Angular Response Research Articles

Localising and identifying radionuclides via energy-resolved angular photon responses

A technique for the in-situ localisation of radioactivity is described whereby the energy-resolved angular photon response of a collimated inorganic scintillation detector is used to derive the spatial arrangement of a variety of radioactive source configurations. The influence of photon radiation (X- and γ ray) incident on the collimated detector is expressed mathematically, by way of a sinc transform embedded to a dynamic linear regression model, to increase the spatial accuracy of the localisation. This approach is tested experimentally with two pairs of like radionuclides, two pairs of different combinations of radionuclides and three different radionuclides to demonstrate its combined isotopic discrimination and spatial localisation capabilities. A fit based on the model referred to above is observed to reproduce the data for the combined X- and γ-ray regions of interest effectively. This allows for increased resolution via interpolation between the data which is observed to improve location accuracy significantly. This research is relevant to applications in autonomous robotic exploration tasks and for the characterisation of contaminated environments associated with nuclear legacies and radiological emergencies.

EURADOS intercomparisons on whole-body dosemeters for photons from 2008 to 2020: analysis and comparison of general results.

Starting in 2008 the European Dosimetry Group (EURADOS) has been performing international intercomparisons (ICs) on photon whole-body dosemeters for individual monitoring services. These ICs have been organized (on a biennial basis) starting 2008 up to 2020 now, each time with a similar set-up but with small alterations in the subsequent irradiation plans. The response for Hp(10) and Hp(0.07) was tested for different radiation qualities, angles of incidences (0°-60°) within a wide range of dose values (0.5-500mSv), to check energy and angular response, linearity, reproducibility and mixed-field response. Within the last 12years almost 15 000 whole body dosemeters have been irradiated and the corresponding response values evaluated. With an increasing number of participants and participating systems (from 62 to 132), this IC program has become an important tool for individual monitoring services to test their whole-body dosimetry systems, compare their results with other services or systems and to improve the quality of their dosimetry. The paper presents and compares the general results of these seven ICs and analyses the dosimetric results for the participating system types.

Development of ring radiation dosemeters using 3D printing.

Extremity radiation monitoring is an important tool for the assessment of occupational exposures to staff at a variety of workplaces where ionising radiation is used. This work shows the feasibility of applying 3D printing for the development of customisable ring dosemeters. The rings were developed using two types of resin, hard and flexible and has the possibility of sterilisation using different techniques. The printed ring dosemeter was associated with BeO optically stimulated dosemeters. The energy and angular response were found within ±20% in the energy range from 24 to 662keV and from 0° to 60° angle of incidence. This contributes to the reduction of measurement uncertainty when compared with currently used thermoluminescent detectors dosemeters. The new ring dosemeter showed a satisfactory response with respect to the performance criteria of the IEC 62387 Standard, in addition to providing improved ergonomics in relation to the commercial ring dosemeter.

EURADOS whole-body dosemeters intercomparisons: lessons learnt from individual results.

Every 2years since 2008, Eurados WG2 has organised a whole-body dosemeters intercomparison (IC) in photon and beta fields. This paper presents the information that individual participants can extract from their results. The irradiation plan of each IC was designed to allow participants check the performance of some important characteristics of their dosimetry systems, in particular: linearity, angular response, energy response and response to mixed fields. The analysis of anomalous responses indicates that many systems can reduce the number of outliers by improving their calibration procedures.

Simulation of Hp(0,07) beta and photon response of a BeOSL finger ring dosemeter.

Simulation of a dosemeter's energy and angular response lowers development cost and time. To support development of a new beta sensitive dosemeter we simulate both the dosemeter and the skin dose in a rod phantom as there are no fluence to dose conversion coefficients in the ICRU Report 47 for electrons. Published spectra for BSS2, N-Series and S-Cs and S-Co were used to define sources, with CAD models used to define the simulation geometry. Simulation tools were validated with experimental beta and photon responses available for the BeOSL photon ring. The developed toolchain was then used to simulate several iterations of a beta sensitive detector element inside a beta ring holder, with the goal to minimise the need for repeated prototype fabrication and characterisation. Simulation results for the final design were compared to measurements on 3D printed prototypes with all radiation qualities, except 90Sr/90Y 0°, falling within measurement uncertainty.

