Stable Detector Research Articles

Alpha radiation induced space charge stability effects in semi-insulating silicon carbide semiconductors compared to diamond

Although the use of semi-insulating silicon carbide material for radiation detection purposes has been previously demonstrated, its use in practical applications has been inhibited by space charge stability issues caused by defect concentrations within the material, the so called polarisation effect, by which the count rate and resultant spectrum changes with irradiation time.This is a result of the charge carriers generated during irradiation filling deep level defects within the material, causing space charge buildup and de-activating that trap level until the trapped charge is re-emitted. Consequently, the time dependence of the polarisation effect has been determined by a combination of parameters that can be influenced during operation, namely the incident radiation intensity, ambient light, temperature and bias. The material properties have also been considered through the use of materials with different defect capture cross sections, concentrations and energy level.A thorough characterisation of the alpha irradiation induced polarisation phenomenon in semi-insulating silicon carbide has been conducted to demonstrate that stable operation detectors are in fact possible with this material. The effects were compared to single crystal diamond and polycrystalline diamond, which are known to exhibit similar polarisation issues.The polarisation rate as an effect of incident flux, bias and temperature was determined, with the depolarisation rate as a function of ambient light and bias also demonstrated. Consequently it has been shown that stable operation can be maintained for detectors made from semi-insulating SiC material of active thickness 350μm at incident alpha radiation fluxes of <0.7 alphas per second per mm2 with high operating biases (>±400V). Furthermore, polarisation can be suitably managed or reduced through the use of light illumination and elevated temperatures (373K).

A failure detector for HPC platforms

Building an infrastructure for exascale applications requires, in addition to many other key components, a stable and efficient failure detector. This article describes the design and evaluation of a robust failure detector that can maintain and distribute the correct list of alive resources within proven and scalable bounds. The detection and distribution of the fault information follow different overlay topologies that together guarantee minimal disturbance to the applications. A virtual observation ring minimizes the overhead by allowing each node to be observed by another single node, providing an unobtrusive behavior. The propagation stage uses a nonuniform variant of a reliable broadcast over a circulant graph overlay network and guarantees a logarithmic fault propagation. Extensive simulations, together with experiments on the Titan Oak Ridge National Laboratory supercomputer, show that the algorithm performs extremely well and exhibits all the desired properties of an exascale-ready algorithm.

Performance evaluation of local descriptors for maximally stable extremal regions

Visual feature descriptors are widely used in most computer vision applications. Over the past several decades, local feature descriptors that are robust to challenging environments have been proposed. Because their characteristics differ according to the imaging condition, it is necessary to compare their performance consistently. However, no pertinent research has attempted to establish a benchmark for performance evaluation, especially for affine region detectors, which are mainly used in object classification and recognition. This paper presents an intensive and informative performance evaluation of local descriptors for the state-of-the-art affine-invariant region detectors, i.e., maximally stable extremal region detectors. We evaluate patch-based and binary descriptors, including SIFT, SURF, BRIEF, FREAK, the shape descriptor, LIOP, DAISY, GSURF, RFDg, and CNN descriptors. The experimental results reveal the relative performance and characteristics of each descriptor.

Mid-wave infrared liquid crystal shutter for breathalyzer applications

There exists a problem with an in situ diagnostics of contamination of ethyl alcohol in a human being exhaled air. When ethyl alcohol in a mouth blowing (in a gaseous state) exists, the characteristic C H stretch absorption bands in CH 3 and CH 2 functional groups in ethanol (CH 3 CH 2 OH) appear at a wavelength of λ = 3.42 μm. To investigate the presence of ethyl alcohol in exhaled human air, the light beam of λ = 3.42 μm is passing through an air sample. If one alternately measures the intensity of the investigated beam and the reference, a percentage of ethanol in the air sample can be estimated using a sensitive nondispersive infrared (NDIR) system with a stable operating flow mass detector. To eliminate a mechanical chopper and noise generating stepper motors, a photonic chopper as a liquid crystal shutter for λ = 3.42 μm has been designed. For this purpose, an innovative infrared nematic liquid crystal mixture was intentionally prepared. The working mixture was obtained by a selective removal of C H bonds and its exchange by heavier polar substituents, what ensures a lack of absorption band of C H bonds. The paper presents theory, concept and final experimental results of the infrared nematic liquid crystals mixture and the liquid crystal shutter for breathalyzer applications.

