Slow Positron Beam Technique Research Articles

The effect of different surface treatments of 310S austenitic stainless steel on the corrosion behavior in supercritical water using slow positron methods

AbstractThe corrosion behavior of 310S austenitic stainless steel, subjected to different surface treatments machined (MA), sandblasting (SB), and polishing (PO), was exposed to a 550°C supercritical water (SCW) environment. The aged samples were analyzed using variable‐energy slow positron beam techniques. The obtained results revealed that the plastic deformation of the near‐surface region of the MA and SB samples was substantially recovered in the SCW conditions. At least two distinct oxide layers formed, and the oxidation process created a Fe/Cr depletion zone in the inner layer. Various surface treatments, however, led to different corrosion profiles. The depth profile of slow positron beam characterization suggests that significant residual stress and deformation zones on the surfaces of the sandblasted samples probably provided a diffusion path for the oxidation of the 310S. Only the SB samples exhibited a negative weight change after SCW exposure. At the same time, the SB samples showed the highest concentration of the positron traps in this region, which was explained by open‐volume defects associated with the microcracks introduced by sandblasting.

Research progress of coincidence Doppler broadening of positron annihilation measurement technology in materials

Positron annihilation technique is an atomic-scale characterization method used to analyze the defects and microstructure of materials, which is extremely sensitive to open volume defects. By examining the annihilation behaviour of positrons and electrons in open volume defects, local electron density and atomic structure information around the annihilation site can be obtained, such as the size and concentration of vacancies, and vacancy clusters. In recent years, positron annihilation spectroscopy has evolved into a superior tool for characterizing features of material compared with conventional methods. The coincident Doppler broadening technique provides unique advantages for examining the local electronic structure and chemical environment (elemental composition) information about defects due to its effectiveness describing high momentum electronic information. The low momentum portion of the quotient spectrum indicates the Doppler shift generated by the annihilation of valence electrons near the vacancy defect. Changes in the peak amplitudes and positions of the characteristic peaks in the high momentum region can reveal elemental information about the positron annihilation point. The physical mechanism of element segregation, the structural features of open volume defects and the interaction between interstitial atoms and vacancy defects are well investigated by using the coincidence Doppler broadening technology. In recent years, based on the development of Doppler broadening technology, the sensitivity of slow positron beam coincidence Doppler broadening technology with adjustable energy has been significantly enhanced at a certain depth. It is notable that slow positron beam techniques can offer surface, defect, and interface microstructural information as a function of material depth. It compensates for the fact that the traditional coincidence Doppler broadening technique can only determine the overall defect information. Positron annihilation technology has been applied to the fields of second phase evolution in irradiated materials, hydrogen/helium effect, and free volume in thin films, as a result of the continuous development of slow positron beam and the improvement of various experimental test methods based on slow positron beam. In this paper, the basic principles of the coincidence Doppler broadening technique are briefly discussed, and the application research progress of the coincidence Doppler broadening technique in various materials is reviewed by combining the reported developments: 1) the evolution behaviour of nanoscale precipitation in alloys; 2) the interaction between lattice vacancies and impurity atoms in semiconductors; 3) the changes of oxygen vacancy and metal cation concentration in oxide material. In addition, coincident Doppler broadening technology has been steadily used to estimate and quantify the sizes, quantities, and distributions of free volume holes in polymers.

Study on UV-laser fatigue damage of sol-gel antireflective coating using XPS and slow positron beam Doppler broadening spectrum

The fatigue damage behavior of antireflective coating over KDP crystal under vacuum environment was studied with varied UV-laser irradiation, and the dynamic process from initial damage to complete failure of this coating was obtained. Scanning electron microscope (SEM) and slow positron beam (SPB) technique was employed to study the macro- and micro-defects in the process of evolution. The formation of non-bridging oxygen (NBO) and the variation of O/Si ratio along the direction of coating depth were obtained during the damage process based on X-ray photoelectron spectroscopy (XPS). The idea that oxygen with low binding energy absorbs UV light and produces oxygen defects to induce damage was put forward, and the damage mechanism of sol-gel antireflective coating under UV-laser irradiation was given.

