Detector Surface Research Articles

High power density soft x-ray GaAs photodiodes with tailored spectral response

GaAs photodiode arrays have been designed for non-destructive monitoring of x-ray beam position in soft coherent beamline front ends in synchrotron light sources. A shallow p-on-n junction was employed to reduce the device photocurrent density to optimize the operation with beam power densities up to 20 W mm−2, mainly coming from hard x-rays. With this approach, the photocurrent is primarily defined by the excess carriers generated by low-energy x-ray photons absorbed near the detector surface. The p–n junction structures were grown by molecular beam epitaxy and processed into 64-element linear photodiode arrays. The devices were characterized first in the visible range with a high-power Ar-ion laser and then tested in the soft and hard x-ray regions up to 10 keV at two beamlines of the National Synchrotron Light Source II. The responsivity was measured to be 0.16 A W−1 at 0.7 keV and 0.05 A W−1 at 6 keV in agreement with modeling. At higher x-ray energies the measured responsivity was lower than predicted in the framework of the carrier diffusion model; a possible explanation is discussed.

Sensitivity of Cross-Correlation Studies by Using Xmax Information

The investigation about cosmic-ray sources through the study of the arrival direction of the particles is completely dependent on primary mass compositions. This is due to heavier particles having an average larger deflection during propagation in galactic and extragalactic magnetic fields. Recent result from the Auger Collaboration made it possible to obtain information on the chemical composition of the cosmic rays on an event-by-event basis in addition to data from the surface detector. Here, we have investigated the gain in detection efficiency of standard cross-correlation using the Landy–Szalay estimator. Our sample contained only events with the highest Xmax values (corresponding to the lightest charged particles, for which the deflections in magnetic fields are smaller on average). We obtained results showing that that gain depends on the proton fraction ranging from a factor of ∼2 to ∼4.

Design of multi-layer grid in a giant electrostatic collection vessel of ultra-high sensitivity radon monitor

Developing an ultra-high sensitivity electrostatic collection radon monitor benefits the scientific experiments of China Jinping Underground Laboratory. Here, a one cubic meter electrostatic collection vessel with a multi-layer hemispherical metal grid was designed to increase the collection efficiency of positively charged Po-218 ions. The 3D model of the giant electrostatic collection vessel was constructed using the COMSOL Multiphysics simulation software, and the potential and electric field distributions in the vessel were simulated. Numerical simulation results were obtained according to the different radii and voltages applied to the grid. The electric field between the vessel wall and grid, between two grids, and between the grid and surface of the PIPS detector must be set uniformly to reduce the collection time of the positively charged Po-218 ions. Simulation results showed that setting a charged metal grid in the vessel can optimize the electric field distribution, and setting a two-layer charged metal grid in the giant vessel can further increase the cost performance. The average collection times of the electrostatic collection vessel with the two-layer grid along the vertical and oblique lines approximately 15% and 13% of that without the grid. The rates of positively charged Po-218 ions that could pass through the one and two-layer metal grids were 86.78% and 50%. Optimizing the electric field can greatly increase the sensitivity of radon monitors and reduce the humidity restrictions.

Optimization of FLUKA detector model for HPGe array

Monte Carlo codes, such as FLUKA, are widely used to optimize calibration of spectrometric systems. HPGe detector array (HDA) for lung monitoring was modeled in FLUKA code using available information about their geometry and optimized for efficiency using 241Am point source at smaller distances (<10 cm) as in case of in-vivo monitoring scenarios. Thickness of dead layer (DL) on the top and lateral detector surfaces for low energy counting was determined by considering the experimental and simulated efficiency for various energies. Using trial and error method, optimized DL thickness was found out to be 2.5 μm on top surface and 1.8 mm on lateral surfaces for each HPGe detector in the array. For the optimized model, it was found that the simulated and experimental efficiency and the simulated and experimental spectra were in reasonable agreement. Optimization of the HDA was an important benchmarking step to reduce the simulation errors before they are implemented in complex numerical problems using computational phantoms.

