Active Area Of Detector Research Articles

Bragg grating etalon-based optical fiber for ultrasound and optoacoustic detection

Fiber-based interferometers receive significant interest as they lead to miniaturization of optoacoustic and ultrasound detectors without the quadratic loss of sensitivity common to piezoelectric elements. Nevertheless, in contrast to piezoelectric crystals, current fiber-based ultrasound detectors operate with narrow ultrasound bandwidth which limits the application range and spatial resolution achieved in imaging implementations. We port the concept of silicon waveguide etalon detection to optical fibers using a sub-acoustic reflection terminator to a Bragg grating embedded etalon resonator (EER), uniquely implementing direct and forward-looking access to incoming ultrasound waves. Precise fabrication of the terminator is achieved by continuously recording the EER spectrum during polishing and fitting the spectra to a theoretically calculated spectrum for the selected thickness. Characterization of the EER inventive design reveals a small aperture (10.1 µm) and an ultra-wide bandwidth (160 MHz) that outperforms other fiber resonators and enables an active detection area and overall form factor that is smaller by more than an order of magnitude over designs based on piezoelectric transducers. We discuss how the EER paves the way for the most adept fiber-based miniaturized sound detection today, circumventing the limitations of currently available designs.

Experimental analysis of the electric field distribution in semi-insulating GaAs detectors via alpha particles

Semi-insulating gallium arsenide (SI GaAs) detectors offer a promising alternative to commercially available silicon detectors. They demonstrate superior radiation hardness and provide improved efficiency for gamma and X-ray detection, primarily attributed to their higher density. In this study, we examined 350 μm thick SI GaAs detectors featuring front-side Ti/Pt/Au Schottky contacts with varying contact areas, complemented by back-side Ni/AuGe/Au ohmic contacts spanning the entire area. First, the reverse current-voltage characteristics of the prepared detectors were measured. The dependence of the reverse current and the breakdown voltage on the Schottky contact area was revealed. As the contact area decreases, the reverse current decreases and the breakdown voltage increases. The detection performance of the detectors was evaluated by alpha spectrometry using an 241Am source. After irradiation of the detectors from the Schottky electrode, the measured alpha spectra show an increasing CCE with decreasing Schottky contact area. Finally, the correlation between the applied bias voltage and the extent of the active detector area from the edge of the detector contact was investigated.

Spreading of an active region of semi-insulating GaAs detectors after radiation degradation

The radiation hardness of GaAs detectors against high-energy electrons goes up to a few MGy. Their degradation is mainly connected to the decrease of the charge collection efficiency and the increase of the reverse current. On the other hand, an improvement in detection efficiency was observed at low degradation doses. The explanation that this could be caused by an enlargement of the detector active area due to spreading of the collecting electric field caused by radiation-induced defects is studied in this paper. We have used the alpha particles of 241Am, which interact in the GaAs surface layer, to study the enlargement of the detector active region after its degradation by 5 MeV electrons with doses ranging from 24 to 2000 kGy. The results show that the electric field spreads behind the Schottky contact metallization edges not only with increasing applied reverse bias but also with rising cumulative dose of radiation degradation in the dose range from 24 up to 100 kGy, followed by a slight reduction in area size. The electric collecting field keeps larger dimensions than before detector degradation for doses up to 600 kGy. For higher doses than 1000 kGy, the active area of the detector was reduced below its initial size before degradation. Moreover, the improvement of detection efficiency with increasing bias applied becomes weaker with increasing degradation dose. Radiation degradation affects the electric field distribution in semi-insulating GaAs detectors and the results obtained may provide useful knowledge to preparation of multi-pixel GaAs structures for imaging and particle tracking.

Reconfigurable coaxial single-photon LIDAR based on the SPAD array.