Experimental comparison of the (ODS)EUROFER steels implanted by helium ions and irradiated in spallation neutron target

The microstructure of EUROFER and ODS-EUROFER has been characterized by means of positron annihilation spectroscopy (PAS) with a particular focus on the effect of irradiation conditions. Two different irradiation experiments have been used to introduced helium-filled cavities in the studied materials. Materials irradiated in spallation neutron target SINQ have been investigated by conventional positron annihilation spectroscopy, while helium-implanted samples of the same materials have been investigated by slow positron beam technique. With this approach, we were able to obtain a significant amount of positron lifetime and Doppler broadening data and evaluate them with respect to the dpa, irradiation temperature and helium concentration effects. Both types of irradiation experiments confirm a more pronounced creation of growing open-volume defects for the Eurofer steel, comparing to its ODS variant. The bubble-to-void transformation was indirectly but clearly confirmed by the Eurofer specimens. In the case of the ODS Eurofer, the coalescence of helium bubbles, accompanied by saturation of positron mean-lifetime and/or S parameter, was not so evident. This present study provides the first experimental positron annihilation data, showing the onset of void formation in ODS steels.

Implantation profiles and depth distribution of slow positron beam simulated by Geant4 toolkit

The positron implantation profiles and depth distribution in metal, semiconductor, and polymer surfaces are simulated using the Monte-Carlo-method-based Geant4 toolkit. As per the slow positron beam technique, the monoenergetic positron beams (in the range from 1 to 35 keV) with 1.5 mm radius is injected into semi-infinite samples in the present work. The implantation profile of 3.1 keV positrons in Fe is in good agreement with the Makhovian profile. The mean depth and depth resolution exhibit a general negative correlation with the material densities and incident position energy, respectively, while the fixed peak energy of backscattered positrons exhibits a net correlation with atomic number Z. Furthermore, the implantation profiles present better z-axis resolution with increasing incident angle, and this effect is more prominent for low-density materials. The results can provide theoretical support for new measurement methods based on the slow positron beam technique, such as segment measurements and micro-beam scanning measurements.

Effect of temperature and dose on vacancy-defect evolution in 304L stainless steel irradiated by triple ion beam

This study aims to investigate the effects of temperature and dose on the vacancy-defect evolution in 304L stainless steel irradiated by the triple beam of Ni, H, and He ions below 673 K, which is relevant to water-cooled nuclear energy facilities. The irradiation experiments were performed simultaneously using 150-MeV Ni ions whose energy was degraded by passing through a tantalum foil of 8.5-μm thick, 100-keV H ions, and 200-keV He ions at 473, 523, 573, 623, and 673 K, respectively. The irradiation-induced microstructures in the steel were probed by the slow positron beam technique. The results show that the S parameter of the irradiated sample decreases as the temperature increases, and the S parameter of the high-dose irradiated sample decreases further. We explained the results by analyzing the structure of the defects in the irradiated samples at various temperatures and the effects of the annealing effect. In addition, the analysis of the SW plots reveals the transition of the helium-vacancy cluster to the overpressured HemVn (m > n) cluster under the influence of temperature and irradiation dose.

4p-YG-10 低速陽電子ビームを利用した金属多層Ni/Hfの非晶質化過程の評価

4p-YG-10 低速陽電子ビームを利用した金属多層Ni/Hfの非晶質化過程の評価

Experimental study on Ti K shell ionization cross sections induced by 8-9.5 keV positrons

Due to lack of experimental data of the inner shell ionization cross sections induced by low-energy positron, advanced theoretical models developed in recent years cannot be correctly evaluated, and the application of slow positron beam technique is greatly limited. Here we present the method of obtaining reliable experiment data of atomic inner-shell ionization cross section by positron impact. In this work, the slow positron beam device is used to generate 8-9.5 keV positron beams impacting on a pure thick Ti target, and the silicon drift detector (SDD) is adopted to collect the X-ray spectra produced by positrons impacting on thick Ti target, and the incident positron numbers are obtained by applying an HPGe detector to on-line collect annihilation photons. Then the experimental characteristic X-ray yields of Ti K shell impacted by 8-9.5 keV positron could be acquired. Meantime, the simulated characteristic X-ray yields are acquired by the PENELOPE program simulating the experiments. In the comparison between the experimental yields and the simulated yields based on two sets of different inner shell ionization cross section database in the PENELOPE code, i.e. the optical data model (ODM) and the distorted-wave Born approximation model (DWBA), there is a large difference between the simulated data from the ODM theoretical model and the experimental values, while the simulated yields from the DWBA theoretical model are in good agreement with the experimental results. Accordingly, a correction factor is introduced to modify the DWBA theoretical model database which is used in the PENELOPE, and then the experimental process is re-simulated. When the simulated yields and the experimental yields are in the highest consistence, the reliable Ti K shell ionization cross sections impacted by 8-9.5 keV positron could be obtained. The biggest advantage of using this method to obtain atomic inner-shell ionization cross section impacted by positron is that the effects of the multiple scattering of incident positrons in the thick target, from the bremsstrahlung and annihilation photons, and other secondary particles on the experimental characteristic X-rays do not need calculating (the calculation method that has been developed previously cannot give the more correct result about the contribution of the multiple scattering of incident positrons, from the bremsstrahlung and annihilation photons, and other secondary particles to characteristic X-rays).

