Measured Radiation Field Research Articles

Fast Near-Field Frequency-Diverse Computational Imaging Based on End-to-End Deep-Learning Network.

The ability to sculpt complex reference waves and probe diverse radiation field patterns have facilitated the rise of metasurface antennas, while there is still a compromise between the required wide operation band and the non-overlapping characteristic of radiation field patterns. Specifically, the current computational image formation process with a classic matched filter and other sparsity-driven algorithms would inevitably face the challenge of a relatively confined scene information sampling ratio and high computational complexity. In this paper, we marry the concepts of a deep convolutional neural network with computational imaging literature. Compared with the current matched filter and compressed sensing reconstruction technique, our proposal could handle a relatively high correlation of measurement modes and low scene sampling ratio. With the delicately trained reconstruction network, point-size objects and more complicated targets can both be quickly and accurately reconstructed. In addition, the unavoidable heavy computation burden and essential large operation frequency band can be effectively mitigated. The simulated experiments with measured radiation field data verify the effectiveness of the proposed method.

A perception and imaging framework for far-range frequency-division-multiplexed computational imaging

ABSTRACT So far, implementations of frequency-diverse computational framework with metamaterial element have used a frequency sweep across the operating frequency band, where the driving waveguide mode is coupled to subsets of the resonant elements at a corresponding excitation frequency. Scene information interrogating and processing efficiency are relatively confined in current imaging system especially for far-range imaging scenarios. Here, we implement frequency-division methods to parallelize computational imaging (CI). This concept multiplexes the modes in the frequency domain where different subsets of the resonant metamaterial elements are simultaneously excited by wideband multicarrier waveforms, allowing the scene to be encoded with different spatially diverse radiation patterns. Besides, we present a unified fast perception and processing framework for far-range imaging purpose. The proposed technique marries communications concepts to computational imaging, achieving a key development due to the limitations imposed by massive amount of data and burdensome computation. Numerical simulations with the measured radiation field pattern data are conducted to verify the effectiveness the technique.

Nuclear heating measurements for fusion and fission relevant materials in the JSI TRIGA reactor

The knowledge of nuclear heating inside nuclear (fission or fusion) reactor is essential for safe reactor operation, to know and meet limits expressed in terms of cooling requirements, and it represents critical input information for the design of any experimental irradiation device. In the framework of a research collaboration project between the Atomic and Alternative Energy Commission (CEA) in France, and the Jožef Stefan Institute (JSI) in Slovenia, a new project was launched in 2018 with the objective to measure the total heating rates in different materials of interest inside the JSI TRIGA Mark II reactor using the calorimetry technique. Three standard materials, graphite, aluminum and tungsten, and a fusion-relevant material, Eurofer-97, have been selected. The design of the calorimeters to host the four selected material samples is based on the CALMOS and CARMEN differential calorimeters, previously developed at the CEA, which were used to perform nuclear heating measurements in the OSIRIS material testing reactor (MTR) at the Saclay research center.The design of these specific calorimeters, and the dimensioning of the material samples located within, necessitated preliminary particle transport calculations using the MCNP V6.1 Monte Carlo code in order to estimate the expected heating levels in the experimental Central Channel of the core, and to avoid excessive perturbation of the measured radiation field. On the other hand, a parametric study was carried out using the COMSOL multiphysics code, to evaluate the expected temperature differences that could be measured using calorimeters designed specifically for low heating rates in the JSI TRIGA reactor core. A dedicated measurement campaign took place in July 2021 in which heating measurements were carried out at 100 kW reactor power and at nominal reactor power - 250 kW. This paper presents the design and preparation of the calorimeters, their preliminary calibration, the measurements carried out and the analysis of the obtained experimental results.

A Multiwavelength Look at the GJ 9827 System: No Evidence of Extended Atmospheres in GJ 9827b and d from HST and CARMENES Data

