High-energy Electron Research Articles

Spatially Fractionated Radiotherapy with Very High Energy Electron Pencil Beam Scanning

Abstract Objective:
To evaluate spatially fractionated radiation therapy (SFRT) for very-high-energy electrons (VHEEs) delivered with pencil beam scanning. Approach: Radiochromic film was irradiated at the CERN Linear Electron Accelerator for Research (CLEAR) using 194 MeV electrons with a step-and-shoot technique, moving films within a water tank. Peak-to-valley dose ratios (PVDRs), depths of convergence (PVDR≤1.1), peak doses, and valley doses assessed SFRT dose distribution quality. A Monte Carlo (MI) model of the pencil beams was developed using TOPAS and applied to a five-beam VHEE SFRT treatment for a canine glioma patient, compared to a clinical 6 MV VMAT plan. The plans were evaluated based on dose-volume histograms, mean dose, and maximum dose to the planning target volume (PTV) and organs at risk (OARs).
Main Results:
Experimental PVDR values were maximized at 15.5 ± 0.1 at 12 mm depth for 5 mm spot spacing. A depth of convergence of 76.5 mm, 70.7 mm, and 56.6 mm was found for 5 mm, 4 mm, and 3 mm beamlet spacings, respectively. MC simulations and experiments showed good agreement, with maximum relative dose differences of 2% in percentage depth dose curves and less than 3% in beam profiles. Simulated PVDR values reached 180 ± 4, potentially achievable with reduced leakage dose. VHEE SFRT plans for the canine glioma patient showed a decrease in mean dose (>16%) to OARs while increasing the PTV mean dose by up to 15%. Lowering beam energy enhanced PTV dose homogeneity and reduced OAR maximum doses. Significance: The presented work demonstrates that pencil beam scanning SFRT with VHEEs could treat deep-seated tumors such as head and neck cancer or lung lesions, though small beam size and leakage dose may limit the achievable PVDR.

ElectronCT - an imaging technique using very-high energy electrons

The electronCT technique is an imaging method based on the multiple Coulomb scattering of relativistic electrons and has potential applications in medical and industrial imaging. It utilizes a pencil beam of electrons in the very high energy electron (VHEE, 50–250 MeV) range and a single detection layer for the determination of the beam profile. The technique constitutes a projectional, two-dimensional imaging method and thus also qualifies for the tomographic reconstruction of samples. Given the simplicity of the technical setup and its location behind the sample, the electronCT technique has potential synergies with VHEE radiotherapy, making use of the same electron source for both treatment and diagnostics and thus being a candidate for in situ imaging and patient localization. At the same time, several technical challenges arise from the measurement technique when applied for the imaging of living beings. Measurements performed at the ARES linear particle accelerator at an electron energy of 155 MeV using a mouse phantom and a Timepix3 silicon pixel detector assembly demonstrate the feasibility of this technique. Both projectional and tomographic reconstructions are presented and the potential and limits of the technology are discussed.

Initial results of hard X-ray spectroscopy by LaBr[formula omitted](Ce) detector for runaway electron study in Thailand Tokamak-1

Thailand Tokamak-1 (TT-1) successfully achieved its first plasma operation in early 2023. Understanding the behavior of high-energy runaway electrons (RE) during plasma discharges is crucial in TT-1 due to the potential risk of significant damage to in-vessel components. To study the RE behavior and analyze its characteristics, the LaBr3(Ce) detector was employed for measuring hard X-ray emissions in TT-1. In this study, we first characterized the LaBr3(Ce) detector in the laboratory and then performed hard X-ray spectroscopy in TT-1. Calibration sources, including 133Ba, 137Cs, 22Na, and 60Co, with energies up to 1.33 MeV, were used in the laboratory. The detector was calibrated using biased high voltage of -1000 V. It was found to have an energy resolution of approximately 6.2% at an energy of 0.662 MeV. After calibration, the detector was installed at TT-1 to measure hard X-ray. We analyze the hard X-ray emission from discharge #2183 during a selected time interval. It is found that the high-energy hard X-ray emissions reach up to approximately 500 keV. Assuming a simple Maxwellian distribution of the RE population, their temperature is estimated to be 224±5 keV. These findings confirm the presence of high-energy runaway electrons during TT-1’s plasma discharges. However, to accurately derive the runaway electron energy spectrum from the hard X-ray energy spectrum, the unfolding technique is required. In future work, we plan to apply the unfolding method, conduct numerical simulations on the physics of runaway electrons, and employ Monte Carlo simulations on the hard X-ray emissions.

