Conventional Electron Beam Research Articles

Microstructure and mechanical properties in electron beam scanning welded joints of super thick titanium alloy plates

It is generally difficult to obtain good weld formation and excellent properties in super thick titanium alloy joints via conventional electron beam welding (EBW) methods due to the fact that the melt pool flow becomes more unstable as the plate thickness increases. In this study, electron beam scanning welding (EBSW) was utilized to weld 100 mm Ti–6Al–3Nb–3Zr–1Mo titanium alloy plates to improve the weld formation and impact toughness through the scanning effect. The results revealed that there were spatter and cutting defects on the surface and inner pore defect in the normal EBW joint, which could be effectively eliminated via EBSW. The decrease of the amplitude of the fluid flow rate and the change of the velocity direction were mainly responsible for this. A large amount of lamellar α phase with similar orientation was formed in the fusion zone (FZ) due to the fast cooling rate. The joint coefficient for both EBSW and EBW reached 100%, with the joint tensile strength of ∼840 MPa. The impact energy of the FZ in the EBSW joint was 70.5 J, reaching 210.4% of that of the BM (33.5 J). The impact toughness increase ratio in this study was far larger than those for Ti alloy welds ever reported, which was mainly attributed to that the high angle α colony boundaries with high preferred orientation in the FZ deflected the crack propagation direction. This study provides a reference for the strength-toughness design of EBWed joints of super thick Ti6331 titanium alloy.

Automated determination of the ion-recombination correction factor (ksat) in ultra-high dose rate electron radiation therapy.

Plane-parallel ionization chambers are the recommended secondary standard systems for clinical reference dosimetry of electrons. Dosimetry in high dose rate and dose-per-pulse (DPP) is challenging as ionization chambers are subject to ion recombination, especially when dose rate and/or DPP is increased beyond the range of conventional radiotherapy. The lack of universally accepted models for correction of ion recombination in UDHR is still an issue as it is, especially in FLASH-RT research, which is crucial in order to be able to accurately measure the dose for a wide range of dose rates and DPPs. The objective of this study was to show the feasibility of developing an Artificial Intelligence model to predict the ion-recombination factor-ksat for a plane-parallel Advanced Markus ionization chamber for conventional and ultra-high dose rate electron beams based on machine parameters. In addition, the predicted ksat of the AI model was compared with the current applied analytical models for this correction factor. A total number of 425 measurements was collected with a balanced variety in machine parameter settings. The specific ksat values were determined by dividing the output of the reference dosimeter (optically stimulated luminescence [OSL]) by the output of the AM chamber. Subsequently, a XGBoost regression model was trained, which used the different machine parameters as input features and the corresponding ksat value as output. The prediction accuracy of this regression model was characterized by R2-coefficient of determination, mean absolute error and root mean squared error. In addition, the model was compared with the Two-Voltage (TVA) method and empirical Petersson model for 19 different dose-per-pulse values ranging from conventional to UDHR regimes. The Akiake Information criterion (AIC) was calculated for the three different models. The XGBoost regression model reached a R2-score of 0.94 on the independent test set with a MAE of 0.067 and RMSE of 0.106. For the additional 19 random data points, the ksat values predicted by the XGBoost model showed to be in agreement, within the uncertainties, with the ones determined by the Petersson model and better than the TVA method for doses per pulse>3.5Gy with a maximum deviation from the ground truth of 14.2%, 16.7%, and -36.0%, respectively, for DPP>4Gy. The proposed method of using AI for ksat determination displays efficiency. For the investigated DPPs, the ksat values obtained with the XGBoost model were in concurrence with the ones obtained with the current available analytical models within the boundaries of uncertainty, certainly for the DPP characterizing UDHR. But the overall performance of the AI model, taking the number of free parameters into account, lacked efficiency. Future research should optimize the determination of the experimental ksat, and investigate the determination the ksat for DPPs higher than the ones investigated in this study, while also evaluating the prediction of the proposed XGBoost model for UDHR machines of different centers.

