Doppler Broadening Spectroscopy Research Articles

Dehydration of bioethanol using novel polysulfone (PSF)/nonionic surfactants hybrid membranes

This study focuses on developing a novel polysulfone (PSF) dense hybrid membrane modified with nonionic surfactants, Tween 20 (T20) and Triton X-100 (X100), for improved pervaporation (PV) dehydration of bioethanol. The modified membranes were then examined for their ethanol dehydration performance, microscopy and spectroscopy characteristics, surface charge, mechanical and roughness properties, crystallinity structure, differential scanning calorimetry (DSC), swelling, and contact angle (CA) analysis. The free volume structure of the membranes was assessed using positron annihilation lifetime spectroscopy (PALS) and Doppler broadening spectroscopy (DBS). A significant discovery from this analysis was the semi antiplasticizing effect observed when surfactants were added to the PV membranes. The PV results revealed that incorporating 0.5 wt% T20 into PSF significantly improved the total flux and PSI of PSF/T20 to 226.35 g/m2 h and 46578 g/m2 h, respectively. Similarly, the total flux and PSI of hybrid membranes containing X100 increased to 110.19 g/m2 h and 43680 g/m2 h. Consequently, the developed PSF/T20 membranes demonstrated more significant potential for bioethanol dehydration compared to PSF/X100 membranes.

Electrochemical characterization and structural analysis of (In2O3)/(Fe2O3) nanocomposites for high-performance supercapacitors

This study presents a comprehensive investigation of the electrochemical characteristics and structural properties of novel nanocomposites with varying compositions of (In2O3)x/(Fe2O3)1-x, where x ranges from 1 to 0. These nanocomposites were synthesized using a versatile and cost-effective co-precipitation method. The crystallographic structure and morphology of the synthesized samples were thoroughly analyzed using Powder X-ray diffraction (PXRD) and Tunneling Electron Microscopy (TEM). Advanced analytical techniques were employed including Positron Annihilation Lifetime Spectroscopy (PALS) and Coincidence Doppler Broadening Spectroscopy (CDBS) to uncover critical insights into the structural and molecular properties of these nanocomposites. PALS analysis revealed valuable insights into the pore characteristics of the nanocomposites, while CDBS identified crucial molecular interactions within the materials. Electrochemical characterization of the nanocomposites is carried out using cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical-impedance-spectroscopy (EIS) measurements. The (In2O3)0.3/(Fe2O3)0.7 nanocomposite exhibits a remarkable specific capacitance of 945 F g-1 at 1 A g-1 and exceptional rate performance, retaining 93.6% of its specific capacitance at a six-fold higher current density. Moreover, this nanocomposite electrode demonstrates outstanding cyclic stability, maintaining 92.1% of its specific capacitance even after 3000 GCD cycles at 8 A g-1. These findings suggest that the novel composition and integrated electrochemical properties of the (In2O3)0.3/(Fe2O3)0.7 nanocomposite hold great promise for enhancing the performance of next-generation electrochemical capacitors. This research contributes valuable insights into the design and development of advanced energy storage materials with applications in various high-performance energy storage devices.

In-situ positron annihilation spectroscopy during tensile tests on Al alloys

We present a materials analysis method to enable in-situ Doppler broadening spectroscopy (DBS) of the 511 keV annihilation line in matter during tensile tests. This technique allows the correlation between the formation of lattice defects on an atomic scale and the macroscopic physical materials properties stress and strain. By implanting a monoenergetic positron beam into samples of AlMg3 (3.3535) and AlMgSi (3.3206) the onset of plastic deformation was clearly observed in the recorded annihilation spectra during the measurement of the corresponding stress–strain curves. The changes of the DBS spectra are attributed to positron annihilation in (open-volume) defects—predominantly vacancies elastically bound to dislocation lines—formed during plastic deformation. The elastic strain (Hook’s region), however, does not lead to changes in DBS spectra.

