Ion Recombination Research Articles

Degradation Processes in Bipolar Membrane CO2-Electrolysis Studied by Time-Resolved X-Ray Tomography

Electrochemical reduction of carbon dioxide via CO2 co-electrolysis (CO2ELY) is an essential process to produce non-fossil chemical feedstock acting as CO2 sink. The required electrical energy can be harvested from temporal surplus of renewable energy sources like solar or wind. Employing a bipolar electrolyte membrane (BPM) in forward-bias is a promising approach to mitigate fundamental problems of the current technological fore-runner design that employs an anion exchange membrane (AEM). We employed synchrotron time-resolved X-ray tomographic microscopy (XTM) to study degradation processes in BPM CO2ELY.In forward-bias BPM co-electrolysis, the cation exchange layer (CEL) faces the anode to provide favorable acidic conditions for the oxygen evolution reaction. Such acidic anode allows using pure water as electrolyte eliminating the salt precipitation at the cathode observed for AEM CO2ELY. As the second major issue in AEM CO2ELY, (bi)carbonate ions formed at the cathode are transported to the anode presenting a major obstacle for high CO2 conversion efficiency. The then required effort to separate CO2 from the electrolyte further reduces the overall energy efficiency. Employing a BPM and introducing the CEL prevents (bi)carbonate ions reaching the anode. BPM CO2ELY retains at the same time the advantages of AEM CO2ELY of performing CO2 reduction under alkaline conditions with the anion exchange layer (AEL) of the BPM facing the cathode.However, BPM CO2ELY suffers from low current density and poor stability in the range of only a few hours. Current limiting factors and degradation processes as well as the affected components are rarely investigated and poorly understood. Processes that have been brought forward are cathode flooding similar to fuel cells or catalyst poisoning. We employ synchrotron XTM to investigate structural dynamics in CO2ELY during operation. The brilliant synchrotron source allows us to acquire one full high-quality scan with a voxel size of 2.75 um in 1 s. We acquired one scan every minute for one hour during electrochemical operation.The image data reveals the formation of gas bubbles at the AEL-CEL junction and ultimately delamination of the BPM. We explain the gas formation as the recombination of (bi)carbonate ions with hydrogen ions at the junction producing gaseous CO2. This CO2 additionally reaches the anode by diffusion causing partial delamination of the anode catalyst layer. CO2 escaping from the AEL surface at the anode forms high-pressure gas bubbles that break the water wet catalyst layer. A diffusive model considering the transport of ions and neutral CO2 is able to capture the mechanism.Our imaging experiments provide insights not attainable by other diagnostic methods and highlight the need for fundamental research on forward-bias BPM CO2ELY. Knowledge based on AEM CO2ELY and fuel cells is not necessarily directly applicable and specific studies on BPM CO2ELY are required to increase performance and stability.We gratefully acknowledge provision of beamtime at TOMCAT, SLS, Paul Scherrer Insititut, Villigen PSI, Switzerland.Figure 1: Tomographic slice of CO2-electrolyser (cathode to the left) a) before operation and running water through anode b) after 23 minutes operation at 3.5V constant potential showing liquid water dynamics at cathode, membrane swelling, gas formation within the membrane and anode catalyst layer disintegration. Figure 1

TRANSLATE - a Monte Carlo simulation of electron transport in liquid argon

The microphysics of electron and photon propagation in liquid argon is a key component of detector design and calibrations needed to construct and perform measurements within a wide range of particle physics experiments. As experiments grow in scale and complexity, and as the precision of their intended measurements increases, the development of tools to investigate important microphysics effects impacting such detectors becomes necessary. In this paper we present a new time-domain Monte Carlo simulation of electron transport in liquid argon. The simulation models the TRANSport in Liquid Argon of near-Thermal Electrons (TRANSLATE) with the aim of providing a multi-purpose software package for the study and optimization of detector environments, with a particular focus on ongoing and next generation liquid argon neutrino experiments utilizing the time projection chamber technology. TRANSLATE builds on previous work of Wojcik and Tachiya, amongst others, introducing additional processes, including ionization, thus modeling the full range of drift electron scattering interactions. The simulation is validated by benchmarking its performance with swarm parameters from data collected in experimental setups operating in gas and liquid. Program summaryProgram Title:TRANSLATECPC Library link to program files:https://doi.org/10.17632/v3tr6xp53h.1Developer's repository link:https://github.com/davidc1/TRANSLATELicensing provisions: GNU General Public License 3.0Programming language: C▪, pythonExternal routines/libraries used: make, cmake (required), ipython notebook (optional)Nature of problem: Simulation of electron-argon scattering events at energies of 10−3−103 eVSolution method: Monte Carlo time-domain transport of electrons simulating momentum transfer, excitations, and ionization interaction modes utilizing input single and double-differential cross sections.Additional comments including restrictions and unusual features: Effects of ion space-charge or recombination with positive argon ions are not included.