Abstract GJ 9827 is a bright star hosting a planetary system with three transiting planets. As a multiplanet system with planets that sprawl within the boundaries of the radius gap between terrestrial and gaseous planets, GJ 9827 is an optimal target to study the evolution of the atmospheres of close-in planets with a common evolutionary history and their dependence from stellar irradiation. Here we report on the Hubble Space Telescope (HST) and CARMENES transit observations of GJ 9827 planets b and d. We performed a stellar and ISM characterization from the ultraviolet HST spectra, obtaining fluxes for Lyα and Mg ii of F(Lyα) = (5.42 ) × 10−13 erg cm−2 s−1 and F(Mgii) = (5.64 ± 0.24) × 10−14 erg cm−2 s−1. We also investigated a possible absorption signature in Lyα in the atmosphere of GJ 9827b during a transit event from HST spectra, as well as Hα and He i signature for the atmosphere of GJ 9827b and d from CARMENES spectra. We found no evidence of an extended atmosphere in either of the planets. This result is also supported by our analytical estimations of mass loss based on the measured radiation fields for all three planets of this system, which led to a mass-loss rate of 0.4, 0.3, and 0.1 planetary masses per Gyr for GJ 9827b, c, and d, respectively. These values indicate that the planets could have lost their volatiles quickly in their evolution and probably do not retain an atmosphere at the current stage.

Modified Transmission Line Model with a Current Attenuation Function Derived from the Lightning Radiation Field—MTLD Model

In return strokes, the parameters that can be measured are the channel base current and the return stroke speed. For this reason, many return stroke models have been developed with these two parameters, among others, as inputs. Here, we concentrate on the current propagation type engineering return stroke models where the return stroke is represented by a current pulse propagating upwards along the leader channel. In the current propagation type return stroke models, in addition to the channel base current and the return stroke speed, the way in which the return stroke current attenuates along the return stroke channel is specified as an input parameter. The goal of this paper is to show that, within the confines of current propagation type models, once the channel base current and the return stroke speed are known, the measured radiation field can be used to evaluate how the return stroke current attenuates along the channel. After giving the mathematics necessary for this inverse transformation, the procedure is illustrated by extracting the current attenuation curve from the typical wave shape of the return stroke current and from the distant radiation field of subsequent return strokes. The derived attenuation curve is used to evaluate both the subsequent and first return stroke electromagnetic fields at different distances. It is shown that all the experimentally observed features can be reproduced by the derived attenuation curve, except for the subsidiary peak and long zero-crossing times. In order to obtain electromagnetic fields of subsequent return strokes that are in agreement with measurements, one has to incorporate the current dispersion into the model. In the case of first return strokes, both current dispersion and reduction in return stroke speed with height are needed to obtain the desired features.

Simultaneous measurement of the spectral and temporal properties of a LINAC pulse from outside the treatment room

A detection system composed of a CeBr3 scintillating crystal coupled with a photomultiplier tube and connected to a digital oscilloscope was installed in the control room of a Cyberknife™ clinical accelerator during normal irradiation in order to infer the temporal characteristics of the beam and spectral characteristics of the low-intensity scattered radiation present outside the treatment room.Three batches of 20,000 pulses were measured at three different gantry angles. After digitalization and post-processing of the signals, the time profile of the beam pulses was determined with an accuracy of 14 ns with respect to the gating signal, while the energy spectrum of the measured radiation field could be acquired with a resolution of 5.5%.The proposed device makes it possible, thanks to the increased sensitivity of the scintillating crystals and the digital signal processing techniques in place, to monitor the properties of the radiation present outside the bunker produced by the treatment beam, minimizing interference with patient treatment, QA or research activities.

Design of a Broadband Quasi-Optical Mode Converter for $W$ -Band Gyro-TWTs

Mode converters for millimeter waves can reduce the transmission loss, generate the desired mode, and facilitate the application of high-power sources. A W-band broadband quasi-optical mode converter which converts a TE0,1 cylindrical waveguide mode into a linearly polarized Gaussian TEM00 mode has been realized and tested in this paper. The converter is composed of a wavefront transforming mirror, a polarization grating, and a phase correcting system. In order to obtain high conversion efficiency over a wide bandwidth and make the structure of the mode converter much simple and compact, the propagation path of the beam is optimized and a wavefront transforming mirror realized by an ellipsoidal mirror rather than a nonquadratic mirror is introduced. The conversion process in each section is displayed and the working principles are discussed in detail. The mode conversion characteristics are investigated by analyzing the measured radiation field pattern. Results of the measurement agree well with the numerical calculations. The proposed W-band mode converter has a conversion bandwidth of 21% when the mode conversion efficiency is over 95% and the cross polarization is below 1.7%. In addition to high conversion efficiency, low cross-polarization, and broad bandwidth, this converter features easy construction and compact structure.