Quantum Systems for Enhanced High Energy Particle Physics Detectors

Developments in quantum technologies in the last decades have led to a wide range of applications, but have also resulted in numerous novel approaches to explore the low energy particle physics parameter space. The potential for applications of quantum technologies to high energy particle physics endeavors has however not yet been investigated to the same extent. In this paper, we propose a number of areas where specific approaches built on quantum systems such as low-dimensional systems (quantum dots, 2D atomic layers) or manipulations of ensembles of quantum systems (single atom or polyatomic systems in detectors or on detector surfaces) might lead to improved high energy particle physics detectors, specifically in the areas of calorimetry, tracking or timing.

Determination of the Cosmic-Ray Chemical Composition: Open Issues and Prospects

Cosmic rays are relativistic particles that come to the Earth from outer space. Despite a great effort made in both experimental and theoretical research, their origin is still unknown. One of the main keys to understand their nature is the determination of its chemical composition as a function of primary energy. In this paper, we review the measurements of the mass composition above 1015 eV. We first summarize the main aspects of air shower physics that are relevant in composition analyses. We discuss the composition measurements made by using optical, radio, and surface detectors and the limitations imposed by current high-energy hadronic interaction models that are used to interpret the experimental data. We also review the photons and neutrinos searches conducted in different experiments, which, in addition to being important to understand the nature of cosmic rays, can provide relevant information related to the abundance of heavy or light elements in the flux at the highest energies. Finally, we summarize the future composition measurements that are currently being planned or under development.

Optical modelling of a GaAs/GaSb core–shell cone-topped octagonal-faced nanopillar array with periodic trapezoidal textured cut for high photon trapping efficiency

Light reflectance mitigation is the most crucial factor for achieving optimal photodetector performance. In this respect, light-trapping mechanisms based on nanostructures or microstructures such as nanopillars, nanocones and nanopyramids have emerged as the most promising candidate for reducing overall light reflectance. This is because of their large effective irradiation area, multiple scattering of incident light and increased path length of incident rays in these nanostructures. This paper proposes an optical model of a GaAs/GaSb material-based vertically oriented core–shell cone-topped octagonal nanopillar structure with periodical trapezoidal nanotexturization over it to be deployed on a circular planar detector surface with a radius of 50 μm. The geometric analytical investigation of the proposed model reveals 0.999 overall absorbance, 0.995A/W photoresponsivity, and 87% EQE at 1 μm operating wavelength.

Radar Diagnosis of the Thundercloud Electron Accelerator

AbstractThunderstorm Ground Enhancements (TGEs) refer to correlated enhancements in surface electric field and gamma ray flux that are manifestations of electron runaway in the storm overhead. The electric field enhancements can be of positive or negative polarity. In this study, altitude‐resolved S‐band radar observations of graupel are used to demonstrate distinct differences in storm structure linked with these “positive” and “negative” TGEs. The physical interpretation rests on the well‐established temperature‐dependent tripole structure of thunderstorms, with the main negative charge of the tripole acting as an electron repeller. This interpretation is supported by case studies showing altitude‐stable convection, with shallow (deep) development linked with “positive” (“negative”) TGEs, and by case studies of collapsing storms that show upper dipole dominance early and lower inverted dipole dominance later when graupel particles descend from a colder to warmer temperature domain. In the case of many TGEs on Mt Aragats (3.2 km MSL), the temperature‐dependent altitude of downward electron acceleration and avalanching may be sufficiently distant (>500 m) from surface detectors that the energetic electrons (1–10 MeV) are not likely avalanche/runaway electrons. Instead, they are Compton‐scattered and pair‐produced electrons from bremsstrahlung gamma radiation emanating from the high‐field avalanche region aloft. These inferences are consistent with GEANT4 calculations that identify the physical origins of energetic electrons at the surface.

Observation of the temperature and barometric effects on the cosmic muon flux by the DANSS detector

The DANSS detector (Alekseev et al. in JINST 11:P11011, 2016) is located directly below a commercial reactor core at the Kalinin Nuclear Power Plant. Such a position provides an overburden about 50 m.w.e. in vertical direction. In terms of the cosmic rays it occupies an intermediate position between surface and underground detectors. The sensitive volume of the detector is a cubic meter of plastic scintillator with fine segmentation and combined PMT and SiPM readout, surrounded by multilayer passive and active shielding. The detector can reconstruct muon tracks passing through its sensitive volume. The main physics goal of the DANSS experiment implies the antineutrino spectra measurements at various distances from the source. This is achieved by means of a lifting platform so that the data is taken in three positions – 10.9, 11.9 and 12.9 meters from the reactor core. The muon data were collected for nearly four calendar years. The overburden parameters langle E_{thr}cos theta rangle and langle E_{thr} rangle , as well as the temperature and barometric correlation coefficients are evaluated separately for the three detector positions and, in each position, in three ranges of the zenith angle – for nearly vertical muons with cos theta >0.9, for nearly horizontal muons with cos theta <0.36, and for the whole upper hemisphere.