Effect of Ag incorporation on the microstructure and properties of ZnS thin films

In this study, ZnS thin films doped with different content of Ag were deposited on quartz glass substrates by RF magnetron sputtering technique and were annealed at 600 °C in sulfur vapor. The crystal structure, grain size, surface morphology, composition, optical properties and defects of the doped ZnS thin films were analyzed by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), UV–Vis spectroscopy and positron annihilation doppler broadening spectroscopy (DBS). The results showed that all films exhibited the cubic sphalerite structure with a preferred orientation along the (111) crystal plane, and the composition of the doped films were more consistent with the stoichiometric ratio compared to the undoped film. The grain size gradually increased as the Ag content grew, indicating the improvement of crystallinity of the ZnS thin films. Besides, the bandgap values of these ZnS films with good optical transparency in the visible region were decreased from 3.87eV to 3.53eV as the Ag content grew. DBS results also showed that the defect concentration of ZnS films gradually decreased from the surface to the inner layer, and the film defects decreased with the increase of Ag content. However, the types of defects changed when the Ag content increased. Furthermore, the results showed Ag also has an effect on the porosity of ZnS thin films.

Effect of Mo alloying on vacancy-defect evolution and irradiation damage in titanium alloy

The evolution of defects and irradiation damage in Ti and Ti-Mo alloy under hydrogen ion irradiation were investigated by slow positron-beam doppler broadening spectroscopy (DBS) and coincidence doppler broadening spectroscopy (CDB), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD results indicate that the existence of the β phase enhances the solid solubility of hydrogen in Ti-Mo alloy. The metastable γ-TiH hydrides are formed in pure titanium after hydrogen ion irradiation, while no hydride is found in Ti-Mo alloy under the same irradiation conditions. Moreover, DBS and CDB results show that hydrogen vacancy-complexes are formed in Ti and Ti-Mo alloys after hydrogen ion irradiation. Calculated doppler curves trend qualitatively agrees well with the experimental results. The TEM results show lower defect concentration and smaller defect sizes in Ti-Mo alloy with (α + β) than pure titanium. The addition of molybdenum significantly refines the grains and increases the density of the interface, which plays an important role in the management of irradiation-induced defects.

Novel data analysis tool for the evaluation of Coincidence Doppler Broadening Spectra of the positron–electron annihilation line

Coincidence Doppler Broadening Spectroscopy (CDBS) of the 511keV annihilation line reveals the elemental signature at the annihilation site in matter. For this reason, CDBS enables the analysis of foreign atoms in the host matrix, vacancy-solute complexes and precipitates in solids. Due to the lack of a comprehensive program for the analysis of CDBS data we developed a modular python-based open source software solution for the reliable extraction of the annihilation line to provide so-called ratio curves highlighting the elemental signature in the spectra. In particular, the new program allows the readout and spectra averaging of multiple detector pairs. Moreover, we implemented an improved algorithm to further reduce the background by about one order of magnitude at high Doppler shifts.

The Microstructure of Zr/Nb Nanoscale Multilayer Coatings Irradiated with Helium Ions

The effect of helium ion irradiation on the microstructure and properties of composites based on Zr/Nb nanoscale multilayer coatings (NMCs) was studied. X-ray diffraction (XRD), transmission electron microscopy (TEM), and variable-energy Doppler broadening spectroscopy (DBS) were used for the in-depth analysis of defects in the irradiated NMCs. After irradiation of the Zr/Nb NMCs with helium ions at a 1017 ion/cm2 dose, the layered structure was generally retained, but the internal stresses in the layers were increased, which caused wave-like distortion in the ion deposition zone. The Zr/Nb NMCs with an individual layer thickness of 25 nm were characterized by the smallest microstress changes, but single blisters were formed in the near-surface region. The microstructure of the Zr/Nb NMCs with a layer thickness of 100 nm exhibited relatively smaller changes upon helium ion irradiation. The prevailing positron-trapping center was the reduced-electron-density area at the interfaces before and after irradiation of the Zr/Nb NMCs regardless of the layer thickness. However, the layer thickness affected the DBS parameter profiles depending on the positron energy, which was probably due to the different localization of implanted ions within the layers or at the interfaces.