The single-photon avalanche diode (SPAD) array with time-to-digital converter (TDC) circuits on each pixel is an excellent candidate detector for imaging LIDAR systems. However, the low fill-factor of the SPAD array does not allow for efficient use of laser energy when directly adopted in a LIDAR system. Here, we design a reconfigurable coaxial single-photon LIDAR based on the SPAD array and diffractive optical elements (DOEs). We use the DOE and beam expander to shape the laser beam into a laser dot matrix. The total divergence angle of the DOE spot beam is strictly matched to the total field of view (FOV) angle of the SPAD array. Meanwhile, each focused beamlet is individually matched to every active area of the SPAD array detector, which increases the use of output energy about 100 times compared to the diffusion illumination system. Besides, the system uses the active area as the minimum pixel and can support sub-pixel scanning, resulting in higher resolution images. Through this coaxial structure, two different telescope systems after transceiver switching can be reconfigured for imaging targets at different distances. Based on our single-photon LIDAR system, we achieved 3D imaging of targets at 100m and 180m using two different telescope configurations.

Breakthrough light harvesting in time-domain diffuse optics with 100 mm2 silicon photomultiplier

Time-Domain Diffuse Optics (TDDO) technologies are rapidly evolving towards compact and cheap devices, thus progressively reducing the gap with continuous-wave equivalent technologies while providing the additional advantages of higher information content and better depth penetration and selectivity. One of the key limitations for TDDO is the active area of microelectronic time-resolved single-photon detectors as it is not possible to efficiently focus Lambertian light exiting from highly scattering samples into small areas. Therefore, signal-to-noise ratio bottlenecks can be surpassed only by targeting a breakthrough in this direction. In this work we present the validation in laboratory settings of the largest detector (100 mm2 active area with 92% cells fill-factor) ever reported to our knowledge in TDDO applications. To objectively validate this device, we made use of established performance assessment protocols in the field of diffuse optics, which also define standard conditions enabling realistic benchmarking of novel devices. The detector demonstrated the largest light harvesting capability ever reported, capability to measure homogeneous optical properties in line with state-of-the-art devices, and superior depth penetration inside heterogeneous media (in reflectance geometry) with respect to all the previously reported technologies (i.e., >4 cm). The active area breakthrough permits to envisage the first TDDO measurements on different fruits in transmittance geometry, thus increasing the penetration depth with respect to the traditional reflectance approach and making it easier for a future evolution towards real time quality check of fruits on the conveyor belt.

Design and testing of long flexible printed circuits for the ATLAS High Granularity Timing Detector demonstrator

The High Granularity Timing Detector for the ATLAS upgrade is under construction to meet the challenges of the HL-LHC. In order to connect a module, the basic detector element, to the surrounding peripheral electronic board, a flexible printed circuit (FPC) is used as an interconnection for data transmission and power distribution. An identical design for all FPCs is required except for their length, depending on the module position on the detector active area. The design and qualification of a preliminary FPC version, manufactured in 13 different lengths (from 28.5 to 73.2 cm), are presented.

Study of efficiency and gain uniformity at different gas flow rates of a quad-GEM detector

A quad-GEM is particularly useful for its low ion back flow, excellent rate capability, good position resolution, high gain at relatively low operating voltage in the next generation high energy physics experiments. In this work, the efficiency and uniformity of gain of a prototype quad-GEM detector are studied. A simple method is used to estimate the efficiency with the help of an oscilloscope as a triggering and storage device. An efficiency of ≈ 95% is obtained at a voltage of ΔVGEM ≥ 340 V using cosmic muons as a source. A systematic study of the uniformity of gain over the active area of the detector is done with a Fe55 X-ray source.The uniformity of gain has a spread of 11.1% over the active area of the quad-GEM detector for ΔVGEM = 360 V.The effect of gas flow rate and direction of gas flow in determining the gain are investigated for the first time for a quad-GEM detector.It is observed that different flow rates does not affect the gain uniformity significantly. However, the overall gain of the detector initially increases with the gas flow rate and starts to saturate at a higher flow rate.

Novel Algorithm for Radon Real-Time Measurements with a Pixelated Detector.