Rapid Switching of a C-Series Linear Accelerator Between Conventional and Ultrahigh-Dose-Rate Research Mode With Beamline Modifications and Output Stabilization

PurposeIn this study, a decommissioned C-series linear accelerator (linac) was configured to enable rapid and reliable conversion between the production of conventional electron beams and an Ultrahigh-dose-rate (UHDR) electron beamline to the treatment room isocenter for FLASH radiation therapy. Efforts to tune the beam resulted in a consistent, stable UHDR beamline. Methods and MaterialsThe linac was configured to allow for efficient switching between conventional and modified electron output modes within two minutes. Additions to the air system allow for retraction of the X-ray target from the beamline when the 10MV photon mode is selected. With the carousel set to an empty port, this grants access to the higher current pristine electron beam normally used to produce clinical photon fields. Monitoring signals related to the automatic frequency control (AFC) system allows for tuning of the waveguide while the machine is in a hold state so a stable beam is produced from the initial pulse. A pulse counting system implemented on a FPGA-based controller platform controls the delivery to a desired number of pulses. Beam profiles were measured with Gafchromic film. Pulse-by-pulse dosimetry was measured using a custom electrometer designed around the EdgeTM diode. ResultsThis method reliably produces a stable UHDR electron beam. Open field measurements of the 16cm (FWHM) gaussian beam saw average dose rates of 432Gy/s at treatment isocenter. Pulse overshoots were limited and ramp up was eliminated. Over the last year, there have been no recorded incidents that resulted in machine downtime due to the UHDR conversions. ConclusionStable 10MeV UHDR beams were generated to produce an average dose rate of 432Gy/s at the treatment room isocenter. With a reliable pulse-counting beam control system, consistent doses can be delivered for FLASH experiments with the ability to accommodate a wide range of field sizes, source-to-surface distances, and other experimental apparatus that may be relevant for future clinical translation.

Commissioning and initial validation of Eclipse eMC algorithm for the electron FLASH research extension (FLEX) system for pre-clinical studies.

To investigate the feasibility of commissioning the 16 MeV electron FLASH Extension (FLEX) in the commercial treatment planning system (TPS) for biomedical research with cell and mouse models, and in silico treatment planning studies. To commission the FLEX system with the electron Monte Carlo (eMC) algorithm in the commercial TPS, radiochromic film was used to measure the vendor-recommended beam data. Once the beam model was generated for the eMC algorithm, supplemental measurements were collected for validation purposes and compared against the TPS-calculated results. Additionally, the newly commissioned 16 MeV FLASH beam was compared to the corresponding 16 MeV conventional electron beam. The eMC algorithm effectively modeled the FLEX system. The eMC-calculated PDDs and profiles for the 16 MeV electron FLASH beam agreed with measured values within 1%, on average, for 6×6 cm2 and 10×10cm2 applicators. Flatness and symmetry deviated by less than 1%, while FWHM and penumbra agreed within 1mm for both eMC-calculated and measured profiles. Additionally, the small field (i.e., 2-cm diameter cutout) that was measured for validation purposes agreed with TPS-calculated results within 1%, on average, for both the PDD and profiles. The FLASH and conventional dose rate 16 MeV electron beam were in agreement in regard to energy, but the profiles for larger field sizes began to deviate(>10×10cm2) due to the forward-peaked nature of the FLASH beam. For cell irradiation experiments, the measured and eMC-calculated in-plane and cross-plane absolute dose profiles agreed within 1%, on average. The FLEX system was successfully commissioned in the commercial TPS using the eMC algorithm, which accurately modeled the forward-peaked nature of the FLASH beam. A commissioned TPS for FLASH will be useful for pre-clinical cell and animal studies, as well as in silico FLASH treatment planning studies for future clinical implementation.

Spin-filter device using the Zeeman effect with realistic channel and structure parameters

We have theoretically calculated the performance of a Zeeman-type spin polarizer, which consists of ferromagnetic (FM) and metal–insulator–semiconductor (MIS) gate nanostructures on top of an InAs two-dimensional electron gas (2DEG) channel. For the calculations, we have taken a realistic electron concentration, electron effective mass and the effective g-factor of the InAs 2DEG into account. In addition, we have assumed realistic FM and MIS structure sizes by conventional electron beam lithography. In the calculations, we have demonstrated clear oscillation of spin polarization over ±85%. Furthermore, we have shown that it works not only as a spin-polarized current generator but also a detector. In addition, we have proposed a novel spin-filter device utilizing the Zeeman-type spin polarizers. We have found that its conductance characterization allows us to evaluate the operation of Zeeman-type spin polarizers. We expect the Zeeman-type spin polarizers and spin-filter devices to open up a new field of spintronics.