Characterization the microstructure and defects of matrix graphite irradiated with Xe ions

The matrix graphite of pebble fuel elements was irradiated with 1MeV Xe ions at room temperature to fluences of 5.8×1014ions/cm2 and 2.9×1015ions/cm2, respectively. The microstructure and defects of matrix graphite samples were characterized by using scanning electron microscopy (SEM), Raman spectroscopy and slow positron beam techniques. The SEM result reveals that hundred-nanometer sized pores appear at the surface after irradiation and the density of pore increases with fluence. Raman results show that D peak (1350cm−1) and G peak (1580cm−1) are broadened after irradiation. In addition, the G peak position shifts from 1580cm−1 to 1560cm−1 with the linewidth increases from 21cm−1 to 132cm−1, corresponding to the increase in bond-angle disorder as the matrix graphite transforms from microcrystalline to amorphous carbon(a-C). The slow positron beam study shows that the defects-trapped positron S parameter increases with fluence, suggesting that the vacancy-type defects concentration or size of open volume defects increases. The analysis of Raman and slow positron beam consistently conclude that the reason for the phase transition after irradiation is the increase in irradiation-induced vacancy defects accompanied by the overlap of disordered regions.

14th International Workshop on Slow Positron Beam Techniques & Applications

These proceedings arose from the 14th International Workshop on Slow Positron Beam Techniques (SLOPOS14), which was held at Kunibiki Messe, Matsue, Shimane prefecture, Japan, from the 22nd—27th May 2016. Meetings in the SLOPOS series are held every three years.The SLOPOS workshop series has traditionally been devoted to investigations on the production of positron and positronium beams, their fundamental physics and chemistry, and their applications to materials such as metals, semiconductors and soft matter. During the workshop numerous applications using positron and positronium beams were also presented, clearly demonstrating the usefulness of such beams to the determination of surface structure, defect characterization as well as to fundamental scientific studies.For SLOPOS14 the main subjects of the workshop included the following: • Positron transport and beam technology• Pulsed positron beams and positron traps• Defect profiling in bulk and layered structures• Nano structures, porous materials and thin films• Surface and interface analysis• Positronium formation, emission and beams• Positron and positronium interactions with atoms and molecules• Many positrons and anti-hydrogen• Improvement of experimental techniques 106 delegates from 14 countries participated in the SLOPOS14, including 31 student delegates, which was a most encouraging sign for the future. The scientific program comprised 5 plenary talks, 22 invited talks, 32 contributed talks and 46 posters presented during two poster sessions. Student prizes were awarded for the best presented scientific contributions by 4 students from University of College London, Universität der Bundeswehr München and The University of Tokyo.On a sad note, delegates paid tribute to the contributions of our recently deceased colleagues, Prof. A. Seeger, Prof. R.N. West, Prof. T.C. Griffith, and Prof. Z. Tang. Memorial talks were given and a one minute silence was observed before the opening session of workshop in their memory.The workshop would not have been possible without the hard work of the Local Organizing Committee and the International Organizing Committee. We would also like to express our gratitude to the students from Chiba University for their hospitality and efficient support during the workshop.Finally we would like to thank all of the attendees of SLOPOS14 for their scientific contributions to the workshop, and for fruitful discussions in an informal atmosphere.SLOPOS15 will be held in Romania in 2019 and we are all greatly looking forward to the occasion.Masanori Fujinami, Yasuyuki Nagashima, and Brian E. O’Rourke Guest EditorsDecember 2016

Slow positron beam study of corrosion behavior of AM60B magnesium alloy in NaCl solution

The corrosion behavior of super vacuum die-cast AM60B magnesium alloys immersed in a 5wt% NaCl solution was investigated by slow positron beam technique, XRD, XPS, SEM and potentiodynamic polarization tests. The XRD and XPS results indicated that Mg(OH)2 was main corrosion product in the salt solution. With prolonging the immersion time, a significant decrease of Doppler-broadened annihilation line-width parameter near the surface after corrosion was observed and interpreted that the pre-existing interfacial voids between oxide film and matrix might promote the formation of Mg(OH)2 corrosion layer. Polarization tests found that Mg(OH)2 could provide a temporary protection.