Nowadays, radon gas exposure is considered one of the main health concerns for the population because, by carrying about half the total dose due to environmental radioactivity, it is the second cause of lung cancer after smoking. Due to a relatively long half-life of 3.82 days, the chemical inertia and since its parent Ra-226 is largely diffuse on the earth’s crust and especially in the building materials, radon can diffuse and potentially saturate human habitats, with a concentration that can suddenly change during the 24 h day depending on temperature, pressure, and relative humidity. For such reasons, ‘real-time’ measurements performed by an active detector, possibly of small dimensions and a handy configuration, can play an important role in evaluating the risk and taking the appropriate countermeasures to mitigate it. In this work, a novel algorithm for pattern recognition was developed to exploit the potentialities of silicon active detectors with a pixel matrix structure to measure radon through the α emission, in a simple measurement configuration, where the device is placed directly in air with no holder, no collection filter or electrostatic field to drift the radon progenies towards the detector active area. This particular measurement configuration (dubbed as bare) requires an α/β-discrimination method that is not based on spectroscopic analysis: as the gas surrounds the detector the α particles are emitted at different distances from it, so they lose variable energy amount in air depending on the traveled path-length which implies a variable deposited energy in the active area. The pixels matrix structure allows overcoming this issue because the interaction of α, β and γ particles generate in the active area of the detector clusters (group of pixels where a signal is read) of different shape and energy dispersion. The novel algorithm that exploits such a phenomenon was developed using a pixelated silicon detector of the TimePix family with a compact design. An α (Am-241) and a β (Sr-90) source were used to calibrate the algorithm and to evaluate its performances in terms of β rejection capability and α recognition efficiency. Successively, the detector was exposed to different radon concentrations at the ENEA-INMRI radon facility in ‘bare’ configuration, in order to check the linearity of the device response over a radon concentration range. The results for this technique are presented and discussed, highlighting the potential applications especially the possibility to exploit small and handy detectors to perform radon active measurements in the simplest configuration.

Fluorescence detection of a trapped ion with a monolithically integrated single-photon-counting avalanche diode

We report on the demonstration of fluorescence detection from a trapped ion using single-photon avalanche photodiodes (SPADs) monolithically integrated with a microfabricated surface ion trap. The SPADs are located below the trapping positions of the ions and designed to detect 370 nm photons emitted from single 174Yb+ and 171Yb+ ions. We achieve an ion/no-ion detection fidelity for 174Yb+ of 0.99 with an average detection window of 7.7(1) ms. We report a dark count rate as low as 1.2 kcps for room temperature operation. The fidelity is limited by laser scatter, dark counts, and heating that prevents holding the ion directly above the SPAD. We measure count rates from each of the contributing sources and fluorescence as a function of ion position. We use the ion as a calibrated light source along with measurements of the active detector area to estimate a SPAD quantum efficiency of 24 ± 1%.

Minimum Detectable Activity of Pb-210 in Skull From In vivo Measurements: Insights From the Literature

To address the urgent need for the retrospective assessment of the health conditions of people with a history of appreciable radon exposure, a novel technique that directly measures the characteristic γ-rays emitted from Pb-210 in the living skull was developed. Since the first pioneering study in 1968, this technique has experienced continued advancement over more than half a century, where the limit of detection of Pb-210 is a common criterion to assess the performance of the measuring devices. However, researchers have defined the limit of detection in assorted ways, and the measurement conditions often greatly differ from study to study, both of which significantly challenge interstudy comparisons and obscure how various factors make their impacts. In this work, we reanalyze the reported results in the literature according to the minimum detectable activity (MDA) defined by Currie and investigate the effects of key elements therein. Firstly, we focus on the reported background count rates and analyze their dependence on detector’s energy resolution and active area. Secondly, we turn to the reported calibration factors and conduct analysis in the same manner. Thirdly, we calculate MDA for each study and monitor its dependence on the active area of detector and measurement duration. In the limit of the largest achievable active area (∼75000 mm2), it is found that the asymptotic MDA is approximately 6 (4) Bq and 15 (11) Bq under 30 (60) min measurement using NaI-CsI scintillator and HPGe semiconductor detectors, respectively. Finally, we discuss these asymptotic MDA in the context of estimated Pb-210 activity in the skull resulted from a hypothetical history of radon exposure.

