Detector Plane Research Articles

The Lobster Eye Imager for Astronomy Onboard the SATech-01 Satellite

The Lobster Eye Imager for Astronomy (LEIA), a pathfinder of the Wide-field X-ray Telescope of the Einstein Probe mission, was successfully launched onboard the SATech-01 satellite of the Chinese Academy of Sciences on 2022 July 27. In this paper, we introduce the design and on-ground test results of the LEIA instrument. Using state-of-the-art Micro-Pore Optics (MPO), a wide field of view of 346 square degrees (18.°6 × 18.°6) of the X-ray imager is realized. An optical assembly composed of 36 MPO chips is used to focus incident X-ray photons, and four large-format complementary metal-oxide semiconductor (CMOS) sensors, each of size 6 cm × 6 cm, are used as the focal plane detectors. The instrument has an angular resolution of 4′–8′ (in terms of FWHM) for the central focal spot of the point-spread function, and an effective area of 2–3 cm2 at 1 keV in essentially all the directions within the field of view. The detection passband is 0.5–4 keV in soft X-rays and the sensitivity is 2–3 × 10−11 erg s−1 cm−2 (about 1 milliCrab) with a 1000 s observation. The total weight of LEIA is 56 kg and the power is 85 W. The satellite, with a design lifetime of 2 yr, operates in a Sun-synchronous orbit of 500 km with an orbital period of 95 minutes. LEIA is paving the way for future missions by verifying in flight the technologies of both novel focusing imaging optics and CMOS sensors for X-ray observation, and by optimizing the working setups of the instrumental parameters. In addition, LEIA is able to carry out scientific observations to find new transients and to monitor known sources in the soft X-ray band, albeit with limited useful observing time available.

Planar Waveguide NMR Gradients (B0 and B1) for spatiotemporal Investigations of Anticancer Drug Concentration in 3D Cancer Cell Cultures

Despite the progression in cancer therapeutic approaches, cancer is still the leading cause of death worldwide with a steadily increasing incidence rate. In Jordan, CRC is the most common type of cancer among men and the second most common among women, while being one of the most accruing cancers in Germany.
 The difficulties in cancer treatments arise from the poor correlation between in vivo and in in vitro anti-cancer drug testing results and cancer cells resistance to chemotherapy, which are attributed to the heterogeneity of cancer cells, and the interaction of cancer cells with non-cancerous cells in the tumor microenvironment (TME). In addition to, the several mechanisms, that governs DNA damages repair, epigenetics, epithelial to mesenchymal transition (EMT).
 Cell culture techniques have been developed to construct in vitro multicellular cancer spheroids (MTCS) that mimic cell-cells interaction and the cellular organization in the TME. They also illustrate the proliferation gradient of solid tumors, and the nutrition and gas supply to cancer cells at different depth in the spheroid. Therefore, they are considered an excellent in vitro cancer model to study the efficiency and to investigate the penetration depth of the anti-cancer materials.
 Nuclear Magnetic Resonance (NMR) spectroscopy is a reliable analytical method that gives comprehensive and rich chemical information, along with high speciation performance. It is one of the major noninvasive tools for metabolomics, therefore it has been utilized to study the metabolic profiling of freshly isolated- non-destructed tissues, and living in vitro cellular models.
 A micro-imaging technique for real-time NMR investigations is developed to study the penetration depth, rate, and effective diffusion coefficients of anti-cancer materials through cancer spheroids. This technique is based on our patented invention of planar waveguide micro slot NMR detector with on board thermal regulator integrated and a microfluidic device. Based on this innovative development, we are able to perform real-time magnetic resonance spectroscopic imaging (MRSI) on a living synthetic tissue constructed in micrometer scale to monitor drug penetration and diffusion, while providing spectroscopic information about the production and degradation of metabolites in picomoles concentrations.

Interfacial Engineering Enables Perovskite Heteroepitaxial Growth on Black Phosphorus for Flexible X-ray Detectors.

2D materials with atomic-scale thickness and mechanical robustness are required for flexible devices. The superior optoelectronic properties and high-Z atoms in metal halide perovskites render them desirable for X-ray detection, but the intrinsic brittleness is an obstacle hampering the applications in flexible detectors. Herein, an interfacial engineering strategy is demonstrated for the epitaxial growth of methylammonium lead bromide (MAPbBr3 ) on black phosphorus (BP) for flexible X-ray detectors. The mechanically robust, high-quality heterostructure consisting of a Pb transition layer is synthesized for the two-way bridging of BP and MAPbBr3 . Excellent optoelectronic properties such as a high X-ray sensitivity of 1,609 ± 122µCGy-1 cm-2 (80 times higher than that of the commercial amorphous Se), a fast response time of 40 ± 5ms, as well as a low detection limit of 3µGys-1 (about a fifteenth of the medical chest X-ray dose rate) are achieved from the simple and planar direct X-ray detector fabricated on an organic filter membrane. More importantly, these flat and simple devices are bendable and mechanically durable by exhibiting only 10% photocurrent degradation after 200 bending cycles. The novel heterostructure has great potential in large-area, flexible, and sensitive X-ray detection applications.

