Flash X-ray Research Articles

Influence of Sun X-ray Flashes on the Psychological State of a Human in Comparison with Space Weather Conditions: A Study by the Method of Neural Networks and Hierarchical Clustering

Influence of Sun X-ray Flashes on the Psychological State of a Human in Comparison with Space Weather Conditions: A Study by the Method of Neural Networks and Hierarchical Clustering

Comparison of intratumor and local immune response between MV X-ray FLASH and conventional radiotherapies

Background/PurposeInvestigating the antitumor effect and intratumor as well as local immune response in breast cancer-bearing mice after MV X-ray ultra-high dose rate radiotherapy (FLASH-RT) and conventional dose rate radiotherapy (CONV-RT). Materials/MethodsSix-week-old female C57BL/6 mice were inoculated subcutaneously with Py8119 and Py230 breast tumor cells in the inguinal mammary gland and administered 10 Gy abdominal 6 MV X-ray FLASH-RT (125 Gy/s) or CONV-RT (0.2 Gy/s) 15 days after tumor inoculation. Tumor and spleen tissues were obtained at different time points post-irradiation (PI) for analysis of immune cell infiltration using flow cytometry and immunohistochemical (IHC) staining. Intestine tissues were collected 3 days PI to evaluate normal tissue damage and immune cell infiltration. ResultsBoth FLASH-RT and CONV-RT significantly delayed tumor growth. Flow cytometry showed increased CD8+/CD3 + and CD8+/CD4 + ratios, and IHC confirmed a similar increased CD8 + T cell infiltration at 2 weeks PI in Py8119 tumor tissues in both irradiation groups. No statistical difference was observed between the irradiation groups in terms of tumor growth and increased T cell infiltration in the tumor. Unexpectedly, significantly smaller spleen weight and substantially higher CD8+/CD3 + and lower CD4+/CD3 + ratios were observed in the spleens of the FLASH-RT group than in the spleens of the non-irradiated control and CONV-RT groups 4 weeks PI. Pathological analysis revealed severe red pulp expansion in several spleens from the CONV-RT group, but not in the spleens of the FLASH-RT group. Reduced intestinal damage, macrophage and neutrophil infiltration were observed in the FLASH-RT group compared with CONV-RT group. ConclusionsFLASH-RT and CONV-RT effectively suppressed tumor growth and promoted CD8 + T cell influx into tumors. FLASH-RT can induce different splenic immune responses and reduce radiation-induced damage in the spleen and intestine, which may potentially enhance the therapeutic ratio of FLASH-RT.

Preclinical Research Platform for Ocular FLASH Irradiation

<h3>Purpose/Objective(s)</h3> Normal tissue sparing effects from FLASH radiotherapy (RT) are potentially transformative for the treatment of ocular cancers. Reducing damage to the abundant at-risk structures within the eye can prospectively increase visual retention rates, relax treatment margins, and eliminate the need for motion tracking by surgically implanted fiducials. To date, no prior work has explored FLASH-RT effects in the context of the eye. In this work, we have conducted a pilot study of x-ray FLASH effects for ocular irradiation in a preclinical mouse model by measuring the functional and pathological changes in healthy eyes following FLASH or conventional (CONV) dose rate irradiation. <h3>Materials/Methods</h3> An immobilization device was designed to enable focal irradiation to a single mouse eye using a FLASH-capable rotating anode x-ray tube. A 5 mm diameter lead collimator was manufactured to encompass the 3 mm target of the entire eye. Dose and dose rate measurements were performed with calibrated radiographic EBT3 films. Cone-beam CTs were acquired of four C57BL6J mice in immobilization to confirm setup reproducibility, quantified by the mean Hausdorff distance between bone segmentations. Healthy 8-week-old C57BL6J mice were irradiated with 150 kVp x-rays to doses of 21 Gy or 34 Gy at FLASH (right eye) and CONV (left eye) dose rates, respectively. Both eyes were irradiated to limit the influence of varying baseline vision between animals in our analysis. Visual acuity was assessed in 3 mice per dose level using scotopic electroretinography (ERG) up to 2 months post irradiation. Histopathological changes were assessed through H&E staining of harvested eyes. <h3>Results</h3> Mouse setup in our immobilization device was highly reproducible, with a mean Hausdorff distance of 0.34 ± 0.10 mm. Measured dose rates within the field were 67.0 ± 1.9 Gy/s and 1.2 ± 0.1 Gy/s at FLASH and CONV settings, respectively. ERGs revealed that FLASH-irradiated eyes at 21 Gy retained visual function up to 2 months post irradiation, while 21 Gy CONV induced blindness at all sampled time points with more severe surrounding skin effects. At 34 Gy, all eyes were blinded within 1 week, with comparable skin toxicities in the irradiated areas regardless of dose rate. Pathological assessment showed a loss of the photoreceptor layer of the retina from CONV irradiation, which remained intact in FLASH-treated mice. <h3>Conclusion</h3> We have developed a novel platform to study x-ray FLASH effects from ocular irradiation in mice. Functional ERG assay revealed a preservation of visual function from 21 Gy at FLASH dose rates that was not present from 21 Gy CONV. Differential damages between FLASH and CONV irradiations were confirmed through histopathology. This first demonstration of FLASH normal tissue sparing effects in a mouse eye model presents a unique and promising translation opportunity for clinical FLASH treatment. Further studies are ongoing to explore the long-term effects of FLASH radiation on vision and its efficacy on intraocular tumors.