Revisiting the dark matter interpretation of excess rates in semiconductors

In light of recent results from low-threshold dark matter detectors, we revisit the possibility of a common dark matter origin for multiple excesses across numerous direct detection experiments, with a focus on the excess rates in semiconductor detectors. We explore the interpretation of the low-threshold calorimetric excess rates above 40 eV in the silicon SuperCDMS Cryogenic Phonon Detector and above 100 eV in the germanium EDELWEISS Surface detector as arising from a common but unknown origin, and demonstrate a compatible fit for the observed energy spectra in both experiments, which follow a power law of index $\alpha = 3.43^{+0.11}_{-0.06}$. Despite the intriguing scaling of the normalization of these two excess rates with approximately the square of the mass number $A^2$, we argue that the possibility of common origin by dark matter scattering via nuclear recoils is strongly disfavored, even allowing for exotic condensed matter effects in an as-yet unmeasured kinematic regime, due to the unphysically-large dark matter velocity required to give comparable rates in the different energy ranges of the silicon and germanium excesses. We also investigate the possibility of inelastic nuclear scattering by cosmic ray neutrons, solar neutrinos, and photons as the origin, and quantitatively disfavor all three based on known fluxes of particles.

Calculating off-axis efficiency of coaxial HPGe detectors by Monte Carlo simulation

In beam geometries where a directed γ-ray beam hits the surface of a coaxial high purity germanium detector (HPGe), the detector efficiency is sensitive to the position where γ-rays initially hit the detector surface because the structure of the detector is nonuniform. This may cause inaccuracy of the detector efficiency when measured using standard sources that are point-like sources emitting γ-rays isotropically. Obtaining a precise estimation of the full energy peak efficiency of the coaxial HPGe detector in the beam geometry for on-axis and off-axis measurements requires a Monte Carlo simulation. We performed Monte Carlo simulations that calculate the detector efficiency in the beam geometry. The effects of the off-axis distance and γ-ray beam size on the efficiency are quantitatively analyzed. We found that the intrinsic efficiency in the beam geometry is maximized when the beam hits the detector at specific off-axis distances. Our Monte Carlo calculations have been supported by nuclear resonance fluorescence experiments using laser Compton scattering γ-ray beams.

Temperature-dependent charge barrier height of amorphous germanium contact detector

The exploration of germanium (Ge) detectors with amorphous Ge (a-Ge) contacts has drawn attention to the searches for rare-event physics such as dark matter and neutrinoless double-beta decay. The charge barrier height (CBH) of the a-Ge contacts deposited on the detector surface is crucial to suppress the leakage current of the detector in order to achieve a low-energy detection threshold and high-energy resolution. The temperature-dependent CBH of a-Ge contacts for three Ge detectors is analyzed to study the bulk leakage current (BLC) characteristics. The detectors were fabricated at the University of South Dakota using homegrown crystals. The CBH is determined from the BLC when the detectors are operated in the reverse bias mode with a guard-ring structure, which separates the BLC from the surface leakage current (SLC). The results show that CBH is temperature dependent. The direct relation of the CBH variation to temperature is related to the barrier inhomogeneities created on the interface of a-Ge and crystalline Ge. The inhomogeneities that occur at the interface were analyzed using the Gaussian distribution model for three detectors.

Distribution of the time at which an ideal detector clicks

We consider the problem of computing, for a detector surface waiting for a quantum particle to arrive, the probability distribution of the time and place at which the particle gets detected, from the initial wave function of the particle in the non-relativistic regime. Although the standard rules of quantum mechanics offer no operator for the time of arrival, quantum mechanics makes an unambiguous prediction for this distribution, defined by first solving the Schrödinger equation for the big quantum system formed by the particle of interest, the detector, a clock, and a device that records the time and place of detection, then making a quantum measurement of the record at a very late time, and finally using the distribution of the recorded time and place. This leads to the question whether there is also a practical, simple rule for computing this distribution, at least approximately (i.e., for an idealized detector). We argue here in favor of a rule based on a 1-particle Schrödinger equation with a certain (absorbing) boundary condition at the ideal detecting surface, first considered by Werner in 1987. We present a novel derivation of this rule and describe how it arises as a limit of a “soft” detector represented by an imaginary potential.