Commissioning and Initial Validation of Commercial Treatment Planning System for the Electron FLASH Research Extension

The aim of this study was to investigate the feasibility of commissioning the 16 MeV electron FLASH beam in a commercial treatment planning system (TPS) for pre-clinical research purposes. The delivery system consisted of a new commercial solution for which a linear accelerator was modified into a FLASH Research Extension platform. Additionally, preliminary radiation biology results were highlighted to showcase the future use of this system. To commission a commercial electron Monte Carlo (MC) for dose calculation of a 16 MeV FLASH beam in the TPS, radiochromic film was used to measure the vendor-required beam data, e.g., profiles and percent depth dose (PDD) curves for cone sizes of 6 × 6 cm2, 10 × 10 cm2, and 15 × 15 cm2 as well as an in-air profile for a 40 × 40 cm2 open field (no cone). Once the electron MC beam model was generated, additional measurements were collected for validation and compared against the calculated dose from the TPS. A treatment planning comparison between the newly commissioned FLASH beam and the conventional electron beam was conducted. Specifically, the dose-volume histograms (DVHs) for target volumes and organs at risk were investigated for skin cancer cases previously treated with conventional electron beams. Lastly, the FLASH dose distribution predicted by the electron MC for an in vitro cell study setup was validated with radiochromic film measurements, and initial radiobiology tests were conducted using FLASH and conventional dose-rate electron beams. The electron MC calculated dose for the 16 MeV electron FLASH beam agreed with measured PDDs within 1% for all field sizes. The beam profile characteristics, such as penumbra, shape, and full width at half maximum, demonstrated good agreement with less than 0.5 mm difference between the TPS and measurements. There were noticeable differences in the profiles of large fields between the FLASH and conventional dose-rate beam models due to the more forward-peaked FLASH beam. For treatment planning, Regarding DVH, the FLASH dose-rate plan provided comparable plan quality to the conventional dose-rate plan, achieving adequate coverage for the target volumes and sparing the healthy organs and tissues. The electron MC dose prediction for the FLASH beam was also found to be in good agreement with the film measurements of the in vitro cell study setup. Furthermore, the FLASH beam was observed to be more effective with a 20 % increase in killing pancreatic cancer cells compared to the conventional dose rate. The study successfully incorporated the 16 MeV electron FLASH Research Extension into the commercial TPS using electron Monte Carlo for dose calculation. This will be valuable for pre-clinical cell and animal studies. This research also enables FLASH treatment planning studies, a key component for the future implementation of FLASH into clinical care. Further research is necessary to incorporate the radiation biology effect of FLASH into the treatment planning system.

Comparing the DNA-damage RBE of intraoperative and conventional electron beams using a hybrid simulation approach

Purpose Employing electron beam for radiotherapy purposes now has been established as one of the standard cancer treatment modalities. Both dedicated intraoperative and conventional electron beams can be employed in patient irradiation. Due to the differences between accelerating structure and electron beam delivery of dedicated intraoperative radiotherapy (IORT) machines and conventional ones, the initial energy spectra of the produced electron beam by these machines may be different. Accordingly, this study aims to evaluate whether these spectral differences can affect the relevant relative biological effectiveness (RBE) values of intraoperative and conventional electron beams. Materials and methods A hybrid Monte Carlo simulation approach was considered. At first, the head LIAC12 machine (as an IORT accelerator) and Varian 2100C/D (as a conventional accelerator) were simulated by MCNPX code and electron energy spectra at different depths and off-axis distances were scored for two nominal electron energies of 6 and 12 MeV at the field sizes of 6 and 10 cm. Then, the calculated spectra were imported to MCDS code to estimate the induced DNA-damage RBE values. Finally, the obtained RBE values for intraoperative and conventional electron beams were compared together. Results The results showed that the RBE values of the intraoperative electron beam are superior to those obtained for conventional electron beam at the same energy/field size combination. Variations of the depth can regularly affect the RBE value for both conventional and intraoperative electron beams, while no ordered variation trend was observed for RBE with changing the off-axis distance. Variations of electron energy and field size can also influence the RBE value for both types of studied electron beams. Conclusions From the results, it can be concluded the structural differences between the dedicated IORT and conventional Linacs can lead to distinct initial electron energy spectra for intraoperative and conventional electron beams. These physical differences can finally lead to different RBE values for intraoperative and conventional electron beams at the same energy and field size.