The Immune Response and Intestinal Injury after X-Ray FLASH Irradiation in Murine Breast Cancer Transplanted Models

<h3>Purpose/Objective(s)</h3> The present study investigated the anti-tumor effect, immune response, and intestinal injury in breast cancer-bearing mice after ultra-high dose rate radiotherapy (FLASH-RT) and conventional dose rate radiotherapy (CONV-RT). <h3>Materials/Methods</h3> Six-week-old female C57BL/6 mice were inoculated subcutaneously with Py8119 and Py230 breast tumor cells in the inguinal mammary gland, and received 10 Gy abdominal 6 MeV X-ray FLASH-RT (>100 Gy/s) or CONV-RT (0.2 Gy/s) 15 days after tumor inoculation. EBT3 radiographic films were used to confirm the dose. Tumor samples were obtained 2 weeks post-irradiation (PI) in Py8119 tumor-bearing mice, spleen tissues were collected 4 weeks PI in Py230 tumor-bearing mice. Flow cytometry (FC) was performed with tumor and spleen tissues and immunohistochemistry (IHC) staining was performed in tumor tissues to test CD3+, CD4+, and CD8+ T lymphocytes. The number and length of remaining crypts were measured to evaluate acute intestine damage 3 days PI. <h3>Results</h3> Both FLASH-RT and CONV-RT significantly reduced the tumor weights. FC showed increased CD8+/CD3+ and CD8+/CD4+ ratios in tumor tissues and IHC confirmed a similar CD8+ T cells percentage 2 weeks PI, but there is no significant difference between FLASH and CONV groups. Surprisingly, significantly smaller spleen weight and substantially higher CD8+/CD3+ and CD8+/CD4+ ratios in the spleen in FLASH compared with non-irradiated control and CONV groups 4 weeks PI, indicating FLASH might stimulate a systematic immune response. FLASH irradiated mice had more remaining crypts and significantly longer crypt length than CONV irradiated mice, indicating a normal tissue sparing effect of FLASH-RT. <h3>Conclusion</h3> FLASH-RT and CONV-RT effectively suppressed tumor growth and promoted CD8+ T cell influx into the tumor. FLASH-RT resulted in a smaller weight and a higher proliferative rate of CD8+ T cells in the spleen than CONV-RT, which might indicate a different systematic immune effect between FLASH-RT and CONV-RT. FLASH-RT significantly spared the intestine from early damage.

