Initial Electron Energy Research Articles

Fast electron initiated electron–hole pair creation in semiconductors

Through Monte Carlo modeling, it is shown that the statistics of electron–hole pair creation in semiconductors (and by extension, presumably, ion-pair creation in gas proportional counters) are substantially different for fast electrons (and by extension, presumably, alpha particles, ions, etc.) cf. x-ray/γ-ray photons. New variables are introduced to quantify the differences in the statistics: the loss parameter, ζ(E′), which acts on the average e−–h+ pair creation energy; and the broadening factor, B(E′), which acts on the Fano factor. E′ is the initial energy of the fast electron. ζ(E′) and B(E′) are computed for a variety of semiconductor materials. A new equation for the statistically limited energy resolution of a particle counting fast electron spectrometer is established. This new equation supersedes and replaces that for the Fano-limited energy resolution of a particle counting fast electron spectrometer. The implications impact a wide variety of fields wherever fast electrons (or alpha particles, ions, etc.) and/or Fano statistics are used; this includes, inter alia, quantum computing, x-ray excitonics, space science, optoelectronics, nuclear engineering, particle physics, photovoltaics, and even neural response variability in the brain.

Generation of gamma photons and pairs with transverse orbital angular momentum via spatiotemporal optical vortex pulse

We present the generation of well-collimated gamma photons and pairs with extrinsic transverse orbital angular momentum (TOAM) through the head-on collision of an intense spatiotemporal optical vortex (STOV) pulse carrying intrinsic TOAM and a high-energy electron beam. It is found that the TOAM of STOV pulse remains almost unchanged, and the TOAM is conserved in the center-of-mass frame. Moreover, there exhibits a duality for particles TOAM in the CMF and laboratory frame when the initial location of high-energy electron beam is different. Furthermore, the TOAM of gamma photons in the CMF increases while that of positrons decreases as the topological charge of STOV pulse increases, whereas in the LF, the TOAM of both gamma photons and positrons decreases. The result under the same pulse intensity is better than that under the same pulse energy. The increase in the initial energy of high-energy electrons leads to an enhancement of the TOAM of both gamma photons and positrons in both frames. Gamma photons and electrons/positrons with TOAM as a new degree of freedom may have extensive applications in optical communication, astrophysics, nanomaterials, and other fields.

Computational and experimental small field dosimetry using a commercial plastic scintillator detector for the 0.35 T MR-linac

PurposeAlthough plastic scintillator detectors (PSDs) are considered ideal dosimeters for small field dosimetry in conventional linear accelerators (linacs), the impact of the magnetic field strength on the response of the PSD must be investigated. MethodsA linac Monte Carlo (MC) head model for a low-field MR-linac was validated for small field dosimetry and utilized to calculate field output factors (OFs). The MC-calculated OFs were compared with the treatment planning system (TPS)-calculated OFs and measured OFs using a Blue Physics (BP) Model 10 commercial PSD and a synthetic diamond detector. The field-specific correction factors, kQclin,Qmsrfclin,fmsr, were calculated for the PSD in the presence of a 0.35 T and magnetic field. The impact of the source focal spot size and initial electron energy on the MC-calculated OFs was investigated. ResultsGood agreement to within 2 % was found between the MC-calculated OFs and BP PSD OFs except for the 0.415 × 0.415 cm2 field size. The BP PSD kQclin,Qmsrfclin,fmsr correction factors were calculated to be within 1 % of unity. For field sizes ≥1.66 × 1.66 cm2, the MC-calculated OFs were relatively insensitive to the focal spot size and initial electron energy to within 2.5 %. However, for smaller field sizes, the MC-calculated OFs were found to differ up to 9.50 % and 7.00 % when the focal spot size and initial electron energy was varied, respectively. ConclusionsThe BP PSD was deemed suitable for small field dosimetry in MR-linacs without requiring any kQclin,Qmsrfclin,fmsr correction factors.

