Detection Properties Research Articles

Multidimensional model to correct PV device performance measurements taken under diffuse irradiation to reference conditions

In the domain of solar irradiance measurements, a wide range of irradiation conditions exist in indoor and outdoor environments. While the primary calibration of reference solar irradiance detectors is usually performed using only direct irradiance, secondary calibrations are conducted with a diffuse incident irradiance component. If the optical detector properties vary between the reference and the device under test, spectral and angular dependencies of incident irradiance and the detectors’ responsivities may result in a mismatch when referring to defined reference conditions. This becomes particularly significant when photovoltaic (PV) devices are measured under global natural sunlight. In the field of PV metrology, diffuse solar irradiance is commonly considered to be isotropic, which is generally not the case. In this work, we present a novel multidimensional model that introduces spectral-angular effects to this field, with a focus on quantifying their impact on high-accuracy device calibration. Our enhanced approach allows anisotropic solar spectral radiance to be considered for any device orientation, including spectrally resolved ground reflections. To account for these effects, we consider both the spectral radiance of the source and the angular dependent spectral responsivities of the detectors. Angular mismatches of more than 1% were found for the examples investigated. This allowed detailed studies to be carried out on the impact of the detectors’ optical losses and on the resulting mismatch of spectral and angular properties. Our model allows the spectral and angular effects to be determined and corrected, resulting in the measurement uncertainties for high-accuracy outdoor measurements decreasing significantly. It can be also used in other areas of photometric and radiometric applications, where a wide range of irradiance characteristics have an effect on measurements. As a consequence of this study, we propose assigning a directional property to the reference condition defined in international standards (i.e., direct beam only).

Design and Bolometer Characterization of the SPT-3G First-Year Focal Plane

During the austral summer of 2016-17, the third-generation camera, SPT-3G, was installed on the South Pole Telescope, increasing the detector count in the focal plane by an order of magnitude relative to the previous generation. Designed to map the polarization of the cosmic microwave background, SPT-3G contains ten 6-in-hexagonal modules of detectors, each with 269 trichroic and dual-polarization pixels, read out using 68x frequency-domain multiplexing. Here we discuss design, assembly, and layout of the modules, as well as early performance characterization of the first-year array, including yield and detector properties.

FPGA and Embedded Systems Based Fast Data Acquisition and Processing for GEM Detectors

Gas electron multiplier (GEM) detectors (Sauli in Nucl Instrum Methods Phys Res A 805:2–24, 2016. https://doi.org/10.1016/j.nima.2015.07.060 (special issue in memory of Glenn F. Knoll); Buzulutskov in Instrum Exp Tech 50(3):287–310, 2007. https://doi.org/10.1134/S0020441207030013) are widely used for detection of ionizing radiation. When used in the proportional mode, they provide information about time, location, and energy of a detected particle (Chernyshova et al. in Fusion Eng Design, 2017. https://doi.org/10.1016/j.fusengdes.2017.03.107; Altunbas et al. in Nucl Instrum Methods Phys Res A 490(1–2):177–203, 2002. https://doi.org/10.1016/S0168-9002(02)00910-5. http://linkinghub.elsevier.com/retrieve/pii/S0168900202009105). Modern technologies allow full utilization of detector properties, by acquiring the waveform of output current pulses and processing them using sophisticated digital signal processing (DSP) algorithms. The current pulses must be digitized at high speed (up to 125 MHz) with high resolution (up to 12-bits). Due to the high volume of the produced data, it is necessary to provide the high-performance data acquisition system (DAQ) to transmit the data to processing units. Efficient processing of the GEM data requires distributed parallel processing system to perform multiple tasks (Czarski et al. in Rev Sci Instrum 87(11), 11E336, 2016. https://doi.org/10.1063/1.4961559): (1) Filter out the background and transmit only hit related data. (2) Extract the parameters of a hit, describing the time and charge (related to energy). (3) Estimate the hit position by combining information from multiple anode pads. (4) In case of 2D GEM detectors, correlate pulses received from X and Y pads (pixels) or W, U and V pads (pixels). (5) Separate the hits overlapping in space or in time (if possible) to support detector operation at higher rates. The above functionalities may be achieved in different hardware architectures. The typical hardware platforms include FPGA chips, standard or embedded computer systems with different computation accelerators (Wojenski et al. in J Instrum 11(11):C11035, 2016. http://stacks.iop.org/1748-0221/11/i=11/a=C11035; Nowak et al. in J Phys Conf Ser 513(5):052–024, 2014. https://doi.org/10.1088/1742-6596/513/5/052024. http://stacks.iop.org/1742-6596/513/i=5/a=052024?key=crossref.c5912cfa72c30b309821e14c4384948f. The paper shows possible solutions with their feasibility for particular applications.