FLASH Effects Induced by kV X-Rays in a Murine Skin Model

<h3>Purpose/Objective(s)</h3> Current research on FLASH dose rate radiotherapy is predominantly performed with advanced proton or electron accelerators of limited access to the laboratory researcher. Stationary anode orthovoltage x-ray irradiators would be desirable but are currently incapable of supporting the power requirements to operate at FLASH dose rates. In this study, we investigate the use of rotating anode x-ray tubes to overcome these limitations. We present the dosimetric characterization of a rotating anode x-ray system for laboratory FLASH research and its implementation for a pilot study of radiation skin toxicities in mice. <h3>Materials/Methods</h3> A high-capacity rotating anode x-ray tube was installed in our laboratory with a 75-kW generator, operating at 150 kVp with 0.025 mm Cu added filtration. Calibrated radiographic film was irradiated at varying depths in kV solid water to measure output, beam profiles, and depth-dose parameters (PDD). A variety of wild-type mice (GR/GRT, CMV) were irradiated to the hind flank to 38 or 48 Gy at the highest achievable dose rate (FLASH-IR). Conventional dose rate irradiations (CONV-IR) to the same doses were performed at 3 Gy/min using a 220 kVp x-ray irradiator. Visible skin toxicities were assessed weekly and quantified using a skin scoring scale for endpoints of hair loss, erythema, and ulceration (n= 7 per dose at each dose rate). At 8-weeks post irradiation, skin samples were harvested and stained with H&E to assess pathological changes from FLASH-IR or CONV-IR x-rays. <h3>Results</h3> Dose rates peaked at 101 Gy/s in the cathode side of the radiation field from anode heel effects. The total field size at 46 mm SSD was 20 × 20mm². A useable region of 10 × 20 mm² for FLASH studies was defined as the cathode-half of the field, with an average dose rate of 96.1 ± 2.8 Gy/s. The PDD within this region falls to 67% at 5mm depth in solid water and 51% at 10 mm. At 4 weeks post irradiation, CONV-IR mice saw hair loss and erythema in the entire irradiated region, while all FLASH-IR mice retained hair in-field with no change in skin condition. By 8 weeks post irradiation, skin effects in all FLASH-IR mice did not progress beyond hair loss in field, while all CONV-IR mice had progressed to more severe skin toxicities. Pathological assessments are ongoing. Early analysis shows higher frequency of ulceration, dermis hyperplasia, and fibrosis from CONV-IR than FLASH-IR. <h3>Conclusion</h3> This study presents the first observation of FLASH effects induced by a single pulse of kV x-rays in an animal skin toxicity model. FLASH dose rates requisite for preclinical research are achievable with kV x-rays using rotating anode technology. X-ray FLASH effects in skin occur at comparable doses to those published for FLASH electrons and protons. The use of a single x-ray pulse suggests that average dose rate is the necessary condition, in contrast to fine pulse structure, for the induction of FLASH effects.

FLASH X-ray spares intestinal crypts from pyroptosis initiated by cGAS-STING activation upon radioimmunotherapy

DNA-damaging treatments such as radiotherapy (RT) have become promising to improve the efficacy of immune checkpoint inhibitors by enhancing tumor immunogenicity. However, accompanying treatment-related detrimental events in normal tissues have posed a major obstacle to radioimmunotherapy and present new challenges to the dose delivery mode of clinical RT. In the present study, ultrahigh dose rate FLASH X-ray irradiation was applied to counteract the intestinal toxicity in the radioimmunotherapy. In the context of programmed cell death ligand-1 (PD-L1) blockade, FLASH X-ray minimized mouse enteritis by alleviating CD8+ T cell-mediated deleterious immune response compared with conventional dose rate (CONV) irradiation. Mechanistically, FLASH irradiation was less efficient than CONV X-ray in eliciting cytoplasmic double-stranded DNA (dsDNA) and in activating cyclic GMP-AMP synthase (cGAS) in the intestinal crypts, resulting in the suppression of the cascade feedback consisting of CD8+ T cell chemotaxis and gasdermin E-mediated intestinal pyroptosis in the case of PD-L1 blocking. Meanwhile, FLASH X-ray was as competent as CONV RT in boosting the antitumor immune response initiated by cGAS activation and achieved equal tumor control in metastasis burdens when combined with anti-PD-L1 administration. Together, the present study revealed an encouraging protective effect of FLASH X-ray upon the normal tissue without compromising the systemic antitumor response when combined with immunological checkpoint inhibitors, providing the rationale for testing this combination as a clinical application in radioimmunotherapy.