Design of an atomic layer deposition system with in situ reflection high energy electron diffraction

We report the design, fabrication, and testing of an atomic layer deposition (ALD) system that is capable of reflection high energy electron diffraction (RHEED) in a single chamber. The details and specifications of the system are described and include capabilities of RHEED at varied accelerating voltages, sample rotation (azimuthal) control, sample height control, sample heating up to set temperatures of 1050 °C, and either single- or dual-differential pumping designs. Thermal and flow simulations were used to justify selected system dimensions as well as carrier gas/precursor mass flow rates. Temperature calibration was conducted to determine actual sample temperatures that are necessary for meaningful analysis of thermally induced transitions in ALD thin films. Several demonstrations of RHEED in the system are described. Calibration of the camera length was conducted using a gold thin film by analyzing RHEED images. Finally, RHEED conducted at a series of increasing temperatures was used to monitor the crystallization of an ALD HfO2 thin film. The crystallization temperature and the ring pattern were consistent with the monoclinic structure as determined by separate x-ray diffraction-based measurements.

Simultaneous X-Ray and Optical Polarization Observations of the Blazar Mrk 421

We present near-simultaneous X-ray and optical polarization measurements in the high synchrotron peaked (HSP) blazar Mrk 421. The X-ray polarimetric observations were carried out using Imaging X-ray Polarimetry Explorer (IXPE) on 2023 December 6. During IXPE observations, we also carried out optical polarimetric observations using 104 cm Sampurnanand telescope at Nainital and multiband optical imaging observations using 2 m Himalayan Chandra Telescope at Hanle. From model-independent analysis of IXPE data, we detected X-ray polarization with degree of polarization (ΠX) of 8.5% ± 0.5% and an electric vector position angle (ΨX) of 10.°6 ± 1.°7 in the 2−8 keV band. From optical polarimetry on 2023 December 6, in B, V, and R bands, we found values of Π B = 4.27% ± 0.32%, Π V = 3.57% ± 0.31%, and Π R = 3.13% ± 0.25%. The value of Π B is greater than that observed at longer optical wavelengths, with the degree of polarization suggesting an energy-dependent trend, gradually decreasing from higher to lower energies. This is consistent with that seen in other HSP blazars and favors a stratified emission region encompassing a shock front. The emission happening in the vicinity of the shock front will be more polarized due to the ordered magnetic field resulting from shock compression. The X-ray emission, involving high-energy electrons, originates closer to the shock front than the optical emission. The difference in the spatial extension could plausibly account for the observed variation in polarization between X-ray and optical wavelengths. This hypothesis is further supported by the broadband spectral energy distribution modeling of the X-ray and optical data.

Spatial distribution of gamma rays produced by axially symmetric polarized and optical vortex lasers

The polarization properties and spatial distribution of electromagnetic radiation emitted from a high-energy electron can be calculated using the Lienard-Wiechert potentials. These properties are characterized by changes in electron orbitals. In Thomson or Compton scattering by relativistic electrons, which involves the interaction between electrons and a laser, the transverse motion of the electrons is induced by the laser's electric field. The polarization characteristics and spatial distribution of emitted radiation in linearly and circularly polarized laser fields have been extensively studied. In this paper, using a CdTe image sensor, the spatial distribution of MeV gamma rays generated by a 90-degree collision between a 750 MeV electron beam and an axially symmetric polarized laser was measured. The axially symmetric polarized laser, which includes radially and azimuthally polarized components, was created from a linearly polarized laser using a spatially variant retarder known as an s-waveplate. The spatial distribution of gamma rays exhibited a peak at the center, similar to linearly and circularly polarized gamma rays, but differed in overall contour from both. This result suggested that axially symmetric polarized lasers generated gamma rays with different polarization states. Moreover, the contour was observed to change with the polarization axis of the axially symmetric polarized laser, likely owing to the nonuniform distribution of the laser's polarization intensity. Additionally, the spatial distribution of gamma rays produced by circularly polarized optical vortex lasers was measured, showing that their contours corresponded to those of nonvortex circularly polarized lasers. Published by the American Physical Society 2024

