Radiation Field Components Research Articles

Estimation of lightning channel-base current from far electromagnetic field in the case of inclined channel

• Expressions to estimate the current peak from the far-field peak considering channel tilt are derived. • Expressions to reconstruct the entire current waveform from the field waveform are derived. • The expressions are derived for three most widely used engineering return-stroke models. • This is the first attempt to solve the inverse problem (infer sources from fields) for inclined channels. The inclination of a lightning return-stroke channel significantly affects the waveform of the associated electromagnetic field. In this paper, we have derived mathematical expressions to estimate the peak and waveshape of lightning return-stroke current at the channel base from the waveform of electromagnetic field observed more than some tens of kilometers away from an inclined lightning channel. Three models of the lightning return stroke are considered, which are the transmission-line (TL) model, the modified TL model with linear current decay with height (MTLL), the modified TL model with exponential current decay with height (MTLE). The peak of the lightning return-stroke current at the channel base is estimated from the peak of observed lightning electric or magnetic field using an analytical relation between the peak of channel-base current and that of the radiation field component for an inclined channel. The waveform of the channel-base current is reconstructed from the electric or magnetic field waveform using a relation between the channel-base current and the sum of induction and radiation field components for an inclined channel. It has been shown that the peak and waveshape of current at the base of an inclined channel are sufficiently accurately estimated with the proposed expressions. This work is the first attempt to solve the inverse problem (infer source parameters from electromagnetic fields) for the case of inclined lightning channel. Solving this problem is important for developing methodology of remote measurements of lightning currents.

Characterization of Stray Radiation Produced by a Proton Beam in an Anthropomorphic Phantom with Dental Implants Using a Pixel Detector

<h3>Purpose/Objective(s)</h3> We investigated the scattered radiation produced by a collimated proton beam in the case of head and neck cancer using an anthropomorphic head phantom with human-like anatomy, with two dental implants inserted. Using high-resolution semiconductor pixel detectors, we measured and analyzed the backscatter radiation with particle identification resolving power. This research is focused on giving quantitative information about the radiation field components. <h3>Materials/Methods</h3> A treatment plan was designed on a standard X-ray CT which contained the implants at the center of the tumor. Two irradiations of an anthropomorphic head phantom were performed with clinical proton beams: one without metallic implants (plastic inserts) and one with dental implants. Two titanium cylindrical inserts of 1 cm length and 0.33 cm diameter were placed in the phantom's upper jaw like the molar's replacements. The planning target volume (PTV) is shaped so that the dental inserts are centered in the target volume. A scattered fixed proton beam with a nominal energy of 170 MeV was delivered to the phantom using collimators and boluses designed to shape and stop the beam according to the treatment plan. Scattered primary and secondary radiation was detected with hybrid semiconductor pixel detectors, placed at 4 cm behind the PTV. Detailed description of the mixed-radiation field was performed with spectral (energy loss) and tracking (direction) sensitivity. <h3>Results</h3> Measurements included a low intensity proton beam to assess the particle tracking response and identification resolving power in both situations (with and without implants). In this manner, the components of the radiation field were observed and analyzed. Based on their characteristic directional-sensitive spectral-track signal in the detector, both primary and secondary protons can be distinguished from light charged particles. This was done by analyzing single particle pixelated clusters morphology, spectral and directional sensitive parameters. Directional fluxes and linear energy transfer (LET) spectra of charged particle groups provide information about the scattered radiation field. <h3>Conclusion</h3> We present novel information about dental metallic implants' influences in a proton-based treatment. Preliminary results show differences in the LET distributions of the scattered radiation when the implants are in place, respectively, when they are missing. Further analyses will be done to provide a detailed dissemination of contribution for every type of particle.