A comprehensive Monte Carlo simulation of the neutron response of multi-element microdosimetric detectors based on THick Gas Electron Multiplier.

We present comprehensive Monte Carlo simulations for the neutron response of the multi-element microdosimetric detector based on THick Gas Electron Multiplier (THGEM). Simulations were carried out using the MCNP6.2 code to calculate the deposited energy spectrum in the gaseous sensitive volumes for three different configurations, 7 × 3, 19 × 5, 37 × 7 that occupy a cylindrical volume of 5-cm diameter by 5-cm length. The energy response was computed from 10keV to 2MeV. The response variation was investigated between sensitive volumes as well as between layers. The simulated energy response showed a good agreement against the evaluated fluence-to-kerma conversion coefficients in the energy region 10-100keV, whereas discrepancies were observed in the region above 250keV. The angular response simulations showed a variation of less than 10%.

Sum and difference patterns synthesis with common excitation amplitude

This paper focuses on the joint optimization problem of sum and difference patterns with common excitation amplitudes and separate excitation phases. The objective is to reduce the complexity of the antenna system while still maintaining a certain degree-of-freedom (DoF) in synthesizing dual-patterns. The problem is formulated with angular response and common excitation amplitude constraints, making it a nonconvex optimization problem. To address this, we introduce two groups of auxiliary variables to decouple the excitation vector from the complex nonconvex constraints. This allows the original problem to be effectively solved via alternately determining the closed-form solutions for several single-variable optimization subproblems. Additionally, our approach is extended to scenarios involving dynamic range ratio (DRR) reduction, aiming to lower the cost and difficulty of hardware implementation. Theoretical analysis and simulation results are provided to demonstrate that the proposed algorithm can converge to the Karush-Kuhn-Tucker points of the original problem. It is also observed that our approach is capable of generating desired dual-patterns with common excitation amplitudes, regardless of the presence or absence of DRR control.

Polarization imaging and edge detection with image-processing metasurfaces

Optical metasurfaces have been recently explored as ultrathin analog image differentiators. By tailoring the momentum transfer function, they can perform efficient Fourier filtering—and thus potentially any linear mathematical operation—on an input image, replacing bulky 4f systems. While this approach has been investigated in different platforms, and a few techniques have been explored to achieve the required angular response, little effort has been devoted so far to tailor and control also the polarization response of an image-processing metasurface. Here, we show that edge-detection metasurfaces can be designed with tailored polarization responses, while simultaneously preserving an isotropic response. In particular, we demonstrate numerically and experimentally single-layer silicon metasurfaces yielding efficient Laplacian operation on a 2D image with either large polarization asymmetry, or nearly polarization-independent response. In the former case, we show that a strongly asymmetric polarization response can be used to unlock more sophisticated on-the-fly image processing functionalities, such as dynamically tunable direction-dependent edge detection. In parallel, metasurfaces with dual-polarized response are shown to enable efficient operation for unpolarized or arbitrarily polarized images, ensuring high efficiency. For both devices, we demonstrate edge detection within relatively large numerical apertures and with excellent isotropy and intensity throughput. Our study paves the way for the broad use of optical metasurfaces for sophisticated, massively parallel analog image processing with zero energy requirements.

An improved measurement of frequency-dependent shear properties of highly compliant materials using a dynamic Kibble’s method

While methods exist to characterize the Young’s modulus and loss factor of viscoelastic materials, there are fewer methods to characterize the shear modulus and loss factor in shear. We previously presented an experimental apparatus that applied dynamic torque on rod-like viscoelastic materials with diameters of 0.5 cm to 2 cm and lengths of 10 cm to 30 cm. The torque was applied using Lorentz forces and measured using a dynamic version of Kibble’s method (similarly, the Watt method). Here, we present a modified version of this apparatus that has several notable improvements over the previously reported version. Improvements include a stronger, more uniform magnetic field and a direct measurement of the angular response of the specimen using a laser and photo-diode configuration. Moreover, the direct measurement of the angular response eliminates the need to know other geometric quantities (such as the radius of the electromagnetic coil), which further reduces the uncertainty of the measured torque. The measurement of the angular response and applied torque are fit to models in order to determine the shear moduli and loss factor. We demonstrate this improved technique on rod-like specimens of different highly-compliant viscoelastic materials.

