Collection Efficiency Measurements Research Articles

Aerosol collection efficiency enhancement in HVAC systems through electrical field-Induced filter media polarization

Electrically enhanced media filters improve filtration efficiency in heating, ventilation, and air conditioning (HVAC) systems. Enhancement is accomplished by placing a uniquely formulated media material which can be polarized between arrays of wire electrodes. We explore the implementation of an electrically enhanced filtration system to both quantify the level of enhancement in filtration efficiency achievable in conditions representative of HVAC systems, and to determine the mechanism of collection enhancement. Measurements were carried out on a system comprised of a MERV 11 base filter, two arrays of upstream electrodes, and one array of downstream electrodes. Collection efficiency measurements reveal a strong dependency on the applied voltage across all examined face velocities. At a particle diameter of 0.3 μm, the collection efficiencies showed marked increases of 51.6%, 47.2%, and 30.7% from the zero-field level to a voltage of 10 kV at flow rates of 850, 1700, and 2550 m3 hr−1, respectively. Notably, this enhancement in collection efficiency is maintained even after particle loading on the filter. Charge state examinations revealed minimal changes in particle charge levels within the filter unit, demonstrating that the enhancement of filter performance is driven by dielectrophoretic motion and to a lesser extent electrophoretic motion.

Neutron radiation induced effects in 4H-SiC PiN diodes

Silicon carbide (SiC) is a wide band gap semiconductor and an attractive candidate for applications in harsh environments such as space, fusion, or future high luminosity colliders. Due to the large band gap, the leakage currents in SiC devices are extremely small, even after irradiation to very high fluences, enabling operation without cooling and at high temperatures. This study investigates the effect of neutron irradiation on 50 μm p-n 4H-SiC diodes using current-voltage, capacitance-voltage, and charge collection efficiency (CCE) measurements up to neutron fluences of 1 × 1016 n eq/cm2. The leakage currents of the investigated devices remained extremely small, below 10 pA at 1.1 kV reverse bias. In the forward bias, a remarkable drop of the current was observed, which was attributed to an increased epi resistivity due to compensation of the epi layer doping by deep-level defects. The CCE was evaluated for alpha particles from a radioactive source, a 62.4 MeV proton beam at the MedAustron ion therapy center and using UV-TCT. The charge collection efficiency in reverse bias was shown to scale directly with the 1 MeV equivalent fluence Φeq as CCE∝Φeq -0.63±0.01. A CCE better than 50% was able to be obtained for fluences up to 1 × 1015 n eq/cm2. Because of the low currents in the forward direction, particle detection was also possible in forward bias, where the CCE was found to be increased relative to reverse bias. Furthermore, a significant dependency on the amount of injected charge was observed, with the CCE surpassing 100% in alpha and UV-TCT measurements, requiring further systematic investigation.

Constant vs. cyclic flow when testing face masks and respirators as source control devices for simulated respiratory aerosols

SARS-CoV-2 spreads by infectious aerosols and droplets from the respiratory tract. Masks and respirators can reduce the transmission of infectious respiratory diseases by collecting these aerosols at the source. The ability of source control devices to block aerosols can be tested by expelling an aerosol through a headform using constant airflows, which are simpler, or cyclic airflows, which are more realistic but require more complex methods. Experiments with respirators found that using cyclic vs. constant flows affected the amount of aerosol inhaled, but similar comparisons have not been made for source control devices with exhaled aerosols. We measured the collection efficiencies for exhaled aerosols for two cloth masks, two medical masks with and without an elastic mask brace, a neck gaiter, and an N95 filtering facepiece respirator using 15 L/min and 85 L/min constant and cyclic flows and a headform with pliable skin. The collection efficiencies for the 15 L/min cyclic flow, 15 L/min constant flow, and 85 L/min constant flow were not significantly different in most cases. The apparent collection efficiencies for the 85 L/min cyclic flow were artificially increased by rebreathing and refiltration of the aerosol from the collection chamber. The collection efficiencies correlated well with the fit factors (ρ > 0.95) but not the filtration efficiencies (ρ < 0.54). Our results suggest that the aerosol collection efficiency measurements of source control devices are comparable when testing the devices using either constant or cyclic airflows and that the potential for aerosol rebreathing must be considered when conducting experiments.

A Study of the Radiation Tolerance and Timing Properties of 3D Diamond Detectors.