Decomposition of the dose conversion factor based on fluence spectra of secondary charged particles: Application to lateral dose profiles in photon fields.

The dose conversion factor plays an important role in the dosimetry by enabling the absorbed dose in the sensitive volume of a detector to be converted into the absorbed dose in the surrounding medium (in most cases water). The purpose of this paper is to demonstrate that a specific fluence-based approach for the decomposition of the dose conversion factor is in particular useful for the interpretation of the influences of detector properties on measurements under nonreference conditions. Data for the dose conversion factor and secondary fluence spectra were obtained by the Monte Carlo method. The calculation of the secondary charged particle fluence (electrons and positrons) in the sensitive detector volume was imbedded into the code for the calculation of absorbed dose in the detector. The decomposition method into subfactors is based on the use of these fluence data applied to a stepwise transition from the dose at the point of measurement next to a pure water detector and finally to the fully simulated detector geometry. Each subfactor is obtained as a ratio, at which the stopping power only is different in the numerator and the denominator or at which the fluence only is different in the numerator and the denominator. This method was applied at photon dose profiles obtained in water at different radiation qualities and with various detectors of cylindrical type. The resulting subfactors can be well identified as a stopping power ratio and as perturbation factors each reflecting particular detector properties. Two of them (f1 and f4 ) are equivalent with perturbation factors which have already been introduced by other authors previously. These are the volume perturbation factor and the extracameral perturbation factor. Subfactor f2 denoted as medium perturbation factor was found to resemble the density perturbation factor. Results obtained for the volume perturbation factor applied to dose profiles measured with cylindrical detectors confirm that the volume effect can be well described by a convolution of the true profile in water with a Gaussian kernel. It was found that the sigma parameter depends on the cylinder radius only and amounts almost exactly to half of its value. The medium perturbation factor strongly depends on the density of the detector medium. For an air-filled detector, the influence of the air again can be described by a Gauss convolution, however, with a less good agreement. For detectors with a density of the cavity medium larger than that of water, for instance, for a diamond detector, it was found that there is a tendency of compensation between the volume averaging effect and the medium effect. The fluence-based decomposition of the dose conversion factor leads to a fluence-based formulation of perturbation factors, referred to as volume, medium, and extracameral perturbation factor. These factors offer useful explanations for the behavior of detectors in nonreference conditions. An example was given for cylindrical detectors at dose profile measurements.

OA237] The output factor measurements of cyberknife system using various detectors