Deep learning method for identifying mass composition of ultra-high-energy cosmic rays

We introduce a novel method for identifying the mass composition of ultra-high-energy cosmic rays using deep learning. The key idea of the method is to use a chain of two neural networks. The first network predicts the type of a primary particle for individual events, while the second infers the mass composition of an ensemble of events. We apply this method to the Monte-Carlo data for the Telescope Array Surface Detectors readings, on which it yields an unprecedented low error of 7% for 4-component approximation. We also discuss the problems of applying the developed method to the experimental data, and the way they can be resolved.

A New Projection Based Method for the Classification of Mechanical Components Using Convolutional Neural Networks

AbstractDigital engineering is increasingly established in the industrial routine. Especially the application of machine learning on geometry data is a growing research issue. Driven by this, the paper presents a new method for the classification of mechanical components, which utilizes the projection of points onto a spherical detector surfaces to transfer the geometries into matrices. These matrices are then classified using deep learning networks. Different types of projection are examined, as are several deep learning models. Finally, a benchmark dataset is used to demonstrate the competitiveness.

Simultaneous 3D measurement for infrared chips with speckle interferometry

Temperature-induced deformation in the infrared detector chip is a key index for evaluating image aberration and stress concentration. Development of an evaluation means for simultaneous characterization of 3D deformation is of great interest to engineering societies. In this study, an integrated device based on speckle interferometry has been developed for evaluation of the three-dimensional (3D) deformation of the infrared detector chip with variations of temperature. With the use of a 3CCD color camera and a group of optical fibers, the 3D displacement components of the detector surface are measured simultaneously during the cooling process. A temporal phase shifting scheme based on GPU parallel computing has been proposed to enable quantitatively real-time 3D measurement in three image layers at a rate of 20 fps. The integrated device has been validated with a benchmark test. The experimental results show a good agreement with the theoretical solution validating the stability and accuracy of the experimental device. The developed speckle interferometry device provides an accurate means in simultaneously evaluating the 3D deformation of the infrared detector chip due to temperature variations.

Development of a liquid argon detector with high light collection efficiency using tetraphenyl butadiene and a silicon photomultiplier array

Abstract To increase the light collection efficiency of a liquid argon (LAr) detector, we optimized the evaporation technique of tetraphenyl butadiene (TPB) on the detector surface and tested the operability of a silicon photomultiplier at LAr temperature. TPB converts LAr scintillations (vacuum ultraviolet light) to visible light, which can be detected using high-sensitivity photosensors. Because the light collection efficiency depends on the deposition mass of TPB on the inner surface of the detector, we constructed a well-controlled TPB evaporator to ensure reproducibility and measured the TPB deposition mass using a quartz crystal microbalance sensor. After optimizing the deposition mass of TPB (30 $\rm \mu g/cm^2$ on the photosensor window and 42 $\rm \mu g/cm^2$ on the detector wall), the observed light yield was 12.8 ± 0.3 p.e./keVee using photomultiplier tubes with a quantum efficiency of approximately 30% for TPB-converted light. We also tested the low-temperature tolerance of the silicon photomultiplier, which has a high photon detection efficiency, in a LAr environment. It detected the LAr scintillations converted by TPB with a photon detection efficiency exceeding 50%.