Rounded square ring resonator based add drop filter for WDM applications using two dimensional photonic crystals

In this paper, Two Dimensional Photonic Crystals based Add Drop filter (ADF) is designed for DWDM applications. The existing work concentrates in Coarse Wavelength Division Multiplexing and few filters reported for DWDM with non-uniform channel spacing, and low quality factor. The proposed ADF enhances the quality factor using Rounded Square Ring Resonator (RSRR) for ensuring efficient bandwidth in supporting WDM systems. The design consists of bus waveguide, drop waveguide and RSRR with inner quasi-square ring in the square lattice. The dielectric constant of the Si rod is 11.68 which are hosted in the air. The line defect is created by removing 4 rods (Quasi ring) in the center of the inner square ring. The line defect in the ring resonator is used to reduce the radiation field components surrounded by the resonator. The performance parameters of ADF are investigated using 2D Finite Difference Time Domain algorithm. The proposed ADF drops a channel at 1636.2 nm, with the bandwidth of 0.7 nm, high quality factor of 2337, and the dropping efficiency of about 100%. The size of the device is 412.76 µm2. It is highly sufficient to support WDM systems for future Photonic Integrated Circuits (PIC). Further, the impact of functional parameters such as transmission efficiency, quality factor, bandwidth are investigated by varying the structural parameters, namely, adjacent rod radius, scatterer rod radius, coupling rod radius, lattice constant, inner rod radius and rod radius.

Principal Component Analysis applied to neutron dosimetry based on PADC detectors and FNTDs

Solid State Nuclear Track Detectors (SSNTD) have been used as passive dosimeters for many decades. Fast neutron detection is performed by detecting recoil protons generated in a hydrogenous material (neutron converter). The dose is estimated by multiplying the recoil protons track-spots density present on the detector surface by a calibration coefficient obtained from reference irradiations. Therefore, one needs to automatically and reliably discriminate between the track-spots induced by recoil-protons and the spurious signal engendered either by material imperfections or by other ionising particles interactions. The objective of this work is to demonstrate and apply a method, based on the multivariate statistical tool named Principal Component Analysis (PCA), aiming at identifying and filtering out the spurious signal in track detectors. The advantage of this approach is that it can be applied to any type of SSNTD, provided apt definition of initial physical variables describing each track-spot. To show that, we applied the method to poly-allyl diglycol carbonate (PADC) detectors, to filter the signal generated by material imperfections, and to fluorescence nuclear track detectors (FNTDs), to remove the signal induced by other radiation field components. After filtering, dose assessments were compared with reference values of exposures, showing satisfactory agreement. In case of the FNTDs, the procedure proved to be effective regardless of the crystal colouration, which is known to affect signal-rejection techniques based on track-spots fluorescence intensity. The technique also offers the advantage of self-adjusting the filtering parameters based on the currently analysed detector set, as long as calibration and unirradiated detectors are included in the dataset.

Considerations on the composition and spectra of the secondary radiation fields inside the E1 experimental area at ELI-NP

At the new ultrahigh power laser facility ELI NP, experiments on the interaction of high power lasers and matter will be conducted. These experiments are expected to produce beams of highly energetic particles resulting in secondary radiation fields which will be highly complex and rather difficult to measure given their specifics (extremely short bursts, with time widths in the range of nanoseconds). The ELIFLUKA project was started to assess the doses in the areas surrounding the experimental halls, to evaluate the efficiency of the existing shielding solutions, to propose, if necessary, their optimization, and give optimal ways to monitor the radiation fields that might affect the facility personnel. The present paper is focused on the results concerning the composition and the spectra of the secondary radiation fields inside the E’ experimental hall. A complex FLUKA geometry of the El area was built according to the real design of the experimental hall. With FLUKA we calculated the particle fluencies, the spatial distribution and spectra of each component of the radiation field, corresponding to two limit source terms, characterised by a thermal energy distribution with 40 MeV average and 250 MeV cut-off, and a second one with a flat energy distribution with 500 MeV average and 50 MeV FWHM. The FLUKA code was used to calculate all particle fluence spatial distribution inside the experimental hall, as well as the fluences and spectra for the main components of secondary radiation fields. These results can be used to design various experimental setups at E1 in such a way that the instruments would be positioned without risking significant activation and/or radiation damage and they provide a source term for the shielding calculations using the classical methods, as usually requested by the regulatory authorities.