Purpose In Stereotactic Radiosurgery, the extremely high radiation dose is delivered to the target in a single or few fractions using narrow radiation fields. The radiation fields are collimated with 12 fixed circular collimators ranging from 5 to 60 mm in diameter in CyberKnife which is a robotic radiosurgery system. The accuracy of the output factors directly affects the accuracy of treatment delivery to the patients. The output factor (OF) measurement of small fields is very problematic and the small field measurements are more sensitive to physical properties of detectors. The aim of the present study is to perform the relative OF measurements of 12 fixed collimators in CyberKnife system using different detectors. Methods In this study, the OF measurements of 12 fixed collimators were made with CyberKnife system at maximum dose depth in water equivalent RW3 slab phantom using PTW 60019 microDiamond, PTW 31014 0.015 cc PinPoint, PTW 31010 0.125 cc Semiflex, EBT3 Gafchromic film and GR-200A TLD. All detectors were positioned at the center of the radiation field with the point laser from treatment head. The measured data were compared with Monte Carlo (MC) factors. Results The OF values measured at 30 mm and greater collimator sizes were found similar for all detectors. The OF values decrease rapidly as the collimator size becomes smaller. The measured data with TLD and microDiamond detector at the smallest collimator sizes such as 7.5, 10, 12.5 and 15 mm were found very similar with MC factors. Conclusions 0.125 cc Semiflex ion chamber may lead to large uncertainties in the OF measurements for the smallest collimator sizes. TLD and microDiamond detector show similar results for all collimator sizes except 5 mm. TLD is an utilizable dosimetric tool in the small field OF measurements by means of its small active volume.

Carrier Transport Properties of CdTe Detector under Polarization Condition

Carrier Transport Properties of CdTe Detector under Polarization Condition

Theory of interaction-dependent instability in quantum detection by means of a Luttinger liquid tunnel junction: A rigorous theorem

The low-temperature regime of charge-qubit decoherence due to its Coulomb interaction with electrons tunneling through Luttinger liquid quantum-point contact (QPC) is investigated. The study is focused on quantum detector properties of Luttinger liquid QPC. It is shown, that in low-temperature limit the respective perturbative decoherence- and acquisition of information timescales both tend to diverge, thus, shadowing a true picture of low-temperature quantum detection for such quantum systems. Here I prove two general mathematical statements (S-theorem and S-lemma) about exact re-exponentiation of Keldysh-contour ordered T-exponent for arbitrary Luttinger liquid tunnel Hamiltonian. As the result, decoherence- and acquisition of information time-scales as well as QPC quantum detector efficiency rate are calculated exactly and are shown to have a dramatic dependence on repulsive interaction between electrons in 1D leads of QPC. Discovered abrupt decrease of QPC quantum detector efficiency $ Q $ with the increase of $ g $ in the close vicinity of value $ g_{cr}(T) $ represents a fingerprint of interaction-dependent instability of all the quantum detection procedure for any Luttinger liquid QPC quantum detector at definite low enough temperatures $ T_{cr}(g) $. The reasons behind these effects are discussed. Also, it is shown that such the low-temperature detection instability effect is able to explain a large unclear mismatch between expected and observed decoherence timescales in two well-known experiments (J.Gorman, D.G.Hasko, D.A.Williams, Phys.Rev.Lett., 95, 090502 (2005); K.D.Petersson, J.R.Petta, H.Lu, A.C.Gossard, Phys.Rev.Lett., 105, 246804 (2010);) on charge-qubit quantum dynamics.

A comprehensive theoretical comparison of proton imaging set-ups in terms of spatial resolution

We present a comprehensive analytical comparison of four types of proton imaging set-ups and, to this end, develop a mathematical framework to calculate the width of the uncertainty envelope around the most likely proton path depending on set-up geometry, detector properties, and proton beam parameters. As a figure of merit for the spatial resolution achievable with each set-up, we use the frequency at which the modular transfer function of a density step decreases below 10%. We verify the analytical results with Monte Carlo simulations.We find that set-ups which track the angle and position of individual protons in front of and behind the phantom would yield an average spatial resolution of 0.3–0.35 lp mm−1 assuming realistic geometric parameters (i.e. 30–40 cm distance between detector and phantom, 15–20 cm phantom thickness). For set-ups combining pencil beam scanning with either a position sensitive detector, e.g. an x-ray flat panel, or with a position insensitive detector, e.g. a range telescope, we find an average spatial resolution of about 0.1 lp mm−1 for an 8 mm FWHM beam spot size. The pixel information improves the spatial resolution by less than 10%. In both set-up types, performance can be significantly improved by reducing the pencil beam size down to 2 mm FWHM. In this case, the achievable spatial resolution reaches about 0.25 lp mm−1. Our results show that imaging set-ups combining double scattering with a pixel detector can provide sufficient spatial resolution only under very stringent conditions and are not ideally suited for computed tomography applications. We further propose a region-of-interest method for set-ups with a pixel detector to filter out protons which have undergone nuclear reactions and discuss the impact of tracker detector uncertainties on the most likely path.