Development of THGEM-like detectors with diamond-like carbon resistive electrodes

We developed resistive THGEM (RTGEM) films with diamond-like carbon (DLC), a robust resistive material with adjustable resistivity. The RTGEM films were manufactured by coating DLC layers on PCB via magnetron sputtering and then mechanically drilling holes. RTGEM detector prototypes with different configurations with sensitive area ranging from 5 × 5 cm2 to 20 × 100 cm2 were successfully fabricated. To achieve higher gain, resistive well (RWELL) detectors were introduced by coupling single-faced RTGEM to anode PCB via resistive DLC layers. The RTGEM manufacturing process is simpler and efficient compared with the conventional THGEM with metallic electrodes, making it suitable for large-scale production. The resistive material can limit the energy of discharges occurring at high gas gains, making the detectors more robust. The single-stage RTGEM detectors achieved gains >103 and demonstrated good long-term gain stability. A large-area RTGEM detector (active area: 20 × 100 cm2) had good gain uniformity (∼12%). RWELL detectors achieved gains >8 × 103. Detailed fabrication process and performance study results are presented in this article.

Influence of Deposited Material Energy on Superconducting Properties of the WSi Films

WSi thin films have the advantages for creating SNSPDs with a large active area or array of detectors on a single substrate due to the amorphous structure. The superconducting properties of ultrathin WSi films substantially depends on their structure and thickness as the NbN films. Scientific groups investigating WSi films mainly focused only on changes of their thickness and the ratio of the components on the substrate at room temperature. This paper presents experiments to determine the effect of the bias potential on the substrate, the temperature of the substrate, and the peak power of pulsed magnetron sputtering, which is the equivalent of ionization, a tungsten target, on the surface resistance and superconducting properties of the WSi ultrathin films. The negative effect of the substrate temperature and the positive effect of the bias potential and the ionization coefficient (peak current) allow one to choose the best WSi films formation mode for SNSPD: substrate temperature 297 K, bias potential -60 V, and peak current 3.5 A.

Development and Validation of End-to-End Test for Stereotactic Radiosurgery

The purpose of this study is to evaluate End to End test and dosimetric test of small field SRS MapCHECK dosimeter. The Fundamental properties of the SRS MapCHECK Diode Detector such as reproducibility, linearity, Energy dependence, Dose rate dependency and output factor are studied for 6MV FFF energy photon beams. All dosimetric test carried out on a medical accelerator consisting High definition 120 multileaf collimator (HD120 MLC), provide stereotactic treatments. End to End test of SRSMapCHECK carried out with StereoPHAN Cylindrical Phantom with CT and MRI inserts. The E2E test includes MRI scan, CT scan, Target contouring on CT/MRI scan, MRI/CT image fusion, Treatment planning and Dose delivery. SRS MapCHECK comprise of 1013 solid state diode detector, are equally spaced at 2.47mm. The active detector area is 0.48mm x 0.48mm and resolution is 0.007mm3. The maximum field size is 7 X 7 cm2. Before to start dosimetric measurement the calibration of SRS MapCHECK and StereoPHAN is necessary. The calibration process includes background measurement, array calibration and StereoPHAN factor calculation. The reproducibility of SRS MapCHECK checked by measuring output for 5 consecutive days for 6MV FFF beam with field size 5x5cm2. The Linearity of dose measurement also evaluated. The response of SRS MapCHECK to different energy (6, 10 & 15MV) also studied. Dose rate dependency also studied by varying dose rate from 400 to 1400 MU/min. Output Factor for different field sizes ranging from 1 x 1 cm2 to 7 x 7 cm2 was measured. Geometric accuracy of inserts volumes are find with CT and MRI fusion. Actual Insert volumes of Central Sphere, Right Sphere, Left Sphere are 4.17cc and 0.52 cc, 0.52cc respectively. The TPS measured volume on CT scan is 4.09cc, 0.52cc and 0.53 cc respectively similarly on MRI TPS measured volume is 4.22cc, 0.50cc and 0.52cc. The % variation on CT volume is less than 2%. For MRI the % difference for right sphere is -4.0%, central and left side are less than 2% The reproducibility of SRS MapCHECK output is well within less than 2% of the first day measurement. The SRS MapCHECK showed linear dose response for energy 6 MV FFF. Energy Dependency checked for 6MV, 10MV and 15MV with fixed dose rate 600MU/min it showed linear response to energy. We found SRS MapCHECK are independent on dose rate. Output factor was measured and compared with pinpoint chamber 0.015cc. SRS MapCHECK showed under response compared to pinpoint chamber for field size 1 x 1 cm2 to 4 x 4 cm2 and showed over response from the 5 x 5 cm2 to 7 x 7 cm2 The gamma analysis done with Dose difference 3% and Dose to agreement 3mm, we also checked with DAT 2mm, 1mm with threshold 10%. The result of gamma passing is 97.6%, 96.8% and 95.8 % respectively. All dosimetric test performed on SRS MapCHECK are comparable with ionization chamber measurement and clinically acceptable. It is an effective tool for E 2 E test and patient’s specific QA for SRS Patients.