Characterisation of defects in porous silicon as an anode material using positron annihilation Doppler Broadening Spectroscopy

Here we present Positron Annihilation Doppler Broadening Spectroscopy (PADBS) as a powerful method to analyse the origin and development of defect processes in porous silicon structures as a result of alloying with lithium for the use in battery anode applications. Several prepared anodes were lithiated (discharged against Li+/Li) and de-lithiated (charged) with different capacities followed by a distinct treatment procedure and an analysis using the Delft Variable Energy Positron Beam. The results presented here show that we can distinguish two different processes attributed to (1) structural changes in silicon as a result of the alloying process, and (2) the formation of defects that initiate degradation of the material. The limit at which the porous material can be used for at least the first two cycles without the occurrence of damage can thus be accurately determined by using the PADBS technique.

Distribution of Hydrogen and Defects in the Zr/Nb Nanoscale Multilayer Coatings after Proton Irradiation.

Radiation damage is one of the significant factors limiting the operating time of many structural materials working under extreme conditions. One of the promising directions in the development of materials that are resistant to radiation damage and have improved physical and mechanical properties is the creation of nanoscale multilayer coatings (NMCs). The paper is devoted to the experimental comprehension of changes in the defect structure and mechanical properties of nanoscale multilayer coatings (NMCs) with alternating layers of Zr and Nb under irradiation. Series of Zr/Nb NMCs with different thicknesses of individual layers were fabricated by magnetron sputtering and subjected to H+ irradiation. The evolution of structure and phase states, as well as the defect state under proton irradiation, was studied using the methods of high-resolution transmission electron microscopy (HRTEM), X-ray diffraction analysis (XRD), glow discharge optical emission spectroscopy (GDOES), and positron annihilation spectroscopy (PAS). The layer-by-layer analysis of structural defects was carried out by Doppler broadening spectroscopy (DBS) using a variable-energy positron beam. To estimate the binding energy and the energy paths for the hydrogen diffusion in Zr/Nb NMCs, calculations from the first principles were used. When the thickness of individual layers is less than 25 nm, irradiation causes destruction of the interfaces, but there is no significant increase in the defect level, the S parameter (open volume defects amount) before and after irradiation is practically unchanged. After irradiation of NMC Zr/Nb with a thickness of layers 50 and 100 nm, the initial microstructure is retained, and the S parameter is significantly reduced. The GDOES data reveal the irregular H accumulation at the interface caused by significant differences in H diffusion barriers in the bulk of Zr and Nb multilayers as well as near the interface’s region.

Micro-defects evolution of (Al0.33Cr0.21Fe0.28Zr0.18)O2 and (Al0.33Cr0.2Mn0.09Fe0.22Zr0.16)O2 induced by hydrogen ions irradiation