Experimental measurements of two elastic taut-slack mooring configurations for the multi-float M4 WEC

Moorings are a vital and often problematic component of any floating offshore renewable energy system, whether for wind or wave energy conversion, and here we consider the multi-float WEC system M4 in a 122 configuration. Previous experimental work has shown elastic cables to reduce extreme snap loads by a factor of about 6 when considering single cables between the bow float and a mooring buoy, and between the mooring buoy and the bed [1]. Here we compare results for two alternative configurations designed to reduce the mooring footprint as well as extreme snap loads. The first system, shown in Figure 1 (a), consists of a large surface buoy connected to the seabed with three equi-spaced elastic cables in pre-tension, with a single elastic cable to the bow float. The second system, shown in Figure 1 (b) has a smaller submerged buoy, again connected to the seabed with three equi-spaced elastic cables in pre-tension, however, this is connected to a smaller surface buoy which is subsequently connected to the bow float. Both systems are taut-slack. In this paper we present experimental measurements taken at the COAST laboratory at the University of Plymouth. Both configurations are tested in irregular (JONSWAP) wave conditions up to limiting steepness, with run times of 35 mins at 1:40 scale or about 3.5 hours full scale. Peak, mean and rms bed loads for both configurations are presented along with rms and peak relative angular pitch response with drive train disengaged (free hinge between mid and stern floats).
 References[1] P. Stansby et al., “Experimental study of mooring forces on the multi-float WEC M4 in large waves with buoy and elastic cables,” Ocean Eng., vol. 266, no. P4, p. 113049, 2022.

The Influence of Random Internal Waves on the Characteristics of a Horizontal Antenna in a Shallow Sea

The effect of random internal waves on the gain and pattern of a horizontal antenna array in a shallow sea has been investigated. An algorithm for calculating the correlation matrix of the point source field at the grating aperture is proposed. The antenna gain is analyzed for different spatial processing methods: the beam forming method, the optimal linear processing method, and the optimal quadratic processing method. The effect of internal waves on the directivity pattern is described by the dispersion of the angular response of the grating. Numerical simulation results are presented for a model summer-type waveguide and an exponential Brunt–Väisälä frequency profile. The empirical internal wave spectrum proposed earlier from the SWARM95 experiment is used. The dependences of the antenna array characteristics on the number of its elements, orientation with respect to the source, radiation frequency, and the acoustic characteristics of the bottom are analyzed.

Characterization of a 0.8 mm3 Medscint plastic scintillator detector system for small field dosimetry

Objective. Plastic scintillator detectors (PSDs) have demonstrated ability to meet requirements of small field dosimetry. Medscint developed a 1 mm long, 1 mm diameter cylindrical PSD with effective volume of 0.8 mm3. Clinically relevant, small field dosimetric properties of this detector, combined with a novel scintillation dosimetry system—HYPERSCINT RP-200, and HYPERDOSE analysis software were evaluated in this study. Approach. This novel scintillator-based dosimetry system was characterized with 6 MV-WFF and 10 MV-FFF x-ray beams delivered by Varian TrueBeamTM linear accelerator. The detector was characterized for leakage, short-term repeatability, dose response linearity, angular response, dose rate response, and field size dependence for radiation field sizes of 0.25 × 0.25 to 10 × 10 cm2. Measured detector specific output ratios were compared with microDiamond output factors to determine small field output correction factors, Main results. The dosimetry system showed excellent short-term repeatability with standard deviation of only 0.04 ± 0.01%. It demonstrated good dose linearity with variations less than 1.0% for 14.4 cGy and above. The dosimetry system was found to be independent of dose rate and angle of irradiation, with deviations for both below 0.5%. Leakage was found to be comparable to background readings. For 6 MV-WFF energy beams, detector specific output ratios for field sizes down to 1 × 1 cm2 agreed with output factors measured with PTW TN60019 microDiamond, thus, equates to unity for these field sizes. For 10 MV-FFF energy beams, detector specific output ratios for field sizes down to 2 × 2 cm2 agreed with PTW TN60019 microDiamond output factors, thus, equates to unity for these field sizes. for field sizes down to 0.5 × 0.5 cm2 were determined to be within 6% of unity for both 6 MV-WFF and 10 MV-FFF energy beams. Significance. The HYPERSCINT RP-200 dosimetry system coupled with a 0.8 mm3 PSD showed excellent dosimetric properties and was found to be clinically relevant for relative dosimetry down to field sizes of 0.5 × 0.5 cm2 and potentially smaller.

