Electron Bremsstrahlung Research Articles

Electromagnetic Signal of a Proton Beam in Biological Tissues for a Potential Range-Verification Approach in Proton Therapy

In the present work we investigate the fundamental properties of a proton beam's electromagnetic signal as a candidate for range verification in proton therapy. We compute the electric and magnetic fields from a pulsed proton beam in biological tissues in a cylindrical geometry via a dedicated analytical solution of the Maxwell equations. The tissues are specified through their dielectric response and stopping power, where we consider a straight trajectory with a range that corresponds to protons with an initial energy of 150 MeV. We analyze the characteristics of the pulse and the impact of the pulse shape. The effect of the tissue's conductivity on the deposited charges is specifically taken into account. In addition, we calculate and analyze the radiative pulse through the Li\'enard-Wiechert approach. We find that the conductivity charge relaxation has a big influence on the electric field strength, even in the presence of boundaries. It strongly depends on its environment, i.e., the permittivity, conductivity, and boundaries of the surrounding tissues. The electric field that originates from the primary protons vanishes in a time scale of ns. Conversely, the magnetic field is independent of its environment and constant in strength during a rectangular pulse ($10\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{s}$). For $\ensuremath{\mu}\mathrm{A}$ peak beam currents it lies in the pT range, 10 cm away from the beam axis, and is therefore detectable through, e.g., optical magnetometry. Its spatial profile, however, does not exhibit a distinct feature with respect to the range, but decreases rather smoothly and characteristically along the beam axis. The typical velocity dependence of the magnetic field strength is suppressed, due to the increasing charge density downstream. Finally, the primary protons give rise to an electromagnetic pulse in the radio spectrum (it peaks at approximately 9 GHz). It originates spherically around the range and consists partially of bremsstrahlung and Cherenkov radiation. Yet, a broader comparison to other radiation sources, e.g., secondary electron bremsstrahlung, is required. Based on our findings, we conclude that the magnetic field signal has favorable properties that motivate its detection experimentally for range-verification purposes.

SiPM-matrix readout of two-phase argon detectors using electroluminescence in the visible and near infrared range

Proportional electroluminescence (EL) in noble gases is used in two-phase detectors for dark matter searches to record (in the gas phase) the ionization signal induced by particle scattering in the liquid phase. The “standard” EL mechanism is considered to be due to noble gas excimer emission in the vacuum ultraviolet (VUV). In addition, there are two alternative mechanisms, producing light in the visible and near infrared (NIR) ranges. The first is due to bremsstrahlung of electrons scattered on neutral atoms (“neutral bremsstrahlung”, NBrS). The second, responsible for electron avalanche scintillation in the NIR at higher electric fields, is due to transitions between excited atomic states. In this work, we have for the first time demonstrated two alternative techniques of the optical readout of two-phase argon detectors, in the visible and NIR range, using a silicon photomultiplier matrix and electroluminescence due to either neutral bremsstrahlung or avalanche scintillation. The amplitude yield and position resolution were measured for these readout techniques, which allowed to assess the detection threshold for electron and nuclear recoils in two-phase argon detectors for dark matter searches. To the best of our knowledge, this is the first practical application of the NBrS effect in detection science.

Bremsstrahlung cannon design for shock ignition relevant regime.

We report on the optimization of a BremsStrahlung Cannon (BSC) design for the investigation of laser-driven fast electron populations in a shock ignition relevant experimental campaign at the Laser Megajoule-PETawatt Aquitaine Laser facility. In this regime with laser intensities of 1015 W/cm2-1016 W/cm2, fast electrons with energies ≤100 keV are expected to be generated through Stimulated Raman Scattering (SRS) and Two Plasmon Decay (TPD) instabilities. The main purpose of the BSC in our experiment is to identify the contribution to x-ray emission from bremsstrahlung of fast electrons originating from SRS and TPD, with expected temperatures of 40 keV and 95 keV, respectively. Data analysis and reconstruction of the distributions of x-ray photons incident on the BSC are described.

Measurement of the helicity asymmetry E for the reaction gamma prightarrow pi ^0 p

A measurement of the double-polarization observable E for the reaction gamma prightarrow pi ^0 p is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C_4H_9OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from E_gamma =600 to 2310 MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.