We present a study on the radiation tolerance and timing properties of 3D diamond detectors fabricated by laser engineering on synthetic Chemical Vapor Deposited (CVD) plates. We evaluated the radiation hardness of the sensors using Charge Collection Efficiency (CCE) measurements after neutron fluences up to 1016 n/cm2 (1 MeV equivalent.) The radiation tolerance is significantly higher when moving from standard planar architecture to 3D architecture and increases with the increasing density of the columnar electrodes. Also, the maximum applicable bias voltage before electric breakdown increases significantly after high fluence irradiation, possibly due to the passivation of defects. The experimental analysis allowed us to predict the performance of the devices at higher fluence levels, well in the range of 1016 n/cm2. We summarize the recent results on the time resolution measurements of our test sensors after optimization of the laser fabrication process and outline future activity in developing pixel tracking systems for high luminosity particle physics experiments.

Collecting fog with vertical fibres: Combined laboratory and in-situ study

Fog harvesting is an application of aerosol filtration to capture water droplets from fog by using nets, called fog collectors. It is a promising technique for freshwater supply in arid and semi-arid regions. In this study, we investigate the collection efficiency of harp-like fog collectors consisting of vertical fibres. We conduct well-controlled laboratory scale experiments on model fog collectors and develop a predictive theoretical model accounting for the liquid distribution on the fibres and for aerodynamic effects. Without using any adjustable parameter, we obtain a good agreement between our theoretical model and laboratory scale experimental results. Furthermore, we perform collection efficiency measurements on an in-situ pilot scale fog collector, accompanied by a description of the fog's microphysical properties. Comparing the results of our pilot scale and laboratory scale experiments and the theoretical model developed, we propose a method to accurately evaluate the efficiency of our collector, with simultaneous measurements of collected water volume and fog characteristics.

Determination of the ion collection efficiency of the Razor Nano Chamber for ultra-high dose-rate electron beams.

BackgroundUltra‐high dose‐rate (UHDR) irradiations (>40 Gy/s) have recently garnered interest in radiotherapy (RT) as they can trigger the so‐called “FLASH” effect, namely a higher tolerance of normal tissues in comparison with conventional dose rates when a sufficiently high dose is delivered to the tissue. To transfer this to clinical RT treatments, adapted methods and practical tools for online dosimetry need to be developed. Ionization chambers remain the gold standards in RT but the charge recombination effects may be very significant at such high dose rates, limiting the use of some of these dosimeters. The reduction of the sensitive volume size can be an interesting characteristic to reduce such effects.PurposeIn that context, we have investigated the charge collection behavior of the recent IBA Razor™ Nano Chamber (RNC) in UHDR pulses to evaluate its potential interest for FLASH RT.MethodsIn order to quantify the RNC ion collection efficiency (ICE), simultaneous dose measurements were performed under UHDR electron beams with dose‐rate‐independent Gafchromic™ EBT3 films that were used as the dose reference. A dose‐per‐pulse range from 0.01 to 30 Gy was investigated, varying the source‐to‐surface distance, the pulse duration (1 and 3 μs investigated) and the LINAC gun grid tension as irradiation parameters. In addition, the RNC measurements were corrected from the inherent beam shot‐to‐shot variations using an independent current transformer. An empirical logistic model was used to fit the RNC collection efficiency measurements and the results were compared with the Advanced Markus plane parallel ion chamber.ResultsThe RNC ICE was found to decrease as the dose‐per‐pulse increases, starting from doses above 0.2 Gy/pulse and down to 40% of efficiency at 30 Gy/pulse. The RNC resulted in a higher ICE for a given dose‐per‐pulse in comparison with the Markus chamber, with a measured efficiency found higher than 85 and 55% for 1 and 10 Gy/pulse, respectively, whereas the Markus ICE was of 60 and 25% for the same doses. However, the RNC shows a higher sensitivity to the pulse duration than the Advanced Markus chamber, with a lower efficiency found at 1 μs than at 3 μs, suggesting that this chamber could be more sensitive to the dose rate within the pulse.ConclusionsThe results confirmed that the small sensitive volume of the RNC ensures higher ICE compared with larger chambers. The RNC was thus found to be a promising online dosimetry tool for FLASH RT and we proposed an ion recombination model to correct its response up to extreme dose‐per‐pulses of 30 Gy.

Optical Pump–Terahertz Probe Study of HR GaAs:Cr and SI GaAs:EL2 Structures with Long Charge Carrier Lifetimes