Quantifying the Electron Energy of Mars Aurorae Through the Oxygen Emission Brightness Ratio at 130.4 and 135.6 nm

AbstractMars discrete aurorae are caused by accelerated electrons precipitating into the atmosphere and interacting with species such as atomic oxygen. However, the energy of the electrons causing these aurorae remains currently unclear: no simultaneous and concurrent measurements of electron analyzers and spectrometers have been performed so far, preventing from assessing the exact energy of the downgoing auroral electrons. Several auroral emissions have been observed so far on Mars, among which are two oxygen emissions in the far ultraviolet at 130.4 and 135.6 nm. In this study, we simulate the vertical distribution of these auroral oxygen emissions with an electron transport calculation coupled with a radiative transfer model to account for the optical thickness of the atmosphere for the 130.4‐nm triplet. We show that the brightness ratio of these oxygen emissions is independent of the downward electron energy flux and only slightly depends on the atomic oxygen atmospheric composition. In contrast, the brightness ratio is strongly related to the initial energy of the auroral electrons. Measuring the brightness ratio is therefore a unique tool to remotely estimate the energy of the electrons causing the Mars discrete aurorae. We compare our model results with observations from the Emirates Mars Ultraviolet Spectrometer on board the Emirates Mars Mission and find that electrons with typical energies of 250–300 eV are compatible with the observed ratio of 5.

Выбор формы временной зависимости ускоряющего напряжения для моделирования спектральных характеристик гиротрона мегаваттного уровня мощности

The spectral characteristics of the gyrotron with a megawatt power level in the 170 GHz range were modeled numerically. The calculations were carried out using the large particle method implemented in the KARAT code. The problem of three-dimensional modeling of the excitation of an asymmetric type mode was reduced to a 2.5-dimensional one. For this model, the presence of high-frequency fluctuations at the output of high-voltage power supplies, which determine the initial energy of electrons, was taken into account. The relationship between the shape and width of the radiation spectrum of the simulated gyrotron and the time dependence of the accelerating voltage has been studied. It is shown that the best agreement with experimental data is obtained by combining a relatively slow sawtooth change in particle energy with fast random fluctuations.

Electron transport characteristics in water under electrostrictive effect

The transport characteristics of electrons are crucial for the initiation and development of pulse discharge in water. In this work, we develop a physical model of electron transport that consides elastic and inelastic collision cross sections. The purpose of this study is to investigate frequency variations of elastic collisions, ionization and excitation collisions with different initial electron energy values, and to explore the characteristic of electron energy loss in water. The Monte Carlo method is employed to track structure characteristics of electron transmission and scattering under varying energy values. The results show that the electrons of lower energy (~20 eV) are significantly impacted by the water molecule scattering, hence their transmission capacities are weakened. When the incident energy of electron reaches 100 eV, the scattering deviation distance is roughly equivalent to the transmission depth, about 6–8 nm, and the maximum deviation angle <i>θ</i><sub>shift</sub> ~ 60°. When the electron incident energy is in a range of 10–1000 eV, the number of elastic collisions is much greater than the number of excitation and ionization collisions, and the number of ionization collisions and excitation collisions increases significantly with the increase of electron energy. The higher the electron incident energy, the greater the energy loss is. However, the energy loss decreases sharply with the extension of penetration distance. For the ionization collision, the average ionization energy loss, <i>W</i>, decreases rapidly with the increase of electron energy, and ultimately maintains at a level of 20–30 eV, which is consistent with the experimental results reported.

Evolution of the resonances of small water cluster anions (H2O) n ⩽19 − in helium droplets upon attachment of electrons

Using a high-resolution electron monochromator, we studied the formation of (H2O) n ⩽19 − cluster ions upon collisions of free low-energy electrons with water clusters embedded in helium droplets. The anion efficiency curves as a function of the initial electron energy were measured for the cluster sizes n = 2–8, 10, 13, 16, and 19. The present experimental results show that the shape of the resonance yields is dependent on the size of the water cluster anion. The results are discussed in terms of the different electron states available for the excess electron from a linear cluster structure to three-dimensional cluster structures as the number of water molecules within the cluster increases.