Microwave-induced selective decomposition of cellulose: Computational and experimental mechanistic study

Understanding microwave-material interactions will help facilitate the utilization of microwave technology in gasification and renewable energy production. In this study, cellulose was used as a model compound to simulate the organic matter in biomass, and its catalytic decomposition under a microwave (MW) field was studied to identify structural changes from the reaction. The study was conducted using a MW source coupled to a fixed-bed gas-flow reactor, mass spectroscopic, and Fourier transform infrared spectroscopy post-reaction analysis. Zeolite 13X was chosen as a microwave absorber to study the catalytic enhancement of the decomposition of cellulose. Density functional theory (DFT) was used to gain insights into the molecular transformations occurring in the presence of a static electric field, which was used to simulate the electric field component of the microwave electromagnetic radiation providing a theoretical basis for molecular sites to be selectively heated. Theoretical calculations demonstrated that both the positive and negative portion of the electric field interact with the permanent dipoles of the cellulose leading to Debye-type loss processes and localized heating indicated by the decomposition through the glycosidic bond breaking mechanism. The theoretical result was verified using infrared spectroscopic analysis of the pure cellulose during microwave heating. The theoretical calculations help to elucidate the dipoles and molecular bonds in the cellulose structure, which are more sensitive to selectively localized heating as compared to other bonds and conventional heating. Physically mixing Zeolite 13X with the cellulose led to a significant enhancement in the decomposition rate of the glycosidic bond. Zeolite 13X enhanced the glycosidic O–C decomposition at lower MW power (lower temperatures), whereas the O–H functional group required higher MW power (higher temperature) for its decomposition. The DFT study coupled with the reaction studies revealed that the electric field polarizability, and subsequent, localized heating, is dependent upon both the direction and the orientation of the cellulose. Gas products revealed that applying 250 W of MW power led to the production of CO, H2, along with some CO2, CH4, and benzene at 305 °C. Reaction under 500, 750, and 1000 W of power at constant temperature (305 °C) revealed that higher power led to the complete decomposition of cellulose to mostly CO, H2, and CO2.

Radiation patterns of a horizontal electric dipole in a four-layered region and applications for microstrip antennas

ABSTRACTThe present work focuses on the radiation field excited by a horizontal electric dipole (HED) in a four-layered region composed of a perfect conductor covered with two dielectrics and the air above. Analytical expressions for the radiation field are derived for the case of both the source and the observation point being on or near the air-dielectric boundary. The propagation characteristics of the interference phenomenon are investigated. The radiation field components undergo sharp interference as the relative permittivities and dielectric layer thicknesses increase. When the observation angle , the trapped surface wave predominates in the total field. Otherwise, the total field is determined primarily by the lateral wave. Due to the useful applications for microstrip antennas, radiation patterns of a patch antenna with specific current distributions are investigated. Some special cases of interest are discussed. The proposed formulas offer the potential to develop planar four-layered circuit structures.

Proposal of a FLUKA-based radiation monitoring system for the laser driven electron acceleration area at ELI-NP

FLUKA simulations were used to design a dosimetry monitoring system for the typical electron acceleration experiments in the E6 area of the ELI-NP building. The FLUKA geometry of the E6 experimental area was built by using data extracted from the latest available version of the corresponding Catia file, including all the building and beamline transport elements. Based on that geometry we calculated H*(10) in a Cartesian binning over E6 and neighbouring areas for the worst case scenario: a 38 GeV Gaussian electron source term. The fluence rates of the secondary prompt radiation field components were mapped throughout the E6 experimental area. The results were used to determine the most important contributor to the dose and the areas with the highest exposure, as well as the positioning of the detectors for radiation monitoring. We propose solutions for some practical issues: proper choice of the detector type and proper detector positioning in accordance with the characteristics of the radiation field (dose range, field components, energy ranges).

Neutron spectrometry at JINR nuclear facilities

Abstract A long-term experience in the spectrometry of neutrons of a wide energy range at nuclear-physical facilities of the Joint Institute for Nuclear Research is described. Neutrons are the main components of radiation fields behind shielding and in the environment. Because of the big difference in the physics of interaction with matter of neutrons of different energies, a wide ensemble of neutron spectral distributions, from thermal to neutron energies of hundreds of MeV, is observed at the facilities. The article describes the methods used at the JINR for measuring neutron spectra in fields of mixed scattered radiation and presents examples of different neutron spectra.