The Existence Regions for Direct Three-Body Recombination of Cesium and Bromide Ions in the Presence of Krypton, Xenon, and Mercury Atoms

The Existence Regions for Direct Three-Body Recombination of Cesium and Bromide Ions in the Presence of Krypton, Xenon, and Mercury Atoms

Numerical Prediction of Changes in Atmospheric Chemical Compositions During a Solar Energetic Particle Event on Mars

AbstractPrecipitation of solar energetic particles (SEPs) into planetary atmospheres causes changes in atmospheric chemical composition through ionization, dissociation, and excitation of atmospheric molecules. In contrast to the terrestrial atmosphere, where depletion of ozone in the polar mesosphere has been studied by observations and models for decades, there have been no studies on the effects of SEPs on the neutral chemical composition of Mars' present‐day atmosphere. This study provided the first estimate of the impacts of SEPs on neutral chemical composition in the present‐day Martian atmosphere coupling a Monte Carlo model and a one‐dimensional photochemical model. Our results showed that ozone density in the Martian atmosphere might decrease in the altitude range of 20–60 km with a factor 10 maximum enhancement occurring at 40 km during a Halloween‐class SEP event due to an enhanced concentration of HOx. The depletion of ozone occurred in the altitude range of 20–60 km, corresponding to the penetration of protons with an energy range of 4.6–46 MeV. Such ozone depletion should be detected by Trace Gas Orbiter/Nadir and Occultation for MArs Discovery during intense SEP event. A 75% depletion of the ozone density at 40 km can be expected during SEP events occurring once in every 1 year. Therefore, ozone concentration in the Martian atmosphere might sufficiently decrease during a SEP event as on Earth, but through different chemical pathways driven by CO2 ionization and CO recombination catalytic cycle.

Gas heating by inductively coupled low-pressure chlorine process plasmas

The mechanism of gas heating in low-pressure inductively coupled chlorine plasma is analyzed using a self-consistent two-dimensional axisymmetric fluid plasma model that is coupled with the compressible Navier–Stokes equations. For gas pressures of 10 and 20 mTorr and the discharge power in the range 0.1–1.3 kW, the main reactions contributing to gas heating were the ion–ion recombination reactions and the quenching of electronically excited chlorine atoms. At the same time, the energy released by the electron impact dissociation reaction of molecular chlorine is negligible due to its high degree of dissociation within the plasma bulk. The comparison between the results of our simulations and the fitting equation proposed in the literature show qualitative agreement, although there is significant quantitative discrepancy.

Temporal evolution of laser-induced ionization and recombination processes in argon-helium mixture

Preparation of metastable atoms (1s5) through laser-induced preionization holds the potential to mitigate the electromagnetic interference (EMI) issues associated with the large volume, atmospheric pressure discharge of traditional optically pumped rare-gas metastable laser (OPRGL). In this work, we conducted experimental investigations into the temporal evolution of the Ar 763.5 nm (2p6→1s5) spectral line in Ar-He mixture. These experiments unveiled the intricate interaction mechanism involving the laser, Ar atoms, He atoms, and free electrons within the laser-induced plasma. Our findings highlight the dual contributions of the multiphoton ionization and the inverse bremsstrahlung process to the initial plasma formation. Notably, the time-resolved atomic emission spectrum at 763.5 nm reveals two distinct regimes, namely Regime1 and Regime2. Regime1 primarily arises from the “excitation + radiation + collisional relaxation” process, wherein excited states Ar atoms, populated via multiphoton excitation and electron impact excitation, accumulate on the 2p6 level. Conversely, Regime2 is predominantly a result of the “ion-electron recombination” process. In this regime, highly excited states Ar atoms are generated through the recombination of ion and electron, subsequently populating the 2p6 level through a combination of radiation and collisional relaxation channels. The differences in the temporal evolution between 763.5 nm and 811.5 nm spectral lines can be attributed to the distinct radiation and collisional relaxation channels in the two aforementioned processes.