Electron Acceleration in Magnetic Islands in Quasi-parallel Shocks

We report new theories and simulations for electron acceleration in magnetic islands generated by magnetic reconnection in the shock turbulence in a quasi-parallel shock, using a 2 and 1/2 dimensional particle-in-cell simulation. When an island is moving, unmagnetized electrons are accelerated by the Hall electric field pointing toward the island center. In a stationary island, some electrons are energized by “island betatron acceleration” due to the induction electric field when the island core magnetic field changes with time. In the simulation, almost all of the high-energy electrons in the shock transition region that show a power-law distribution are accelerated in ion-skin-depth-scale magnetic flux ropes, and about half of them are accelerated by the Hall electric field and island betatron acceleration. These mechanisms can produce a power-law electron distribution, and also inject electrons into the diffusive shock acceleration. The mechanisms are applicable to quasi-parallel shocks with high Alfvén Mach numbers (M A > 10), including planetary bow shocks and shocks in astrophysical objects such as supernova remnants.

Investigating Charge-Induced Transformations of Metal Nanoparticles in a Radically-Inert Liquid: A Liquid-Cell TEM Study.

We present a novel in situ liquid-cell transmission electron microscopy (TEM) approach to study the behavior of metal nanoparticles under high-energy electron irradiation. By utilizing a radically-inert liquid environment, we aim to minimize radiolysis effects and explore the influence of charge-induced transformations. We observed complex dynamics in nanoparticle behavior, including morphological changes and transitions between amorphous and crystalline states. These transformations are attributed to the delicate interplay between charge accumulation on the nanoparticles and enhanced radiolysis, suggesting a significant role for charge-assisted processes in nanoparticle evolution. Our findings provide valuable insights into the fundamental mechanisms driving nanoparticle behavior at the nanoscale and demonstrate the potential of liquid-cell TEM for studying complex physicochemical processes in controlled environments.

THE COMPUTER MODEL EXPERIMENT FOR STUDYING MECHANISMS OF FORMATION OF RADIATION-STIMULATED DEFECTS IN MAGNESIUM-ALUMINUM SPINEL

In the work in the Geant 4 software a computer model of the experiment on the study of the efficiency of formation of radiation-stimulated defects in magnesium aluminum spinel under irradiation with high-energy electrons and gamma quanta was developed. Under irradiation with electrons it was found that defects in the crystal lattice of spinel arise both under direct knocking out of atoms from the nodes and under photonuclear reactions. For energies of primary electrons of 25… 30 MeV the efficiency of formation of defects due to photonuclear reactions is several times higher compared to direct knocking out of atoms from the nodes of the crystal lattice. Under irradiation of samples with monoenergetic gamma quanta it was found that the efficiency of formation of defects is an order of magnitude higher than under irradiation with electrons of the same energy due to processes of photofission of nuclei.

Mechanistic study of β-Ga2O3 nitridation by RF nitrogen plasma for GaN heteroepitaxy

The transformation of 2¯01β-Ga2O3 to h-GaN under exposure to RF nitrogen plasma was monitored in situ by reflection high-energy electron diffraction. Analysis of the reaction kinetics reveals that the nitridation process is initiated by the formation of an oxynitride phase and proceeds via two-dimensional nucleation and growth of wurtzite GaN grains. X-ray photoelectron spectra suggest a Ga−(NxO1−x) type configuration dominates the surface early in the nitridation process. The surface restructuring is followed by a diffusion-fed phase transformation, which propagates the wurzite GaN structure into the substrate upon reaching 70% nitrogen anion site occupation, corresponding to the oxygen solubility in h-GaN. A direct correlation is observed between the nitridated film morphology and the epitaxial film crystallinity, demonstrating control of the residual strain, lateral coherence, and mosaicity in subsequent GaN epitaxy by the nitridation conditions. This study provides mechanistic details of the nitridation reaction of 2¯01β-Ga2O3 facilitating the optimization of the nitridation process toward improving GaN-2¯01β-Ga2O3 heterojunctions.