Silicon Carbide detectors for nuclear physics experiments at high beam luminosity

Silicon carbide is a very promising material for next generation nuclear physics experiments at high beam luminosity. Such activities require devices able to sustain high fluxes of particles (up to 1014 ions/cm2) in order to determine the cross sections of very rare nuclear phenomena. One of these activities is the NUMEN project, which aims, through the double charge exchange reactions, to impact in the determination of nuclear matrix elements entering in the expression of half-life of the neutrino-less double beta decay. Due to the very low cross sections, these features can just be explored at fluences which exceed by far those tolerated in state of the art solid state detectors, typically used in this kind of experiments. The SiC technology offers today an ideal response to such challenges, giving the opportunity to cope the excellent properties of silicon detectors with the radiation hardness, thermal stability and visible blindness of SiC material.

A Wearable Detector for Simultaneous Finger Joint Motion Measurement.

This paper presents a wearable and stretchable detector for simultaneous finger joint motion measurement, providing the feasible technical solutions to solve the problems existing in the current devices. The sensor array installed in the detector consists of 14 custom-made bending sensors and an inertial measurement unit with high accuracy. The glove support for a sensor array, which is made of three silicone materials with different elasticity, not only overcomesthedrawbacks of cloth support, but also addresses the compatibility between the stretch substrate and the inelastic sensing components. Besides, two-section electrical connection avoids the problems caused by the external wires in traditional solutions to enhance the durability of glove. The experiment results indicated that the wearable detector offers a good user experience by exerting a small force on fingers. The device also shows a strong durability as it worked properly after tens of thousands of bending. The measurement tests on a single sensor demonstrated that two kinds of sensors are both with high accuracy. Besides, the hand goniometric system has an excellent performance in terms of hand motion detection. The measurement error of the device in subjects with different hand sizes is within a reasonable range. The good properties of the sensory detector allow it to be applied in clinical applications.

Comparison of semi-insulating GaAs and 4H-SiC-based semiconductor detectors covered by LiF film for thermal neutron detection

In this contribution we have focused on comparison of spectroscopic properties of semi-insulating (SI) GaAs and 4H-SiC detectors of thermal neutrons fabricated at the Institute of Electrical Engineering SAS in Piešťany. 6LiF reactive film has been applied on Schottky contact as a convertor of thermal neutrons to detectable charged particles (tritons and α particles). Optimal thickness of the 6LiF film has been determined for front side irradiation using MCNPX code to be ca 25 μm. From the energies deposited by secondary charged particles in the active volume of a detector, corresponding responses have been calculated for different thicknesses of the 6LiF conversion layer. The calculated responses have been compared with those collected by measurements using thermal neutrons generated by 239Pu-Be neutron source. Thermal neutron spectra have been recorded by SI GaAs and 4H-SiC detectors using different 6LiF film thicknesses. Generally, in spite of limited spectroscopic performances of the studied detectors, two hills related to tritons (2.73 MeV) and α particles (2.05 MeV) are discernible in all spectra beside a noise peak positioned in the low energy region. The specific differences between SI GaAs and 4H-SiC detector response to thermal neutrons will be closely discussed in the paper.

