention in the W-Ti samples is higher after sequential He and D implantation when compared with single D implantation. The diffractogram of W-Ti samples implanted with He evidence a broadening of the W peaks. This effect is believed to be associated with the high volume fraction of the bubbles that may cause internal stress fields inducing extended defects like dislocations which distort the crystal lattice.

Measurement of differential cross section of D(3He,p)4He from 0.8 MeV to 3.6 MeV

Abstract Precise knowledge of the nuclear reaction cross-section is crucial for nuclear reaction analysis methods and its applications. In order to apply nuclear reaction analysis methods to Plasma Facing Materials studies on 4.5 MV electrostatic accelerator at Peking University, differential cross-section for d(3He,p) α at several backward angles was measured with a relative error about ± 6.2 % , gives detailed information at the laboratory angle of 135° from 800 keV to 3600 keV, as well as a rough angular distribution from 130° to 160°.

Depth profiling Li in electrode materials of lithium ion battery by 7Li(p,γ)8Be and 7Li(p,α)4He nuclear reactions

A proton induced γ-ray emission method based on 7Li(p,γ)8Be proton capture reaction and a nuclear reaction analysis method involving 7Li(p,α)4He reaction are described for depth profiling Li in the electrode materials, graphite and lithium cobalt oxide for example, of a Li-ion battery. Depth profiling by 7Li(p,γ)8Be reaction is accomplished by the resonance at 441keV and involves the measurement of 14.6 and 17.6MeV γ-rays, characteristic of the reaction, by a NaI(Tl) detector. The method has a detection sensitivity of ∼0.2at% and enables profiling up to a depth ≥20µm with a resolution of ≥150nm. The profiling to a fairly large depth is facilitated by the absence of any other resonance up to 1800keV proton energy. The reaction has substantial off-resonance cross-sections. A procedure is outlined for evaluating the off-resonance yields. Interferences from fluorine and aluminium are major limitation of this depth profiling methodology. The depth profile measurement by 7Li(p,α)4He reaction, on the other hand, utilises 2–3MeV protons and entails the detection of α-particles at 90° or 150° angles. The reaction exhibits inverse kinematics at 150°. This method, too, suffers interference from fluorine due to the simultaneous occurrence of 19F(p,α)16O reaction. Kinematical considerations show that the interference is minimal at 90° and thus is the recommended angle of detection. The method is endowed with a detection sensitivity of ∼0.1at%, a depth resolution of ∼100nm and a probing depth of about 30µm in the absence and 5–8µm in the presence of fluorine in the material. Both methods yielded comparable depth profiles of Li in the cathode (lithium cobalt oxide) and the anode (graphite) of a Li-ion battery.

Hydrogen release from irradiated elastomers measured by Nuclear Reaction Analysis

Ion irradiation appears as an interesting method of modification of elastomers, especially friction and wear properties. Main structural effect caused by heavy ions is a massive loss of hydrogen from the surface layer leading to its smoothening and shrinking. The paper presents the results of hydrogen release from various elastomers upon irradiation with H+, He+ and Ar+ studied by using Nuclear Reaction Analysis (NRA) method. The analysis of the experimental data indicates that the hydrogen release is controlled by inelastic collisions between ions and target electrons. The last part of the study was focused on preliminary analysis of mechanical properties of irradiated rubbers.

Application of PIGE, BS and NRA techniques to oxygen profiling in steel joints using deuteron beam

In order to study the oxygen content and to characterize the oxygen depth profile on the surface of welded steel joints in the function of the applied shielding gases, particle induced gamma-ray emission (PIGE), backscattering spectrometry (BS) and nuclear reaction analysis (NRA) methods were used. The measurements were carried out at 1.0, 1.4 and 1.8MeV deuteron energies. From the PIGE oxygen and carbon elemental maps (1000×1000μm2) taken with a beam of 2×2μm2 beam size, oxygen rich regions were chosen for the depth profile analysis. The investigated depth was ∼6μm using particle detection (BS, NRA), which was extended to ∼11μm with the application of the differential-PIGE method, using the numerical integration of experimental cross-section data. The oxygen depth profiles show systematic discrepancy in the oxide layer thickness and composition between the two different kind of shielding gases.