SU‐F‐T‐486: A Simple Approach to Performing Light Versus Radiation Field Coincidence Quality Assurance Using An Electronic Portal Imaging Device (EPID)

Purpose:To develop an accurate, straightforward, and user‐independent method for performing light versus radiation field coincidence quality assurance utilizing EPID images, a simple phantom made of readily‐accessible materials, and a free software program.Methods:A simple phantom consisting of a blocking tray, graph paper, and high‐density wire was constructed. The phantom was used to accurately set the size of a desired light field and imaged on the electronic portal imaging device (EPID). A macro written for use in ImageJ, a free image processing software, was then use to determine the radiation field size utilizing the high density wires on the phantom for a pixel to distance calibration. The macro also performs an analysis on the measured radiation field utilizing the tolerances recommended in the AAPM Task Group #142. To verify the accuracy of this method, radiochromic film was used to qualitatively demonstrate agreement between the film and EPID results, and an additional ImageJ macro was used to quantitatively compare the radiation field sizes measured both with the EPID and film images.Results:The results of this technique were benchmarked against film measurements, which have been the gold standard for testing light versus radiation field coincidence. The agreement between this method and film measurements were within 0.5 mm.Conclusion:Due to the operator dependency associated with tracing light fields and measuring radiation fields by hand when using film, this method allows for a more accurate comparison between the light and radiation fields with minimal operator dependency. Removing the need for radiographic or radiochromic film also eliminates a reoccurring cost and increases procedural efficiency.

Analysis and Demonstration of Two Spherical Mode Expansion Resolution Algorithms

The measured radiation field of an antenna may be expanded in a series of vector spherical modes in a specified spherical coordinate system. Such an expansion may be resolved, by means of an iterative algorithm, into two constituent vector spherical mode expansions in two other specified spherical coordinate systems. The sum of these constituent expansions is equal to the original total radiation field. The purpose of such a resolution is to separate the radiation fields due to two identified parts of the original antenna which together constitute the entire radiating structure. Once the resolution has been accomplished, one may study the radiation from the currents on the two parts of the antenna individually including mutual interaction to all orders. This is to be distinguished from measurement of the radiation fields of the two parts individually because that measurement does not include the mutual interaction. A demonstration measurement of a two antenna system is described and iterative postmeasurement processing is employed to identify the radiation from currents on the two constituent antennas of the overall radiating structure. The results are compared with those of an earlier approximate noniterative algorithm developed for the same purpose and the differences are discussed.

Cadmium zinc telluride based infrared interferometry for X-ray detection

Cadmium Zinc Telluride (CZT) is a wide band gap semiconductor for room temperature radiation detection. The electro-optic Pockels effect of the material has been exploited in the past to study electric field non-uniformities and their consequence on conventional detector signals in CZT, by imaging the intensity distribution of infrared (IR) light transmitted through a device placed between crossed polarizers. Recently, quantitative monitoring of extremely high intensity neutron pulses through the change of transmitted IR intensity was demonstrated, offering the advantage to place sensitive electronics outside the measured radiation field. In this work, we demonstrate that X-ray intensity can be deduced directly from measuring the change in phase of 1550 nm laser light transmitted through a 7 × 7 × 2 mm3 CZT based Pockels cell in a simple Mach Zehnder interferometer. X-rays produced by a 50 kVp Mo X-ray tube incident on the CZT cathode surface placed at 7 mm distance cause a linearly increasing phase shift above 0.3 mA tube current, with 1.58 ± 0.02 rad per mA for an applied bias of 500 V across the 2 mm thick device. Pockels images confirm that the sample properties are in agreement with the literature, exhibiting electric field enhancement near the cathode under irradiation, which may cause the non-linearity at low X-ray tube anode current settings. The laser used to probe the X-ray intensity causes itself some space charge, whose spatial distribution does not seem to be exclusively determined by the incident laser position, i.e., charge carrier generation location, with respect to the electrodes.

A Time Domain Equivalent Source Model of an Impulse GPR Antenna Based on Measured Radiation Fields

Ground Penetrating Radar (GPR) is a valuable tool for determining bridge deck health. The ability to simulate scattering from bridge deck elements and the complex interactions between them, as well as from changes due to the presence and relative location of defects is important for understanding observed responses. These simulations can be performed using electromagnetic computational modeling techniques such as Finite-Difference Time Domain (FDTD). In order to accurately model the GPR investigation, it is necessary to have a time domain equivalent source model that can launch and receive electromagnetic waves into the computational space that replicates the signals transmitted and received by the physical GPR antenna. However, due to complexity of design and proprietary information, the GPR unit is typically very difficult, or even impossible, to fully model with sufficient detail. For bridge deck applications, simulation in two-dimensions adequately captures much of the three-dimensional scattering. Two-dimensional simulations have significant computational savings over three-dimensions, and are more feasible to be iteratively implemented to solve inverse problems. The work presented here uses experimental results and presents a computational approach to determine the characteristics suitable for excitation of a two-dimensional FDTD model.