Identification and characterization of goat milk key flavor compounds and their precursors in electron beam irradiation and pasteurization on raw

The electron beam irradiation causes changes in goat milk flavor, which may arise from complex reactions such as fat oxidation. This study aimed to investigate the effects of electron beam irradiation and pasteurization on thiobarbituric acid reactive substance values and the fatty acid composition in goat milk. The multivariate analysis of aroma compounds in goat milk was performed using electron nose and Gas Chromatography and Mass Spectrometry (GC–MS). The results showed that both conventional heat treatments, including pasteurization and electron beam irradiation, resulted in fat content alteration in goat milk. The degree of fat oxidation was proportional to the irradiation dose, with a significant increase in saturated fatty acid content and a significant decrease in unsaturated fatty acid content after irradiation. The multivariate statistical analysis showed that the difference in flavor between milk treated with a high dose (5 kGy) of radiation and raw goat milk was larger. Further, 2,4-dimethyl-1-heptene, 3-methyl pentane, 3,3,5-trimethyl heptane, 2-pentanone, and 1-octene might be the characteristic substances accounting for the flavor difference between raw goat milk, pasteurized milk, and irradiated milk. C10:0, C12:0, C14:0, C16:1, C17:0, and C18:1n9t fatty acids might be the main precursors for the formation of off-flavors of irradiated milk. The results indicated that pasteurization and electron beam irradiation led to flavor alterations in goat milk, and high doses of irradiation might intensify fat oxidation and produce more flavoring compounds.

Enhanced electron beam and X-ray beam therapy by applying nanoparticle heterojunctions: A Monte Carlo simulation

Cancer has become one of the major diseases that seriously threaten human health. In order to improve the therapeutic gain ratio (TGF) of conventional X-ray and electron beams, we studied the dose enhancement effect and secondary electrons emission of Au–Fe nanoparticle heterostructures by Monte Carlo method. Under the irradiation of 6 MeV photon and 6 MeV electron beams, the Au–Fe mixture has a dose enhancement effect. For this reason, we explored the secondary electrons production that leads to dose enhancement. For 6 MeV electron beam irradiation, Au–Fe nanoparticle heterojunctions have an higher electrons emission than Au and Fe nanoparticles. When cubic, spherical and cylindrical heterogeneous structures are considered, the electron emission of the columnar Au–Fe nanoparticles is the highest, with a maximum value of 0.00024. For 6 MV X-ray beam irradiation, Au nanoparticle and Au–Fe nanoparticle heterojunction have similar electrons emission, while Fe nanoparticle has the lowest one. When cubic, spherical and cylindrical heterogeneous structures are considered, the electron emission of the columnar Au–Fe nanoparticles is the highest, with a maximum value of 0.000118. This study contributes to improve the tumor-killing effect of conventional X-ray radiotherapy treatment and has guiding significance for the research of new nanoparticles.