Straightforward Synthesis Methodology for Obtaining Excellent ORR Electrocatalysts From Biomass Residues Through a One Pot‐High Temperature Treatment Approach

AbstractMaterials prepared from biomass residues are potential candidates to substitute the Pt‐based commercial electrocatalysts in oxygen reduction reaction (ORR). Although some investigations have reported activity and durability comparable to Pt/C using biomass‐derived catalysts based on Fe─N─C sites, it remains a challenge to decrease the environmental impact of the production of these materials. A straightforward procedure is developed to obtain excellentORR electrocatalysts from biomass residues which requires a single high‐temperature treatment. The final washing step is avoided by optimizing the initial amount of Fe precursor (FeC2O4). Besides the formation of iron oxide nanoparticles, a highly dispersed Fe phase is detected by High Angle Annular Dark Field Scanning Transmission Electron Microscopy and Energy Dispersive X‐Ray Spectroscopy (HAADF‐STEM‐XEDS) analysis as well as graphitic carbon structures. The best performance for almond shell‐based electrocatalysts is achieved for the sample containing 4.6 wt. % of Fe. The procedure developed is also applied to oceanic posidonia and eucalyptus residues, also showing excellent ORR behavior. The best sample is studied in a primary Zn‐air battery (ZAB) obtaining a maximum power density of 59 mW cm−2 and 755 mAh gZn−1 capacity.

Degradation of piroxicam and celecoxib from aqueous solution by high-energy electron beam as a Sustainable method

Non-steroidal anti-inflammatory drugs (NSAIDs) are one of the most commonly prescribed drugs that can reduce pain. This study aimed to measure the concentration of piroxicam and celecoxib in Iranian hospitals, as well as the effect of electron beam irradiation on the degradation of these pollutants in synthetic and real samples. The high-performance liquid chromatography (HPLC) was used to detect the residual analytes in the samples. The Response Surface Methodology (RSM) was used to design the experiment conditions that investigate the effect of electron beam irradiation on degradation of piroxicam and celecoxib from synthetic samples, and then according to the optimum condition, the experiments were carried out for real wastewater samples. The results of wastewater analysis shown that the mean concentration of PIRO and CELE were 6.32 ± 2.5 and 11.5 ± 3.2 μg/L, respectively. Also, the findings show that 98.98 % and 97.62 % of piroxicam and celecoxib was degraded, respectively, when the optimum conditions (pH = 4, electron beam irradiation = 8 kGy, and concentrations of 60 μg/L for piroxicam and 50 μg/L for celecoxib) were applied. Results show that the degradation rates of piroxicam and celecoxib in the real wastewater sample at optimum condition were 89.6 % and 84.25 %, respectively. So, electron beam irradiation is a long-lasting and promising method for removal emerging contaminants from wastewater, like non-steroidal anti-inflammatory drugs, that can't be removed by conventional wastewater treatment methods; so, it can be used in combination with conventional wastewater treatment methods.

Nanoplasma formation and expansion ignited by an intense FEL: a study using pump-probe electron spectroscopy

Abstract We demonstrate real-time observations of nanoplasma formation and expansion using intense extreme-ultraviolet (XUV) and near-infrared (NIR) pump--probe electron spectroscopy. We identified the formation of a nanoplasma by the sudden enhancement of low-energy electron emission within a few tens of femtoseconds after XUV excitation, which indicates considerable heating of the clusters by the NIR field. 
We probed the subsequent expansion of the nanoplasma by monitoring the transient resonant enhancement of high-energy electron emission. The dependence of the resonance on the XUV intensity is explained by the expansion speed of the XUV-induced nanoplasma.