Experimental study of UC polycrystals in the prospect of improving the as-fabricated sample purity

Uranium and plutonium carbides are candidate fuels for Generation IV nuclear reactors. This study is focused on the characterization of uranium monocarbide samples. The successive fabrication steps were carried out under atmospheres containing low oxygen and moisture concentrations (typically less than 100ppm) but sample transfers occurred in air. Six samples were sliced from four pellets elaborated by carbothermic reaction under vacuum. Little presence of UC2 is expected in these samples. The α-UC2 phase was indeed detected within one of these UC samples during an XRD experiment performed with synchrotron radiation. Moreover, oxygen content at the surface of these samples was depth profiled using a recently developed nuclear reaction analysis method. Large oxygen concentrations were measured in the first micron below the sample surface and particularly in the first 100–150nm. UC2 inclusions were found to be more oxidized than the surrounding matrix. This work points out to the fact that more care must be given at each step of UC fabrication since the material readily reacts with oxygen and moisture. A new glovebox facility using a highly purified atmosphere is currently being built in order to obtain single phase UC samples of better purity.

Study of correlation of deuterium content in a-C:D dust induced by laser irradiation from the co-deposited surface with the grain size and velocity

In the study described here, the laser ablation method was applied to clean thick (40–60 μm) a-C:D co-deposits on the ALT-II limiter blade from the TEXTOR tokamak, and at the same time to characterize the ejected particles formed during ablation and measure the amount of fuel carried by them. Ablation was accomplished by ∼ 3.5 ns, 0.5 J Nd:YAG laser pulses in either vacuum or an O2 atmosphere at different pressures. Fast camera tracking of the process provided an estimate of the population and velocity of up to 100 m s−1 for larger dust particles. In the same experiment, the dust particles were caught using ultra-light Si aerogel collectors placed in front of the ablation target. SEM analysis of aerogel surfaces verified the speed estimate, providing the trapped particles’ size distribution and particle yield during ablation. The D/C atomic concentration ratio was measured with the 3HE ion beam nuclear reaction analysis method in deposited layers before ablation and with a micro-ion beam in individual particles on aerogel collectors. This indicated that most of the D was thermally released during ablation, leaving no more than 5% of its original amount in the particles. The effect of ablation conditions on the acceleration of ejected particles, their population, composition and D content is the main subject of this paper.

Ion beam analyses for Li2TiO3 blanket candidate material

Combined NRBS (non-Rutherford backscattering spectroscopy) and NRA (nuclear reaction analysis) methods have been applied to Li2CO3 samples with Li of various isotopic compositions. Densities of the component elements as well as the isotopic composition of Li have been determined within an error of about 10% or less. The NRBS method has also been applied to a high-density Li2TiO3 sample to investigate double-shell formation under CO2 absorption. By showing appearance of a Ti-free layer on the sample surface, usefulness of the method for investigation of the mechanism of the double-shell formation is demonstrated.

Nuclear reaction analysis of Ge ion-implanted ZnO bulk single crystals: The evaluation of the displacement in oxygen lattices

The displacement of oxygen lattices in Ge ion-implanted ZnO bulk single crystals is studied by nuclear reaction analysis (NAR), photoluminescence (PL), and Van der Pauw methods. The Ge ion-implantation (net concentration: 2.6×1020cm−3) into ZnO is performed using a multiple-step energy. The high resistivity of ∼103Ωcm in un-implanted samples remarkably decreased to ∼10−2Ωcm after implanting Ge-ion and annealing subsequently. NRA measurements of as-implanted and annealed samples suggest the existence of the lattice displacement of O atoms acting as acceptor defects. As O related defects still remain after annealing, these defects are not attributed to the origin of the low resistivity in 800 and 1000°C annealed ZnO.