The micro-defects evolution of (Al 0 . 33 Cr 0 . 21 Fe 0 . 28 Zr 0.18 )O 2 and (Al 0 . 33 Cr 0 . 2 Mn 0 . 09 Fe 0 . 22 Zr 0.16 )O 2 thin films irradiated with low energy (60 eV) hydrogen ions (H + ) is investigated through Transmission Electron Microscopy (TEM) and the slow positron Doppler broadening spectroscopy (DBS) technique in this work. The results revealed that some perfect dislocation loops with Burgers vector b = a/2<1 1 0> were observed as the quaternary (Al 0 . 33 Cr 0 . 21 Fe 0 . 28 Zr 0.18 )O 2 irradiated with a fluence of 5.2 × 10 22 cm −2 . The micro defects are mainly vacancy (V), hydrogen vacancy complex (i.e. H–V complex), and vacancy dislocation loops. However, after the fluence increased to 1.2 × 10 23 cm −2 , the phase of (Al 0 . 33 Cr 0 . 21 Fe 0 . 28 Zr 0.18 )O 2 transformed from FCC structure to amorphous, suggesting that the weak ionic bonds between the cations with O. The defects mainly exist as large amounts of hydrogen bubbles, some H–V complex and few voids. As the addition of little Mn element, the phase of quinary (Al 0 . 33 Cr 0 . 2 Mn 0 . 09 Fe 0 . 22 Zr 0.16 )O 2 was unstable and easily produce precipitate under the irradiation temperature. And the micro-defects in (Al 0 . 33 Cr 0 . 2 Mn 0 . 09 Fe 0 . 22 Zr 0.16 )O 2 irradiated with 5.2 × 10 22 cm −2 mainly exist as V, H–V complex and some vacancy clusters. While the fluence increase to 1.2 × 10 23 cm −2 , the defects mainly exist as H–V complex and hydrogen bubbles. • The defects evolution of the two HEOs induced by H + irradiation behave differently. • The ionic bonds between the cations with O in (Al 0 . 33 Cr 0 .. 21 Fe 0 . 28 Zr 0.18 )O 2 are weak. • As the addition of Mn, the phase of (Al 0 . 33 Cr 0 . 2 Mn 0 . 09 Fe 0 . 22 Zr 0.16 )O 2 was unstable. • Hydrogen diffuse into both the surface and inner direction of films.

Ion beam-based coincidence Doppler broadening spectroscopy of positron annihilation radiation: The experiences of Tehran Van de Graaff lab

Coincidence Doppler Broadening Spectroscopy of positron annihilation radiation is developed using high energy gamma-rays instead of standard positron source for defect assessment in thick samples. A 2.5 MeV proton beam of a Van de Graaff accelerator is used to generate high-energy gamma-ray through 19Fp,αγ16O nuclear reaction. The collimated gamma-ray is used to generate positron inside the sample. The performance of the technique to support the positron annihilation spectroscopy experiment is evaluated by investigation of the defect evolution of five low-carbon steel samples preloaded during the uniaxial tension test. The variation of the S-parameter versus strain is investigated and discussed considering the engineering stress-strain curve of the samples. Moreover, the advantages and limitations of the technique over the conventional CDBS are discussed. The developed spectrometer provides a systematic approach for the defect assessment in thick high-Z elements samples.

Positron annihilation studies on N+ implantation induced vacancy type defects and its recovery in SI: 6H- SiC

Variable energy positron beam with Doppler broadening spectroscopy (DBS) was used to investigate the depth-resolved defects formed by two fluencies of 130 keV N+ implanted in Semi Insulating (SI) 6H-SiC. The implanted ions induced damages near the surface and to a depth of 300 nm as simulated by SRIM analysis. Defects recovery, accumulation, and its behavior with two annealing temperatures were also considered. Defect types and its effect on annealing were analyzed from the changes in electron momentum and modeled as layers using variable energy positron fitting (VEPFIT) methods. Inclusion of electric field strength in the fitting procedure supported layer characteristics and the state of charge carriers. Di-vacancies, vacancy complexes observed in the damaged layers were agglomerated at the surface and tend to cure on annealing.