Microdosimetric analysis of monoenergetic electrons and beta-emitting radionuclides based on mesh-type cell models and RBE prediction

AimsMicrodosimetric indicators are commonly used to describe the energy deposition characteristics of ionizing radiation at the subcellular and DNA levels to predict radiation-induced biological effects. Monoenergetic electrons and beta-emitting radionuclides (β nuclides) have a certain range in low-density media, and their microdosimetric indicators in the cell nucleus are of great significance for understanding the characteristics of different types of β nuclides and the evaluation of relative biological effectiveness (RBE). MethodsMicrodosimetry in the nucleus is greatly affected by cell morphology, so in this paper, based on laser confocal tomography images of BEAS-2B and L-O2 cell lines, two types of mesh-type cell models were constructed to restore the morphological features of real cells. The Geant4-DNA toolkit was used to simulate the lineal energy and dose distribution of monoenergetic electrons (0.1 keV-1 MeV) and 5 types of beta nuclides (Cs-137, Cs-134, C-14, I-131, and H-3) in the cell nucleus with different initial energies. The effects of factors such as initial energy, sensitive site (radius = 2 nm, 10 nm, 30 nm, 300 nm), and cell type on microdosimetric quantities in the nucleus and their predictions of nuclide RBE were analysed. ResultsThe results show that for the same type of nuclide, there are different RBE values between BEAS-2B and L-O2 cells, with Cs-134 having a difference of 17.75% and H-3 having a difference of 10.58%. In addition, the mean lineal energy in the nucleus fluctuates with changes in the initial energy and sampling site radius of monoenergetic electrons, especially for low and medium energies where the sampling site radius has a significant effect. Moreover, the proximity functions of monoenergetic electrons with an initial energy below 1 keV are greatly affected by the cell shape, and those above 20 keV are greatly affected by the model volume. ConclusionsThe study confirms the necessity of using mesh cell models for microdosimetric analysis in the cell nucleus and predicting its biological effects by combining mesh models of real human cells to simulate microdosimetric indicators of monoenergetic electrons and beta-emitting nuclides. The estimation of the RBE of β nuclides achieved in this study has reference value for predicting radiobiological damage in different cell types.

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

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

Low energy electron injection for direct laser acceleration

The feasibility of ionization injection for Direct Laser Acceleration (DLA) of electrons up to hundreds of MeV has been studied analytically. Criteria for effective injection determining a range of background and in-channel plasma parameters, laser intensity, etc., were found using phase portraits of the system deduced from the simplified analytical model. The found optimal trajectory in the phase space corresponds to the electron with low (few eV) initial energy experiencing ∼109 times energy gain. For this to occur, electron density should be a few percent of the critical density, while the in-channel electron density should be ∼3 times lower. The analytically obtained dependence of the energy gain on the initial electron longitudinal and transverse momenta corresponds well to the results of exact numerical simulations of an electron motion in the plasma channel. To test the theory, a series of PIC simulations were carried out. PIC simulation confirms the model if the plasma channel has appropriate parameters. The developed approach can form the basis for further studies of electron injection in DLA varying plasma and laser parameters as well as initial electron energies.

The critical effect of electron acceleration under enhanced electric field near cathode on the formation of runaway electrons and diffuse discharge in atmosphere

Runaway electrons (RAEs) are believed to affect the dynamics of ultra-fast gas breakdown significantly. In this work, considering the field enhancement effect near the micro-protrusion on the cathode surface, the formation of RAEs and diffuse discharge in atmospheric pressure air is investigated by two-dimensional particle-in-cell/Monte Carlo collision simulation. It is found that the beam amplitude of RAEs is dictated by the field enhancement factor and the initial energy of electrons obtained near the micro-protrusion is decisive for their converting to RAEs, which precede the low energy electrons and guide the discharge propagation by improving pre-ionization. As a result, the discharge transfers from the filamentary mode without RAEs to the diffuse mode under the high pre-ionization degree due to RAEs and a wide streamer with a diameter comparable with the gap distance is formed, which transfers from spherical to conical shape. The results of this study illustrate the fundamental process of RAE formation and how RAEs influence streamer dynamics during ultra-fast gas breakdown process.

Structure and material study of dielectric laser accelerators based on the inverse Cherenkov effect

Dielectric laser accelerators (DLAs) are considered promising candidates for on-chip particle accelerators that can achieve high acceleration gradients. This study explores various combinations of dielectric materials and accelerated structures based on the inverse Cherenkov effect. The designs utilize conventional processing methods and laser parameters currently in use. We optimize the structural model to enhance the gradient of acceleration and the electron energy gain. To achieve higher acceleration gradients and energy gains, the selection of materials and structures should be based on the initial electron energy. Furthermore, we observed that the variation of the acceleration gradient of the material is different at different initial electron energies. These findings suggest that on-chip accelerators are feasible with the help of these structures and materials.