Depth profiling of high energy nitrogen ions implanted in the 〈1 0 0〉, 〈1 1 0〉 and randomly oriented silicon crystals

This work reports on the experimentally obtained depth profiles of 4MeV 14N2+ ions implanted in the 〈100〉, 〈110〉 and randomly oriented silicon crystals. The ion fluence was 1017particles/cm2. The nitrogen depth profiling has been performed using the Nuclear Reaction Analysis (NRA) method, via the study of 14N(d,α0)12C and 14N(d,α1)12C nuclear reactions, and with the implementation of SRIM 2010 and SIMNRA computer simulation codes. For the randomly oriented silicon crystal, change of the density of silicon matrix and the nitrogen “bubble” formation have been proposed as the explanation for the difference between the experimental and simulated nitrogen depth profiles. During the implantation, the RBS/C spectra were measured on the nitrogen implanted and on the virgin crystal spots. These spectra provide information on the amorphization of the silicon crystals induced by the ion implantation.

Origins of low resistivity in Al ion-implanted ZnO bulk single crystals

The origins of low resistivity in Al ion-implanted ZnO bulk single crystals are studied by combining Rutherford backscattering spectroscopy (RBS), nuclear reaction analysis (NRA), photoluminescence (PL), and Van der Pauw methods. The Al-ion implantation (peak concentration: 2.6 × 1020cm−3) into ZnO is performed using a multiple-step energy. The resistivity decreases from ∼104 Ω cm for un-implanted ZnO to 1.4 × 10−1 Ω cm for as-implanted, and reaches 6.0 × 10−4 Ω cm for samples annealed at 1000 °C. RBS and NRA measurements for as-implanted ZnO suggest the existence of the lattice displacement of Zn (Zni) and O (Oi), respectively. After annealing at 1000 °C, the Zni related defects remain and the Oi related defects disappear. The origin of the low resistivity in the as-implanted sample is attributed to the Zni (∼30 meV [Look et al., Phys. Rev. Lett. 82, 2552 (1999)]). In contrast, the origin of the low resistivity in the sample annealed at 1000 °C is assigned to both of the Zni related defects and the electrically activated Al donor. A new PL emission appears at around 3.32 eV after annealing at 1000 °C, suggesting electrically activated Al donors.

Hydrogen loss from elastomers subjected to ion irradiation

Hydrogen release from various elastomers upon irradiation with H +, He + and Ar + ions has been studied using nuclear reaction analysis (NRA) method. A massive loss of hydrogen atoms upon irradiation has been noted, the results point to the saturation of hydrogen content at about 10 at.%. The analysis of the experimental data indicates that the hydrogen release is controlled by inelastic collisions between ions and target electrons.

Measurement of 1H(15N, αγ)12C Nuclear Reaction Analysis Method at Atmosphere with Glass Capillary

In order to obtain 3D mapping of the hydrogen distribution in solids in-situ, the nuclear reaction analysis (NRA) measurement has been carried out by using a tapered glass capillary to focus and introduce the incidence beam to the sample under atmosphere. A Y thin film covered with Pd was used for this measurement. In the N2 gas, hydrogen absorbed by the Y film was observed at a pressure up to 8×103 Pa. In the H2 gas and air, on the other hand, substantial γ-ray signals were observed at 15N energies of 6400~7200 keV, which obscured the signal originating from the Y sample. The origin of this signal is discussed.

Dynamic surface barrier effects on hydrogen storage capacity in Mg–Ni films

Hydrogen distribution profiles in Mg–Ni films deposited on quartz substrate by the magnetron-sputter co-deposition of Mg and Ni atoms have been investigated after hydrogenation at 8 × 10 5 Pa hydrogen pressure at temperatures 210, 230 and 250 °C during 1, 3, 6 and 72 h using elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA) methods. Oxygen distribution profiles in the near-surface region have been measured by ERDA. It is shown that hydrogen storage capacity decreases as hydrogenation temperature increases from 210 to 250 °C for fixed hydrogenation duration and changes not monotonously as function of hydrogenation time for a fixed temperature. To explain variations of storage capacity as function of hydrogenation temperature and time, the structural film changes have been studied by X-ray diffraction technique, and surface topography was analysed using scanning electron microscopy. We suggest that registered results may be explained on the basis of assumption about the dynamic properties of surfaces which modify the hydrogen uptake mechanism.