Electrical properties study under radiation of the 3D-open-shell-electrode detector

Since the 3D-Open-Shell-Electrode Detector (3DOSED) is proposed and the structure is optimized, it is important to study 3DOSED’s electrical properties to determine the detector’s working performance, especially in the heavy radiation environments, like the Large Hadron Collider (LHC) and it’s upgrade, the High Luminosity (HL-LHC) at CERN. In this work, full 3D technology computer-aided design (TCAD) simulations have been done on this novel silicon detector structure. Simulated detector properties include the electric field distribution, the electric potential distribution, current-voltage (I-V) characteristics, capacitance-voltage (C-V) characteristics, charge collection property, and full depletion voltage. Through the analysis of calculations and simulation results, we find that the 3DOSED’s electric field and potential distributions are very uniform, even in the tiny region near the shell openings with little perturbations. The novel detector fits the designing purpose of collecting charges generated by particle/light in a good fashion with a well defined funnel shape of electric potential distribution that makes these charges drifting towards the center collection electrode. Furthermore, by analyzing the I-V, C-V, charge collection property and full depletion voltage, we can expect that the novel detector will perform well, even in the heavy radiation environments.

Application of Timepix3 based CdTe spectral sensitive photon counting detector for PET imaging

Positron emission tomography (PET) is a nuclear medicine functional imaging technique. It is used in clinical oncology (medical imaging of tumors and the search for metastases), and pre-clinical studies using animals. PET uses small amounts of radioactive materials (radiotracers) and a special photon sensitive camera. Most of these cameras use scintillators with photomultipliers as detectors. However, these detectors have limited energy sensitivity and large pixels. Therefore, the false signal caused by a scattering poses a significant problem. In this work we study properties of position, energy and time sensitive semiconductor detector of Timepix3 type and its applicability for PET measurements. This work presents an initial study and evaluation of two Timepix3 detectors with 2 mm thick CdTe sensors used in simplified geometry for PET imaging. The study is performed on 2 samples —a capillary tube and a cylindrical plexiglass phantom with cavities. Both samples are filled with fluodeoxyglucose (FDG) solution that is used as a radiotracer. The Timepix3 offers better properties compared to conventional detectors —high granularity (55μm pixel pitch), good energy resolution (1 keV at 60 keV) and sufficient time resolution (1.6 ns). The spectral sensitivity of Timepix3 together with coincidence/anticoincidence technique allows for significant reduction of background signal caused by Compton scattering and internal X-ray fluorescence of Cd and Te.

Dosimetric properties of KMgF3:Tb + PTFE

This work presents the results obtained from the dosimetric properties of the new radiation detectors of KMgF3:Tb + PTFE. The thermoluminescent material was obtained by microwave technique. The polycrystalline powder obtained was mixed with polytetrafluoroethylene resin powder in the ratio 2:3 to make dosimeters in pellet form. The thermoluminescent response of these new detectors presented a linear behavior, in the dose range between 1 and 1000 Gy 60Co gamma radiation, the repeatability test in the measurements, during ten cycles of heat treatment, irradiation and readouts, showed ± 3.7% DS, the stability test of thermoluminescent signal, during two months showed that the fading is practically null. For the results obtained, this new detector could be very useful for radiation dosimetry, in clinical applications.

Thermally induced fading of Mn-doped YAP nanoceramics

Thermally induced fading of the thermoluminescent (TL) detectors in the form of YAlO3:Mn ceramics prepared from the nanocrystalline materials synthesized by the solution combustion method have been measured and analyzed in comparison with the single crystalline YAlO3:Mn detectors studied previously. The observed differences in thermoluminescent and dosimetric properties of nanoceramic and single crystalline detectors are discussed in terms of peculiarities of the nanoceramic material.