An MLC calibration method using a detector array

The authors have developed a quantitative calibration method for a multileaf collimator (MLC) which measures individual leaf positions relative to the MLC backup jaw on an Elekta Synergy linear accelerator. The method utilizes a commercially available two-axis detector array (Profiler 2; Sun Nuclear Corporation, Melbourne, FL). To calibrate the MLC bank, its backup jaw is positioned at the central axis and the opposing jaw is retracted to create a half-beam configuration. The position of the backup jaws field edge is then measured with the array to obtain what is termed the radiation defined reference line. The positions of the individual leaf ends relative to this reference line are then inferred by the detector response in the leaf end penumbra. Iteratively adjusting and remeasuring the leaf end positions to within specifications completes the calibration. Using the backup jaw as a reference for the leaf end positions is based on three assumptions: (1) The leading edge of an MLC leaf bank is parallel to its backup jaw's leading edge, (2) the backup jaw position is reproducible, and (3) the measured radiation field edge created by each leaf end is representative of that leaf's position. Data from an electronic portal imaging device (EPID) were used in a similar analysis to check the results obtained with the array. The relative leaf end positions measured with the array differed from those measured with the EPID by an average of 0.11+/-0.09 mm per leaf. The maximum leaf positional change measured with the Profiler 2 over a 3 month period was 0.51 mm. A leaf positional accuracy of +/-0.4 mm is easily attainable through the iterative calibration process. The method requires an average of 40 min to measure both leaf banks. This work demonstrates that the Profiler 2 is an effective tool for efficient and quantitative MLC quality assurance and calibration.

Using 1-D models to interpret the reflectance anisotropy of 3-D canopy targets: issues and caveats

This paper evaluates 1) to what extent one-dimensional (1-D) models can be used to represent the magnitude and directionality of the surface reflectance field of heterogeneous canopy targets at different spatial resolutions, and 2) whether this usage results in significant biases in the estimation of the corresponding state variables. It will be seen that when both the 1-D and three-dimensional (3-D) models account for all features of the measured radiation field, then-in the absence of further information regarding the nature and structure of the target-the use of a 3-D model may amount to an over-interpretation of the available data. The simplified surface structure formulation contained within the 1-D model, on the other hand, may affect the values of the state variables that such models will retrieve. This is because the shape of the reflectance anisotropy of the 3-D target is almost always different from that of a structurally homogeneous (1-D) canopy with the same state variable values but no foliage clumping. By consequence the 1-D canopies that are capable of mimicking the bell (or bowl) shaped reflectance anisotropy of 3-D targets will tend to feature lower leaf area index, higher soil albedo and, in particular, predominantly erectophile (or plagiophile) leaf normal distributions.

The Fine Structure of Positive Lightning Return-Stroke Radiation Fields

The electric fields generated by lightning flashes striking the North Sea were measured, with a time resolution better than a few tens of nanoseconds, at Fano island in Denmark. The measuring station was located a few tens of meters away from the high water mark at the west coast of the island. This particular location made it possible to capture, with minimal propagation effects, the electromagnetic fields from lightning flashes striking the North Sea. The waveforms were recorded by a measuring system that could provide a time resolution of about 10 ns. The data recorded had the following features. The initial rising part of the positive return-stroke fields contains a slow front followed by a fast transition. The duration of the slow front of the positive return-stroke fields had an average of 8.3 /spl mu/s and its amplitude, measured as a fraction of the initial peak, had an average of 0.61. The 10%-90% rise time of the fast rising portion of the positive return-stroke fields was about 0.26 /spl mu/s, on average. The average peak value of the measured radiation fields normalized to 100 km was 15.7 V/m. The mean of the peak value of the time derivative of the radiation fields was 25 V/m//spl mu/s. The full width at half maximum of the radiation field derivative had a mean of 170 ns.

Radiation fields from whispering-gallery modes of oxide-confined vertical-cavity surface-emitting lasers

Near- and far-field radiation patterns are analyzed for whispering-gallery-mode lasing in native-oxide-confined vertical-cavity surface-emitting lasers. Calculations from classical antenna theory based on the higher-order Bessel functions are compared with experiment and shown to be a useful predictor of the measured radiation fields. The most interesting features of the lasing modes are the multiple and uniformly distributed intensity spots in the near and far fields.