Simulation of positron backscattering and implantation profiles using Geant4 code**Project supported by the National Natural Science Foundation of China (Grant Nos. 11175171 and 11105139).

For the proper interpretation of the experimental data produced in slow positron beam technique, the positron implantation properties are studied carefully using the latest Geant4 code. The simulated backscattering coefficients, the implantation profiles, and the median implantation depths for mono-energetic positrons with energy range from 1 keV to 50 keV normally incident on different crystals are reported. Compared with the previous experimental results, our simulation backscattering coefficients are in reasonable agreement, and we think that the accuracy may be related to the structures of the host materials in the Geant4 code. Based on the reasonable simulated backscattering coefficients, the adjustable parameters of the implantation profiles which are dependent on materials and implantation energies are obtained. The most important point is that we calculate the positron backscattering coefficients and median implantation depths in amorphous polymers for the first time and our simulations are in fairly good agreement with the previous experimental results.

Depth‐resolved slow positron beam analysis of ECR proton and argon implanted graphite and boron nitride system

Layered materials and sp2 hybridized structures like graphite and hexagonal‐boron nitride (h‐BN) have been subjected to electron cyclotron resonance (ECR) ion beam implantation of proton and argon ions at different fluences and studied primarily employing slow positron beam technique using positron annihilation Doppler broadening spectroscopy (DBS). The results show remarkable structural perturbation effects in the implantation areas around the depth of ∼200–300 nm from the top surface, in both the systems but with glaring differences in the trends of the line shape analysis in terms of S and W parameters. Due to proton and argon ion implantation, structurally damaged lattice with open volume defects exists in graphite. But, for both the ion implantations at the high fluence, profound clustering effect of the respective atoms within the interstitial space are evident in h‐BN. The structural effects of both graphite and h‐BN lattice after the said implantation have been studied and corroborated through grazing incidence X‐ray diffraction (GI‐Xray) method and Raman scattering spectroscopy as complementary analytical techniques.

Applications and progress of slow positron beam technique in the study of metal/alloy microdefects

In recent decades, the positron annihilation spectroscopy technique has been used to characterize the microdefects of materials due to its advantages of non-destruction and high sensitivity on an atomic level. Positron annihilation spectroscopy technique is widely used in the microstructure study of thin film material surface and interface due to the rapid development of the slow positron beam technology. The slow positron beam technique can provide depth distribution information about material surface microstructure. Therefore, it is widely used to study the distributed defect concentrations in crystalline materials and the properties of thin films, surfaces and interfaces of layered materials. This article summarizes the slow positron beam technique applications and progress in the study of metal alloy materials. Firstly, this article introduces the slow positron beam technology development and application research achievement in detail. Secondly, it provides how to acquire the slow positron beam, introduces some kinds of and the principles of experimental measurements, and the major methods include Doppler bradening spectroscopy, coincidence Doppler broadening and PL. Thirdly, according to the defects induced by different ways, the latest experimental results about the material internal microdefect formation mechanism, evolution mechanism, defect feature research, such as microstructure, chemical environment, electron density and momentum distribution are introduced. The methods of inducing defects mainly include irradiation, physical deformation and chemical corrosion. Particles irradiation can be classified as four parts according to the different types of particles. In addition, monolayer and multilayer thin films have also been summarized. Finally, the new technique of thermal desorption spectroscopy and experimental measurements of age-momentum correlation are proposed. We can know that positron annihilation spectroscopy technology is a very special and effective nuclear spectroscopy analysis method in material microstructure study, and the slow positron beam technique makes it possible to study the depth distribution information about the thin film material surface microstructure. There is no doubt that this technique will play a huge role in the progress of material science and the creation of industrial material.