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.

Charged Particle Pseudorapidity Distributions Measured with the STAR EPD

In 2018, in preparation for the Beam Energy Scan II, the STAR detector was upgraded with the Event Plane Detector (EPD). The instrument enhanced STAR’s capabilities in centrality determination for fluctuation measurements, event plane resolution for flow measurements, and in triggering overall. Due to its fine radial granularity, it can also be utilized to measure pseudorapidity distributions of the produced charged primary particles, in EPD’s pseudorapidity coverage of 2.15<|η|<5.09. As such a measurement cannot be done directly, the response of the detector to the primary particles has to be understood well. The detector response matrix was determined via Monte Carlo simulations, and corrected charged particle pseudorapidity distributions were obtained in Au + Au collisions at the center of mass collision energies sNN = 19.6 and 27.0 GeV using an iterative unfolding procedure. Several systematic checks of the method were also done.

Laser-driven muon production for material inspection and imaging

We numerically show that laser-wakefield accelerated electron beams obtained using a PetaWatt-scale laser system can produce high-flux sources of relativistic muons that are suitable for radiographic applications. Scalings of muon energy and flux with the properties of the wakefield electron beams are presented. Applying these results to the expected performance of the 10-PW class laser at the Extreme Light Infrastructure Nuclear Physics (ELI-NP) demonstrates that ultra-high power laser facilities currently in the commissioning phase can generate ultra-relativistic muon beams with more than 104 muons per shot reaching the detector plane. Simple magnetic beamlines are shown to be effective in separating the muons from noise, allowing for their detection using, for example, silicon-based detectors. It is shown that a laser facility like the one at ELI-NP can produce high-fidelity and spatially resolved muon radiographs of enclosed strategically sensitive materials in a matter of minutes.

Inclusion of a GaAs detector model in the Photon Counting Toolkit software for the study of breast imaging systems.

We present an upgraded version of the Photon Counting Toolkit (PcTK), a freely available by request MATLAB tool for the simulation of semiconductor-based photon counting detectors (PCD), which has been extended and validated to account for gallium arsenide (GaAs)-based PCD(s). The modified PcTK version was validated by performing simulations and acquiring experimental data for three different cases. The LAMBDA 60 K module planar detector (X-Spectrum GmbH, Germany) based on the Medipix3 ASIC technology was used in all cases. This detector has a 500-μm thick GaAs sensor and a 256 × 256-pixel array with 55 μm pixel size. The first validation was a comparison between simulated and measured spectra from a 109Cd radionuclide source. In the second validation study, experimental measurements and simulations of mammography spectra were generated to observe the performance of the GaAs version of the PcTK with polychromatic radiation used in conventional x-ray imaging systems. The third validation study used single event analysis to validate the spatio-energetic model of the extended PcTK version. Overall, the software provided a good agreement between simulated and experimental data, validating the accuracy of the GaAs model. The software could be an attractive tool for accurate simulation of breast imaging modalities relying on photon counting detectors and therefore could assist in their characterization and optimization.

Measurements of the Kr (e,2e) differential cross section in the perpendicular plane from 2 to 120 eV above the ionization threshold

New (e, 2e) differential cross section measurements from krypton are presented in the perpendicular plane, where the incident electron beam is orthogonal to the scattered and ejected electrons that map out a detection plane. New data were obtained at incident energies from 30 eV to 120 eV above the ionization potential (IP), the experiment being configured to detect scattered and ejected electrons with equal energy. The results are compared to previous measurements from 2 eV to 50 eV above the IP and to calculations from different models in this energy range. The new experiments confirm the results from previous measurements. The results are also compared to recent data for argon acquired under the same kinematic conditions, to highlight similarities and differences that are observed.