Synchrotron-driven Instabilities in Relativistic Plasmas of Arbitrary Opacity

Recent work has shown that synchrotron emission from relativistic plasmas leads the electron distribution to form an anisotropic ring in momentum space, which can be unstable to both kinetic and hydrodynamic instabilities. Fundamental to these works was the assumption that the plasma was optically thin, allowing all emitted radiation to escape. Here, we examine the behavior of these instabilities as the plasma becomes more optically thick. To do this, we extend a recently developed Fokker–Planck operator for synchrotron emission and absorption in mildly relativistic plasmas to ultrarelativistic plasmas. For a given set of plasma parameters, photons emitted by higher-energy electrons tend to be higher frequency, and thus more easily escape the plasma. As a result, the ratio of the photon emission rate (radiative drag) to absorption rate (radiative diffusion) for a given electron is extremely energy dependent. Given this behavior, we determine the critical parameters that control the opacity, and show how the plasma gradually transitions to become more isotropic and stable at higher opacity.

Study of the use of sodium thiocyanate as an indicator for three-dimensional dosimetry

Three-dimensional dosimetry allows the determination of dosimetric quantities with a volumetric gradient. With Fricke Gel it is possible to make measurements of this nature due to the restriction of ions in this dosimeter caused by the presence of a gelatinous matrix. When ion indicators are added to Fricke Gel, the diffusion of the ions is further hampered and, in addition, the use of optical measurement techniques for the determination of the absorbed dose becomes possible. In this study, a new ferric ion indicator possibility for Fricke Gel is evaluated. Sodium thiocyanate was added to the Fricke Gel matrix and the effect of this addition was analyzed in a gamma radiation field and in a high-energy electron beam. The obtained results demonstrated the possibility of using this indicator as a binding agent in the Fricke Gel dosimeter. In the gamma irradiation field, the dosimeter showed a linear response with the absorbed dose between 5 Gy and 150 Gy, in addition to presenting visual evidence of the spatial distribution of the radiation field to which it is subjected.

Significant role of secondary electrons in the formation of a multi-body chemical species spur produced by water radiolysis.

Scientific insights into water photolysis and radiolysis are essential for estimating the direct and indirect effects of deoxyribonucleic acid (DNA) damage. Secondary electrons from radiolysis intricately associated with both effects. In our previous paper, we simulated the femtosecond (1 × 10- 15s) dynamics of secondary electrons ejected by energy depositions of 11-19eV into water via high-energy electron transport using a time-dependent simulation code. The results contribute to the understanding of simple "intra-spur" chemical reactions of tree-body chemical species (hydrated electrons, hydronium ion and OH radical) in subsequent chemical processes. Herein, we simulate the dynamics of the electrons ejected by energy depositions of 20-30eV. The present results contribute to the understanding of complex "inter-spur" chemical reactions of the multi-body chemical species as well as for the formation of complex DNA damage with redox site and strand break on DNA. The simulation results present the earliest formation mechanism of an unclear multi-body chemical species spur when secondary electrons induce further ionisations or electronic excitations. The formation involves electron-water collisions, i.e. ionisation, electronic excitation, molecular excitation and elastic scattering. Our simulation results indicate that (1) most secondary electrons delocalise to ~ 12nm, and multiple collisions are sometimes induced in a water molecule at 22eV deposition energy. (2) The secondary electrons begin to induce diffuse band excitation of water around a few nm from the initial energy deposition site and delocalise to ~ 8nm at deposition energies ~ 25eV. (3) The secondary electron can cause one additional ionisation or electronic excitation at deposition energies > 30eV, forming a multi-body chemical species spur. Thus, we propose that the type and density of chemical species produced by water radiolysis strongly depend on the deposition energy. From our results, we discuss formation of complex DNA damage.

Study of modulation in complex refractive indices induced by ultrafast relativistic electrons using infrared and THz probe pulses.