Highly collimated intense radiation from electron collisions with a tightly focused linearly polarized laser pulse.

The use of high-energy radiation generated by electron collisions with a laser pulse is an effective method to treat cancer. In this paper, the spatial properties of radiation produced by electron collisions with a tightly focused linearly polarized laser pulse are investigated. Theoretical derivations and numerical simulations within the framework of classical electrodynamics show that the stronger the laser intensity, the higher the initial electron energy, and the longer the laser pulse, which can produce greater radiation power. An increase in the laser intensity expands the range of electron radiation and therefore reduces the collimation of the radiation. The collimation in the radiation is better when colliding with an electron of higher initial energy. The phenomenon that the radiated power of the electron varies periodically with the initial phase of the laser is also found. The results of this paper have important implications to produce strongly radiating and highly collimated rays.

Commissioning of Elekta Infinity™ 6 MV flattening filter-free using Monte Carlo simulation

Commissioning a simulation model of the linear accelerator (Linac) in radiotherapy needs to be done to validate the dose distribution accuracy. For this purpose, the Monte Carlo simulation method is commonly employed, and it involves using the EGSnrc software. This software consists of BEAMnrc for modeling Linac and DOSXYZnrc for calculating dose distribution in a water phantom. This study used Monte Carlo simulation to commission the Linac Flattening Filter-Free (FFF) Elekta Infinity™ 6 MV photon mode. The commissioning results show that the simulated dose distribution satisfied the acceptance criteria of simulation results using initial electron energy of 6.9 MeV at 5 × 5, 10 × 10, and 20 × 20 cm2 field sizes with average local difference of percent depth dose (PDD) of about 2.99%. The dose and dmax increasedwith higher initial electron energy increased, while percentage depth dose (PDD) decreased at smaller field sizes. At larger field sizes, the dose profile widened and the PDD Linac FFF decreased more significantly than PDD Linac Flattening Filter (FF). Additionally, both exhibited differences in the uniformity of dose values in the umbra area. The surface dose for a 10 × 10 cm2 field size was 25.2% and 34.4% for both 6 MV-FF and 6 MV-FFF, respectively.

The brightness of the CO Cameron bands in the martian discrete aurora: A study based on revised cross sections

We analyze the consequences of the new laboratory measurements of the emissions cross sections of the Cameron bands excited by electron impact on CO2 and CO in the Mars aurora. We use Monte Carlo simulations to investigate the importance of these changes and their dependence on the initial electron energy. The Mars Climate Database (MCD) is used as an input for the temperature and neutral density profiles. Auroral density profiles of O2+, CO2+ and electrons in the aurora are calculated for a range of precipitating electron energies. The total nadir brightness of the Cameron bands is reduced by a factor of 4.5 at 150 eV and 5.1 at 700 eV relative to calculations made with the previously recommended cross section. The relative contributions to the production of the Cameron bands by electron collisions with CO2 and CO are examined. It varies with the CO/CO2 density ratio near the emission peak that depends on the neutral model and season. Dissociative recombination of CO2+ ions provides a contribution between 10% and 45% at the altitude of maximum production of the a 3Π state. The efficiency of the nadir brightness of the Cameron bands is 2.5–3.6 kilorayleighs per incident electron energy flux of 1 mW m−2, with a small dependence on the initial electron energy. Model simulations predict that the intensity ratio of the Cameron bands to the CO2+ UV doublet (UVD) depends on the electron initial energy. It varies from 2.0 at 500 eV to 5.3 at 50 eV, for both Ls = 90° and 225°.