Characterization of the INFN proton CT scanner for cross-calibration of x-ray CT

Objective. The goal of this study was to assess the imaging performances of the pCT system developed in the framework of INFN-funded (Italian National Institute of Nuclear Physics) research projects. The spatial resolution, noise power spectrum (NPS) and RSP accuracy has been investigated, as a preliminary step to implement a new cross-calibration method for x-ray CT (xCT). Approach. The INFN pCT apparatus, made of four planes of silicon micro-strip detectors and a YAG:Ce scintillating calorimeter, reconstructs 3D RSP maps by a filtered-back projection algorithm. The imaging performances (i.e. spatial resolution, NPS and RSP accuracy) of the pCT system were assessed on a custom-made phantom, made of plastic materials with different densities ((0.66, 2.18) g cm−3). For comparison, the same phantom was acquired with a clinical xCT system. Main results. The spatial resolution analysis revealed the nonlinearity of the imaging system, showing different imaging responses in air or water phantom background. Applying the Hann filter in the pCT reconstruction, it was possible to investigate the imaging potential of the system. Matching the spatial resolution value of the xCT (0.54 lp mm−1) and acquiring both with the same dose level (11.6 mGy), the pCT appeared to be less noisy than xCT, with an RSP standard deviation of 0.0063. Concerning the RSP accuracy, the measured mean absolute percentage errors were (0.23+−0.09)% in air and (0.21+−0.07)% in water. Significance. The obtained performances confirm that the INFN pCT system provides a very accurate RSP estimation, appearing to be a feasible clinical tool for verification and correction of xCT calibration in proton treatment planning.

A Cooperative Detection of DDoS Attacks Based on CNN-BiLSTM in SDN

In view of the problem that detecting DDoS attack traffic in traditional SDN depends on the controller continuously collecting traffic and running the detection model, resulting in excessive controller overhead, low detection efficiency, increased traffic forwarding delay, and easy to cause "single point of failure", a cooperative detection method of DDoS attack in SDN based on information entropy and deep learning is proposed, which divides part of the detection task into the data plane for detection based on information entropy and uses the improved CNN-BiLSTM model to detect DDoS attack traffic on control plane. The experimental results show that, compared with the SVC-RF method in recent years, the accuracy of the proposed CNN-BiLSTM model is increased by 0.74%, the detection rate is increased by 1.42%, and the false alarm rate is reduced by 1.5%. Compared with the BiLSTM model, the accuracy is increased by 0.75%, the detection rate is increased by 0.64%, and the false alarm rate is reduced by 1.14%. Compared with the RF method, the accuracy is increased by 2.34%, the detection rate is increased by 3.88%, and the false alarm rate is reduced by 4%. Compared with the traditional single point detection method which only depends on the controller, the proposed switch-controller cooperative detection method reduces the CPU occupancy of the controller by about 12% and the detection time by about 13 seconds.

Influence of temperature on measurements of the Two Photon Absorption – Transient Current Technique in silicon planar detectors using a 1550 nm femtosecond fibre laser

The effect of temperature on the excess charge carrier generation and collection, injected using two photon absorption at a wavelength of 1550 nm, is investigated in a 285 μm thick, p-type silicon planar detector, with a bulk resistivity of 3.7 kΩ cm. Charge collection measurements are performed for temperatures between −20 °C to 20 °C. The collected charge decreases by about 8% when the temperature is lowered from 20 °C to −20 °C, which is linked to a decreasing excess charge carrier generation. Further, a decreasing time over threshold is observed for decreasing temperatures, which is associated to an increasing charge carrier mobility.

Design of a Prism-Grating Wide Spectral Range Transmittance Imaging Spectrometer.

As spectroscopic detection technology rapidly advances, back-illuminated InGaAs detectors with a wider spectral range have emerged. Compared to traditional detectors such as HgCdTe, CCD, and CMOS, InGaAs detectors offer a working range of 400-1800 nm and exhibit a quantum efficiency of over 60% in both the visible and near-infrared bands. This is leading to the demand for innovative designs of imaging spectrometers with wider spectral ranges. However, the widening of the spectral range has led to the presence of significant axial chromatic aberration and secondary spectrum in imaging spectrometers. Additionally, there is difficulty in aligning the system optical axis perpendicular to the detector image plane, resulting in increased challenges during post-installation adjustment. Based on chromatic aberration correction theory, this paper presents the design of a wide spectral range transmission prism-grating imaging spectrometer with a working range of 400-1750 nm using Code V. The spectral range of this spectrometer covers both the visible and near-infrared regions, which is beyond the capability of traditional PG spectrometers. In the past, the working spectral range of transmission-type PG imaging spectrometers has been limited to 400-1000 nm. This study's proposed chromatic aberration correction process involves selecting optical glass materials that match the design requirements and correcting the axial chromatic aberration and secondary spectrum, ensuring that the system axis is perpendicular to the detector plane and easy to adjust during installation. The results show that the spectrometer has a spectral resolution of 5 nm, a root-mean-square spot diagram less than 8 μm over the full field of view, and an optical transfer function MTF greater than 0.6 at a Nyquist frequency of 30 lp/mm. The system size is less than 90 mm. Spherical lenses are employed in the system design to reduce manufacturing costs and complexity while meeting the requirements of wide spectral range, miniaturization, and easy installation.

