Intrinsic Detector Research Articles

Quantifying bunch-mode influence on photon-counting detectors at SPring-8.

Count-loss characteristics of photon-counting 2D detectors are demonstrated for eight bunch-modes at SPring-8 through Monte Carlo simulations. As an indicator, the effective maximum count rate was introduced to signify the X-ray intensity that the detector can count with a linearity of 1% or better after applying a count-loss correction in each bunch-mode. The effective maximum count rate is revealed to vary depending on the bunch-mode and the intrinsic dead time of the detectors, ranging from 0.012 to 0.916 Mcps (megacounts per second) for a 120 ns dead time, 0.009 to 0.807 Mcps for a 0.5 µs dead time and 0.020 to 0.273 Mcps for a 3 µs intrinsic detector dead time. Even with equal-interval bunch-modes at SPring-8, the effective maximum count rate does not exceed 1 Mcps pixel-1. In other words, to obtain data with a linearity better than 1%, the maximum intensity of X-rays entering the detector should be reduced to 1 Mcps pixel-1 or less, and, in some cases, even lower, depending on the bunch-mode. When applying count-loss correction using optimized dead times tailored to each bunch-mode, the effective maximum count rate exceeds the values above. However, differences in the effective maximum count rate due to bunch-modes persist. Users of photon-counting 2D detectors are encouraged to familiarize themselves with the count-loss characteristics dependent on bunch-mode, and to conduct experiments accordingly. In addition, when designing the time structure of bunch-modes at synchrotron radiation facilities, it is essential to take into account the impact on experiments using photon-counting 2D detectors.

Transient‐Current Technique Characterization of Diamond Detector and Proposal of a Diamond Detector with Charge Amplification

Diamond holds promise as a potential candidate for future particle detectors owing to its remarkable electronic, mechanical, and thermal properties. However, a notable limitation is the need for a comprehensive model characterizing intrinsic diamond detectors. To address this, a specialized model integrated into the technology computer‐aided design simulation program is developed. The model's validation is accomplished through its application to the evaluation of an intrinsic diamond detector. Our investigation emphasizes three key attributes: charge carrier mobility, charge carrier lifetime, and the effective charge density within the bulk material. These attributes are carefully assessed using the transient current technique. Furthermore, our model serves as a valuable tool in the analysis of the quality of an high‐pressure high‐temperature diamond crystal and in the optimization of a diamond detector's design, exploiting the charge multiplication effect. This comprehensive methodology advances our grasp of diamond detector behavior and facilitates the development of even more sophisticated devices.

Intrinsic background of EJ-309 liquid scintillator detectors

In deep-underground experiments, intrinsic detector background can exceed the external one, limiting the detection sensitivity. Intrinsic background in liquid scintillator neutron detectors consists of α particles emitted from radioactive impurities in the detector housing (and possibly in the liquid). We present the results of long background measurements of 12 EJ-309 liquid organic scintillators detectors in the deep-underground Gran Sasso National Laboratory of the Italian Institute of Nuclear Physics. These detectors are a part of the detection array for the SHADES ERC project that aims to measure the very low cross section (down to picobarn) of the astrophysically important reaction 22Ne(α,n)25Mg. With an exposure of ∼35 days we identify an actinide concentration in the detector housing of 8.4(1.8)sta(1.4)sys×10−2ppm and 1.62(0.57)sta(0.03)sys×10−1ppm of 238U and 232Th, resulting in 64 α particle counts per hour. The half-life of 214Po was also determined as 163.7(11)μs.