A 500kV, 10kA, 40ns coaxial Marx generator pulser for cable fed flash x-ray system.

Flash x-ray (FXR) systems are used for dynamic radiography. Depending on the speed of the object, these systems typically require a very short pulse duration (∼25ns) for image acquisition without motion blur. The conventional Marx generators with zigzag discharge paths result in higher inductance; hence, they do not meet the requirement of shorter pulse duration (30-40ns) and low impedance (40-60 Ω) simultaneously. A coaxial Marx generator has been designed and developed, which is capable of generating 500kV peak voltages and 10kA peak current within a 40ns pulse duration. The CST simulation of the coaxial Marx generator has been carried out to validate the design parameters. The FXR electron beam diode is powered by this Marx generator. Experiments were carried out to measure the x-ray parameters like pulse width, source size, x-ray energy spectrum, penetration depth, and cone angle. The maximum measured x-ray dose was 62 mR at 1m distance from the source window. The x-ray radiograph demonstrates a penetration depth of 32mm in steel kept at 2.5m distance from the source for 500kV diode voltages.

A portable flash x-ray generator powered by an explosive driven ferroelectric generator.

In order to develop a portable flash x-ray source, a compact explosive pulsed power source based on an explosive-driven ferroelectric generator (EDFEG) is investigated numerically and experimentally in this paper. The EDFEG is used as a primary power supply to charge a pulse capacitor, and then the capacitor outputs high current through an inductor and an electrical exploding opening switch (EEOS). Finally, a high voltage fast pulse is generated on a diode, which generates x rays. A circuit model was built to analyze the performance of this compact pulsed power source. A portable flash x-ray generator prototype was constructed in our laboratory. The typical experimental results illustrated that after metal wires of the EEOS exploded, a high-voltage fast pulse with a peak value of 180kV, a rise time of 2.8ns, and a pulse width of 30ns was generated on the x-ray diode. Meanwhile, an x-ray pulse with a pulse width of 19ns, a focus of about 1mm, and a dose of 100 mR at 15cm was obtained.

Characterization of sub-picosecond laser-produced fast electrons by modeling angularly resolved bremsstrahlung measurements with 3D hybrid particle-in-cell code

Hard x-rays produced by intense laser-produced fast electrons interacting with solids are a vital source for producing radiographs of high-density objects and implosion cores for inertial confinement fusion. Accurate calculation of hard x-ray sources requires a three-dimensional (3D) simulation geometry that fully models the electron transport dynamics, including electron recirculation and the generation of absolute photon yields. To date, 3D simulations of laser-produced bremsstrahlung photons over tens of picoseconds and code benchmarking have not been performed definitively. In this study, we characterize sub-picosecond laser-produced fast electrons by modeling angularly resolved bremsstrahlung measurements for refluxing and non-refluxing targets using the 3D hybrid particle-in-cell (PIC), Large Scale Plasma code. Bremsstrahlung radiation and escaped electron data were obtained by focusing a 50-TW Leopard laser (15 J, 0.35 ps, 2 × 1019 W/cm2) on a 100-μm-thick Cu foil and a Cu with a large plastic backing (Cu–CH target). Data for both the Cu and Cu–CH targets were reproduced for simulations with a given set of electron parameters. Comparison of the simulations revealed that the hard x-ray emission from the Cu target was significantly longer in duration than that from the Cu–CH target. The benchmarked hybrid PIC code could prove to be a powerful tool in the design and optimization of time- and angular-dependent bremsstrahlung sources for flash x-ray and gamma-ray radiography.