Study on the Influence of Electron Beam Radiation Sterilization Method on Chinese Mural Pigment

Murals are one of the important cultural heritages of mankind. The microbial control of murals is an important subject in mural painting conservation. In recent years, electron beam radiation sterilization has attracted more and more attention in the field of cultural relic protection. Murals are immovable cultural relics, so conventional electron beam irradiation equipment can not be used. However, the development of small mobile electron beam irradiation equipment shows the potential of radiation’s application in the sterilization protection of immovable cultural relics such as murals. A feasibility study of radiation sterilization in mural paintings is needed to investigate the effect of sterilization and the influence of sterilization dose on the stability of mural painting pigments and bonding materials. In this paper, the radiation effects of typical bacteria in tomb murals and mineral pigment powder in ancient Chinese paintings were studied in a laboratory. Firstly, aeromonas hydrophila (Aer.h) and penicillium flavigenum (PNC) were selected as representative strains to determine the appropriate sterilization dose for murals. Then, the effects of radiation on seven kinds of ancient Chinese mineral pigments and white calcium carbonate in the ground layer were verified. The results are as follows: the radiation dose of 10 kGy can effectively remove the two typical strains. This sterilization dose will cause a color difference in calcium carbonate and lead white, while other color pigments are essentially stable. Based on the color difference and UV-vis intensities of the four white carbonate samples, the color change in two of them increased with increasing the dose up to 30 kGy, after which signs of saturation began to appear. X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) spectra showed that the chemical structure of the samples did not change after irradiation. The formation of free radicals in treated samples was confirmed using an electron paramagnetic resonance (EPR) spectrum test. According to all characterization results, the color difference between the four white carbonate samples may be due to the combination of unpaired electrons and defects in the process of electron beam irradiation to form color centers. After forming the color center, the light absorption of the four samples changed. This is a reversible change, but the samples will take a long time to return to their original state. This study focuses on the influence of electron beam radiation on pigment composition, which is a preliminary exploration of whether radiation sterilization can be applied to the protection of ancient Chinese mural paintings, and the experimental results can provide basic data for later application.

Atom-by-Atom Direct Writing.

Direct-write processes enable the alteration or deposition of materials in a continuous, directable, sequential fashion. In this work, we demonstrate an electron beam direct-write process in an aberration-corrected scanning transmission electron microscope. This process has several fundamental differences from conventional electron-beam-induced deposition techniques, where the electron beam dissociates precursor gases into chemically reactive products that bond to a substrate. Here, we use elemental tin (Sn) as a precursor and employ a different mechanism to facilitate deposition. The atomic-sized electron beam is used to generate chemically reactive point defects at desired locations in a graphene substrate. Temperature control of the sample is used to enable the precursor atoms to migrate across the surface and bond to the defect sites, thereby enabling atom-by-atom direct writing.

A study of structural effect on the spectral property of metallic cross-hole array in mid-infrared wavelengths

Based on the earlier success in developing multichannel detection in long (8–14 μm) infrared wavelengths, this paper reports our recent progress for spectral filters in the mid-infrared band of 4–10 μm by introducing a new design with metallic cross annular hole array. The effects of structural dimensions on filtering performance were investigated by numerical simulations with the finite-difference time-domain method and experimentally verified by optical characterizations of fabricated filters made by electron beam lithography. The transmission peaks were optimized with the maximum transmittance of 62%. The existing problem of low spectral resolution of transmittances was tackled by using a thick Au film for the filter, which remains a big challenge for conventional electron beam lithography. By modeling ice lithography in amorphous solid water for constructing the filter, it was found that ice lithography certainly possesses significant advantage in replicating nanoscale features with high aspect ratio. The proposed ice lithography in this work provides an effective solution for the nanofabrication of high performance filters with dense elements in an array in the mid-infrared wavelengths.

A Comparison of Low-Temperature Deformation Behavior and Fracture in Low-Carbon Steel Specimens Obtained by Electron Beam Additive Manufacturing and Conventional Casting and Normalization

In the present work, the microstructure, phase composition, and temperature dependence of the mechanical properties and fracture micromechanisms of low-carbon steel produced by conventional casting and electron beam additive manufacturing have been studied. Regardless of the manufacturing method, the phase composition of steel consists of ferrite with an insignificant fraction of carbides (pearlite grains in both types of steel and single coarse precipitates in the additively fabricated one). It was shown that the studied steels are characterized by a strong temperature dependence on yield strength and ultimate tensile strength. At T = 77 K, both types of steel are characterized by high strength properties, which decrease with increasing test temperatures up to 300 K. In addition, all deformation curves are characterized by the presence of a yield drop and yield plateau over the entire temperature range under study (77 K-300 K). A decrease in test temperature from 300 K to 77 K leads to a change in the fracture micromechanism of the steels from a dimple fracture to a cleavage one. Despite the similar deformation behavior and strength properties, the additively fabricated steel possesses lower elongation to failure at 77 K due to an insignificant fraction of coarse precipitates, which assists the nucleation of brittle cracks.