Neutron radial collimator using Zr–Gd alloy foil as collimating blade for engineering material diffractometer

In this study, 50-μm-thick Zr–Gd alloy foil was used as the collimating blade for a neutron radial collimator. Very thin Zr–Gd alloy foil presents excellent mechanical properties and low neutron transmission compared with a Mylar foil blade coated with gadolinium oxide (Gd2O3). The tensile strength of the 50-μm Zr–80Gd alloy foil is 135 MPa with a 4% thick tolerance, whereas the tensile strength for the 100-μm Mylar foil blade is 50 MPa with a 10% thick tolerance. The neutron transmission for 50-μm-thick Zr–80Gd alloy foil is 35.352% (1-Å neutron), which performs better than the Mylar foil blade because of the high content of gadolinium. Considering the blade thickness, the gauge volume width for different blade thicknesses was calculated analytically and optimized using McStas. The neutronic properties of a 2-mm gauge volume radial collimator with 240 blades of 50-μm Zr–80Gd alloy foils were simulated using MCNPX. The neutron-to-gamma ratio at the detector surface of the Zr–Gd alloy was higher than that of the Mylar foil blade. The transmission of the radial collimator was 93.6%, and a 2-mm gauge volume was simulated. The construction of a radial collimator using the Zr–Gd alloy blades is in progress. This shows that the Zr–Gd alloy foil provides a new type of high-quality neutron radial collimator blade.

Design of a Barometer-Based Pulse-Taking Device With In Vivo Validation Against High-Frequency Ultrasound Pulse Wave Imaging

Wrist-site pulse-sensing devices have drawn increasing attention for daily monitoring of human body conditions in the context of western medicine and modernization of traditional Chinese medicine (TCM) palpation. Existing tactile pulse sensors are deemed to only access the superficial tissue layer as surface detectors but have not been validated against medical imaging of the radial artery and its pulsation. We hereby proposed to employ high-frequency (15.6MHz) and high frame-rate (1000fps) ultrasound radial pulse wave imaging (US-rPWI) to substantiate human radial pulse-taking. We first presented an easy-to-fabricate, cost-effective pulse-sensing prototype based on a commercial off-the-shelf (COTS) barometer. The prototype performance was evaluated using a homemade pressurized vessel-mimicking phantom and 30 different <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vitro</i> pulses outputted from a TCM palpation training machine. Phantom experiments evidenced accurate portrayal of dynamic pressure waveforms (mean distortion ratio: 3.38±0.07%, compared with the ground truth). <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">In vivo</i> validation on human pre- and post- prandial pulses was further performed. US-rPWI revealed significantly diminished pulse amplitudes and gradual waveform deformation from the arterial wall to the skin layer. Nevertheless, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vivo</i> pulse waveforms detected at the skin surface by the prototype were highly correlated (correlation coefficient: 0.926±0.07) with those obtained from the radial arterial wall by US-rPWI. Moreover, the changes in post-prandial pulse waveforms detected by both the prototype and US-rPWI were in excellent agreement with those in TCM literature, thus demonstrating the sensitivity of human pulse-taking in quantitative assessment of health conditions at the point of care and providing more clinical evidence for the modernization of TCM sphygmology.

Observation of variations in cosmic ray single count rates during thunderstorms and implications for large-scale electric field changes

We present the first observation by the Telescope Array Surface Detector (TASD) of the effect of thunderstorms on the development of cosmic ray single count rate intensity over a 700 km2 area. Observations of variations in the secondary low-energy cosmic ray counting rate, using the TASD, allow us to study the electric field inside thunderstorms, on a large scale, as it progresses on top of the 700 km2 detector, without dealing with the limitation of narrow exposure in time and space using balloons and aircraft detectors. In this work, variations in the cosmic ray intensity (single count rate) using the TASD, were studied and found to be on average at the ∼(0.5–1)% and up to 2% level. These observations were found to be both in excess and in deficit. They were also found to be correlated with lightning in addition to thunderstorms. These variations lasted for tens of minutes; their footprint on the ground ranged from 6 km to 24 km in diameter and moved in the same direction as the thunderstorm. With the use of simple electric field models inside the cloud and between cloud to ground, the observed variations in the cosmic ray single count rate were recreated using CORSIKA simulations. Depending on the electric field model used and the direction of the electric field in that model, the electric field magnitude that reproduces the observed low-energy cosmic ray single count rate variations was found to be approximately between 0.2 GV–0.4 GV. This in turn allows us to get a reasonable insight on the electric field and its effect on cosmic ray air showers inside thunderstorms.2 MoreReceived 19 November 2021Accepted 3 January 2022DOI:https://doi.org/10.1103/PhysRevD.105.062002© 2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAtmospheric scienceCosmic rays & astroparticlesInterdisciplinary PhysicsParticles & Fields