Charge collection efficiency of commercially available parallel-plate ionisation chambers in ultra-high dose-per-pulse electron beams

Objective. This investigation aims to experimentally determine the charge collection efficiency (CCE) of six commercially available parallel-plate ionisation chamber (PPIC) models in ultra-high dose-per-pulse (UHDPP) electron beams. Approach. The CCE of 22 PPICs has been measured in UHDPP electron beams at the National Metrology Institution of Germany (PTB). The CCE was determined for a dose per pulse (DPP) range between 0.1 and 6.4 Gy (pulse duration of 2.5 μs). The results obtained with the different PPICs were compared to evaluate the reproducibility, intra- and inter-model variation, and the performance of a CCE empirical model. Main results. The intra-model variation was, on average, 4.0%, which is more than three times the total combined relative standard uncertainty and was found to be greater at higher DPP (up to 20%). The inter-model variation for the PPIC with 2 mm electrode spacing, which was found to be, on average, 10%, was also significant compared to the relative uncertainty and the intra-model variation. The observed CCE variation could not be explained only by the expected deviation of the electrode spacing from the nominal value within the manufacturing tolerance. It should also be noted that a substantial polarity effect, between 0.914(5) and 1.201(3), was observed, and significant intra- and inter-model variation was observed on this effect. Significance. For research and pre-clinical study, the commercially available PPIC with a well-known CCE (directly measured for the specific chamber) and with a small electrode spacing could be used for relative and absolute dosimetry with a lower-limit uncertainty of 1.6% (k = 1) in the best case. However, to use a PPIC as a secondary standard in UHDPP electron beams for clinical purposes would require new model development to reduce the ion recombination, the polarity effect, and the total standard uncertainty on the dose measurement.

The Synergetic Ionic and Electronic Features of MAPbI3 Perovskite Films Revealed by Electrochemical Impedance Spectroscopy

AbstractPerovskites have emerged as a forerunner of electronics research due to their vast potential for optoelectronic applications. The numerous combinations of constituent ions and the potential for doping of perovskites lead to a high demand to track the underlying electronic properties. Solution‐based electrochemistry is particularly promising for detailed and facile assessment of perovskites. Here, electrochemical impedance spectroscopy (EIS) of methylammonium lead iodide (MAPbI3) thin films is performed and model them with an equivalent circuit that accounts for solvent, ionic, and thin film effects. A dielectric constant consistent with prior AC studies and a diffusion constant harmonious with cation motion in MAPbI3 are extracted. An electrical double layer thickness in the perovskite film of 54 nm is obtained, consistent with lithium doping in perovskite films. Comparing the EIS and equivalent circuit model of perovskite films to control ITO‐only data enabled the assignment of the ions at each interface. This comparison implied a double layer of primarily lithium ions inside the perovskite film at the solution interface with significant recombination of ions on the solution side of the interface. This demonstrates EIS as a powerful tool for studying the fundamental charge accumulation and transport processes in perovskite thin films.

Survey on reference dosimetry practice in Hokuriku region, Japan.

This study aimed to obtain reference dosimetry practices for flattened photon and electron beams. A questionnaire survey on these practices was sent to 37 facilities that performed radiotherapy using these beams in Fukui, Ishikawa, Niigata and Toyama, Japan. The survey comprised equipment (dosemeters, water phantoms, thermometers, barometers and hygrometers) and procedures for reference dosimetry (water used as the phantoms, verification of chamber placement, periodic checks of ion recombination- and polarity-corrections, pre-irradiation and relative humidity monitoring). Responses were received from 19 institutions. In the 19 institutions, a reference-class dosemeter was used for the reference dosimetry. In 6 of the 19 institutions, a 10-year-old or older dosemeter was used. Any barometers, thermometers and hygrometers were not recalibrated. Dosimetry equipment necessitates regular maintenance. Moreover, it is necessary to have a backup dosimetry system in clinics to account for potential malfunctions or instances when the primary system is sent for calibration.