Vibration response analysis of a two-stage vibration isolation system for large airborne equipment

PurposeThis paper aims to propose a two-stage vibration isolation system for large airborne equipment to isolate aircraft vibration load.Design/methodology/approachFirst, the vibration isolation law of the discrete model of large airborne equipment under different damping ratios, stiffness ratios and mass ratios is analyzed, which guides the establishment of a three-dimensional solid model of large airborne equipment. Subsequently, the vibration isolation transfer efficiency is analyzed based on the three-dimensional model of the airborne equipment, and the angular and linear vibration responses of the two-stage vibration isolation system under different frequencies are studied.FindingsFinally, studies have shown that the steady-state angular vibration at the non-resonant frequency changes little. In contrast, the maximum angular vibration at the resonance peak reaches 0.0033 rad, at least 20 times the response at the non-resonant frequency. The linear vibration at the resonant frequency is at least 2.14 times the response at the non-resonant frequency. Obviously, the amplification factor of linear vibration is less than that of angular vibration, and angular vibration has the most significant effect on the internal vibration of airborne equipment.Originality/valueThe two-stage vibration isolation equipment designed in this paper has a positive guiding significance for the vibration isolation design of large airborne equipment.

The energy and angular Hp(3,α) response of commercial eye-lens dosemeters to photon and beta particle radiation

In 2012, the International Commission on Radiological Protection recommended a reduction of the equivalent dose limit for the lens of the eye from 150 mSv to 50 mSv per year, with a maximum 5-year average of 100 mSv. This noticeable reduction imposes more demands on the performance on personnel eye-lens dosimetry. Regulatory authorities of various jurisdictions worldwide followed some or all, of the ICRP recommendations and implemented reduced occupational lens of eye dose limits in their legislation. Commercial dosimetry service providers have risen to the challenges by developing new dosemeter technologies, and some in-house dosimetry services have developed their own eye-lens dosemeters. The results of the energy and angular response, to photon and beta radiation, of three commercial dosemeters are reported here. Their performances are compared to those of the dosemeter developed, in-house, by Canadian Nuclear Laboratories. With some adjustments to their calibrations, the responses of all dosemeters, could be within the performance limits set by the ISO 14146 and the IEC 62387 standards for the conditions of the tests that were performed.

Evaluation and improvement of angular response for a commercial 2D detector array for patient-specific QA.

MatriXX ionization chamber array has been widely used for the composite dose verification of IMRT/VMAT plans. However, in addition to its dose response dependence on gantry angle, there seems to be an offset between the beam axis and measured dose profile by MatriXX for oblique beam incidence at various gantry angles, leading to unnecessary quality assurance (QA) fails. In this study, we investigated the offset at various setup conditions and how to eliminate or decrease it to improve the accuracy of MatriXX for IMRT/VMAT plan verification with original gantry angles. We measured profiles for a narrow beam with MatriXX located at various depths in increments of 0.5mm from the top to bottom of the sensitive volume of the array detectors and gantry angles from 0° to 360°. The optimal depth for QA measurement was determined at the depth where the measured profile had minimum offset. The measured beam profile offset varies with incident gantry angle, increasing from vertical direction to lateral direction, and could be over 3cm at vendor-recommended depth for near lateral direction beams. The offset also varies with depth, and the minimum offset (almost 0 for most oblique beams) was found to be at a depth of ∼2.5mm below the vendor suggested depth, which was chosen as the optimal depth for all QA measurements. Using the optimal depth we determined, QA results (3%/2mm Gamma analysis) were largely improved with an average of 99.4% gamma passing rate (no fails for 95% criteria) for 10 IMRT and VMAT plans with original gantry angles compared to 94.1% using the vendor recommended depth. The improved accuracy and passing rate for QA measurement performed at the optimal depth with original gantry angles would lead to reduction in unnecessary repeated QA or plan changes due to QA system errors.