Amorphous silicon intrinsic photomixing detector for optical ranging

Today’s optical range finders or 3D imagers suffer from significant drawbacks and do not allow to combine performance (sensitivity, precision) with simplicity, and scalability enabling very-large scale integration with minimum footprint. Here, we present the amorphous silicon Intrinsic Photomixing Detector (IPD) for direct and highly sensitive optical envelope mixing. The ability to generate a photocurrent that is proportional to the nonlinear mixing of two optical modulation envelope functions enables high performance Time-of-Flight optical ranging at low light levels down to ~0.1mWcm−2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim \\!0.1\\,{{{{{\\rm{mW}}}}}}{{{{{\\rm{cm}}}}}}^{-2}$$\\end{document} at 444nm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$444\\,{{{{{\\rm{nm}}}}}}$$\\end{document}. The IPD exceeds MHz bandwidth, covers a broad distance detection range from 10cm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10\\,{{{{{\\rm{cm}}}}}}$$\\end{document} to 101m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$101\\,{{{{{\\rm{m}}}}}}$$\\end{document}, and achieves a mean depth resolution below 44mm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$44\\,{{{{{\\rm{mm}}}}}}$$\\end{document} for distances up to 25m\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$25\\,{{{{{\\rm{m}}}}}}$$\\end{document}. The IPD paves the way towards simple but high-performance photodetectors that allow for very-large scale integration on top of silicon or flexible electronics at low costs with pixel fill factors up to 100%.

Gate voltage control of helicity-dependent photocurrent and polarization detection in (Bi1−xSbx)2Te3 topological insulator thin films

Optical helicity provides us with an effective means to control the helicity-dependent photocurrent in the spin-momentum-locked surface states of topological insulators (TIs). Also, the TIs show potential in polarization detection as an intrinsic solid-state optical chirality detector for easier integration and fabrication. However, the complex photoresponses with the circular photogalvanic effect, the linear photogalvanic effect, and the photon drag effect in the TIs prevent them from direct chirality detection of the elliptically polarized light. Here, by fitting with the theoretical models to the measured photocurrents, the microscopic origin of different components of the helicity-dependent photocurrent has been demonstrated. We show a comprehensive study of the helicity-dependent photocurrent in (Bi1−xSb x )2Te3 thin films of different thicknesses as a function of the light incident angle and the gate-tuned chemical potential. The observation of the light incident angle dependence of the helicity-dependent photocurrent provides us with a polarization detection strategy using a TI thin film without the use of any additional optical elements, and the detection accuracy can be enhanced by gate tuning. Additionally, the Stokes parameters can be extracted by arithmetic operation of photocurrents measured with different incident angles and gating voltages for complete characterization of the polarization states of a light beam. Using this means, we realize the polarization detection and the Stokes parameters analysis with a single device. Our work provides an alternative solution to develop miniaturized intrinsic polarization-sensitive photodetectors.

Intrinsic photomixing detector based on amorphous silicon for envelope mixing of optical signals

In this work, a promising device for direct optical envelope mixing, the Intrinsic Photomixing Detector (IPD) based on hydrogenated amorphous silicon, is reported. The IPD directly generates a photocurrent proportional to the nonlinear mixing of two optical modulation envelope functions. Experiments illustrate efficient mixing in the visible range at low light levels down to ϕ1 = 4.36 mW/cm2 (444 nm) and ϕ2 = 1.03 mW/cm2 (636 nm). Modulation frequencies exceeding the MHz range are demonstrated. Electro-optical simulations identify defect-induced electrical field screening within the absorber to cause the nonlinear mixing process, opening-up the opportunity to tailor devices toward application-specific requirements. The IPD functionality paves the way toward very simple but high-performance photodetectors for 3D imaging and ranging for direct optical convolutional sensors or for efficient optical logic gates. Using amorphous silicon provides a photodetector material base, which can easily be integrated on top of silicon electronics, enabling fill factors of up to 100%.