Investigating the influence of absorber layer thickness on the performance of perovskite solar cells: A combined simulation and impedance spectroscopy study

Absorber thickness is one among keys parameters that can have significant effects on the performance of the solar cell. An appropriate absorber thickness should be chosen to optimize the performance of the cell.The main objective of this work is to offer a perovskite solar cell with high efficiency using a suitable thickness of the active layer. Therefore, this study focuses on the optimization of the solar cell thickness, which can also be achieved by using simulation with SCAPS-1D, to predict the performance of the cell at different thicknesses. In this case, the four main parameters; the short circuit current density, the open-circuit voltage, fill factor and power of conversion efficiency, were extracted and analyzed from I–V characteristics at different thicknesses. In addition, the complex impedance data were also generated by using simulation with SCAPS-1D. To the best of our knowledge, this approach was not used before for many works carried out by SCAPS-1D simulation; where these studies were limited to I-V characteristics. This novel approach to investigating the electrical response of this solar cell concerning thickness involves the integration of complex impedance and modulus functions. This integration enables us to discern the respective contributions of ionic diffusion and recombination processes, through our deconvolution procedure, the results obtained indicate the absorber layer thickness increases, the diffusion and recombination processes are affected differently, subsequently influencing the overall performance of the solar cell. Both methodologies employed in this study consistently identified the maximum efficiency at an optimal thickness of 700 nm.

Transition from MAR to EIR of deuterium plasma detachment in NAGDIS-II

Volumetric plasma recombination in a detached deuterium (D) plasma was experimentally studied in the linear plasma device NAGDIS-II. The radial distributions of the electron temperature (T e ) and the electron density (n e ) were measured by upstream and downstream laser Thomson scattering (LTS) systems and D-atom excited states of the Balmer series (n = 3–7) were measured by optical emission spectroscopy (OES). The results indicated that the electron static pressure, particle flux and heat flux present a two-step reduction with an increasing neutral pressure, suggesting that molecule activated recombination (MAR) and electron–ion recombination (EIR) were activated, respectively. The difference in the distributions of the atomic state population densities was observed to be a feature of the transition from the MAR-dominant phase to the EIR-dominant phase. The transition between the two phases had a distinct boundary at T e ∼0.7 eV, which was considered a transition point between the phases. The ratios of the atomic state population densities showed different features in the two phases, and are expected to be useful in characterizing the phase and degree of plasma detachment.

Monte Carlo modelling of a prototype small-body portable graphite calorimeter for ultra-high dose rate proton beams

Background and purposeAccurate dosimetry in Ultra-High Dose Rate (UHDR) beams is challenging because high levels of ion recombination occur within ionisation chambers used as reference dosimeters. A Small-body Portable Graphite Calorimeter (SPGC) exhibiting a dose-rate independent response was built to offer reduced uncertainty on secondary standard dosimetry in UHDR regimes. The aim of this study was to quantify the effect of the geometry and material properties of the device on the dose measurement. Materials and methodsA detailed model of the SPGC was built in the Monte Carlo code TOPAS (v3.6.1) to derive the impurity and gap correction factors, kimp and kgap. A dose conversion factor, DwMC/DgMC, was also calculated using FLUKA (v2021.2.0). These factors convert the average dose to its graphite core to the dose-to-water for a 249.7 MeV mono-energetic spot-scanned clinical proton beam. The effect of the surrounding Styrofoam on the dose measurement was examined in the simulations by substituting it for graphite. ResultsThe kimp and kgap correction factors were 0.9993 ± 0.0002 and 1.0000 ± 0.0001, respectively when the Styrofoam was not substituted, and 1.0037 ± 0.0002 and 0.9999 ± 0.0001, respectively when substituted for graphite. The dose conversion factor was calculated to be 1.0806 ± 0.0001. All uncertainties are Type A. ConclusionsImpurity and gap correction factors, and the dose conversion factor were calculated for the SPGC in a FLASH proton beam. Separating out the effect of scatter from Styrofoam insulation showed this as the dominating correction factor, amounting to 1.0043 ± 0.0002.