A model for negative first return strokes in lightning flashes

A model is introduced to describe negative first return strokes in lightning ground flashes. The basic assumptions made are similar to those used previously to describe the subsequent return strokes. The model predictions are in general agreement with experimental observation. The model predicts the relationships between (a) peak current and the peak electric radiation field and (b) the peak derivatives of current and electric radiation field. These relationships can be used in the remote sensing of first return stroke current parameters through the measured radiation fields.

Chromosome Aberrations in Human Fibroblasts Induced by Monoenergetic Neutrons. I. Relative Biological Effectiveness

The relative biological effectiveness (RBE) of neutrons for many biological end points varies with neutron energy. To test the hypothesis that the RBE of neutrons varies with respect to their energy for chromosome aberrations in a cell system that does not face interphase death, we studied the yield of chromosome aberrations induced by monoenergetic neutrons in normal human fibroblasts at the first mitosis postirradiation. Monoenergetic neutrons at 0.22, 0.34, 0.43, 1, 5.9 and 13.6 MeV were generated at the Accelerator Facility of the Center for Radiological Research, Columbia University, and were used to irradiate plateau-phase fibroblasts at low absorbed doses from 0.3 to 1.2 Gy at a low dose rate. The reference low-LET, low-dose-rate radiation was 137Cs-gamma rays (0.66 MeV). A linear dose response (Y = alphaD) for chromosome aberrations was obtained for all monoenergetic neutrons and for the gamma rays. The yield of chromosome aberrations per unit dose was high at low neutron energies (0.22, 0.34 and 0.43 MeV) with a gradual decline with the increase in neutron energy. Maximum RBE (RBEm) values varied for the different types of chromosome aberrations. The highest RBE (24.3) for 0.22 and 0.43 MeV neutrons was observed for intrachromosomal deletions, a category of chromosomal change common in solid tumors. Even for the 13.6 MeV neutrons the RBEm (11.1) exceeded 10. These results show that the RBE of neutrons varies with neutron energy and that RBEs are dissimilar between different types of asymmetric chromosome aberrations and suggest that the radiation weighting factors applicable to low-energy neutrons need firmer delineation. This latter may best be attained with neutrons of well-defined energies. This would enable integrations of appropriate quality factors with measured radiation fields, such as those in high-altitude Earth atmosphere. The introduction of commercial flights at high altitude could result in many more individuals being exposed to neutrons than occurs in terrestrial workers, emphasizing the necessity for better-defined estimates of risk.

Collisional-radiative simulations of a radiative pumping experiment

Emission and absorption spectra have been recorded both time resolved and time integrated from radiatively pumped, indirectly heated, aluminium plasmas. At the measured density and temperature, using the measured radiation field which pumps the plasma, ab initio collisional-radiative calculations show excellent agreement with the observations. The sensitivity of the data to the rates of various processes has been investigated. For the conditions of this particular experiment it is demonstrated that radiative and autoionization rates are dominant, while collisional processes have no detectable effect. It is further demonstrated that radiative transfer within the plasma needs to be taken into account properly in order to simulate the experiment successfully.

In SituGamma Spectrometry of Piping in a CANDU Heat Transport System – Application During Decontamination

n in situ pipe gamma spectrometry technique was applied to determine the activity within piping during various stages of CANDU reactor decontaminations. Measurements were performed in general radiation fields up to ∼500 mR/h and required both the detector and the pipe being scanned to be appropriately shielded from other neighboring piping. Measured counts were interpreted using a pipe source efficiency calibration with due regard to its distance dependence. Cobalt-60 was the dominant radionuclide on the piping before the decontamination. Deposition of I24Sb occurred on out-core piping surfaces during the decontamination.The spectrometry measurements were supplemented with contact radiation field measurements, which were performed using survey detectors housed within specially designed pipe shields. Radiation fields estimated from measured radionuclide activities were compared with the measured radiation fields. On average, the ratio of measured to estimated fields was ∼72%. Reasons for this discrepancy are discussed.

Transverse and temporal mode dependence on mirror contrast in microcavity lasers

Optically pumped vertical-cavity surface-emitting lasers with four cavities differing in mirror contrast ratio are fabricated and the steady-state and gain-switched operations are studied. Experimental data show the dependence of the steady-state and dynamic response of the lasing mode on the cavity, gain region, and temperature. Coupling between the transverse radiation pattern and the gain-switched pulse width in time is shown to exist. The results are analyzed by relating the measured radiation fields to the spatial extent and frequency content of the stimulated emission source.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>