Exploring the impact of incoherent Compton scattering on X-ray pair distribution function analysis of disordered materials

X-ray atomic pair distribution function (XPDF) measurements using a two-dimensional area detector have been of great value in studying atomic structures of materials with varying degrees of disorder. However, an area detector does not have energy resolution. Thus, incoherent inelastic Compton scattering and fluorescence are not discriminated, contaminating coherent elastic scattering. This paper investigates the effects of random noise from incoherent scattering on XPDF analysis. To conduct the study, the elastic scattering, Compton scattering and fluorescence of In0.33Ga0.67As alloy were separately measured using an intrinsic Ge solid-state detector with energy resolution. It is found that the addition of Compton scattering with a noise-to-signal ratio of about 0.8% results in the smearing of diffuse scattering in the high-Q region. Moreover, adding extra noise from fluorescence increases the smearing, overwhelming the diffuse scattering. Additionally, simulated data of elastic and Compton scattering on ferroelectric Ba(Ti0.8Zr0.2)O3 were used to investigate the evolution of noise fluctuation and its effects on the XPDF as a function of total intensity.

Hardware Immune System for Embedded IoT

Malware is a major threat to present-day computing systems. With the rapid growth of Internet of Things (IoT) devices and their usage in safety critical systems, security has become increasingly important. Securing IoT devices is a challenge for designers, as they are generally resource constrained, which makes real-time software-based malware detection difficult or infeasible. A promising alternative approach is to utilize intrinsic hardware-based malware detectors to alleviate power and performance overheads. In this brief, we introduce a novel Hardware Immune System (HWIS), a stand-alone, hardware-supported malware detection approach for microprocessors that leverages Artificial Immune Systems for detecting botnet activity. This technique is intended for low-power, resource constrained and network facing embedded devices. The proposed model is capable of detecting botnet behavior with an accuracy of 96.7% and F1-score of 0.96. The technique is implemented in hardware and verified using Spartan-7 FPGA. Our technique achieves power, LUTs, FFs, DSPs, and BRAMs utilization overheads of 0.6%, 8.5%, 11.8%, 0%, and 0%, respectively, with no impact on delay using the RISC-V CPU as a baseline.

Potential alpha particle detection with thin poly (ether sulfone) substrates

Plastics without fluorescent-molecule doping have attracted increasing attention as radiation detection components in measurement systems to ensure safe nuclear reactors and radiation facilities. A promising candidate is poly (ether sulfone) (PES), which is resistant to environmental stress. Here, we show that transparent PES responds rapidly to alpha particles despite its amber colouration. Specifically, 1- and 5 mm-thick PES samples were exposed to an 241Am radioactive source, and the induced PES fluorescence was acquired with a photodetector. The overall system responses were comparable to the intrinsic detector response. The averaged time profiles of the acquired fluorescence pulses for each sample exhibited leading edges that exponentially increased with rise times of 3.3 ± 0.1 ns. The falling tails exponentially decreased with decay times of 12.4 ± 0.1 ns and 12.1 ± 0.3 ns. The maximum intensity from the 1 mm-thick sample was approximately 2.4 times greater than that from the 5 mm-thick sample. This knowledge will lead to future PES applications in radiation measurements.

5‐HT7 receptors expressed in the mouse parafacial region are not required for respiratory chemosensitivity

A brainstem homeostatic system senses CO2/H+ to regulate ventilation, blood gases and acid‐base balance. Neurons of the retrotrapezoid nucleus (RTN) and medullary raphe are both implicated in this mechanism as respiratory chemosensors, but recent pharmacological work suggested that the CO2/H+‐sensitivity of RTN neurons is mediated indirectly – by raphe‐derived serotonin acting on 5‐HT7 receptors. To investigate this further, we characterized Htr7 transcript expression in phenotypically identified RTN neurons using multiplex single cell qRT‐PCR and RNAscope. Although present in multiple neurons in the parafacial region of the ventrolateral medulla, Htr7 expression was undetectable in most RTN neurons (Nmb+/Phox2b+) concentrated in the densely packed cell group ventrolateral to the facial nucleus. Where detected, Htr7 expression was modest and often associated with RTN neurons that extend dorsolaterally to partially encircle the facial nucleus. These more dorsolateral Nmb+/Htr7+ neurons tended to express high levels of Nmb and low levels of the intrinsic RTN proton detectors, Gpr4 and Kcnk5. In mouse brainstem slices, CO2‐stimulated firing in RTN neurons was mostly unaffected by a 5‐HT7 receptor antagonist, SB269970 (n=11/12). At the whole animal level, microinjection of SB269970 into the RTN of conscious mice blocked respiratory stimulation by co‐injected LP‐44, a 5‐HT7 receptor agonist, but had no effect on CO2‐stimulated breathing in those same mice. We conclude that Htr7 is expressed by a minor subset of RTN neurons with a molecular profile distinct from the established chemoreceptors and that 5‐HT7 receptors have negligible effects on CO2‐evoked firing activity in RTN neurons or on CO2‐stimulated breathing in mice.