Rapid, stable and self-powered perovskite detectors via a fast chemical vapor deposition process

Organometal halide perovskite materials are outstanding candidates not only for solar cells but also for photo-detection.

Computed tomography approach to quality control of the Inconel 718 components obtained by additive manufacturing (SLM)

Computed tomography (CT) has been used in the industry for more than 30 years, mainly due to the interest of its application in non-destructive tests. Recently, the development of more powerful tools with more stable X-ray sources and detectors drives their use in manufacturing and quantitative metrology with some micrometer precision. This technology is the best choice for verifying components manufactured by Selective Laser Melting (SLM) or additive manufacturing using pre-deposited powder layer by layer in a protective atmosphere. The main benefit offered by SLM is the freedom for designing complex geometries. However, the assurance of homogeneous density in some components limits its use. The geometrical quality control of the whole component needs new solutions.The objective of this research work is to verify components through computerized tomography for both porosity detection and geometrical reconstruction of simple entities in INCONEL® 718 components manufactured by SLM. Traceability is assured using CMM and confocal microscopy.

Long-Term Stable Surface Treatments on CdTe and CdZnTe Radiation Detectors

The spectral resolution and charge collection efficiency (CCE) of cadmium telluride (CdTe) and cadmium zinc telluride (CZT) room-temperature x-ray and gamma-ray detectors are often limited by high surface leakage current due to conducting surface species created during detector fabrication. Surface treatments play a major role in reduction of this surface leakage current. The effect of various types of surface etching and passivation on the leakage current and thereby the spectral energy resolution, CCE, and internal electric field profile of CdTe/CZT detectors has been studied. The main aim of this work is preparation of long-term stable detectors with strongly reduced leakage current. The time stability of the current–voltage characteristic and spectral resolution was investigated during 21 days and 1 year, respectively, after performing surface treatments. Our results suggest that the optimal detector preparation method is chemomechanical polishing in bromine-ethylene glycol solution followed by chemical etching in bromine-methanol solution then surface passivation in potassium hydroxide or ammonium fluoride (NH4F/H2O2). Detectors prepared using this optimal treatment exhibited low leakage current, high spectral resolution, and long-term stability compared with those subjected to other surface preparation methods.

Keypoint-based copy-move detection scheme by adopting MSCRs and improved feature matching

Copy-move detection is to find the existence of duplicated regions in an image. In this paper, an effective method based on region features is proposed to detect copy-move forgeries, especially when the image is multiple copied or with multiple copy-move groups. Firstly, maximally stable color region detector is applied to extract features, and these features are represented by Zernike moments. Then an improved matching strategy considering n best-matching features is applied to deal with the multiple-copied problem. Moreover, a hierarchical cluster algorithm is developed to estimate transformation matrices and confirm the existence of forgery. Based on these matrices, the duplicated regions can be located at pixel level. Experimental results indicate that the proposed scheme outperforms other similar state-of-the-art techniques.

High precision momentum calibration of the magnetic spectrometers at MAMI for hypernuclear binding energy determination

We propose a new method for absolute momentum calibration of magnetic spectrometers used in nuclear physics, using the time-of-flight (TOF) differences of pairs of particles with different masses. In cases where the flight path is not known, a calibration can be determined by using the TOF differences of two pair combinations of three particles. A Cherenkov detector, read out by a radio frequency photomultiplier tube, is considered as the high-resolution and highly stable TOF detector. By means of Monte Carlo simulations it is demonstrated that the magnetic spectrometers at the MAMI electron-scattering facility can be calibrated absolutely with an accuracy δp/p≤10−4, which will be crucial for high precision determination of hypernuclear masses.