Effect of Striking a Cone-Shaped Mountain Top on the Far Lightning-Radiated Electromagnetic Field

This paper presents the computed lightning-radiated vertical electric field and azimuthal magnetic field at the ground level at observing distances ranging from 0.3 to 50 km from the lightning channel for striking the cone-shaped mountain top, by using the two-dimensional finite-difference time-domain method in cylindrical coordinate systems. It is found that the mountain height and the inclination angle have a significant effect on the lightning-radiated electromagnetic field both for the close and far observing distances. For the lightning-radiated vertical electric field, the enhancement of the far field beyond several kilometers (mainly radiation field component) is due to the reflection process in the transition between the mountain terrain and the flat ground, but the reduction of close field near the mountain terrain (mainly quasi-electrostatic field component) is due to the shadowing effect, but not due to such reflection. For the lightning-radiated azimuthal magnetic field, the field values for different mountain terrains, including the mountain height and inclination angle, increase both for close and far observing distances.

DOSIMETRIC EVALUATION OF LASER-DRIVEN X-RAY AND NEUTRON SOURCES UTILIZING XG-III PS LASER WITH PEAK POWER OF 300 TERAWATT.

Current short-pulse high-intensity lasers can accelerate electrons and proton/ions to energies of giga-electron volts. For certain advanced applications, laser-accelerated electrons and protons are optimised for high-energy X-ray and neutron generation at the XG-III picosecond (ps) laser beamline. These energetic X-ray and neutron beams can significantly affect radiation safety at the facility; therefore, proper evaluation of the radiological hazards induced by laser-driven X-ray and neutron sources is required. This study presents a dosimetric evaluation of laser-driven X-ray and neutron sources at the XG-III ps laser beamline. The 'source terms' of the laser-accelerated electrons and protons are characterised utilising the particle-in-cell method and an analytical model, respectively. The Monte Carlo code FLUKA is used to calculate prompt and residual dose yields due to all radiation field components and the number of residual activated nuclei. Our results can provide a reference for radiation hazard analysis at short-pulse high-intensity laser facilities worldwide.

Super defect inside photonic crystal ring resonator to enhance Q factor

A design is proposed to enhance the quality factor of a photonic crystal ring resonator. A super defect is employed inside the ring resonator, which consists of variation of hole dimensions inside the ring resonator in such a way that the radiation field components of the resonant nanocavity are forced to get cancelled in order to reduce radiation loss. After this forced cancellation, the improved Q factor is calculated as 18,000. This photonic crystal ring resonator can be used for sensing applications like force sensing, pressure sensing, biochemical sensing, and communication applications like demultiplexing.

A unified engineering model of the first stroke in downward negative lightning

AbstractEach stroke in a negative cloud‐to‐ground lightning flash is composed of downward leader and upward return stroke processes, which are usually modeled individually. The first stroke leader is stepped and starts with preliminary breakdown (PB) which is often viewed as a separate process. We present the first unified engineering model for computing the electric field produced by a sequence of PB, stepped leader, and return stroke processes, serving to transport negative charge to ground. We assume that a negatively charged channel extends downward in a stepped fashion during both the PB and leader stages. Each step involves a current wave that propagates upward along the newly formed channel section. Once the leader attaches to ground, an upward propagating return stroke neutralizes the charge deposited along the channel. Model‐predicted electric fields are in reasonably good agreement with simultaneous measurements at both near (hundreds of meters, electrostatic field component is dominant) and far (tens of kilometers, radiation field component is dominant) distances from the lightning channel. Relations between the features of computed electric field waveforms and model input parameters are examined. It appears that peak currents associated with PB pulses are similar to return stroke peak currents, and the observed variation of electric radiation field peaks produced by leader steps at different heights above ground is influenced by the ground corona space charge.

Influence of cosmic radiation spectrum and its variation on the relative efficiency of LiF thermoluminescent detectors – Calculations and measurements