Changes induced in structure and optical properties of PM-355 nuclear track detector due to laser irradiation

ABSTRACTPM-355 is a class of polymeric solid-state nuclear track detectors which has a lot of applications in several radiation detection fields. Samples from sheets of PM-355 have been exposed to infrared (IR) laser fluences ranging from 1 to 12.8 J/cm2. The effect of IR laser radiation on the structural properties of PM-355 has been investigated using X-ray diffraction and Fourier transform infrared spectroscopy. The results indicate that the samples exhibit chain scission under the effect of laser irradiation up to 4.2 J/cm2, thus producing free radicals that led to the formation of new bonds started and continued until 12.8 J/cm2. This reduces the ordering structure, giving the PM-355 polymer more resilience. In addition, the laser irradiation at the fluence range 4.2–12.8 J/cm2 led to a more compact structure of PM-355, which resulted in an improvement in its isotropic nature with an increase in Vickers hardness and refractive index. Further, the color changes due to laser irradiation were computed using the transmission data in the wavelength range of 370–780 nm. It is found that the color intensity, which is the color difference between the irradiated samples and the non-irradiated one, increases with increasing the laser fluence, largely depending on the proportions of the blue color component.

Optimized "detectors" for dynamics analysis in solid-state NMR.

Relaxation in nuclear magnetic resonance (NMR) results from stochastic motions that modulate anisotropic NMR interactions. Therefore, measurement of relaxation-rate constants can be used to characterize molecular-dynamic processes. The motion is often characterized by Markov processes using an auto-correlation function, which is assumed to be a sum of multiple decaying exponentials. We have recently shown that such a model can lead to severe misrepresentation of the real motion, when the real correlation function is more complex than the model. Furthermore, multiple distributions of motion may yield the same set of dynamics data. Therefore, we introduce optimized dynamics "detectors" to characterize motions which are linear combinations of relaxation-rate constants. A detector estimates the average or total amplitude of motion for a range of motional correlation times. The information obtained through the detectors is less specific than information obtained using an explicit model, but this is necessary because the information contained in the relaxation data is ambiguous, if one does not know the correct motional model. On the other hand, if one has a molecular dynamics trajectory, one may calculate the corresponding detector responses, allowing direct comparison to experimental NMR dynamics analysis. We describe how to construct a set of optimized detectors for a given set of relaxation measurements. We then investigate the properties of detectors for a number of different data sets, thus gaining an insight into the actual information content of the NMR data. Finally, we show an example analysis of ubiquitin dynamics data using detectors, using the DIFRATE software.

自供能TiO2纳米管紫外探测器的制备与性能研究

自供能TiO₂纳米管紫外探测器的制备与性能研究

Simulation Study on Charged Particle Discrimination Properties of CdTe Detectors

In this paper, a theoretical description of the shape of pulses initiated by α-particles and protons penetrating in planar cadmium telluride (CdTe) detectors is presented and the dependence of the shape of pulses on the energy of charged particles, as well as, the thickness of the detectors are discussed. The results of our calculations indicate that for protons and α-particles with energies above ~5 MeV a strong correlation exists between the specific ionization of the charged particles and the shape of output charge pulses, making planar CdTe detectors a promising candidate for the discrimination of charged particles in nuclear physics experiments.

Evaluation of Timepix3 based CdTe photon counting detector for fully spectroscopic small animal SPECT imaging

The imaging method of SPECT (Single Photon Emission Computed Tomography) is used in nuclear medicine for diagnostics of various diseases or organs malfunctions. The distribution of medically injected, inhaled, or ingested radionuclides (radiotracers) in the patient body is imaged using gamma-ray sensitive camera with suitable imaging collimator. The 3D image is then calculated by combining many images taken from different observation angles. Most of SPECT systems use scintillator based cameras. These cameras do not provide good energy resolution and do not allow efficient suppression of unwanted signals such as those caused by Compton scattering. The main goal of this work is evaluation of Timepix3 detector properties for SPECT method for functional imaging of small animals during preclinical studies. Advantageous Timepix3 properties such as energy and spatial resolution are exploited for significant image quality improvement. Preliminary measurements were performed on specially prepared plastic phantom with cavities filled by radioisotopes and then repeated with in vivo mouse sample.