Advances on Sensitive Electron-Injection Based Cameras for Low-Flux, Short-Wave Infrared Applications

Short-wave infrared (SWIR) photon detection has become an essential technology in the modern world. Sensitive SWIR detector arrays with high pixel density, low noise levels and high signal-to-noise-ratios are highly desirable for a variety of applications including biophotonics, light detection and ranging, optical tomography, and astronomical imaging. As such many efforts in infrared detector research are directed towards improving the performance of the photon detectors operating in this wavelength range. We review the history, principle of operation, present status and possible future developments of a sensitive SWIR detector technology, which has demonstrated to be one of the most promising paths to high pixel density focal plane arrays for low flux applications. The so-called electron-injection (EI) detector was demonstrated for the first time (in 2007). It offers an overall system-level sensitivity enhancement compared to the p-i-n diode due to a stable internal avalanche-free gain. The amplification method is inherently low noise, and devices exhibit an excess noise of unity. The detector operates in linear-mode and requires only bias voltage of a few volts. The stable detector characteristics, makes formation of high yield large-format, and high pixel density focal plane arrays less challenging compared to other detector technologies such as avalanche photodetectors. Detector is based on the mature InP material system (InP/InAlAs/GaAsSb/InGaAs), and has a cutoff wavelength of 1700 nm. It takes advantage of a unique three-dimensional geometry and combines the efficiency of a large absorbing volume with the sensitivity of a low-dimensional switch (injector) to sense and amplify signals. Current devices provide high-speed response ~ 5 ns rise time, and low jitter ~ 12 ps at room temperature. The internal dark current density is ~ 1 μA/cm2 at room temperature decreasing to 0.1 nA/cm2 at 160 K. EI detectors have been designed, fabricated, and tested during two generations of development and optimization cycles. We review our imager results using the first-generation detectors. In the second-generation devices, the dark current is reduced by two orders of magnitude, and bandwidth is improved by 4 orders of magnitude. The dark current density of the EI detector is shown to outperform the state-of-the-art technology, the

Characterisation of Silicon Diode Arrays for Dosimetry in External Beam Radiation Therapy

Modern stereotactic radiation therapy modalities utilize small beams and large dose gradients to deliver radiation in few fractions, reducing the possibility to correct for mistakes during the treatment process. Therefore, in order to ensure best possible treatment for the patient, quality assurance for such treatments necessitates a stable, linear, and sensitive radiation detector with high spatial resolution and radiation hardness. In this work, two silicon detector arrays with high spatial resolution have been characterized by 6 MV and 18 MV medical LINAC irradiation, and 5.5 MeV He2+ heavy ion microprobe. A maximum discrepancy of 0.6 mm in field size has been found when comparing to two-dimensional radiochromic film dose profile, and charge collection efficiency obtained by means of ion beam induced charge collection (IBICC) is 66% when operating the array in photovoltaic mode. Radiation damage study by photons and photoneutrons is presented.

Sensitive and transportable gadolinium-core plastic scintillator sphere for neutron detection and counting

Neutron detection forms a critical branch of nuclear-related issues, currently driven by the search for competitive alternative technologies to neutron counters based on the helium-3 isotope. The deployment of plastic scintillators shows a high potential for efficient detectors, safer and more reliable than liquids, more easily scalable and cost-effective than inorganic. In the meantime, natural gadolinium, through its 155 and mostly 157 isotopes, presents an exceptionally high interaction probability with thermal neutrons. This paper introduces a dual system including a metal gadolinium core inserted at the center of a high-scale plastic scintillator sphere. Incident fast neutrons are thermalized by the scintillator shell and then may be captured with a significant probability by gadolinium 155 and 157 nuclei in the core. The deposition of a sufficient fraction of the capture high-energy prompt gamma signature inside the scintillator shell will then allow discrimination from background radiations by energy threshold, and therefore neutron detection. The scaling of the system with the Monte Carlo MCNPX2.7 code was carried out according to a tradeoff between the moderation of incident fast neutrons and the probability of slow neutron capture by a moderate-cost metal gadolinium core. Based on the parameters extracted from simulation, a first laboratory prototype for the assessment of the detection method principle has been synthetized. The robustness and sensitivity of the neutron detection principle are then assessed by counting measurement experiments. Experimental results confirm the potential for a stable, highly sensitive, transportable and cost-efficient neutron detector and orientate future investigation toward promising axes.