Asymmetric metasurface photodetectors for single-shot quantitative phase imaging.

The visualization of pure phase objects by wavefront sensing has important applications ranging from surface profiling to biomedical microscopy, and generally requires bulky and complicated setups involving optical spatial filtering, interferometry, or structured illumination. Here we introduce a new type of image sensors that are uniquely sensitive to the local direction of light propagation, based on standard photodetectors coated with a specially designed plasmonic metasurface that creates an asymmetric dependence of responsivity on angle of incidence around the surface normal. The metasurface design, fabrication, and angle-sensitive operation are demonstrated using a simple photoconductive detector platform. The measurement results, combined with computational imaging calculations, are then used to show that a standard camera or microscope based on these metasurface pixels can directly visualize phase objects without any additional optical elements, with state-of-the-art minimum detectable phase contrasts below 10 mrad. Furthermore, the combination of sensors with equal and opposite angular response on the same pixel array can be used to perform quantitative phase imaging in a single shot, with a customized reconstruction algorithm which is also developed in this work. By virtue of its system miniaturization and measurement simplicity, the phase imaging approach enabled by these devices is particularly significant for applications involving space-constrained and portable setups (such as point-of-care imaging and endoscopy) and measurements involving freely moving objects.

A Monte Carlo study to evaluate and optimise the angular dependence of the Octa – A 2D silicon array detector used for dosimetry in stereotactic radiotherapy

PurposeA detector assembly based on a 2D silicon array sensor, Octa, was previously demonstrated to be accurate for small field relative dosimetry. Experimental studies showed angular dependence of the response that has also variations with the field size. A Monte Carlo simulation model was developed and used in this work to study how the detector assembly's components contribute to the observed angular dependence. MethodsGeant4 was used as the Monte Carlo code. A detailed model of the Octa detector and its packaging was placed in the centre of a solid water phantom with the central sensitive volumes (SVs) located at the isocentre and irradiated at polar angles from 0 to 180° (the beam was normal to the detector plane at 0°). Phase-space files from the IAEA database were used to model a CyberKnife X-ray beam with collimator diameters of 5, 10, and 15 mm. Reference simulations were compared with previous experimental results. To investigate the impact of the assembly's materials, simulations were conducted by iteratively substituting the non-water-equivalent materials of certain components with solid water. In terms of geometry, the influence of the dimensions of an air gap on top of the SVs and the silicon substrate thickness were investigated. ResultsPresence of the silicon surrounding the detector's SVs caused the highest decrease in energy deposition – up to (27 ± 1)%. Thickness of the air gap placed on top of the SVs had no effect at angles below 90°, but for 90–180°, it showed the largest impact on the variation in angular dependence between fields of different sizes – from (6 ± 2)% for 1 mm gap to (24 ± 2)% for 2 mm gap. The variation in the silicon substrate thickness and the air gap's lateral length, as well as presence of the PCB layer did not show significant influence on the angular response. ConclusionFurther development of the detector assembly's design can be driven by mechanical robustness to provide reliability for clinical routine without sacrificing angular dependence. Current design is recommended for use at angles 0–90°: it has shown independence of the angular response from small field size variation and it was previously optimised to be correction-free in output factor measurements. The air gap dimensions are recommended as the main variable parameters for optimisation for further studies when small X-ray beams are measured by the detector positioned in axial plane.