Meteorological Characteristics of Energetic Atmospheric Phenomena

Thunderclouds act as the sources of energetic radiation, the main components of which are gamma particles and electrons. The radiation can be registered by satellite or ground-based detectors. The effect is caused by the bremsstrahlung of electrons accelerated by the cloud electric field. The study of high-energy atmospheric phenomena requires analyzing the data on the distribution of cloud particles and the electrical structure formed by them. In this study, the comparison of the information on meteorological conditions for energetic emission from thunderclouds obtained from satellite observations in the infrared and optical ranges is performed.

Lower Hybrid Current Drive in High Aspect Ratio Tokamaks

A multi-machine study has been carried out to investigate the impact of a strongly bounded wave propagation domain on the Lower Hybrid current drive, a condition which occurs principally in high aspect ratio tokamaks. In this regime, the condition of kinetic resonance can be far above the upper boundary of the propagation domain, and may not be achieved by the usual toroidal upshift. Therefore no tail of fast electrons can be pulled out from the thermal bulk. Nevertheless, while tokamak plasmas are in principle almost transparent to the wave in this regime so-called “unbridgeable spectral gap”, full current drive is well achieved for the two tokamaks considered in this study, TRIAM-1M (Zushi et al. Nucl Fusion 43:1600, 2003) and WEST (Bourdelle et al. Nucl Fusion 55:063017, 2015), both characterized by a very large aspect ratio \(R/a>5.5\). The case of the high aspect ratio tokamak HL-2A (Liu et al. Nucl Fusion 45:S239, 2005) for which the wave propagation domain has also an upper boundary, but close to the resonance condition, is considered by comparison. First principles modeling of the rf-driven current and the fast electron bremsstrahlung using the ALOHA/C3PO/LUKE/R5-X2 chain of codes shows unambiguously that the spectral gap must be already filled at the separatrix in order to reproduce quantitatively observations and some important parametric dependencies. This result is an important milestone in the physics understanding of the Lower Hybrid current drive, highlighting the existence of a powerful and likely universal alternative mechanism to bridge the spectral gap, that is not related to toroidal magnetic refraction. With an initially broad power spectrum, lobes with low parallel refractive indexes that carry most of the plasma current can be absorbed in almost single pass, restoring the full validity of the ray-tracing approximation for describing the propagation of the Lower Hybrid wave in cold plasmas.

The Resonant Bremsstrahlung of Ultrarelativistic Electrons on a Nucleus with Radiation of Hard Gamma-Quanta in the Presence of a Pulsed Field of the X-ray Pulsar

The investigation scrutinizes the circulation of the large-scaled fluxes of ultrarelativistic electrons near the neutron stars. This work focuses on the effects that occur during the adjustment of the strong electromagnetic field near the X-ray pulsars. Particularly, this study analyzes the resonant high-energy spontaneous bremsstrahlung of ultrarelativistic electrons in the pulsed fields of a nucleus and X-ray pulsar. Specific attention is given to the pulsed character of the field model. Under the resonant conditions the intermediate virtual electron within the electromagnetic field transforms into a real particle. As a result, the initial second-order process with accordance to the fine structure constant effectively splits into two first-order effects: the stimulated Compton process and the field-assisted scattering of an electron on a nucleus. In this research we obtain the resonant differential cross-sections with registration of frequency and radiation angle of a hard gamma-quantum. To summarize, the resonant differential cross-section of the effect within the external pulsed electromagnetic field of X-ray pulsar significantly exceeds the corresponding cross-section without an external field.

Influence of Synchrotron and Photorecombinational Radiation on Alfven Wave Absorption by Dissipative Plasma

A mathematical model of the Alfven wave absorption is proposed, the study of which is based on the equations of two-fluid electromagnetic hydrodynamics (EMHD) having taken the electron inertia and bremsstrahlung into account. Special attention is paid to the research of the additional effects of photorecombinational and synchrotron radiation. The investigation revealed, in particular, the finite depth of the Alfven wave penetration into the plasma. Another important effect is the establishment of the parameters of the absorbed Alfven wave and their convergence to the quasi-stationary regime.