5-HT7 receptors expressed in the mouse parafacial region are not required for respiratory chemosensitivity.

A brainstem homeostatic system senses CO2/H+ to regulate ventilation, blood gases and acid–base balance. Neurons of the retrotrapezoid nucleus (RTN) and medullary raphe are both implicated in this mechanism as respiratory chemosensors, but recent pharmacological work suggested that the CO2/H+ sensitivity of RTN neurons is mediated indirectly, by raphe‐derived serotonin acting on 5‐HT7 receptors. To investigate this further, we characterized Htr7 transcript expression in phenotypically identified RTN neurons using multiplex single cell qRT‐PCR and RNAscope. Although present in multiple neurons in the parafacial region of the ventrolateral medulla, Htr7 expression was undetectable in most RTN neurons (Nmb +/Phox2b+) concentrated in the densely packed cell group ventrolateral to the facial nucleus. Where detected, Htr7 expression was modest and often associated with RTN neurons that extend dorsolaterally to partially encircle the facial nucleus. These dorsolateral Nmb +/Htr7 + neurons tended to express Nmb at high levels and the intrinsic RTN proton detectors Gpr4 and Kcnk5 at low levels. In mouse brainstem slices, CO2‐stimulated firing in RTN neurons was mostly unaffected by a 5‐HT7 receptor antagonist, SB269970 (n = 11/13). At the whole animal level, microinjection of SB269970 into the RTN of conscious mice blocked respiratory stimulation by co‐injected LP‐44, a 5‐HT7 receptor agonist, but had no effect on CO2‐stimulated breathing in those same mice. We conclude that Htr7 is expressed by a minor subset of RTN neurons with a molecular profile distinct from the established chemoreceptors and that 5‐HT7 receptors have negligible effects on CO2‐evoked firing activity in RTN neurons or on CO2‐stimulated breathing in mice.Key points Neurons of the retrotrapezoid nucleus (RTN) are intrinsic CO2/H+ chemosensors and serve as an integrative excitatory hub for control of breathing.Serotonin can activate RTN neurons, in part via 5‐HT7 receptors, and those effects have been implicated in conferring an indirect CO2 sensitivity.Multiple single cell molecular approaches revealed low levels of 5‐HT7 receptor transcript expression restricted to a limited population of RTN neurons.Pharmacological experiments showed that 5‐HT7 receptors in RTN are not required for CO2/H+‐stimulation of RTN neuronal activity or CO2‐stimulated breathing.These data do not support a role for 5‐HT7 receptors in respiratory chemosensitivity mediated by RTN neurons.

Работы по ядерной спектроскопий выполненные с участием Монгольских Сотрудников в ЛЯП

Decay schemes of 150-157Er and 148-161Ho have been studied. β-, γ-, X-rays and conversion electrons were investigated and ten new isotopes and isomeric states were identified at the first time. Endpoint energies of β*-spectrum were measured using an intrinsic germanium detector, and Qec values have been obtained. A group of proton emitters of Au, Ir, Re and Ta have been identified, and the proton drip line was determined. Anisotropics of the gamma rays in well deformed Yb isotopes have been measured from the decay of radioactive Lu oriented at at low temperature. Multipole mixing ratio of the hundreds transitions have been deduced, about 170 of them uniquely and unambiguous spin assignments were made for 30 levels. External perturbations of two 171Yb levels have been observed.
 Study of the decay for 112-118In isotopes were the first nuclear physics experimental work in Mongolia. Mini-orange β*-spectrometer was constracted in Dubna for the inner conversion electrons measurements for neutron deficit nuclides. Measured conversion coclTicicnts were used for determination the transition mullipolaritics. A specific method for efficiency calibration of mini-orange spectrometer was applied using the continuous β* -spectrum of 90Sr in energy range from 500 to 2200 keV.