Newfound X-ray flashes might shed light on their own origins

Newfound X-ray flashes might shed light on their own origins

A Light-curve Analysis of the X-Ray Flash First Observed in Classical Novae

An X-ray flash, expected in a very early phase of a nova outburst, was at last detected with the SRG/eROSITA in the classical nova YZ Reticuli 2020. The observed flash timescale, luminosity, and blackbody temperature substantially constrain the nova model. We present light-curve models of the X-ray flash for various white dwarf (WD) masses and mass-accretion rates. We have found the WD mass in YZ Ret to be as massive as M WD ∼ 1.3 M ☉ with mass-accretion rates of yr−1, including the case where the mass-accretion rate is changing between them, consistent with the SRG/eROSITA observation. The X-ray observation confirms the luminosity to be close to the Eddington limit at the X-ray flash. The occurrence of optically thick winds, with the photospheric radius exceeding ∼0.1 R ☉, terminated the X-ray flash of YZ Ret by strong absorption. This sets a constrain on the starting time of wind mass loss. A slight contamination of the hydrogen-rich envelope by the core material seems to be preferred to explain the very short duration of the X-ray flash.

The Texas A&M University Hypervelocity Impact Laboratory: A modern aeroballistic range facility.

Novel engineering materials and structures are increasingly designed for use in severe environments involving extreme transient variations in temperature and loading rates, chemically reactive flows, and other conditions. The Texas A&M University Hypervelocity Impact Laboratory (HVIL) enables unique ultrahigh-rate materials characterization, testing, and modeling capabilities by tightly integrating expertise in high-rate materials behavior, computational and polymer chemistry, and multi-physics multiscale numerical algorithm development, validation, and implementation. The HVIL provides a high-throughput test bed for development and tailoring of novel materials and structures to mitigate hypervelocity impacts (HVIs). A conventional, 12.7mm, smooth bore, two-stage light gas gun (2SLGG) is being used as the aeroballistic range launcher to accelerate single and simultaneously launched projectiles to velocities in the range 1.5-7.0 km/s. The aeroballistic range is combined with conventional and innovative experimental, diagnostic, and modeling capabilities to create a unique HVI and hypersonic test bed. Ultrahigh-speed imaging (10M fps), ultrahigh-speed schlieren imaging, multi-angle imaging, digital particle tracking, flash x-ray radiography, nondestructive/destructive inspection, optical and scanning electron microscopy, and other techniques are being used to characterize HVIs and study interactions between hypersonic projectiles and suspended aerosolized particles. Additionally, an overview of 65 2SLGG facilities operational worldwide since 1990 is provided, which is the most comprehensive survey published to date. The HVIL aims to (i) couple recent theoretical developments in shock physics with advances in numerical methods to perform HVI risk assessments of materials and structures, (ii) characterize environmental effects (water, ice, dust, etc.) on hypersonic vehicles, and (iii) address key high-rate materials and hypersonics research problems.

Three-Dimensional Particle-in-Cell Analysis of Mechanical Design Tolerances of the Scorpius Injector With Warp

This article examines the mechanical design tolerances for the Scorpius injector using a 3-D particle-in-cell (PIC) code. In order to meet its objective as a high-fidelity, multipulse flash X-ray source, the accelerator has requirements for the electron beam in order to minimize the spot size of the beam focused onto a foil target to create high fluence X-rays at energies greater than 10 MeV. The requirements for alignment of the cathode, anode beam pipe, focusing solenoids, and transport solenoids specified using Trak and AMBER are independently verified using a 3-D electrostatic/magnetostatic model of the Scorpius injector, including transverse magnetic field errors that arise from mechanical alignment errors. It is predicted that the injector will meet the performance requirements for radiographic operation and has a design margin to correct for potentially unforeseen operating conditions.

Dual-pulse generation from a velvet cathode with a new inductive voltage adder for x-ray flash radiography applications

The evolution of two intense pulsed electron beams for an x-ray flash radiography application is characterized in a coupling of experimental and simulation studies. For this purpose, experiments were performed at Commissariat \`a l'Energie Atomique et aux Energies Alternatives with a new dual-pulse inductive voltage adder named ``Mi2.'' This experimental setup has been designed and built to produce two intense pulsed electron beams of 2 kA, 700 keV, and 80 ns full width at half maximum from a velvet cold cathode. The delay between the pulses ranges from tens of nanoseconds to a few microseconds. This study quantifies the effect of the plasma dynamics on the beam current of the second pulse, which represents an important parameter from the beam transport point of view. A multidimensional particle-in-cell simulation model is used to provide a numerical analysis in order to determine the influence of velvet plasma dynamics on the second pulse. Analysis of the experimental results indicates that the motion of the electron extraction zone within the expanding plasma remains lower than 1 mm for $3\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$ delay, inducing a minor impact on the beam current extracted from the velvet cathode. Based on the developed model, this plasma expansion induces an increase of 5% for the current extracted from the second pulse with a delay of $1\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$ for two pulses having the same voltage, which is consistent with linear induction accelerator injector parameters for multiple pulse use.