Comparing radiolytic production of H2O2 and development of Zebrafish embryos after ultra high dose rate exposure with electron and transmission proton beams.

The physico-chemical and biological response to conventional and UHDR electron and proton beams was investigated, along with conventional photons. The temporal structure and nature of the beam affected both, with electron beam at ≥1400Gy/s and proton beam at 0.1 and 1260Gy/s found to be isoefficient at sparing zebrafish embryos.

An Approach to Focus the Sheet Electron Beam in the Planar Microstrip Line Slow Wave Structure

Planar microstrip line slow wave structures (PML-SWSs) have great prospects in the millimeter and terahertz wave fields. However, the development of the devices employing PML-SWSs is severely limited due to the focusing difficulties. Compared with the conventional sheet electron beam (SEB) SWS, the asymmetric boundary condition of PML-SWS and high local electric field further increase the instabilities of the SEB transport in PML-SWS. A new approach, named the uniform magnetic focusing system with the matching electric field (UMFS-MEF), is presented in this article, which can effectively solve these issues. The simulation results illustrate that the expansion rate of the SEB in UMFS-MEF is significantly lower than that in the conventional uniform magnetic focusing system (CUMFS) with the same magnetic field strength <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${B}_{z}$ </tex-math></inline-formula> . Moreover, the present calculation results show that the UMFS-MEF requires only 10.6% of the magnetic field strength of CUMFS for maintaining the same expansion rate. This means that the UMFS-MEF can effectively suppress the instabilities, and employ a very low magnetic field to maintain the stabilities of the SEB transport. Finally, we give several other schemes to realize the method.

Scale mass gain, morphology and phase composition of air and steam oxidized electron beam melted and cast Ti–48Al–2Nb-0.7Cr-0.3Si alloys

Oxidation resistance of γ - TiAl alloy RNT650 exposed to air and steam at 650 °C for 1000 h is reported. The samples were prepared either by conventional casting (CM) or electron beam melting (EBM). The materials were analysed using XPS, XRD, SEM and STEM/EDS techniques. Mass gains in both alloys were comparable and relatively small for air oxidation, but for steam treatment the mass increase in the EBM alloy was up to 50% more than in the CD material. Mass gain showed a faster growth of the scale in the steam treated material. The oxidized materials developed thin nano-crystalline scales predominantly of aluminium and titanium oxides arranged in TiO2+Al2O3/TiO2/Al2O3 sublayers. Whiskers were detected sticking above the scale surfaces, with density much higher in steam treated specimens.

Low-energy X-ray irradiation: A novel non-thermal microbial inactivation technology.

Over the last several decades, food irradiation technology has been proven neither to reduce the nutritional value of foods more than other preservation technologies, nor to make foods radioactive or dangerous to eat. Furthermore, food irradiation is a non-thermal food processing technology that helps preserve more heat sensitive nutrients than those found in thermally processed foods. Conventional food irradiation technologies, including γ-ray, electron beam and high energy X-ray, have certain limitations and drawbacks, such as involving radioactive isotopes, low penetration ability, and economical unfeasibility, respectively. Owing to the recent developments in instrumentation technology, more compact and cheaper tabletop low-energy X-ray sources have become available. The generation of low-energy X-ray, unlike γ-ray, does not involve radioactive isotopes and the cost is lower than high energy X-ray. Furthermore, low-energy X-ray possesses unique advantages, i.e., high linear energy transfer (LET) value and high relative biological effect (RBE) value. The advantages allow low-energy X-ray irradiation to provide a higher microbial inactivation efficacy than γ-ray and high energy X-ray irradiation. In the last few years, various applications reported in the literature indicate that low-energy X-ray irradiation has a great potential to become an alternative food preservation technique. This chapter discusses the technical advances of low-energy X-ray irradiation, microbial inactivation mechanism, factors influencing its efficiency, current applications, consumer acceptance, and limitations.