Ionic Mobility and Charge Carriers Recombination Analyzed in Triple Cation Perovskite Solar Cells

In this work, a study of a characterization technique based on open circuit voltage decay is carried out to obtain the recombination resistance of mobile charge carriers and ionic migration in triple cation perovskite solar cells. The devices were fabricated with the structure FTO/TiO2/Cs0.05FA1−XMAXPb(I1−XBrX)3/spiroOMetad/Au. An equivalent circuit, created in Ngspice, was developed adjusting the capacitance and resistance values to fit the experimental open circuit voltage (Voc) decay curves observed. The aim of this study is to associate the perovskite ionic migration with the Voc characteristic time of charge transport in triple cation perovskite solar cells. Thus, an analysis of the open circuit voltage transient behavior was made by taking measurements of the photovoltage as a function of time. The results indicate that the technique shows charge recombination while the device is illuminated. In addition, an enhancement of the recombination resistance when increasing the FA+ concentration was observed. Finally, the transient behavior was associated with MA+, FA+, Cs+ and I− migration, obtaining an ionic mobility in the range between 10−10 to 10−12 cm2 (Vs)−1.

Evaluation of ion chamber response for applications in electron FLASH radiotherapy.

Ion chambers are required for calibration and reference dosimetry applications in radiation therapy (RT). However, exposure of ion chambers in ultra-high dose rate (UHDR) conditions pertinent to FLASH-RT leads to severe saturation and ion recombination, which limits their performance and usability. The purpose of this study was to comprehensively evaluate a set of commonly used commercially available ion chambers in RT, all with different design characteristics, and use this information to produce a prototype ion chamber with improved performance in UHDR conditions as a first step toward ion chambers specific for FLASH-RT. The Advanced Markus and Exradin A10, A26, and A20 ion chambers were evaluated. The chambers were placed in a water tank, at a depth of 2cm, and exposed to an UHDR electron beam at different pulse repetition frequency (PRF), pulse width (PW), and pulse amplitude settings on an IntraOp Mobetron. Ion chamber responses were investigated for the various beam parameter settings to isolate their dependence on integrated dose, mean dose rate and instantaneous dose rate, dose-per-pulse (DPP), and their design features such as chamber type, bias voltage, and collection volume. Furthermore, a thin parallel-plate (TPP) prototype ion chamber with reduced collector plate separation and volume was constructed and equally evaluated as the other chambers. The charge collection efficiency of the investigated ion chambers decreased with increasing DPP, whereas the mean dose rate did not affect the response of the chambers (±1%). The dependence of the chamber response on DPP was found to be solely related to the total dose within the pulse, and not on mean dose rate, PW, or instantaneous dose rate within the ranges investigated. The polarity correction factor (Ppol ) values of the TPP prototype, A10, and Advanced Markus chambers were found to be independent of DPP and dose rate (±2%), while the A20 and A26 chambers yielded significantly larger variations and dependencies under the same conditions. Ion chamber performance evaluated under different irradiation conditions of an UHDR electron beam revealed a strong dependence on DPP and a negligible dependence on the mean and instantaneous dose rates. These results suggest that modifications to ion chambers design to improve their usability in UHDR beamlines should focus on minimizing DPP effects, with emphasis on optimizing the electric field strength, through the construction of smaller electrode separation and larger bias voltages. This was confirmed through the production and evaluation of a prototype ion chamber specifically designed with these characteristics.

Technical note: Point-by-point ion-recombination correction for accurate dose profile measurement in high dose-per-pulse irradiation field.