Defects introduced by helium irradiation at different temperatures in W and W-5wt%Re alloy

W and W-5wt%Re alloy were irradiated by 50 keV helium ions at RT, 200 °C, 350 °C and 500 °C to investigate the influence of temperature on the microdefects and surface morphology in the sample. The microdefects in the subsurface region and the surface damage caused by irradiation were characterized by Doppler broadening spectroscopy (DBS) of slow positron beam, transmission electron microscope (TEM) and scanning electron microscopy (SEM), respectively. The results show that a large number of vacancy-type defects were produced after helium ions irradiation, especially at 500 °C, the vacancy-type defects of W alloy are higher than that of W-5wt%Re alloy, which indicated that Re restricted the behavior of vacancy-type defects in tungsten to some extent. The surface irradiation damage such as crystal gap enlargement, grain fell off and pores were observed at different irradiation temperatures. Compared with the coral-like structure observed in W, the circular objects and Hilly-gully structure were observed in W-5wt%Re alloy, and both of them increased and grew with the increase of irradiation temperature. It was speculated that the presence of Re led to the difference by analyzing the formation mechanism of the coral-like structure and the Hilly-gully structure.

The investigation of distribution on size and concentration of helium bubbles in Y-bearing ODS steel using by SAXS and GIXRD

The nucleation and growth of the helium bubble in the structure material usually were subjected to temperature in a thermodynamic environment. In this study, Y-bearing oxide dispersed strengthened (ODS) ferritic/martensitic steels were used as the research material. The Y-bearing ODS steel samples with a thickness of 30 microns were irradiated successively by helium ions with three energies of 300 keV, 400 keV and 550 keV at room temperature and 450°C respectively. Firstly, the evolution of defects caused by H e + irradiation is analyzed by using slow positron beam Doppler broadening spectroscopy (DBS) in positron annihilation spectroscopy technology (PAS). The formation and growth of helium bubbles are deduced from the changes in the concentration of vacancy-type defects. The increase in the size of the helium bubbles at high temperatures leads to a certain distortion of the crystal lattice, which is also verified by analyzing the grazing incidence X-ray diffraction (GIXRD) patterns. The characterization of radius and concentration of helium bubbles in samples irradiated at room temperature and 450°C have been studied by Small Angle X-ray Scattering (SAXS) and Transmission Electron Microscopy (TEM). The results showed that the intensity (I) ~ q-vector (q) curves of samples vary with irradiation temperature over ranges of 0.13 ≤ q ≤ 4.6 nm −1 , which is attributed to the growth of helium bubbles at different irradiation temperature. It is found that the average size of helium bubbles under room temperature irradiation is about 1.78 nm, and the size distribution is narrow, while at the irradiation temperature of 450°C, the size of helium bubbles increases to 2.9 nm, and the size distribution is wider. This result is also verified from the TEM analysis. Besides, the shape of helium bubbles was assumed roughly and tends to spherical with higher temperatures.

Studies of Defect Structure in Epitaxial AlN/GaN Films Grown on (111) 3C-SiC.

Several aspects such as the growth relation between the layers of the GaN/AlN/SiC heterostructure, the consistency of the interfaces, and elemental diffusion are achieved by High Resolution Transmission Electron Microscopy (HR-TEM). In addition, the dislocation densities together with the defect correlation lengths are investigated via High-Resolution X-ray Diffraction (HR-XRD) and the characteristic positron diffusion length is achieved by Doppler Broadening Spectroscopy (DBS). Moreover, a comparative analysis with our previous work (i.e., GaN/AlN/Si and GaN/AlN/Al2O3) has been carried out. Within the epitaxial GaN layer defined by the relationship (111) 3C-SiC || (0002) AlN || (0002) GaN, the total dislocation density has been assessed as being 1.47 × 1010 cm−2. Compared with previously investigated heterostructures (on Si and Al2O3 substrates), the obtained dislocation correlation lengths (Le = 171 nm and Ls =288 nm) and the mean distance between two dislocations (rd = 82 nm) are higher. This reveals an improved crystal quality of the GaN with SiC as a growth template. In addition, the DBS measurements upheld the aforementioned results with a higher effective positron diffusion length = 75 ± 20 nm for the GaN layer.