Protecting the EBE coatings from vacuum-air-shift by ion assistance or ALD capping layer

Vacuum-air-shift causes trouble to conventional electron beam evaporation (EBE) coatings. This study compares the protection effect of ion assistance and the ALD (atomic layer deposition) Al 2 O 3 capping layer. The vacuum-air-shift was reproduced on an EBE Ta 2 O 5 single-layer film, a Ta 2 O 5 /SiO 2 double-layer coating, and a high-reflectance mirror. Similar samples were prepared by EBE assisted with ion beam bombardment. Part of the as-deposited coatings were capped by ALD Al 2 O 3 film with a thickness of about 100 nm. The vacuum-air-shift of the samples was tested with an in-situ spectrophotometer. The cross-section of the coatings was imaged by a scanning electron microscope. The ion assistance was found to reduce the vacuum-air-shift to a limit extent, while the ALD capping film was found to eliminate the vacuum-air-shift. The mechanism of the two protection techniques was analyzed, and their usage was compared and discussed. The ALD capping technique may be used in high precision EBE coatings with convenience and low cost.

Comparing the dosimeter-specific corrections for influence quantities of some parallel-plate ionization chambers in conventional electron beam dosimetry

The performance characteristics of some widely employed parallel-plate ionization chambers in dosimetry of conventional high energy electron beams were evaluated and compared in the present study following the recommendations of the IAEA TRS-398 reference dosimetry protocol.Three different types of PTW-made parallel-plate ionization chambers including Roos (TM34001), Markus (TM23343), and Advanced Markus (TM34045) were employed, and correction factors for polarity (kpol), recombination (ks), and quality conversion factor (kQ,Q0) were determined at different nominal electron energies of 4, 6, 9, 12, 16, and 20 MeV produced by a Varian Trilogy clinical Linac. All measurements were performed inside a MP3-M automatic water phantom in the reference condition of 100 cm SSD (source to surface distance), reference measurement depth (zref), and 10 × 10 cm2 field size at the phantom surface.The maximum and minimum range of kpol deviations from unity were respectively found for Markus and Roos ionization chambers. The maximum ks values also belonged to the Markus ionization chamber, while the minimum ks values were observed for the Advanced Markus chamber. The measured ks values through recommendations of the TRS-398 dosimetry protocol were in good accordance with those obtained by Jaffe-plot analysis for all considered ionization chambers. The type of employed ionization chamber can minimally affect the measured electron beam quality index (R50), while it can have a more considerable impact on kQ,Q0 value, especially in the case of the Markus chamber.From the results, it can be concluded that the Roos and Advanced Markus ionization chambers have a superior performance in the case of electron beam dosimetry, although all considered ionization chambers fulfilled the criteria requested by relevant reference dosimetry protocols.

Effect of surface treatment technique on properties and performance of Na2WO4‐TiO2‐MnOx/SiO2 for oxidative coupling of methane

AbstractBACKGROUNDOxidative coupling of methane (OCM) is a promising catalytic process for the conversion of methane to higher‐valued hydrocarbons (C2+). In this study, Na2WO4‐TiO2‐MnOx/SiO2 (NWTM) catalysts were obtained by various treatment techniques, including conventional calcine (CC, 800 °C), cold plasma (CP, 7 kV, 1 Hz), microwave radiation (MW, 800 °C), and electron beam radiation (EB, 4000 kGy), with no surface treatment (WT) as a benchmark method.RESULTSThe results showed substantial differences in catalytic performance. The catalyst prepared by the cold plasma method provided the highest performance in the activity (20.91% C2+ yield with 48.04% C2+ selectivity and 43.52% CH4 conversion) at the early stage of testing (1–4 h).CONCLUSIONHowever, the catalyst prepared by microwave radiation achieved the most stable active phases for the 24‐h testing period and yielded the highest C2+ for a five‐cycle reusability test. The catalyst prepared by electron beam radiation was found to have the lowest C2+ activity due to the poor distribution of the active elements. © 2021 Society of Chemical Industry (SCI).