Reducing Calibration Time in PET Systems Based on Monolithic Crystals.

In the past years, the gamma-ray detector designs based on the monolithic crystals have demonstrated to be excellent candidates for the design of high-performance PET systems. The monolithic crystals allow to achieve the intrinsic detector resolutions well below state-of-the-art; to increase packing fraction thus, increasing the system sensitivity; and to improve lesion detectability at the edges of the scanner field of view (FOV) because of their intrinsic depth of interaction (DOI) capabilities. The bottleneck to translate to the clinical PET systems based on a large number of monolithic detectors is eventually the requirement of mechanically complex and time-consuming calibration processes. To mitigate this drawback, several methods have been already proposed, such as using non-physically collimated radioactive sources or implementing the neuronal networks (NN) algorithms trained with simulated data. In this work, we aimed to simplify and fasten a calibration process of the monolithic based systems. The Normal procedure consists of individually acquiring a 11 × 11 22Na source array for all the detectors composing the PET system and obtaining the calibration map for each module using a method based on the Voronoi diagrams. Two reducing time methodologies are presented: (i) TEST1, where the calibration map of one detector is estimated and shared among all others, and (ii) TEST2, where the calibration map is slightly modified for each module as a function of their detector uniformity map. The experimental data from a dedicated prostate PET system was used to compare the standard calibration procedure with both the proposed methods. A greater similarity was exhibited between the TEST2 methodology and the Normal procedure; obtaining spatial resolution variances within 0.1 mm error bars and count rate deviations as small as 0.2%. Moreover, the negligible reconstructed image differences (13% deviation at most in the contrast-to-noise ratio) and almost identical contrast values were reported. Therefore, this proposed method allows us to calibrate the PET systems based on the monolithic crystals reducing the calibration time by approximately 80% compared with the Normal procedure.

The microdosimetric one-hit detector model for calculating the relative efficiency of the alanine pellet dosimeter in low energy X-ray beams

The alanine pellet dosimeter is a widely used reference dosimeter in both medical and industrial dosimetry across a wide range of beam qualities. A challenge when using alanine in low energy X-ray beams is its strong energy dependence; a significant decline is observed in the alanine response per dose-to-water relative to irradiations in a cobalt-60 reference field. This decrease is caused by the physical difference in alanine to water dose ratios combined with a radiochemical decrease in the intrinsic detector efficiency but is difficult to characterize mainly due to experimental uncertainties.Here we have applied a microdosimetric one-hit detector model to characterize the intrinsic detector efficiency of the alanine pellet dosimeter in low energy X-ray beams. Microdosimetric distributions were estimated from track structure calculations using the Geant4-DNA Monte Carlo software, where literature data was used to determine free model parameters.The model was applied to two sets of X-ray spectra with low (40 kV to 170 kV) and medium (100 kV to 300 kV) tube potential, covering a wide range of beam qualities. A relative detector efficiency of 0.937 was obtained for the low energy set with variations between −1.0% and 1.5%, whereas the efficiency varied between approximately 0.925 and 0.985 for the medium energy set, with a strong correlation to the half-value layer of the beam.It is concluded, that the half-value layer of an X-ray beam is not sufficient characterization to uniquely determine the relative efficiency of an alanine pellet dosimeter. However, the variation in relative efficiency with respect to the half-value layer is small.