Electric-Field Mapping of Optically Perturbed CdTe Radiation Detectors.

In radiation detectors, the spatial distribution of the electric field plays a fundamental role in their operation. Access to this field distribution is of strategic importance, especially when investigating the perturbing effects induced by incident radiation. For example, one dangerous effect that prevents their proper operation is the accumulation of internal space charge. Here, we probe the two-dimensional electric field in a Schottky CdTe detector using the Pockels effect and report on its local perturbation after exposure to an optical beam at the anode electrode. Our electro-optical imaging setup, together with a custom processing routine, allows the extraction of the electric-field vector maps and their dynamics during a voltage bias-optical exposure sequence. The results are in agreement with numerical simulations, allowing us to confirm a two-level model based on a dominant deep level. Such a simple model is indeed able to fully account for both the temporal and spatial dynamics of the perturbed electric field. This approach thus allows a deeper understanding of the main mechanisms affecting the non-equilibrium electric-field distribution in CdTe Schottky detectors, such as those leading to polarization. In the future, it could also be used to predict and improve the performance of planar or electrode-segmented detectors.

A novel Compton camera with an annular absorber for enhancing the imaging efficiency in regions directly ahead: A simulation study

ABSTRACT Compton camera is an extremely important technology to observe the prompt emissions from gamma-ray bursts. To improve the imaging efficiency of regions directly ahead of the system, a novel Compton camera with an annular absorber was proposed and evaluated. The sensitivity and angular resolution of such a Compton camera were compared with those of a typical Compton camera with two planar detectors. The scatterers of the two cameras were identical and contained 8 × 8 GAGG crystals, with dimensions 10 × 10 × 5 mm3. The absorber in the typical Compton camera contained 8 × 8 GAGG crystals, each measures 10 × 10 × 10 mm3. Sixty-four GAGG crystals, each also measuring 10 × 10 × 10 mm3, were arranged in an annular shape with an inner radius of ~51.5 mm and an outer radius of ~73.9 mm. A point gamma-ray source (511 keV) and a distributed source placed 1000 mm away from the center of the scatterer were subsequently imaged by the two cameras. By changing the scatterer-to-absorber distance, the efficiency and angular resolution of the two cameras were calculated and compared with each other. With slightly better angular resolution, the novel Compton camera significantly enhanced the system detection efficiency. This enhancement depended on scatterer-to-absorber distance. When the distance was 130 mm, the enhancement was nearly 50%.

511-CAM mission: a pointed 511 keV gamma-ray telescope with a focal plane detector made of stacked transition edge sensor microcalorimeter arrays

The 511 keV γ-ray emission from the galactic center region may fully or partially originate from the annihilation of positrons from dark matter particles with electrons from the interstellar medium. Alternatively, the positrons could be created by astrophysical sources, involving exclusively standard model physics. We describe here a new concept for a 511 keV mission called 511-CAM (511 keV gamma-ray camera using microcalorimeters) that combines focusing γ-ray optics with a stack of transition edge sensor microcalorimeter arrays in the focal plane. The 511-CAM detector assembly has a projected 511 keV energy resolution of 390 eV full width half maximum or better, and improves by a factor of at least 11 on the performance of state-of-the-art Ge-based Compton telescopes. Combining this unprecedented energy resolution with sub-arcmin angular resolutions afforded by Laue lens or channeling optics could make substantial contributions toward identifying the origin of the 511 keV emission through discovering and characterizing point sources and measuring line-of-sight velocities of the emitting plasmas.

Patient-specific quality assurance for IMRT delivery: A multicentre study

IMRT is a commonly used technique for radiotherapy. This is the first multicentre study conducted nationally for assessing the quality of IMRT delivery in participating centres by cross-checking local QA results with on-site measurements using novel MOSkin detector and a commercial two-dimensional planar detector. By using MOSkin, 40 measurement points were evaluated, with 18% (8 points) showing deviations of more than ±5% from the predicted dose, while 82% of the results were within the recommended tolerance level of ±5% for on-site and end-to-end IMRT/VMAT audits. Most centres passed the 95% points of the gamma criteria of 3%/3 mm for planar dose measurement, which is consistent with other similar studies and within the confidence limits recommended by AAPM TG119. By benchmarking their performance with the recommended tolerance levels for IMRT delivery, participating centres can improve their quality continuously. In conclusion, the study found that participating centres generally met the international guidelines for IMRT delivery standards.