Objective 
Achieving ultra-precise temporal resolution in ionizing radiation detection is essential, particularly in positron emission tomography, where precise timing enhances signal-to-noise ratios and may enable reconstruction-less imaging. A promising approach involves utilizing ultrafast modulation of the complex refractive index, where sending probe pulses to the detection crystals will result in changes in picoseconds (ps), and thus a sub - 10 ps coincidence time resolution can be realized. Towards this goal, here, we aim to first measure the ps changes in probe pulses using an ionizing radiation source with high time resolution.
Approach 
We used relativistic, ultrafast electrons to induce complex refractive index and use probe pulses in the near-infrared (800 nm) and terahertz (THz, 300 µm) regimes to test the hypothesized wavelength-squared increase in absorption coefficient in the Drude free-carrier absorption model. We measured BGO, ZnSe, BaF2, ZnS, PBG, and PWO with 1 mm thickness to control the deposited energy of the 3 MeV electrons, simulating ionization energy of the 511 keV photons. 
Main results 
Both with the 800 nm and THz probe pulses, transmission decreased across most samples, indicating the free carrier absorption, with an induced signal change of 11% in BaF2, but without the predicted Drude modulation increase. To understand this discrepancy, we simulated ionization tracks and examined the geometry of the free carrier distribution, attributing the mismatch in THz modulations to the sub-wavelength diameter of trajectories, despite the lengths reaching 500 µm to 1 mm. Additionally, thin samples truncated the final segments of the ionization tracks, and the measured initial segments have larger inter-inelastic collision distances due to lower stopping power (dE/dx) for high-energy electrons, exacerbating diffraction-limited resolution. 
Significance
Our work offers insights into ultrafast radiation detection using complex refractive index modulation and highlights critical considerations in sample preparation, probe wavelength, and probe-charge carrier coupling scenarios.

Improving storage duration of tomatoes (Solanum lycopersicum) through electron beam technology.

Electron beam (EB) technology typically consists of high-energy electron streams produced by a linear accelerator. Although promising, the use of EB irradiation as a technique to delay ripening and prevent spoilage in tomatoes has not been extensively investigated. In this study, the effectiveness of EB irradiation in prolonging the shelf life of tomatoes postharvest was investigated. The results indicated that EB irradiation successfully reduced microbial contamination and decay, preserved key quality attributes (such as total soluble solids, titratable acidity, pH, and firmness), and significantly minimized weight loss. Notably, the treatment delayed the biosynthesis of lycopene, a key indicator of ripening, without adversely affecting phenolic content and antioxidant activity, which remained consistent regardless of irradiation. Additionally, different methods for detecting irradiation were evaluated. Thermoluminescence analysis proved to be the most dependable technique, especially for doses exceeding 600Gy, due to its high sensitivity and specificity. In contrast, photostimulated luminescence and electron spin resonance analyses showed limitations in accurately identifying the irradiation status of foods with high moisture content, such as tomatoes. This study confirms that EB irradiation, while maintaining postharvest quality, extends the shelf life of tomatoes by 5-10days, suggesting its potential for commercial application in food preservation.

Registration of the auroral near-UV emission by the orbital detector TUS

The TUS detector is a highly sensitive orbital telescope. Due to the polar orbit of the spacecraft, the detector made observations of the UV luminosity of the atmosphere above the aurora oval. Events with intensity variations characteristic of pulsating auroras have been registered. The events are located along the equatorial boundary of the auroral oval and occur during long-term geomagnetic disturbances. Comparison with data from charged particle detectors shows the presence of an increased flux of precipitating high-energy electrons (with energies above 100 keV) simultaneously with UV pulsations.

Surface finishing of 3D-printed Ti–6Al–4 V alloy by electrolyte plasma polishing: Process optimization and microstructure

The electrolyte plasma polishing (EPP) technology is proposed to remove the unmelted powder particles and oxide film for high-quality surface finishing of 3D-printed Ti–6Al–4 V alloy. An orthogonal experiment is conducted to investigate multiple factors that contribute to the surface quality of the alloy during the polishing process. The optimal parameters determined for the EPP process are a voltage of 300 V, a polishing time of 12 min, a polishing depth of 12 cm, and a temperature of 75 °C. Based on the extent of the effect, the factors influencing surface roughness were ranked: voltage > time > depth > temperature. The surface crest and trough area of the alloy is substantially reduced after polishing, while the average roughness experienced a reduction of 76 %. The improvement in surface quality is attributed to the corrosion of the oxide layer by F ions in the electrolytic solution, and the melting of surface protrusions due to the impact of high-energy electrons under high-temperature and high-pressure conditions during plasma discharge. Additionally, the surface hardness of the material decreases slightly, but its corrosion resistance and hydrophobicity are enhanced, and the calibration rate of the EBSD sample can reach 92.51 %, demonstrating that it is an excellent surface finishing technique. Hence, EPP is a promising approach for smoothening 3D-printed metals, especially for alloy parts with complex geometry and porous structure.