Effect of Neutral Bremsstrahlung on the Operation of Two-Phase Argon Detectors

Two-phase noble liquid detectors are widely used in experiments for dark matter search. Ionization signals caused by particle scattering in a noble-gas liquid are commonly recorded using the effect of proportional electroluminescence in the gas phase. In addition to the standard electroluminescence mechanism based on vacuum ultraviolet emission of noble gas excimers, the mechanism of electron bremsstrahlung on neutral atoms with a continuous spectrum from ultraviolet to near infrared range was recently revealed. In this paper, we demonstrate the effect of bremsstrahlung on characteristics of a DarkSide-50 two-phase argon detector. In particular, the sag of the electroluminescent gap grid and the contribution of the fast component to the proportional electroluminescence signal will be estimated.

Calculation of secondary electron bremsstrahlung in the binary encounter approximation using Dirac–Hartree–Fock–Slater velocity distributions

One of the main factors that determine the detection limit in particle-induced X-ray emission (PIXE) spectrometry is the continuous X-ray background. In the case of impinging protons, a complete description requires five radiative processes. Among them, secondary electron bremsstrahlung (SEB) is one of the largest contributions and describes the bremsstrahlung radiated by the electrons ejected from the target atoms by proton impact. The calculation of SEB cross sections in the binary encounter approximation (BEA) entails knowledge of the velocity distributions (VDs) of the atomic electrons. For this purpose, analytical hydrogenic VDs are currently used for all the (sub)shells. In the present work, numerical VDs calculated from Dirac–Hartree–Fock–Slater (DHFS) wave functions are employed. Additionally, a compact equation for the SEB differential cross section is derived. Results for the ionisation and SEB cross sections of Al, Ag, and Au calculated from the DHFS and hydrogenic VDs are compared in detail.

X-Ray Emission from Jupiter’s Galilean Moons: A Tool for Determining Their Surface Composition and Particle Environment

Abstract We analyze archival Chandra X-ray Observatory observations of Jupiter to search for emission from the Galilean moons. X-ray emission has previously been reported from Io and Europa using a subset of these data. We confirm this detection, and marginally detect X-ray emission from both Ganymede and Callisto as well. The X-ray spectrum of Europa is strongly peaked around the neutral oxygen fluorescence line (525 eV), while Io’s has peaks at both oxygen and sulfur (2308 eV) plus a broad continuum between 350 and 5000 eV. Ganymede’s spectrum is similar to Io’s, but without the sulfur peak. A few events, mostly clustered around the oxygen line, are detected from Callisto. Using measurements by the Galileo mission of the specific intensity of ambient protons and electrons, we model the X-ray spectra and flux of the moons from two processes: particle-induced X-ray emission (PIXE) from the impact of energetic protons and X-ray emission from electron bremsstrahlung. With uncertainties of a factor of a few, the electron bremsstrahlung and PIXE models overestimate the X-ray flux from Europa, preventing us from making a definitive statement about the origin of the X-ray emission. The PIXE model of Io predicts emission lines at O and S similar to those observed, but underestimates their flux by nearly two orders of magnitude. Based on this discrepancy in the PIXE flux, combined with the detected broadband continuum in the spectrum, we conclude that the X-ray emission from Io is due to electron bremsstrahlung. Likewise, because of Ganymede’s broad continuum, we tentatively conclude that its X-ray emission is also due to electron bremsstrahlung. Callisto is too faint in the X-rays to draw any conclusion. Obtaining in situ X-ray observations of the moons would provide a direct measurement of their elemental composition.

Dose image prediction for range and width verifications from carbon ion-induced secondary electron bremsstrahlung x-rays using deep learning workflow.