Design and Performance of Amorphous Silicon Based on Uncooled Bolometer-Type Infrared Focal Plane Arrays

Uncooled bolometric type thermal detectors , combined into a matrix and placed into a focal plane array have the following characteristics : low cost , operation at room temperature , compatibility with the silicon CMOS technology , and high detecting performance ; therefore recently it became a hot spot in infrared or terahertz detection field . The performance of uncooled infrared focal plane detector arrays depends on the optimization of critical parameters which are determined by geometrical design and the electrical , optical , and thermal physical properties of the detector materials . We report the study of a fabrication process and characterization of two (2D) dimensional arrays of uncooled microbolometers based on silicon (α- Si ) thermo-sensing films . Because these arrays substantially reduce sensor size , they are becoming the preferred format for most modern applications .

Infrared Gas Detection and Concentration Inversion Based on Dual-Temperature Background Points

Gas detection based on infrared thermal imaging is applied in many areas, but it is generally applied as a qualitative detection method to observe the target area; on the other hand, quantitative research on gas concentration is less common, the measurement accuracy is poor, and the calculation method of concentration in the commonly adopted transmission model is also complicated. In this paper, based on the radiance transfer model of gas infrared imaging technology, the influence of gas concentration, gas temperature, and background temperature on gas imaging detection is investigated, a gas detection and concentration inversion method based on dual-temperature background points is proposed, and the effects of the choice of reference band on background temperature correction are analyzed in relation to the changing trend of dual-band radiance difference. To verify the effectiveness of this method, a gas detection system with dual-temperature background spots was constructed in this paper utilizing a cooled mid-wave infrared focal plane detector plus a reference filter and a measurement filter, which achieved a promising concentration accuracy of less than 10% for carbon dioxide at a detectable range. Meanwhile, an infrared imaging system with a noise equivalent temperature difference (NETD) of 40 mK was employed to simulate the detection of methane, which enables the detection and concentration inversion of methane gas at a minimum concentration of 500 ppm·m at a distance of 1 km, which proves the capability of long-range detection.

Neutron irradiation of Hydrogenated Amorphous Silicon p-i-n diodes and charge selective contacts detectors

Hydrogenated amorphous silicon is a well-known detector material for its radiation resistance. For this reason it has been used in particle beam flux measurements and in solar panels designed for space applications. This study concern 10μm thickness, p-i-n and charge selective contacts planar diode detectors which were irradiated with neutrons to two fluence values: 1016neq/cm2 and 5 × 1016neq/cm2. In order to evaluate their radiation resistance, detector leakage current and response to x-ray photons have been measured. The effect of annealing for performance recovery at 100 °C for 12 and 24 h has also been studied. The results for the 1016neq/cm2 irradiation show a factor 2 increase in leakage current that is completely recovered after annealing for p-i-n devices while charge selective contacts devices show an overall decrease of the leakage current at the end of the annealing process compared to the measurement before the irradiation. X-ray dosimetric sensitivity degrades, for this fluence, at the end of irradiation, but partially recovers for charge selective contact devices and increases for p-i-n devices at the end of the annealing process. Concerning the 5 × 1016neq/cm2 irradiation test (for p-i-n structures only), due to the activation that occurred during the irradiation phase, the measurements were taken after 146 days of storage at around 0 °C, during this period, a self-annealing effect may have occurred. Therefore, the results after irradiation and storage show a noticeable degradation in leakage current and x-ray sensitivity with a small recovery after annealing.

Spatial aliasing quantification and sampling frequency selection in imaging sensors.

Sampling, whether it be spatial or temporal, is a common occurrence. A result of this fact is the need for an anti-aliasing filter, which effectively limits high frequencies and prevents them from folding over and appearing as a low(er) frequency when sampled. In typical imaging sensors, such as optics plus focal plane detector(s), the optical transfer function (OTF) acts as a spatial anti-aliasing filter. However, decreasing this anti-aliasing cutoff frequency (or lowering the curve in general) via the OTF is tantamount to image degradation. On the other hand, the lack of high-frequency attenuation produces aliasing within the image, which is another form of image degradation. In this work, aliasing is quantified, and a method for sampling frequency selection is brought forth.