The influence of rhenium addition on the distribution of vacancy-type defects in tungsten

To investigate the influence of transmutation rhenium on the irradiation-induced defects in tungsten , H + and He + irradiation of 50 keV with a fixed fluence of 1 × 10 16 atoms·cm −2 were conducted on W x Re ( x =0, 3, 5 and 25 wt.%) alloys, respectively. Doppler Broadening Spectroscopy and Coincidence Doppler Broadening Spectroscopy both based on slow positron beam were employed in the current work to characterize the depth distribution and the chemical surroundings of the irradiation-induced defects. The results showed that under 723K irradiation, Re addition suppressed the accumulation of vacancy-type defects compared with pure W. This suppression was enhanced by increasing Re content in W. An obvious Re-related peak from (7-28) × 10 −3 m 0 c was observed in CDB spectra of well-annealed W-Re alloys. The irradiation effect led to the height deviation of Re-related peak. The decrease of the Re-related peak could be attributed to the formation of irradiation-induced defects in irradiated samples, and the reduction of positron annihilation fraction with core electrons of Re.

Recent Progress on the Positron Annihilation Experiments on Irradiated Ferritic/Martensitic Steels Containing Helium

The well-known and often acceptable radiation tolerance of ferritic/martensitic (f/m) steels can be severely diminished when neutron irradiation is accompanied by the production of helium. The presence of helium in the irradiated materials changes the kinetics of the nucleation, recombination, and clustering of the radiation-induced defects. High production rates of helium may lead to a non-negligible volumetric bubble swelling at relatively low temperatures. Extrapolation of the knowledge gained from neutron irradiation experiments to fusion or spallation environments is additionally complicated due to the unknown and comprehensive effects of dpa rate, temperature, the presence of sinks in the crystal lattice and others. To improve the understanding of the microstructure and irradiation parameters effects, close attention must be paid to the early stages of the radiation damage. It is expected that the pre-existing vacancy-type defects, attributed to lattice distortion at the grain/subgrain boundaries and oxide-matrix interfaces, are effective sinks for primary defects and helium, i.e. they control the formation and growth of helium-vacancy agglomerations. This early-stage radiation damage, however, cannot be captured by conventional transmission electron microscopy, and thus other experimental techniques are called for. One of the most perspective experimental approaches to investigate small vacancy-type defects, with a high sensitivity to confined helium, is to utilize positron annihilation spectroscopy (PAS). In particular, two spectroscopy techniques, positron annihilation lifetime spectroscopy (PALS) and Doppler broadening spectroscopy (DBS) of the annihilation line, can be beneficially used for the characterization of helium-vacancy clusters. This paper reviews the recent positron annihilation spectroscopy characterization of various irradiation experiments involving helium. Mainly two types of irradiation experiments are addressed, helium implantation and spallation neutron source irradiation experiments. Discussion is aimed at the potential of PAS in the early-stage formation of helium bubbles and the investigation of the effects of irradiation parameters in defect production and accumulation.

FACILITIES FOR NANO MATERIALS EXAMINATION AT THE PULSTAR REACTOR

The PULSTAR is a 1-MWth nuclear research reactor located at North Carolina State University. It is fueled by uranium dioxide assemblies enriched to 4% or 6% in U-235 and is currently under licensing for operation at 2-MWth power. The PULSTAR is a center for irradiation testing and pre/post irradiation examination of materials. Among its unique capabilities are positron annihilation spectroscopy (PAS) and neutron powder diffraction (NPD) facilities. The PAS facility provides an intense positron beam reaching 6 × 108 e+/s, which drives two spectrometers; the e+-PAS and the Ps-PAS, used for studies of defects in thin film materials. A Na-22 bulk PAS system is also operational, which is used for studying millimeter scale materials. All spectrometers are capable of performing Doppler Broadening Spectroscopy (DBS) and Positron Annihilation Lifetime Spectroscopy (PALS). To date, the PAS systems have been used to characterize various materials (unirradiated and irradiated) that include graphite, soft matter, and metal-organic frameworks (MOF). The NPD facility uses a double focusing single crystal silicon rotating monochromator producing neutron beams with different energies. A position sensitive detection bank covers a scattering angle of 5°-125°. The facility is used in the examination of unirradiated and irradiated materials including graphitic materials, magnetic materials without rare-earth elements, and anode materials used in lithium batteries. The collected diffraction patterns can be processed to produce atomic pair distribution functions. The PAS and NPD facilities are available through user programs including the US DOE’s Nuclear Science User Facilities (NSUF) and the US NSF’s Research Triangle Nanotechnology Network (RTNN).