High-resolution monolithic LYSO detector with 6-layer depth-of-interaction for clinical PET

The system spatial resolution of whole-body positron emission tomography (PET) is limited to around 2 mm due to positron physics and the large diameter of the bore. To stay below this ‘physics’-limit a scintillation detector with an intrinsic spatial resolution of around 1.3 mm is needed. Currently used detector technology consists of arrays of 2.6–5 mm segmented scintillator pixels which are the dominant factor contributing to the system resolution. Pixelated detectors using smaller pixels exist but face major drawbacks in sensitivity, timing, energy resolution and cost. Monolithic continuous detectors, where the spatial resolution is determined by the shape of the light distribution on the photodetector array, are a promising alternative. Without having the drawbacks of pixelated detectors, monolithic ones can also provide depth-of-interaction (DOI) information. In this work we present a monolithic detector design aiming to serve high-resolution clinical PET systems while maintaining high sensitivity. A 50 × 50 × 16 mm3 Lutetium–Yttrium oxyorthosilicate scintillation crystal with silicon photomultiplier (SiPM) backside readout is calibrated in singles mode by a collimated beam obtaining a reference dataset for the event positioning. A mean nearest neighbour (MNN) algorithm and an artificial neural network for positioning are compared. The targeted intrinsic detector resolution of 1.3 mm needed to reach a 2 mm resolution on system level was accomplished with both algorithms. The neural network achieved a mean spatial resolution of 1.14 mm FWHM for the whole detector and 1.02 mm in the centre (30 × 30 mm2). The MNN algorithm performed slightly worse with 1.17 mm for the whole detector and 1.13 mm in the centre. The intrinsic DOI information will also result in uniform system spatial resolution over the full field of view.

Self-Reset Image Sensor With a Signal-to-Noise Ratio Over 70 dB and Its Application to Brain Surface Imaging

In this study, we propose a complementary-metal-oxide-semiconductor (CMOS) image sensor with a self-resetting system demonstrating a high signal-to-noise ratio (SNR) to detect small intrinsic signals such as a hemodynamic reaction or neural activity in a mouse brain. The photodiode structure was modified from N-well/P-sub to P+/N-well/P-sub to increase the photodiode capacitance to reduce the number of self-resets required to decrease the unstable stage. Moreover, our new relay board was used for the first time. As a result, an effective SNR of over 70 dB was achieved within the same pixel size and fill factor. The unstable state was drastically reduced. Thus, we will be able to detect neural activity. With its compact size, this device has significant potential to become an intrinsic signal detector in freely moving animals. We also demonstrated in vivo imaging with image processing by removing additional noise from the self-reset operation.

Intrinsic detector sensitivity analysis as a tool to characterize ArcCHECK and EPID sensitivity to variations in delivery for lung SBRT VMAT plans.

PurposeTo investigate intrinsic sensitivity of an electronic portal imaging device (EPID) and the ArcCHECK detector and to use this in assessing their performance in detecting delivery variations for lung SBRT VMAT. The effect of detector spatial resolution and dose matrix interpolation on the gamma pass rate was also considered.Materials and methodsFifteen patients’ lung SBRT VMAT plans were used. Delivery variations (errors) were introduced by modifying collimator angles, multi‐leaf collimator (MLC) field sizes and MLC field shifts by ±5, ±2, and ±1 degrees or mm (investigating 103 plans in total). EPID and ArcCHECK measured signals with introduced variations were compared to measured signals without variations (baseline), using OmniPro‐I'mRT software and gamma criteria of 3%/3 mm, 2%/2 mm, 2%/1 mm, and 1%/1 mm, to test each system's basic performance. The measurement sampling resolution for each was also changed to 1 mm and results compared to those with the default detector system resolution.ResultsIntrinsic detector sensitivity analysis, that is, comparing measurement to baseline measurement, rather than measurement to plan, demonstrated the intrinsic constraints of each detector and indicated the limiting performance that users might expect. Changes in the gamma pass rates for ArcCHECK, for a given introduced error, were affected only by dose difference (DD %) criteria. However, the EPID showed only slight changes when changing DD%, but greater effects when changing distance‐to‐agreement criteria. This is pertinent for lung SBRT where the minimum dose to the target will drop dramatically with geometric errors. Detector resolution and dose matrix interpolation have an impact on the gamma results for these SBRT plans and can lead to false positives or negatives in error detection if not understood.ConclusionThe intrinsic sensitivity approach may help in the selection of more meaningful gamma criteria and the choice of optimal QA device for site‐specific dose verification.