Collision of two interacting electrons on a mesoscopic beam splitter: Exact solution in the classical limit

Experiments on collisions of isolated electrons guided along the edges in quantum Hall setups can mimic mixing of photons with the important distinction that electrons are charged fermions. In the so-called electronic Hong-Ou-Mandel (HOM) setup uncorrelated pairs of electrons are injected towards a beamsplitter. If the two electron wave packets were identical, Fermi statistics would force the electrons to scatter to different detectors, yet this quantum antibunching may be confounded by Coulomb repulsion. Here we model an electronic HOM experiment using a quadratic 2D saddle point potential for the beamsplitter and unscreened Coulomb interaction between the two injected electrons subjected to a strong out-of-plane magnetic field. We show that classical equations of motion for the drift dynamics of electrons' guiding centers take on the form of Hamilton equations for canonically conjugated variables subject to the saddle point potential and the Coulomb potential where the dynamics of the center-of-mass coordinate and the relative coordinate separate. We use these equations to determine collision outcomes in terms of a few experimentally tuneable parameters: the initial energies of the uncorrelated electrons, relative time delay of injection and the shape of the saddle point potential. A universal phase diagram of deterministic bunching and antibunching scattering outcomes is presented with a single energy scale characterizing the increase of the effective barrier height due to interaction of coincident electrons. We suggest clear-cut experimental strategies to detect the predicted effects and give analytical estimates of conditions when the classical dynamics is expected to dominate over quantum effects.

Effects of initial three-dimensional electron energy distribution on terahertz Bloch oscillations in a biased semiconductor superlattice

We investigate how the initial three-dimensional energy distribution of electrons created by femtosecond pump pulses in a biased semiconductor superlattice affects terahertz Bloch oscillations, which imitate a step response to a bias electric field. The emitted terahertz waveforms are well reproduced from a damped oscillation current with capacitive nature, exhibiting shorter relaxation times and worse temporal resolutions for central pump photon energies that are outside the range of ordinary electron excitation into the conduction first miniband. This indicates that in-plane excess energy changes the relaxation time via scattering processes, while partial use of the pump pulse spectrum reduces the temporal resolution.

Effect of the thermalization of secondary electron energies on plasma formation during the irradiation of heavy ions

This study aims at understanding the effect of the thermalization of secondary electrons produced by incident heavy-ion impact ionization on plasma formation. The motions of the secondary electrons were simulated using pseudo-initial secondary electron energy distribution functions. These simulations allowed us to estimate the times when thermalization occurred and the probabilities of secondary electrons escaping the electric field created near the incident ion path according to the initial secondary electron energy distribution functions. The probabilities and thermalization processes were found to be almost independent of these functions which indicated that the secondary electrons were thermalized before the plasma was formed.

ДОЗИМЕТРИЯ ТРИТИЯ НА КЛЕТОЧНОМ УРОВНЕ

Introduction 1. Tritium radioisotope and its energy spectrum 2. Methods for calculating doses from radiation of radionuclides 2.1 General equation for absorbed dose rate 2.2 Absorbed dose rate versus average energy 2.3 Formulas for calculating dose and S-values ​​from radiation of radionuclides 2.4 Method of dose point nuclei 2.5 MIRD effective stopping power method 2.6 Geometric factor 3. Analysis of S-value calculations by various methods 3.1 Values ​​of the CSDA range at low initial electron energies 3.2 Comparison of S-value calculations for low energy electrons 3.3 Comparison of tritium S-value calculations 4. Evaluation of S-value calculations in the absence of spherical symmetry Conclusion

Plasma wave electron acceleration in IFEL mechanism with quadruple wiggler and ion channel guiding

In this paper, the electron acceleration by plasma wave in IFEL mechanism in the presence of a quadruple magnetic field and ion channel guiding effects has been investigated both analytically and numerically. The results illustrate that the increasing of the quadruple wiggler amplitude and wavelength up to an optimum value has considerable effects on the electron acceleration and its relativistic dynamics in laser ion channel. It was found that in the presence the optimum values of quadruple wiggler amplitude and wavelength, the electron energy gain increases more than 90% than that obtained in the absence of the wiggler. Moreover, the numerical simulations reveal that if the electrons are thrown with higher initial kinetic energy into the wiggler field, they can longer remain in the acceleration phase of the plasma wave and gain more energy from the wave. Therefore, it turns out that, in a laser-plasma accelerator, the electron acceleration and its relativistic dynamics can be tuned by the wiggler field strength, wiggler wavelength, and initial kinetic energy of electrons. The favorable results of studies in this field can be promising for the new generation of the laser-plasma accelerators based on the wiggler structures.