Defects in H/He neutral beam irradiated potassium doped tungsten alloy by positron annihilation technique

Pure tungsten (W) is a primary plasm-facing material (PFM) candidate because of its superior properties, but it still has some drawbacks. In order to solve these problems, various methods have been used to improve the performances of tungsten-based materials. Potassium (K) doping, as one of the typical dispersion-strengthening methods for W materials, improves low temperature brittleness, reduces the ductile-brittle transition temperature, and suppresses the recrystallization. Meanwhile, it also improves the thermal shock resistance and fracture toughness of the material by introducing nano-sized K bubbles. However, this method brings a large number of defects inevitably. In fact, the K bubbles and the dislocations which are pinned by these K bubbles can affect the morphology and evolution of hydrogen (H) and helium (He) atoms in the alloys. As a very sensitive method to detect vacancy-type defects in materials, positron annihilation spectroscopy is used to study the irradiation damage caused by H and He atoms in this paper. The calculation of positron lifetime shows that positrons are more sensitive to the vacancy-type defects. Bounding of H and He with vacancies reduces the positron lifetime because of the increase of valence electron density. Combining the calculated results with the positron annihilation lifetime spectrum (PLAS) results shows that the W-K alloy is easier to promote the H atoms to release. Besides, it also more likely to form larger He bubbles which can be estimated by positron lifetime values. The result is also confirmed by the measurements from the scanning electron microscope (SEM) and slow positron Doppler broadening spectroscopy (DBS). The defects in the W-K alloy such as K bubbles and their pinned dislocations can act as diffusion channels to promote the H atoms to release, which gives rise to a smoother surface under the pure H irradiation. Meanwhile, under the condition of the H+6%He irradiation, the K bubbles and their pinned dislocations in the W-K alloy become the capture center of He atoms, promote their nucleation and grow into larger He bubbles. Moreover, under the action of stress and temperature gradient, some of the He bubbles migrate to the surface and release, this process is conducive to the recovery of related defects and the reduction of radiation damage.

Study on the interaction between He and defects induced by He-ion irradiation in W and W5Re alloy

To investigate the interaction between He atom and irradiation-induced defects in W and W5Re, multiple energetic He ions with damage dose ranging from 0.84 dpa to 1.63 dpa were selected in the present study to implant into W and W5Re samples. Doppler broadening spectroscopy (DBS) and coincidence Doppler broaden spectroscopy (CDB) based on slow positron beam and synchrotron X-ray diffraction technology were employed in the current work. Under the same dose (≤ 1 × 1021 ions m−2) irradiation at room temperature, the depth distribution of vacancy-type defects in W and W5Re is similar. With the increase of irradiation dose, the vacancy-type defects in W continue to grow through absorbing and merging. However, Re atoms are more likely to hinder this growth mechanism, leading to an accumulation of high density but small size vacancy-type defects in W5Re. The HenVm complexes in W continuously attract the mobile interstitial He atom and then induce the trap mutation in the implanted region. Micro-voids and large He bubbles (∼ μm) exceed the recognition of positron. Re atoms has strong the attraction to vacancies and positron affinity. The possible compound of Re and HenVm complexes makes it easier for positron to characterize the He-related and Re-related information around the defect sites. The lattice swelling is similar for the W and W5Re because the structure of HenVm cluster or He bubble can destroy the lattice periodicity and increase the lattice stress in the implanted region.