High-performance diamond radiation detectors produced by lift-off method

For stable semiconductor detector operation under harsh environments, an ideal single-crystal diamond without a charge trapping centre is required. For this study, a self-standing single-crystal CVD diamond was fabricated using a lift-off method. The reduction of charge trapping factors such as structural defects, point defects, and nitrogen impurities, was attempted using 0.2% of low-methane concentration growth and using a full metal seal chamber. A high-quality self-standing diamond with strong free-exciton recombination emission was obtained. Charge collection efficiencies were 100.1% for holes and 99.8% for electrons, provided that and . Energy resolutions were 0.38% for both holes and electrons. We produced a high-performance diamond radiation detector using the productive lift-off method.

Development of stable nuclear radiation detectors based on n-silicon/cobalt-phthalocyanine heterojunctions

Abstract n-silicon/cobalt-phthalocyanine (CoPc) heterojunction based nuclear detectors have been fabricated using thermally evaporated CoPc films. Two different thicknesses of CoPc film (viz. 100 nm and 200 nm) were tried out to make detectors by depositing on chemically polished n-Si wafers. Gold film on CoPc was used as electrical contact. The detectors were characterized by measuring their current–voltage ( I–V ) and leakage current–time ( I–t ) characteristics, followed by alpha energy spectra obtained on exposure to α-particles. Variation of alpha energy resolution with applied reverse bias voltage for each of the detectors was also studied. The detectors showed very low leakage current and high breakdown voltage as compared to conventional Au/n-Si surface barrier detectors. Finally, the durability of the detectors was established by measuring their I–V characteristics and energy resolution for nearly 15 months.

Development of a Schottky CdTe Medipix3RX hybrid photon counting detector with spatial and energy resolving capabilities

A multichip CdTe-Medipix3RX detector system was developed in order to bring the advantages of photon-counting detectors to applications in the hard X-ray range of energies. The detector head consisted of 2×2 Medipix3RX ASICs bump-bonded to a 28mm×28mm e− collection Schottky contact CdTe sensor. Schottky CdTe sensors undergo performance degrading polarization which increases with temperature, flux and the longer the HV is applied. Keeping the temperature stable and periodically refreshing the high voltage bias supply was used to minimize the polarization and achieve a stable and reproducible detector response. This leads to good quality images and successful results on the energy resolving capabilities of the system.

Solid State Organic X-Ray Detectors Based on Rubrene Single Crystals

In this work we report the results on the investigation of rubrene single crystals as solid state direct ionizing radiation detectors. With the aim to understand how electrical properties, and in particular a large charge carrier mobility, affect the radiation detection process in organic semiconducting single crystals, we compare the detection performance of rubrene-based devices with those of 1,5-dinitronaphthalene (DNN)-based ones. DNN has been recently proven to be a stable and reliable X-ray direct detector, operating at very low voltages, in air and at room temperature, with a carrier mobility values about two orders of magnitude lower than rubrene. We demonstrate here that the large charge carrier mobility of rubrene crystals does not result in a better X-rays detection performance. In fact, rubrene devices are shown to be less performing than DNN as detectors, with lower sensitivity to X-rays, poorer stability and reproducibility, and longer rise and decay times of the signal.