Optical Chirality Detection Using a Topological Insulator Transistor

AbstractOptical chirality is an effective means in screening molecules and their enantiomers in bioengineering, and recently has garnered attention as an implementation of qubits in quantum information processing. The conventional detection of circularly polarized light (CPL) is based on phase retardation and polarization separation using multiple optical components. An intrinsic solid‐state chirality detection device would be favorable for easier integration and implementation. Optical spin injection to the spin‐momentum‐locked topological surface states of topological insulators (TIs) by circularly polarized light leads to a directional DC photocurrent and hence possible circular polarization detection. However, this DC photocurrent is also accompanied by other photo‐responses. Here, a photodetection strategy using a TI transistor which senses CPL without the use of any additional components is demonstrated, it achieves a uniform response over the entire device with a sensitivity ≈5.6%. The Stokes parameters can also be extracted by arithmetic operation of photocurrents obtained with different bias and gate for a complete characterization of a polarized light beam. Therefore, this method enables chirality detection and Stokes parameter analysis using a single device. The proposed miniaturized intrinsic chirality detectors facilitate polarimetry sensing in applications from circular dichroism spectroscopy to biomedical diagnosis.

Distractor-aware discrimination learning for online multiple object tracking

Online multi-object tracking needs to overcome the intrinsic detector deficiencies, e.g., missing detections, false alarms, and inaccurate detection responses, to grow multiple object trajectories without using future information. Various distractions exist during this growing process like background clutters, similar targets, and occlusions, which present a great challenge. We in this work propose a method for learning a distractor-aware discriminative model that can handle continuous missed and inaccurate detection problems due to the occlusion or the motion blur. To deal with target appearance variations, a relational attention learning mechanism is proposed to capture the distinctive target appearances by selectively aggregating features from history states with weights extracted from their appearance topological relationship. Based on the discrimination model, a multi-stage tracking pipeline is designed for automatic trajectory initialization,propagation, and termination. Extensive experimental analyses and comparisons demonstrate its state-of-the-art performance on widely used challenging MOT16 and MOT17 benchmarks. The source code of this work is released to facilitate further studies on the multi-object tracking problem.11Implementation code link: https://github.com/ZongweiZhou1/DDLTracker

Study on the noise characteristics of GaAs-based blocked-impurity-band (BIB) detectors

Terahertz (THz) photodetector has attracted great attention from worldwide scientists for its applications in security check, biomedical treatment, and astronomical observation. In the performance evaluation of the THz photodetector, the noise level is one of the critical parameters. The Gallium Arsenide (GaAs) blocked-impurity-band (BIB) detector, which is fabricated from intrinsic GaAs-based photoconductive detectors, reveals an attractive advantage of low dark current value and high signal to noise ratio (SNR). In this work, the epitaxial GaAs BIB detector was fabricated and its noise behavior under various bias was investigated at the temperature of 3.5 K. The measured noise consists of flicker noise (1/f noise), shot noise, thermal noise and measurement noise. The effect of bias and operation temperature (TOpe) on the noise characteristics of a GaAs-based BIB detector has been studied by numerical simulation for suppressing device noise. According to the simulation, the total noise gradually increases with TOpe, and dominated by the shot noise. Our work may provide useful theoretical support to solve the critical epitaxial growth bottleneck of GaAs BIB detector and improve its performance for the applications of astronomical observation, security check, etc.