Lithium fluoride thermoluminescent detectors (TLD) were used for cosmic radiation dosimetry already in early 1960s. Since that time they have been constantly applied in numerous space missions for personal dosimetry, area monitoring, phantom measurements and dosimetry for biological experiments. The relative efficiency of TLDs, defined as the ratio of their response to a given radiation and to a reference radiation, is not constant, but depends on ionization density. This raises a question about the relative efficiency of TLDs exposed to the complex cosmic radiation spectrum encountered in Earth's orbit, which consists of a variety of particles, including heavy ions, the spectrum of which covers an extremely broad energy range. The present work is an attempt to find an answer to this question.The particle energy spectra were calculated for realistic flight conditions of the International Space Station (ISS). The calculation of the Galactic Cosmic Ray (GCR) component was based on the input spectra generated with the DLR model for solar minimum (2009) and solar maximum (2000) conditions. Contributions of trapped protons were estimated based on the AP8 model for solar minimum and maximum taking into account the altitude variations of the ISS. The interactions of the primary particles with the ISS were simulated with GEANT4 using a shielding geometry derived from the mass distribution of the Columbus Laboratory of the ISS and several constant aluminum shieldings. The calculated spectra were convoluted with the experimental data on the relative TL efficiency measured for ions ranging from H to Xe at various particle accelerators for two commonly applied TL-materials, namely LiF:Mg,Ti and LiF:Mg,Cu,P.The results showed the differences in the average TL-efficiency for these two TL-materials. For LiF:Mg,Ti the relative efficiency is within a few percent from unity for any of the analyzed values of shielding, altitude and solar cycle conditions. This means that one can assume cosmic radiation doses measured in Low Earth Orbit (LEO) with LiF:Mg,Ti detectors to be correct within such uncertainty. LiF:Mg,Cu,P underestimates the cosmic radiation doses by more than 15% in all cases. Altitude and solar cycle were found to have a very weak influence on the TL efficiency. In contrast, the influence of shielding thickness is quite significant. The reason for this is a change of contributions of radiation field components: trapped protons dominate at low shielding (97% of dose at 1 g/cm2), but are negligible above 60 g/cm2, as well as changes within GCR spectrum (increase of dose due to lower LET secondaries for higher shielding). Shielding thickness affects both TLD types in different ways: the efficiency of LiF:Mg,Cu,P increases with increasing shielding thickness, while the efficiency of LiF:Mg,Ti shows some fluctuations, with a weak minimum for 60 g/cm2. The response ratio of these TLDs decreases monotonically with the shielding thickness and could be used as an indicator for the average shielding conditions in which the TLDs were exposed.

Deep-subwavelength imaging of both electric and magnetic localized optical fields by plasmonic campanile nanoantenna.

Tailoring the electromagnetic field at the nanoscale has led to artificial materials exhibiting fascinating optical properties unavailable in naturally occurring substances. Besides having fundamental implications for classical and quantum optics, nanoscale metamaterials provide a platform for developing disruptive novel technologies, in which a combination of both the electric and magnetic radiation field components at optical frequencies is relevant to engineer the light-matter interaction. Thus, an experimental investigation of the spatial distribution of the photonic states at the nanoscale for both field components is of crucial importance. Here we experimentally demonstrate a concomitant deep-subwavelength near-field imaging of the electric and magnetic intensities of the optical modes localized in a photonic crystal nanocavity. We take advantage of the “campanile tip”, a plasmonic near-field probe that efficiently combines broadband field enhancement with strong far-field to near-field coupling. By exploiting the electric and magnetic polarizability components of the campanile tip along with the perturbation imaging method, we are able to map in a single measurement both the electric and magnetic localized near-field distributions.

Solid state detectors for dosimetry in the BNCT beam of the LVR-15 research reactor

Dosimetry measurements have been carried out at the epithermal neutron beam of LVR-15 reactor (Řež) moderated by a polyethylene disk placed through the collimator exit. The spatial distributions of thermal neutron fluence rate and of gamma and fast neutron dose rates have been attained. The contributions to the dose of the radiation field components have been assessed with Fricke-gel-layers, by pixel-to-pixel elaboration of the light transmittance images of samples having different isotopic composition and with thermoluminescence detectors, by analysing the shape of the glow curve. An analogous experiment has been carried out at the thermal column HK1 of the same LVR-15 reactor, aimed at neutronography research. Good consistency of all results was obtained.