Velocity tracking of shaped charge wire formation and propagation toward the target

ABSTRACT The formation of shaped charge jets is traditionally studied experimentally using flash X-ray and high-speed camera images. Sequential images obtained through these methods provide insight into the overall properties of the jet, such as jet tip velocity and outline shape. Numerical methods are validated using experimental results of the macroscopic properties by taking absolute velocity contours through the jet and comparing the outline shape. These methods do not describe where, and in which order, discrete parts of the shaped charge liner are located in the jet after formation. Shaped charge jet formation is studied here numerically by tracking the velocity in the flow field using stationary gauges and by placing dynamic gauges on the shaped charge liner. This method provides insight into the physical mechanism of jet formation. It is generally assumed that the shaped charge jet forms from liner inversion, where the liner tip becomes the jet tip that first penetrates the target. This work shows that the liner tip does not form part of the jet but is rather absorbed into the slug. Similarly, PER theory assumes that the outer part of the liner (next to the explosive) flows into the slug and the inner part flows into the jet. It is shown here that this assumption is not valid in all cases. This study is a proof of concept to highlight the advantages of using the method of simultaneous liner and flow field velocity tracking to aid shaped charge optimization activities.

Particle loading as a design parameter for composite radiation shielding

An evaluation of the radiation shielding performance of high-Z-particle-loaded polylactic acid (PLA) composite materials was pursued. Specimens were produced via fused deposition modeling (FDM) using copper-PLA, steel-PLA, and BaSO4-PLA composite filaments containing 82.7, 75.2, and 44.6 wt% particulate phase contents, respectively, and were tested under broad-band flash x-ray conditions at the Sandia National Laboratories HERMES III facility. The experimental results for the mass attenuation coefficients of the composites were found to be in good agreement with GEANT4 simulations carried out using the same exposure conditions and an atomistic mixture as a model for the composite materials. Further simulation studies, focusing on the Cu-PLA composite system, were used to explore a shield design parameter space (in this case, defined by Cu-particle loading and shield areal density) to assess performance under both high-energy photon and electron fluxes over an incident energy range of 0.5–15 MeV. Based on these results, a method is proposed that can assist in the visualization and isolation of shield parameter coordinate sets that optimize performance under targeted radiation characteristics (type, energy). For electron flux shielding, an empirical relationship was found between areal density (AD), electron energy (E), composition and performance. In cases where EAD≥2 MeV∙cm∙g−1, a shield composed of >85 wt% Cu results in optimal performance. In contrast, a shield composed of <10 wt% Cu is anticipated to perform best against electron irradiation when EAD<2 MeV∙cm∙g−1.

X-ray detection of a nova in the fireball phase.

Novae are caused by runaway thermonuclear burning in the hydrogen-rich envelopes of accreting white dwarfs, which leads to a rapid expansion ofthe envelope and the ejection ofmost of its mass1,2. Theory has predicted the existence of a 'fireball' phase following directly on from the runaway fusion, which should be observable as a short, bright and soft X-ray flash before the nova becomes visible in the optical3-5. Here we report observations of a bright and soft X-ray flash associated with the classical Galactic nova YZ Reticuli 11 h before its 9 mag optical brightening. No X-ray source was detected 4 h before and after the event, constraining the duration of the flash to shorter than 8 h. In agreement with theoretical predictions4,6-8, the source's spectral shape is consistent with a black-body of 3.27+0.11-0.33 × 105 K (28.2+0.9-2.8 eV), or a white dwarf atmosphere, radiating at the Eddington luminosity, with a photosphere that is only slightly larger than a typical white dwarf.