Probing inhomogeneities in nanoscale organic semiconductor films: Depth profiling using slow positron beam and X-ray reflectivity techniques

Depth profiling studies in 200nm organic semiconductor (OSC) films on quartz substrate have been carried out using slow positron beam and X-ray reflectivity (XRR) techniques with the objective of examining structural inhomogeneities in as-deposited film and those annealed at high temperature. Grazing incidence X-ray diffraction and atomic force microscopy measurements are carried out to examine the crystallinity and surface morphology, respectively. In general, annealing is seen to modify the morphology and nanostructure. However, a significant inhomogeneity in nanostructure, marked by a disordered layer with low density region is observed in the film annealed at 200°C from positron as well as XRR measurements. This study highlights the sensitivity of these techniques to defects and inhomogeneities in nanoscale that may have profound influence on device performance.

Microstructure and corrosion behavior of die-cast AM60B magnesium alloys in a complex salt solution: A slow positron beam study

The microstructure and corrosion behavior of high pressure die-cast (HPDC) and super vacuum die-cast (SVDC) AM60B magnesium alloys were investigated in a complex salt solution using slow positron beam technique and potentiodynamic polarization tests. The experiments revealed that a CaCO3 film was formed on the surface of the alloys and that the rate of CaCO3 formation for the SVDC alloy with immersion time was slower than that of the HPDC alloy. The larger volume fraction of β-phase in the skin layer of the SVDC alloy than that of the HPDC alloy was responsible for the better corrosion resistance.

Perspective of Positron Annihilation Spectroscopy in Polymers

Positron annihilation spectroscopy (PAS) is a novel method that provides molecular-level information about complex macromolecular structure in a manner different from, but complementary to, conventional physical and chemical methodology. This paper presents a perspective of PAS in polymeric systems covering 12 aspects: historical, spacial, spherical quantum model, anisotropic structure, voids, positronium chemistry, time, positron annihilation lifetime spectroscopy and data analysis, variable monoenergetic slow positron beam techniques and depth profiling, elemental analysis, multidimensional instrumentation advances in PAS, and free volume and free-volume theories.

Microstructure characterization of early corrosion behavior of AM60B magnesium alloys

The microstructures and corrosion behavior of AM60B magnesium alloys, produced by both high-pressure die casting (HPDC) and super vacuum die casting (SVDC) processes, were investigated by a combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), and slow positron beam technique. XRD confirmed that calcium carbonate (CaCO3) deposited on the surface of alloys during the early stages of corrosion, and the deposition rate of CaCO3 for SVDC with corrosion time was slower than that of HPDC. SEM observation found that the β-phases in the skin surface of SVDC alloy had a greater volume fraction and more continuous distribution than that of HPDC alloy, leading to lower volume fraction of CaCO3 deposited on surface of SVDC alloy for the same corrosion time. The slow positron beam Doppler broadening measurement revealed that the thickness of surface corrosion layer increased with corrosion time. Compared with HPDC alloy, the increase rate of thickness for SVDC alloy is slower, which implied that SVDC alloy exhibited a better corrosion resistance than HPDC alloy.

Microstructure of functional materials probed by positron annihilation spectroscopy

Functional materials which have excellent performances in electrics, magnetics, optics, calorifics, acoustics, mec- hanics, chemistry and biomedicine are widely used in the various high-tech field. Positron annihilation spectroscopy, including positron annihilation lifetime spectroscopy, Doppler broadening spectroscopy and slow positron beam technique, which is especially sensitive to detect various defects, vacancies and microvoids, is a very effectual method to probe the microstructure of materials. Defecs distribution information from the surface to the inner and microstructure variation due to external physical and chemical condition gradual change can be obtained by refined analysis of positron annihilation parameters. Microstructure of Several types of functional materials was studied by positron annihilation spectroscopy. It’s proved that positron annihilation spectroscopy is a unique technique to study the microstructure of materials.

Design and Construction of a Slow Positron Beam for Solid and Surface Investigations

On the basis of the design and construction of the slow positron beam SPONSOR at the Helmholtz-Centre Dresden-Rossendorf an example is given how to build-up a simple slow positron beam for solid surface investigations within a short time and without high financial costs. The system uses a 22Na source and consists of three main parts: (1) the source chamber with a thin film tungsten moderator used in transmission, and a pre-accelerator stage, (2) the vacuum system with magnetic transport, a bent tube for energy selection and an accelerator, (3) the sample chamber with a sample holder, Ge detectors and (4) facilities for remote control and data acquisition. These parts are described in detail. The paper is preferentially addressed to beginners in the field of slow positron beam techniques and other readers being generally interested in positron annihilation spectroscopy.