Detecting scattered light from low-mass molecular cores at 3.6μm

Recently discovered scattered light at 3-5 $\mu$m from low-mass cores (so-called "coreshine") reveals the presence of grains around 1 $\mu$m, which is larger than the grains found in the low-density interstellar medium. But only about half of the 100+ cores investigated so far show the effect. This prompts further studies on the origin of this detection rate. From the 3D continuum radiative transfer equation, we derive the expected scattered light intensity from a core placed in an arbitrary direction seen from Earth. We use the approximation of single scattering, consider extinction up to 2nd-order Taylor approximation, and neglect spatial gradients in the dust size distribution. The impact of the directional characteristics of the scattering on the detection of scattered light from cores is calculated for a given grain size distribution, and local effects like additional radiation field components are discussed. The surface brightness profiles of a core with a 1D density profile are calculated for various Galactic locations, and the results are compared to the approximate detection limits. We find that for optically thin radiation and a constant size distribution, a simple limit for detecting scattered light from a low-mass core can be derived that holds for grains with sizes smaller than 0.5 $\mu$m. The extinction by the core prohibits detection in bright parts of the Galactic plane, especially near the Galactic center. For scattered light received from low-mass cores with grain sizes beyond 0.5 $\mu$m, the directional characteristics of the scattering favors the detection of scattered light above and below the Galactic center, and to some extent near the Galactic anti-center. We identify the local incident radiation field as the major unknown causing deviations from this simple scheme.

Analysis of Large-Scale Phased Antenna Array With Generalized Transition Matrix

This paper presents a numerical method to evaluate the electromagnetic radiating characteristics of a large-scale phased antenna array by using generalized transition matrix modules. Choosing an appropriate reference surface to contain an antenna element, an associated generalized transition matrix (GTM) is defined to establish the relationships between the rotated tangential components of incident field and scattered field on the reference surface. Meanwhile, a mapping vector is constructed to map the excitation sources onto the reference surface as the rotated tangential radiation field components. A GTM module for an antenna unit with feeding source consists of a GTM, a mapping vector, and a specified reference surface. The radiation pattern and mutual coupling effects among units can be analyzed by using the GTM modules of all units, in conjunction with the generalized surface integral equations (GSIEs). The interaction of the excitation port information is included in the field transmission process between the GTM modules as well. For a phased antenna array with fixed element structure and array size, the GTM modules and the coupling matrices among units do not change with the amplitude or phase of the feeding sources. The proposed method is particularly efficient to analyze the property of beam scanning and sidelobe level adjustment of a large-scale phased antenna array. Numerical results are provided to verify the high efficiency and precision of the method.

Approximation characteristic between LEMP on earth surface and channel-base current

Based on the dipole technique, the exact expressions and approximate expressions for LEMP on earth surface are derived from the TL model and specified channel-base current described by a pulse function. According to the comparisons between the exact results and approximate results, the waveforms of LEMP and its derivative are similar to the lightning channel-base current and its derivative, respectively. In near-field, the electric field and its derivative waveforms of the approximate results are essentially coincident with the corresponding waveforms of the exact results within 100 m. The magnetic field waveforms of approximate results are essentially coincident with the waveforms of the exact results within 500 m, and the magnetic field derivative waveforms of the approximate results are essentially coincident with the waveforms of the exact results within 200 m. In far-field, the waveforms of the approximate results are essentially coincident with the waveforms of the exact results in the rising edge before the initial peak value. At the distance beyond 100 km, the waveforms of the radiation field component and the scaled channel-base current appear identical. The difference between the derivative waveforms of the LEMP field and the scaled channel-base current in the first three microseconds is slight and can be ignored.

Study of radiation conditions onboard the International space station by means of the Liulin-5 dosimeter

For estimating radiation risk in space flights it is necessary to determine radiation dose obtained by critical organs of a human body. For this purpose the experiments with human body models are carried out onboard spacecraft. These models represent phantoms equipped with passive and active radiation detectors which measure dose distributions at places of location of critical organs. The dosimetric Liulin-5 telescope is manufactured with using three silicon detectors for studying radiation conditions in the spherical tissue-equivalent phantom on the Russian segment of the International space station (ISS). The purpose of the experiment with Liulin-5 instrument is to study dynamics of the dose rate and particle flux in the phantom, as well as variations of radiation conditions on the ISS over long time intervals depending on a phase of the solar activity cycle, orbital parameters, and presence of solar energetic particles. The Liulin-5 dosimeter measures simultaneously the dose rate and fluxes of charged particles at three depths in the radial channel of the phantom, as well as the linear energy transfer. The paper presents the results of measurements of dose rate and particle fluxes caused by various radiation field components on the ISS during the period from June 2007 till December 2009.