Although flattening filter free (FFF) beams are commonly used in clinical treatment, the accuracy of dose measurements in FFF beams has been questioned. Higher dose per pulse (DPP) such as FFF beams from a linear accelerator may cause problems in dose profile measurements using an ionization chamber due to the change of the charge collection efficiency. Ionization chambers are commonly used for percent depth dose (PDD) measurements. Changes of DPP due to chamber movement during PDD measurement can vary the ion collection efficiency of ionization chambers. In the case of FF beams, the DPP fluctuation is negligible, but in the case of the FFF beams, the DPP is 2.5 ∼ 4 times larger than that of the FF beam, and the change in ion collection efficiency is larger than that of the FF beam. PDD profile normalized by maximum dose depth, 10 cm depth for example, may therefore be affected by the ion collection efficiency. In this study, we investigate the characteristics of the ion collection efficiency change depending on the DPP of each ionization chamber in the FFF beam. We furthermore propose a method to obtain the chamber- independent PDD by applying a DPP-dependent ion recombination correction. Prior to investigating the relationship between DPP and charge collection efficiency, Jaffe-plots were generated with different DPP settings to investigate the linearity between the applied voltage and collected charge. The absolute dose measurement using eight ionization chambers under the irradiation settings of 0.148, 0.087, and 0.008 cGy/pulse were performed. Applied voltages for the Jaffe-plots were 100, 125, 150, 200, 250, and 300V. The ion recombination correction factor Pion was calculated by the two-voltage analysis (TVA) method at the applied voltages of 300 and 100V. The DPP dependency of the charge collection efficiency for each ionization chamber were evaluated from the DPP- Pion plot. PDD profiles for the 10 MV FFF beam were measured using Farmer type chambers (TN30013, FC65-P, and FC65-G) and mini-type chambers (TN31010, TN31021, CC13, CC04, and FC23-C). The PDD profiles were corrected with ion recombination correction at negative and positive polar applied voltages of 100 and 300V. From the DPP-Pion relation for each ionization chamber with DPP ranging from 0.008 cGy/pulse to 0.148 cGy/pulse, all Farmer and mini-type chambers satisfied the requirements described in AAPM TG-51 addendum. However, Pion for the CC13 was most affected by DPP among tested chambers. The maximum deviation among PDDs using eight ionization chambers for 10 MV FFF was about 1%, but the deviation was suppressed to about 0.5% by applying ion recombination correction at each depth. In this study, the deviation of PDD profile among the ionization chambers was reduced by the ion recombination coefficient including the DPP dependency, especially for high DPP beams such as FFF beams. The present method is particularly effective for CC13, where the ion collection efficiency is highly DPP dependent.

Double layer acceleration of ions with differently charged states in a laser induced plasma

The electric field driven acceleration of plasma ions is an intrinsic effect in laser-induced plasma plumes and is responsible for the generation of high-energy ions. At high laser fluences (≥ 2 J/cm2), multiply charged ions are formed and affect the plume expansion dynamics. In this paper, we used kinetic energy-resolved mass spectrometry to investigate the relative abundance and kinetic energy distributions of singly- and doubly-charged ions produced by KrF-laser ablation of nine different oxide targets. The doubly charged metal ions with a lower mass-to-charge (m/z) ratio show narrow energy distributions at high average kinetic energies coinciding with the cutoff energies for the singly-charged ion distributions. The observation suggests that the recombination of higher charged ions plays a prominent role in the formation of the high-energy tail for singly-charged ions. The results are discussed in terms of component volatility and a dynamic double layer, where ions with different m/z values experience different accelerations.

FLASH Radiotherapy and the Use of Radiation Dosimeters.

Radiotherapy (RT) using ultra-high dose rate (UHDR) radiation, known as FLASH RT, has shown promising results in reducing normal tissue toxicity while maintaining tumor control. However, implementing FLASH RT in clinical settings presents technical challenges, including limited depth penetration and complex treatment planning. Monte Carlo (MC) simulation is a valuable tool for dose calculation in RT and has been investigated for optimizing FLASH RT. Various MC codes, such as EGSnrc, DOSXYZnrc, and Geant4, have been used to simulate dose distributions and optimize treatment plans. Accurate dosimetry is essential for FLASH RT, and radiation detectors play a crucial role in measuring dose delivery. Solid-state detectors, including diamond detectors such as microDiamond, have demonstrated linear responses and good agreement with reference detectors in UHDR and ultra-high dose per pulse (UHDPP) ranges. Ionization chambers are commonly used for dose measurement, and advancements have been made to address their response nonlinearities at UHDPP. Studies have proposed new calculation methods and empirical models for ion recombination in ionization chambers to improve their accuracy in FLASH RT. Additionally, strip-segmented ionization chamber arrays have shown potential for the experimental measurement of dose rate distribution in proton pencil beam scanning. Radiochromic films, such as GafchromicTM EBT3, have been used for absolute dose measurement and to validate MC simulation results in high-energy X-rays, triggering the FLASH effect. These films have been utilized to characterize ionization chambers and measure off-axis and depth dose distributions in FLASH RT. In conclusion, MC simulation provides accurate dose calculation and optimization for FLASH RT, while radiation detectors, including diamond detectors, ionization chambers, and radiochromic films, offer valuable tools for dosimetry in UHDR environments. Further research is needed to refine treatment planning techniques and improve detector performance to facilitate the widespread implementation of FLASH RT, potentially revolutionizing cancer treatment.