The design of a scintillation system based on SiPMs integrated with gain correction functionality

Abstract Use of SiPM has been considered as an alternative to PMT, because of its compact size, low-operating voltage, non-sensitive to electromagnetic, low costs and so on. The main limitation for the use of SiPM is due to its small sensitive area compared to PMT that limits the light collection, and therefore the sensor energy resolution. In this article we studied the effect of increasing the number of SiPM by connecting them in parallel to increase the active detection area. This allowed us to compare the different energy resolution measurements. 137Cs has been selected as reference to study the energy resolution for 662 keV gamma-rays. Another investigation was to compare the minimum detectable gamma energy under various SiPM configurations. It has been found that the use of 4 SiPM arrays can greatly improve the energy resolution up to 4% than only one SiPM array, meanwhile use of more than 2 SiPM arrays does not increase the energy resolution significantly. Thus we can conclude that for a large area of cylindrical scintillator (3 × 3 inches), the use of SiPMs are limited to a certain number or certain active area depending on the commercial SiPMs, and its cost should be less than traditional PMT for the cost-effective and compact size considerations. It is well known that the gain of SiPM varies with temperature. In this article, we also calibrated gain to guarantee the same position of photoelectric peak in response of different temperatures.

Single Transparent Piezoelectric Detector for Optoacoustic Sensing-Design and Signal Processing.

In this article, we present a simple and intuitive approach to create a handheld optoacoustic setup for near field measurements. A single piezoelectric transducer glued in between two sheets of polymethyl methacrylate (PMMA) facilitates nearfield depth profiling of layered media. The detector electrodes are made of indium tin oxide (ITO) which is both electrically conducting as well as optically transparent, enabling an on-axis illumination through the detector. By mapping the active detector area, we show that it matches the design form precisely. We also present a straightforward approach to determine the instrument response function, which allows to obtain the original pressure profile arriving at the detector. To demonstrate the validity of this approach, the measurement on a simple test sample is deconvolved with the instrument response function and compared to simulation results. Except for the sputter instrumentation, all required materials and instruments as well as the tools needed to create such a setup are available to standard scientific laboratories.

A normalization method of the volume and geometry of tooth for X-band in vivo EPR dosimetry

The accuracy of in vivo EPR tooth dosimetry may be influenced by the volume and geometry variations in teeth, especially when there is considerable non-uniform sensitivity distribution in the active detection area of the cavity. To solve this problem, the present research proposed a normalization method specifically for X-band EPR in vivo tooth dosimetry. The volume and geometry of the measured tooth were reconstructed by digital image processing with images of the tooth impression slices, which were obtained by a custom-made impression module. The sensitivity distribution in the active detection area was established based on experiments with a point sample. Consequently, a composite normalization process that could calibrate the evaluated dose effectively was carried out by taking into account the influences not only from tooth volume and geometry but also from the non-uniform distribution of sensitivity. The effect and practicability of the method were evaluated by incisor samples. Results showed that the standard deviation could be reduced a maximum of 54.8% approximately after the composite normalization, an improvement compared to results from solely tooth volume. The correlation coefficient of the dose-response curve could be improved from 0.731 to 0.986. The preliminary method provides an approach potentially useful on site after radiation accidents when dealing with the influence of variations in the tooth volume and geometry for X-band EPR in vivo dose estimations.