Imaging of the secondary electron bremsstrahlung (SEB) x rays emitted during particle-ion irradiation is a promising method for beam range estimation. However, the SEB x-ray images are not directly correlated to the dose images. In addition, limited spatial resolution of the x-ray camera and low-count situation may impede correctly estimating the beam range and width in SEB x-ray images. To overcome these limitations of the SEB x-ray images measured by the x-ray camera, a deep learning (DL) approach was proposed in this work to predict the dose images for estimating the range and width of the carbon ion beam on the measured SEB x-ray images. To prepare enough data for the DL training efficiently, 10,000 simulated SEB x-ray and dose image pairs were generated by our in-house developed model function for different carbon ion beam energies and doses. The proposed DL neural network consists of two U-nets for SEB x ray to dose image conversion and super resolution. After the network being trained with these simulated x-ray and dose image pairs, the dose images were predicted from simulated and measured SEB x-ray testing images for performance evaluation. For the 500 simulated testing images, the average mean squared error (MSE) was 2.5×10-5 and average structural similarity index (SSIM) was 0.997 while the error of both beam range and width was within 1mm FWHM. For the three measured SEB x-ray images, the MSE was no worse than 5.5×10-3 and SSIM was no worse than 0.980 while the error of the beam range and width was 2mm and 5mm FWHM, respectively. We have demonstrated the advantages of predicting dose images from not only simulated data but also measured data using our deep learning approach.

Sensitivity improvement of YAP(Ce) cameras for imaging of secondary electron bremsstrahlung x-rays emitted during carbon-ion irradiation: problem and solution

Low-energy x-ray imaging of secondary electron bremsstrahlung x-rays emitted during carbon-ion irradiation is a promising method for range estimation and could be used for imaging with almost clinical dose levels of carbon ion. However, the number of counts in images with clinical dose levels is relatively small, making it difficult to obtain precise range estimations. Since improving the sensitivity of the x-ray camera may solve this issue, we developed two new types of x-ray cameras. One uses a 1 mm thick, 40 mm × 40 mm cerium-doped yttrium aluminum perovskite (YA1O3: YAP(Ce)) scintillator plate combined with a 2 inch square flat panel photomultiplier tube (FP-PMT) contained in a 2 cm thick tungsten shield with a pinhole collimator positioned 50 mm from the scintillator; the other uses a 0.5 mm thick, 20 mm × 20 mm YAP(Ce) scintillator plate combined with a 1 inch square position sensitive photomultiplier tube (PSPMT) contained in the same tungsten shield with a pinhole collimator, but with the scintillator positioned closer (30 mm) to the pinhole collimator to obtain a similar field of view. For both cameras, we used a wider angle (∼55°) pinhole collimator to measure the phantom closer to improve sensitivity. Although the 40 mm × 40 mm YAP(Ce) camera had high system spatial resolution, the background count fractions were high and produced a high count area at the center of the images due to the pulse pileup of the signals. With the 20 mm × 20 mm YAP(Ce) camera, we obtained x-ray images with low background counts without a high count area at the image center. By smoothing the measured images, we were able to estimate the ranges even for clinical dose levels. We therefore confirmed that one of our newly developed YAP(Ce) cameras had high sensitivity and is promising for the imaging of secondary electron bremsstrahlung x-rays during irradiation of carbon ions in clinical conditions.

Resonant Laser-Assisted Process of Ultrarelativistic Electrons Bremsstrahlung in the Field of a Nucleus

The scrutiny of the resonant laser-assisted bremsstrahlung (LAB) of ultrarelativistic electrons within the laser plasma ambience in the field of a nucleus is presented. The kinematics of the explored process can develop within two probable channels. Thus, for the first channel an electron radiates a spontaneous photon and subsequently scatters on a nucleus. In contrast, for the second channel an electron scatters on a nucleus and consequently a spontaneous photon emits. It is important to underline, that within the laser field plasma the ultrarelativistic electron in the intermediate state emerges to the mass shell and transforms into the real particle. Furthermore, the second order effect functionally transmits into two sequential first order procedures (implementing the laser-stimulated Compton process and the laser-assisted Mott scattering) with respect to the fine structure constant. We evaluated the fluctuation of the spontaneous photon resonant frequency for the various initial parameters criteria. As a result, in the investigation a specific diapason of the resonant frequency modification for the second reaction scheme was highlighted when the ultrarelativistic electron at first scatters on a nucleus and then radiates a spontaneous photon. The designated interval consists of three frequency levels in alternative to the first channel interaction pattern. Moreover, the study delineates the occurrence of the particles propagation within a narrow angle cone in the vector direction parallel to the initial electron momentum. To summarize, the article estimates that the magnitude of the differential cross-section in the resonant conditions substantially exceeds the cross-section of the process without the laser plasma ambience. In addition, pulsed laser radiation laboratories (SLAC, FAIR, XFEL, ELI, XCELS) maintain the ability to verify the project calculations.