Hydrogen and oxygen concentration analysis of porous silicon

Elastic recoil detection and Rutherford backscattering spectrometry combined with the nuclear reaction analysis method have been applied for the determination of oxygen, hydrogen and carbon concentration depth profiles of aged p+-type porous Si layers of different low and medium porosities. The plan view and cross-section scanning electron microscopy images have provided with information about both the diameter and silicon skeleton structure of the pores. The concentration depth profiles reveal the existence of a non-homogeneous subsurface porous film several hundred nanometers thick for all the studied samples. Differences in the atomic composition among low and medium porosity layers and the possible origin of various impurities are discussed. The maximum H content in PSi has been observed at the depth of 200–600nm, while the highest oxygen concentration is typical of 200nm thick subsurface layers. The highest obtained ratio of H/Si atomic concentrations reaches the value of 2 for the PSi samples with porosity P of 66%, comparing to NH/NSi=0.27 in the case of P=25% PSi.

IBA of ZrO2:Yb/Si thin films produced by the spray pyrolysis method

A spray pyrolysis method was used to produce thin films of ZrO2 doped with different Yb concentrations on Si(100). The films of these ionic semiconductors have potential applications as solid electrolytes in modern ceramic fuel cells of second generation. The determination of the atomic composition of the films is very important because it strongly affects the chemical and thermal stability, as well as electrical properties of the films. A combination of two Ion Beam Analysis (IBA) methods was applied to obtain the atomic composition of the films. A nuclear reaction analysis (NRA) method using a low energy deuterium beam was applied to measure the oxygen content of the films. Heavy ion Rutherford backscattering (HI-RBS) method using a 12C3+ beam was applied to measure the Yb and Zr atomic profiles of the samples. X-ray diffraction (XRD) and ellipsometry were also employed to determine structural properties and refractive index of the films, respectively. The IBA, XRD and the ellipsometry supply a wide range of information about the film layers, which can be used for qualification as well as for feedback to the films production.

Charge profile at the oxide–semiconductor interface of MOS structure in accumulation

An expression has been obtained for the evaluation of the accumulated charges concentration near to the oxide-semiconductor interface of MOS structures by analysis of C–V characteristics of MOS structures measured in the accumulation regime. Using this expression, the spatial profile of acceptor-like deep levels in the Si substrate of 60 nm SiO2/n-Si structures subjected to hydrogen implantation by 1.6 keV ions has been revealed. The spatial profile of implanted hydrogen in SiO2/n-Si structures of these SiO2/n-Si structures has been established by the method of nuclear reaction analysis. A comparison of both spatial profiles shows that the hydrogen concentration is higher than the concentration of the acceptor-like deep levels in the Si substrate of these SiO2/n-Si structures. Toward the SiO2/Si interface the increase of deep level concentration closely match the increase of hydrogen concentration toward the same interface.

Application of nuclear reaction analysis for the fluorine content measurements under the aging investigations of gas-filled particle detectors

The method of nuclear reaction analysis (NRA) for the investigation of the aging effects in gas-filled detectors caused by fluorine and fluorine-containing compounds has been developed. It was shown that the sensitivity of the proposed method is about 1×10 16 at/cm 3. The accuracy of the element concentration measurement is about 5%. The fluorine concentration and its depth distributions have been measured for different gas mixtures (Ar/CO 2/CF 4) under the total accumulated dose of up to 1.8 C/cm. A direct correlation between the distribution of the fluorine concentration along the wire and the beam irradiation profile was found.