Quality assurance of six cylindrical and two parallel plate chambers by radioactive check device: Influence of chamber age to its performance

PurposeTo evaluate the performances of eight ionization chambers, (two types) manufactured in a time span of 14 years, with radioactive source devices and photon beams. MethodsThe measurements were performed with six Farmer and two parallel plate ionization chambers with appropriate radioactive check devices and accompanying inserts. Some tests were performed with photon beams at linear accelerator. Physical visibility check, stability, linearity of response, directional dependence, determination of leakage current, ion recombination and polarity effect and influence of background radiation tests were conducted and analyzed. ResultsThe performance of all Farmer ionization chambers was in agreement to IEC standard as well as for parallel plate type chambers. Long-term stability of older planparallel chamber was somewhat worse than expected. ConclusionRadioactive check devices have proven to be easy to use in clinical environment. According to results of this work Farmer type ionization chambers showed good quality regardless of the time of production, which make them long-term suitable for clinical dosimetry in radiotherapy. Also, for parallel plate type of ionization chambers the results showed fine agreement with the IEC standard, except long-term stability for older chamber, which needs further investigation.

SOLPS-ITER predictive simulations of the impact of ion-molecule elastic collisions on strongly detached MAST-U Super-X divertor conditions

The role of ion-molecule () elastic collisions in strongly detached divertor conditions has been studied in the MAST-U Super-X configuration using SOLPS-ITER. Two strongly detached steady state solutions were compared, one obtained through a main-ion fuelling scan and the other through a nitrogen seeding scan at fixed fuelling rate. A significant difference in the electron–ion recombination (EIR) levels was observed; significant EIR in strongly detached conditions in the fuelling scan and negligible EIR throughout the seeding scan. This is partly because the fuelling scan achieves electron temperatures () as low as 0.2 eV near the divertor target, compared to 0.8 eV in the seeding scan (EIR increases strongly below eV), and partly due to higher divertor plasma densities achieved in fuelling scan. Features of the strongly detached seeded cases, i.e. higher temperatures and negligible EIR, are recovered in the fuelling scan by turning off elastic collisions. Analysis suggests that dissipation mechanisms like line radiation and charge exchange (important for detachment initiation) become weak when falls below 1 eV, and that elastic collisions are necessary for further heat dissipation and access to strongly recombining conditions in the fuelling scan. In the seeding scan, heat dissipation through elastic collisions is weak. This could be because our nitrogen seeding simulations do not include interactions between nitrogen ions and neutrals, and the strongly detached cases contain high levels of in the divertor. As a result, the acts like a reservoir of energy and momentum which appears to weaken the impact of elastic collisions on the divertor plasma energy and momentum balance, making it more difficult to access recombining conditions. This suggests that some of the differences between seeding and fuelling scans could be because energy and momentum exchange between impurities and neutrals is not sufficiently captured in our simulations.

Al2O3 interfacial layer derived hybrid conductive filament for the reliability enhancement of Ta2O5-based resistive random access memory

This study used an Al2O3 interfacial layer to improve the reliability characteristics of Ag/Ta2O5/Au resistive random access memory (RRAM), such as endurance and retention. The Ag/Ta2O5/Au device without the Al2O3 interfacial layer exhibited a high on/off ratio, low endurance, and poor retention. In Ag/Ta2O5/Au devices, it is difficult to precisely control the formation and rupture of conductive filaments (CFs) owing to the high diffusion coefficient of Ag cations. However, in the RS mechanism of Ag/Ta2O5/Au with an Al2O3 interfacial layer, a hybrid CF composed of Ag cations in Ta2O5 and oxygen vacancies in the Al2O3 layer was formed during the set process. During the reset process, the hybrid CF was stably ruptured by the recombination of oxygen vacancies and oxygen ions at the Al2O3 interfacial layer. This RS mechanism induces stable switching characteristics, improving endurance and retention. Therefore, Ag/Ta2O5/Au with an Al2O3 interfacial layer exhibits relatively high endurance (up to 700 cycles) and excellent retention (up to 1.0 × 104 s) while maintaining a high on/off ratio (>106) compared to those of the Ag/Ta2O5/Au device.