Breakthrough Multi-Messenger Astrophysics with the THESEUS Space Mission

The mission concept THESEUS (Transient High Energy Sky and Early Universe Surveyor) aims at exploiting Gamma-Ray Bursts (GRB) to explore the early Universe, as well as becoming a cornerstone of multi-messenger and time-domain astrophysics. To achieve these goals, a key feature is the capability to survey the soft X-ray transient sky and to detect the faint and soft GRB population so far poorly explored. Among the expected transients there will be high-redshift GRBs, nearby low-luminosity, X-ray Flashes and short GRBs. Our understanding of the physics governing the GRB prompt emission will benefit from the 0.3 keV–10 MeV simultaneous observations for an unprecedented large number of hundreds of events per year. In particular the mission will provide the identification, accurate sky localisation and characterization of electromagnetic counterparts to sources of gravitational wave and neutrino sources, which will be routinely detected during the 2030s by the upgraded second generation and third generation Gravitational Wave (GW) interferometers and next generation neutrino detectors.

Heat management of a compact x-ray source for microbeam radiotherapy and FLASH treatments.

Microbeam and x-ray FLASH radiation therapy are innovative concepts that promise reduced normal tissue toxicity in radiation oncology without compromising tumor control. However, currently only large third-generation synchrotrons deliver acceptable x-ray beam qualities and there is a need for compact, hospital-based radiation sources to facilitate clinical translation of these novel treatment strategies. We are currently setting up the first prototype of a line-focus x-ray tube (LFxT), a promising technology that may deliver ultra-high dose rates (UHDRs) of more than 100 Gy/s from a table-top source. The operation of the source in the heat capacity limit allows very high dose rates with micrometer-sized focal spot widths. Here, we investigate concepts of effective heat management for the LFxT, a prerequisite for the performance of the source. For different focal spot widths, we investigated the temperature increase numerically with Monte Carlo simulations and finite element analysis (FEA). We benchmarked the temperature and thermal stresses at the focal spot against a commercial x-ray tube with similar power characteristics. We assessed thermal loads at the vacuum chamber housing caused by scattering electrons in Monte Carlo simulations and FEA. Further, we discuss active cooling strategies and present a design of the rotating target. Conventional focal spot widths led to a temperature increase dominated by heat conduction, while very narrow focal spots led to a temperature increase dominated by the heat capacity of the target material. Due to operation in the heat capacity limit, the temperature increase at the focal spot was lower than for the investigated commercial x-ray tube. Hence, the thermal stress at the focal spot of the LFxT was considered uncritical. The target shaft and the vacuum chamber housing require active cooling to withstand the high heat loads. The heat capacity limit allows very high power densities at the focal spot of the LFxT and thus facilitates very high dose rates. Numerical simulations demonstrated that the heat load imparted by scattering electrons requires active cooling.

Experiments and modelling for characterisation and validation of a two-phase constitutive model for describing sands under explosive loading

Specification of constitutive equations and validation of advanced material models is a developing area which is yet to be adequate for the complexity of granular geological materials such as sands and soils. In consideration of these materials as an air-solid mixture, the present work suggests a consistent procedure for specifying the constitutive equations to close a two-phase model for these materials. The following data are used: (i) Hugoniot data for the solid constituent specifying the equation of state; (ii) rate sensitive strength data of the solid constituent for the plasticity constitutive equations; (iii) data from Split Hopkinson Pressure Bar (SHPB) tests for the compaction kinetic; and (iv) post-test analysis of encapsulated samples loaded by High Explosive for the consolidation response. The model specified with this procedure and implemented in the CTH hydrocode is validated with independent tests in an axisymmetric setup. The suggested experimental setup observes deformation in time of a circular plate loaded by sand ejecta from a detonating buried HE charge, using flash X-ray radiography. These experiments characterise both temporal and spatial distribution of the impulse and also enable an integral assessment. The experimental investigation of a calcite sand, several silica sand variants, a glass powder and a soil mixture was conducted in the present paper, employing the methodology developed for the material characterisation and model validation. Comparison of the test results for these materials with the calculations demonstrated a good agreement.