Resonant high-energy bremsstrahlung of ultrarelativistic electrons in the field of a nucleus and a weak electromagnetic wave

The actual theoretical research investigates the resonant spontaneous bremsstrahlung (RSB) of ultrarelativistic electrons under the condition of scattering on a nucleus in the field of a weak electromagnetic wave. The progression of the functional mechanism indicates the transformation of the intermediate virtual electron into the real particle state. Therefore, the initial second order process with accordance to the fine structure constant in the light field productively splits into two consequent first order formations: the laser-stimulated Compton effect and the laser-assisted Mott procedure of scattering of an electron on a nucleus. Furthermore, precise examination specifies the resonant kinematics of the RSB system that delineate the configuration of the initial and final electrons with addendum of spontaneous high-energy photon propagation in the narrow angle cone. As a result of the investigation, the calculations determine the scattering differential cross-section of the resonant interaction development. To summarize, the particular cross-section within the resonant ambience significantly exceeds the coordinate cross-section in the approximation of an external field absence. In conclusion, numerous scientific facilities with specialization in pulsed laser radiation (SLAC, FAIR, XFEL, ELI, XCELS) may experimentally validate the computational estimations.

Features and Limiting Characteristics of the Heating of a Substance by a Laser-Accelerated Fast Electron Beam

The features of plasma formation in a substance heated by a laser-accelerated fast electron beam have been studied. These features are related to the ratio of the heating rate to the rate of energy loss because of radiation processes and electronic thermal conductivity, which are governed by the dependence of the energy of the heating beam particles on the beam intensity, which is characteristic of laser-driven electron acceleration. It has been shown that energy losses increase with the beam intensity and significantly limit the maximum temperature of the formed plasma. The possibility of generating an intense γ-radiation pulse of a nonnuclear origin because of the bremsstrahlung of laser-accelerated electrons has been discussed.

Jovian Auroral Ion Precipitation: X‐Ray Production From Oxygen and Sulfur Precipitation

AbstractMany attempts have been made to model X‐ray emission from both bremsstrahlung and ion precipitation into Jupiter's polar caps. Electron bremsstrahlung modeling has fallen short of producing the total overall power output observed by Earth‐orbit‐based X‐ray observatories. Heavy ion precipitation was able to reproduce strong X‐ray fluxes, but the proposed incident ion energies were very high ( 1 MeV per nucleon). Now with the Juno spacecraft at Jupiter, there have been many measurements of heavy ion populations above the polar cap with energies up to 300–400 keV per nucleon (keV/u), well below the ion energies required by earlier models. Recent work has provided a new outlook on how ion‐neutral collisions in the Jovian atmosphere are occurring, providing us with an entirely new set of impact cross sections. The model presented here simulates oxygen and sulfur precipitation, taking into account the new cross sections, every collision process, the measured ion fluxes above Jupiter's polar aurora, and synthetic X‐ray spectra. We predict X‐ray fluxes, efficiencies, and spectra for various initial ion energies considering opacity effects from two different atmospheres. We demonstrate that an in situ measured heavy ion flux above Jupiter's polar cap is capable of producing over 1 GW of X‐ray emission when some assumptions are made. Comparison of our approximated synthetic X‐ray spectrum produced from in situ particle data with a simultaneous X‐ray spectrum observed by XMM‐Newton shows good agreement for the oxygen part of the spectrum but not for the sulfur part.