Inshore ship detection using high-resolution synthetic aperture radar images based on maximally stable extremal region

We present a method for detecting inshore ships using high-resolution synthetic aperture radar (SAR) images. The method first applies preprocessing steps to obtain the solving region of an SAR image, suitable for the berthing rules. Then the ship candidates are extracted based on a maximally stable extremal region detector, while ship detection is applied using an improved constant false alarm rate (CFAR) detector. Finally, based on discrimination processing, false alarms are removed according to compactness, therefore the ultimate detection result is obtained without interference from strong terrestrial clutter or man-made objects. Experimental results show that this method could achieve effective detection of ships in harbors using high-resolution SAR images. This method can reduce the required computation time by 99.7%, compared with the traditional CFAR method.

Landsat-8 Operational Land Imager (OLI) Radiometric Performance On-Orbit

Expectations of the Operational Land Imager (OLI) radiometric performance onboard Landsat-8 have been met or exceeded. The calibration activities that occurred prior to launch provided calibration parameters that enabled ground processing to produce imagery that met most requirements when data were transmitted to the ground. Since launch, calibration updates have improved the image quality even more, so that all requirements are met. These updates range from detector gain coefficients to reduce striping and banding to alignment parameters to improve the geometric accuracy. This paper concentrates on the on-orbit radiometric performance of the OLI, excepting the radiometric calibration performance. Topics discussed in this paper include: signal-to-noise ratios that are an order of magnitude higher than previous Landsat missions; radiometric uniformity that shows little residual banding and striping, and continues to improve; a dynamic range that limits saturation to extremely high radiance levels; extremely stable detectors; slight nonlinearity that is corrected in ground processing; detectors that are stable and 100% operable; and few image artifacts.

Operation of a THGEM-based detector in low-pressure Helium

In view of a possible application as a charge-particle track readout for an Active Target Time Projection Chamber (AT-TPC), the operating properties of THick Gaseous Electron Multipliers (THGEM) in pure low-pressure Helium were investigated. This paper includes the effective gain dependence on pressure for different detector configurations (single-, double-, triple-cascade setup), long-term gain stability and energy resolution from tracks of 5.5 MeV alpha particles. Stable operational conditions and maximum detector gains of 104–107 have been achieved in pure Helium at pressure ranging from 100 torr up to 760 torr. Energy resolution of 6.65% (FWHM) for 690 keV of energy deposited by 5.5 MeV alpha particles at 350 torr was measured. The expected energy resolution for the full track is around 2.4% (FWHM). These results, together with the robustness of THGEM electrodes against spark damage, make THGEM structures highly competitive compared to other technologies considered for TPC applications in an active target operating with pure noble gases, requiring a high dynamic range and a wide operating pressure range down to few hundred torr.

Introduction of the in-orbit test and its performance for the first meteorological imager of the Communication, Ocean, and Meteorological Satellite

Abstract. The first geostationary Earth observation satellite of Korea – the Communication, Ocean, and Meteorological Satellite (COMS) – was successfully launched on 27 June 2010. After arrival at its operational orbit, the satellite underwent an in-orbit test (IOT) that lasted for about 8 months. During the IOT period, the main payload for the weather application, the meteorological imager, went through successful tests for demonstrating its function and performance, and the test results are introduced here. The radiometric performance of the meteorological imager (MI) is tested by means of signal-to-noise ratio (SNR) for the visible channel, noise-equivalent differential temperature (NEdT) for the infrared channels, and pixel-to-pixel nonuniformity for both the visible and infrared channels. In the case of the visible channel, the SNR of all eight detectors is obtained using the ground-measured parameters with the background signals obtained in orbit. The overall performance shows a value larger than 26 at 5% albedo, exceeding the user requirement of 10 by a significant margin. Also, the relative variability of detector responsivity among the eight visible channels meets the user requirement, showing values within 10% of the user requirement. For the infrared channels, the NEdT of each detector is well within the user requirement and is comparable with or better than the legacy instruments, except for the water vapor channel, which is slightly noisier than the legacy instruments. The variability of detector responsivity of infrared channels is also below the user requirement, within 40% of the requirement, except for the shortwave infrared channel. The improved performance result is partly due to the stable and low detector temperature obtained due to spacecraft design, i.e., by installing a single solar panel on the opposite side of the MI.