A systematic approach for reconfigurable reflecting metasurface synthesis: From periodic analysis to far-field scattering

We present a consistent approach for a systematic design of an intelligent reflecting surface (IRS), based on a new unit cell with efficient reconfigurability functionalities and a three-step electromagnetic methodology for a rigorous IRS synthesis. First, we design and simulate a reconfigurable unit cell, in which the reconfigurability is accomplished by varactor diodes. Next, we model the IRS as a periodic structure of infinite size, according to Floquet theory. By utilizing the theory of anomalous reflection, we arrive at approximate analytical solutions to calculate the set of necessary varactor diodes’ capacitances, which is subsequently fine-tuned by a fast optimization process to achieve enhanced operation. Finally, to arrive at a more realistic design, we properly analyze the IRS as a finite-sized structure. To this end, we employ an efficient finite element method (FEM) analysis, with a properly developed simulation tool, in which the IRS is modeled as an equivalent impedance sheet of zero-thickness. Overall, we extract the far-field scattered pattern of the IRS and evaluate the angular and frequency response of the design for normal and oblique incidence. Our results show that the proposed design exhibits very promising characteristics, both in terms of reconfigurability and frequency response that can be exploited in contemporary and future wireless communication systems.

Fluorescent Waveguide Lattices for Enhanced Light Harvesting and Solar Cell Performance.

We present the properties and performance of fluorescent waveguide lattices as coatings for solar cells, designed to address the significant mismatch between the solar cell's spectral response range and the solar spectrum. Using arrays of microscale visible light optical beams transmitted through photoreactive polymer resins comprising acrylate and silicone monomers and fluorescein o,o'-dimethacrylate comonomer, we photopolymerize well-structured films with single and multiple waveguide lattices. The materials exhibited bright green-yellow fluorescence emission through down-conversion of blue-UV excitation and light redirection from the dye emission and waveguide lattice structure. This enables the films to collect a broader spectrum of light, spanning UV-vis-NIR over an exceptionally wide angular range of ±70°. When employed as encapsulant coatings on commercial silicon solar cells, the polymer waveguide lattices exhibited significant enhancements in solar cell current density. Below 400 nm, the primary mode of enhancement is through down-conversion and light redirection from the dye emission and collection by the waveguides. Above 400 nm, the primary modes of enhancement were a combination of down-conversion, wide-angle light collection, and light redirection from the dye emission and collection by the waveguides. Waveguide lattices with higher dye concentrations produced more well-defined structures better suited for current generation in encapsulated solar cells. Under standard AM 1.5 G irradiation, we observed nominal average current density increases of 0.7 and 1.87 mA/cm2 for single waveguide lattices and two intersecting lattices, respectively, across the full ±70° range and reveal optimal dye concentrations and suitable lattice structures for solar cell performance. Our findings demonstrate the significant potential of incorporating down-converting fluorescent dyes in polymer waveguide lattices for improving the current spectral and angular response of solar cell technologies toward increasing clean energy in the energy grid.

Sampling and Reconstructing Angular Domains With Uniform Arrays

The surge of massive antenna arrays in wireless networks calls for the adoption of analog/hybrid array solutions, where multiple antenna elements are driven by a common radio front end to form a beam along a specific angle in order to maximize the beamforming gain. Many heuristics have been proposed to sample the angular domain by trading off between sampling step size and overhead, where arbitrarily small angular step size is only attainable with infinite sampling overhead. We show that, for uniform linear and rectangular arrays, lossless reconstruction of the array’s angular responses at arbitrary angular precision is possible using a finite number of samples without resorting to assumptions of angular sparsity. The proposed method, sampling and reconstructing angular domain (SARA), defines how many and which angles to be sampled and the corresponding reconstruction. This general solution to scan the angular domain can therefore be applied not only to beam acquisition and channel estimation, but also to radio imaging techniques, making it a candidate for future integrated sensing and communications (ISAC). Extensive simulation results for target detection and radio imaging have demonstrated clear advantages of SARA over other considered baselines, both in terms of angular reconstruction performance and computational complexity.