The ISS-CREAM Silicon Charge Detector for identification of the charge of cosmic rays up to Z = 26: Design, fabrication and ground-test performance

The Cosmic Ray Energetics And Mass experiment for the International Space Station (ISS-CREAM) is a space-borne mission designed for the precision measurement of the energy and elemental composition of cosmic rays. The Silicon Charge Detector (SCD), placed at the top of the ISS-CREAM payload, consists of 4 layers. Each layer has 2688 silicon pixels and associated electronics arranged in such a fashion that its active detection area of 78.2 × 73.6 cm2 is free of dead area. The foremost goal of the SCD is to efficiently and precisely measure the charge of cosmic rays passing through it. The 4-layer configuration was chosen to achieve the best precision in measuring the charge of cosmic rays within the constraints on the mass, volume and power allotted to it. The amount of material used for its support structure was minimized as well to reduce the chance of interactions of the cosmic ray within the structure. Given the placement of the SCD, its 4-layer configuration and the minimal amount of material in the cosmic-ray trajectory, the SCD is designed to measure the charge of cosmic rays ranging from protons to iron nuclei with excellent detection efficiency and charge resolution. We present the design and fabrication of the SCD as well as its performance during space environment tests which it underwent successfully. We also present its performance in charge measurement using heavy ions in a beam test at CERN, the European Organization for Nuclear Research.

Enzyme-Free Plasmonic Biosensor for Direct Detection of Neurotransmitter Dopamine from Whole Blood

Complex biological fluids without pretreatment, separation, or purification impose stringent limitations on the practical deployment of label-free plasmonic biosensors for advanced assays needed in point of care applications. In this work, we present an enzyme-free plasmonic neurotransmitter dopamine biosensor integrated with a microfluidic plasma separator. This integrated device allows the in-line separation of plasma directly from the bloodstream and channels it to the active detection area, where inorganic cerium oxide nanoparticles function as local selective dopamine binding sites through strong surface redox reaction. A thorough understanding and engineering of the nanoparticles is carried out to maximize its dopamine sensitivity and selectivity. We obtain detection of dopamine at 100 fM concentration in simulated body fluid and 1 nM directly from blood without any prior sample preparation. The detection selectivity is found to be at least five-times higher compared to the common interfering species. This demonstration shows the feasibility of the practical implementation of the proposed plasmonic system in detection of variety of biomarkers directly from the complex biological fluids.

On-chip THz spectrometer for bunch compression fingerprinting at fourth-generation light sources.

The layout of an integrated millimetre-scale on-chip THz spectrometer is presented and its peformance demonstrated. The device is based on eight Schottky-diode detectors which are combined with narrowband THz antennas, thereby enabling the simultaneous detection of eight frequencies in the THz range on one chip. The size of the active detector area matches the focal spot size of superradiant THz radiation utilized in bunch compression monitors of modern linear electron accelerators. The 3 dB bandwidth of the on-chip Schottky-diode detectors is less than 10% of the center frequency and allows pulse-resolved detection at up to 5 GHz repetition rates. The performance of a first prototype device is demonstrated at a repetition rate of 100 kHz at the quasi-cw SRF linear accelerator ELBE operated with electron bunch charges between a few pC and 100 pC.

Geometry and algorithms to expand 2θ coverage of a 2D detector

A two-dimensional (2D) diffraction pattern is an image representing the diffraction intensity distribution over the detected area. For data evaluations of various materials characterization, such as phase identification, stress, texture, and crystal size, this distribution is further converted into the intensity distribution over 2θ or γ angles. For many applications, especially phase analysis and structure refinement, it is crucial for the two-dimensional (2D) pattern to have a large 2θ range sufficient to cover as many diffraction rings as necessary. The 2θ range covered by a 2D detector is determined by the size of the detector active area and the detector distance from the sample. In order to expand the 2θ coverage with a given 2D detector, one may collect several 2D frames at various swing angles and then merge the multiple frames, or scan the 2D detector over the desired 2θ range during the data collection. This paper introduces the geometry and algorithms to produce accurate 2D diffraction patterns with expanded 2θ coverages from multiple images or scanned images.