X-ray emission characteristics in magnetically driven plasma jet experiments on PTS facility

Jets are commonly observed astrophysical phenomena. To study the x-ray emission characteristics of jets, a series of radial foil Z-pinch experiments are carried out on the Primary Test Stand at the Institute of Fluid Physics, China Academy of Engineering Physics. In these experiments, x-ray emission ranging from the soft region (0.1–10 keV) to the hard region (10 keV–500 keV) is observed when the magnetic cavity breaks. The radiation flux of soft x-rays is measured by an x-ray diode and the dose rate of the hard x-rays by an Si-PIN detector. The experimental results indicate that the energy of the soft x-rays is several tens of kilojoules and that of the hard x-rays is ∼200 J. The radiation mechanism of the x-ray emission is briefly analyzed. This analysis indicates that the x-ray energy and the plasma kinetic energy come from the magnetic energy when the magnetic cavity breaks. The soft x-rays are thought to be produced by bremsstrahlung of thermal electrons (∼100 eV), and the hard x-rays by bremsstrahlung of super-hot electrons (∼mega-electron-volt). These results may be helpful to explain the x-ray emission by the jets from young stellar objects.

X-Ray Spectra from Plasmas with High-energy Electrons: κ-distributions and e−–e− Bremsstrahlung

Abstract Shocks, turbulence, and winds all influence the electron velocity distribution in hot plasmas, exciting lower-energy electrons and generating a high-energy (typically power-law) tail. This effect, typically described as a κ distribution can affect both the line and continuum X-ray spectra emitted by the plasma. Hahn & Savin proposed a “Maxwellian decomposition” to generate the rate coefficients of κ distributions. Using their method and the AtomDB atomic database, we have developed a general model to calculate the emission from a plasma with a κ distribution. We compare our κ results for the charge state distribution and spectra of oxygen with those from KAPPA package with the ion data available within the CHIANTI atomic database. Sufficiently energetic electrons, created either in a κ distribution or merely a very hot Maxwellian plasma, can also emit via electron–electron (e–e) bremsstrahlung, a process not previously included in AtomDB. We have added this process to AtomDB and apply it to calculate the temperature gradients, as well as the total spectra from the post-shock regions of an accreting magnetic cataclysmic variable. We find the contribution of e–e bremsstrahlung to the total spectra exceeds 10% at KT ∼ 100 keV, with the total emissivity in the post-shock accretion stream differing by more than 10% at energies above 60 keV.

On calculating kerma, collision kerma and radiative yields.

To study the relationships between dose (D), kerma (K), and collision kerma ( ) in photon beams and to investigate total radiative yields for electrons and positrons as a function of energy. To do this accurately required calculating collision kerma directly as a function of position in a phantom and making changes to the EGSnrc package (including DOSRZnrc and g applications). Changes were made to the EGSnrc system to allow the user to distinguish events according to their initiating process, most importantly relaxation particles initiated by electron impact ionization as opposed to initiated by photons, especially those events depositing energy below energy cutoffs after relaxation events. Appropriate changes were made to the applications DOSRZnrc and g and a new application, DOSRZnrcKcol, was written. The modified codes are much more robust against changes in simulation parameters such as ECUT and AE and whether or not electron impact ionization is included in the simulation. The radiative yields for electrons generally differ from values in ICRU Report 371 (1984) which only account for radiative losses due to bremsstrahlung. The Monte Carlo calculated g(brems) values are generally greater than the ICRU 37 values due to energy-loss straggling. Plots of D, K and vs depth in megavoltage photon beams show that some "conventional wisdom" does not hold in general (e.g., D is not always greater than K past ) and in general at 10cm depth it is found that D≈K and . The beam radius at which reaches its saturation value depends strongly on the threshold used to define reaching saturation and is generally greater than the radius for lateral charged particle equilibrium used in the TRS-483 Code of Practice for small beam dosimetry2 (Palmans et al, Med Phys. 2018;45:e1123-e1145). The changes to EGSnrc make kerma calculations more accurate but previous calculations with electron impact ionization turned off gave close to correct results. The application DOSRZnrcKcol makes calculating collision kerma more efficient and avoids various approximations used in the past although those approximations are shown to be justified. Including energy-loss straggling when calculating bremsstrahlung radiation yield increases the value. Fluorescence losses and annihilation in flight further increase the radiation yield of electrons and positrons. Results demonstrate the effects of EGSnrc using electron bremsstrahlung production cross sections for positrons and failing to model positron impact ionization.