The time dynamics of nonequilibrium charge carrier relaxation processes in SI GaAs:EL2 (semi-insulating gallium arsenide compensated with EL2 centers) and HR GaAs:Cr (high-resistive gallium arsenide compensated with chromium) were studied by the optical pump–terahertz probe technique. Charge carrier lifetimes and contributions from various recombination mechanisms were determined at different injection levels using the model, which takes into account the influence of surface and volume Shockley–Read–Hall (SRH) recombination, interband radiative transitions and interband and trap-assisted Auger recombination. It was found that, in most cases for HR GaAs:Cr and SI GaAs:EL2, Auger recombination mechanisms make the largest contribution to the recombination rate of nonequilibrium charge carriers at injection levels above ~(0.5–3)·1018 cm−3, typical of pump–probe experiments. At a lower photogenerated charge carrier concentration, the SRH recombination prevails. The derived charge carrier lifetimes, due to the SRH recombination, are approximately 1.5 and 25 ns in HR GaAs:Cr and SI GaAs:EL2, respectively. These values are closer to but still lower than the values determined by photoluminescence decay or charge collection efficiency measurements at low injection levels. The obtained results indicate the importance of a proper experimental data analysis when applying terahertz time-resolved spectroscopy to the determination of charge carrier lifetimes in semiconductor crystals intended for the fabrication of devices working at lower injection levels than those at measurements by the optical pump–terahertz probe technique. It was found that the charge carrier lifetime in HR GaAs:Cr is lower than that in SI GaAs:EL2 at injection levels &gt; 1016 cm−3.

Parasitic p–n junctions formed at V-pit defects in p-GaN

The luminescent and recombination properties of V-pit defects in p-GaN(Mg) grown by metalorganic chemical vapor deposition (MOCVD) were studied by scanning electron microscopy (SEM) in the secondary electron, cathodoluminescence (CL), and electron beam induced current (EBIC) modes, combined with CL spectra measurements and EBIC collection efficiency measurements. Similar studies were performed on low-dislocation-density freestanding n-GaN crystals. For MOCVD p-GaN films, the SEM investigations were supplemented by capacitance–voltage, current–voltage, deep level transient spectroscopy analysis with Ni Schottky diode, and Ohmic contacts. These experiments show that V-pits in p-GaN increase the leakage current of Schottky diodes, as in n-GaN films and crystals. EBIC imaging and EBIC collection efficiency results suggest that in the region of V-pits, a parasitic p–n junction is formed. We also observe that, in V-pits, the CL spectra the contribution of the 3.2 eV defect band is strongly enhanced compared to the 3 eV blue CL band that dominates the spectra.

Biodegradable CA/CPB electrospun nanofibers for efficient retention of airborne nanoparticles

The increase of the industrialization process brought the growth of pollutant emissions into the atmosphere. At the same time, the demand for advances in aerosol filtration is evolving towards more sustainable technologies. Electrospinning is gaining notoriety, once it enables to produce polymeric nanofibers with different additives and also the obtaining of small pore sizes and fiber diameters; desirable features for air filtration materials. Therefore, this work aims to evaluate the filtration performance of cellulose acetate (CA) nanofibers and cationic surfactant cetylpyridinium bromide (CPB) produced by electrospinning technique for retention of aerosol nanoparticles. The pressure drop and collection efficiency measurements of sodium chloride (NaCl) aerosol particles (diameters from 7 to 300 nm) were performed using Scanning Mobility Particle Sizer (SMPS). The average diameter of the electrospun nanofibers used was 239 nm, ranging from 113 to 398 nm. Experimental results indicated that the nanofibers showed good permeability (10−11 m2) and high-efficiency filtration for aerosol nanoparticles (about 100 %), which can include black carbon (BC) and the new coronavirus. The pressure drop was 1.8 kPa at 1.6 cm s-1, which is similar to reported for some high-efficiency nanofiber filters. In addition, it also retains BC particles present in air, which was about 90 % for 375 nm and about 60 % for the 880 nm wavelength. Finally, this research provided information for future designs of indoor air filters and filter media for facial masks with renewable, non-toxic biodegradable, and potential antibacterial characteristics.

Versatile systems for characterization of large-area silicon pad sensors for highly-granular calorimetry

High-granularity calorimeters utilizing silicon pad sensors as main active material are being designed for the CMS endcap calorimeter upgrade and have been proposed for the electromagnetic calorimeters at CLIC, ILC and FCC-ee. The silicon sensors in such experiments are foreseen to cover a very large area of O(1000 m2). They are typically produced from 6- or 8-inch wafers and consist of a few hundred smaller cells, each with an area of O(0.1 to 1.1 cm2). Currently the CMS endcap calorimeter upgrade is in a prototyping phase with the aim of choosing the final sensor design. Flexible systems are needed for quick sensor characterization as close as possible to operating conditions, for testing different prototypes and for quality control during mass production. The ARRAY system consists of an active switching matrix PCB with 512 input channels and a passive probe card specific for each sensor layout prototype. The probe card makes contact with each individual pad through spring-loaded pins. ARRAY is designed to measure the leakage current and capacitance per-cell for different bias voltages, keeping the entire sensor area under bias. The Hexaboard probe card follows a similar principle: readout electronics foreseen to be used in the final CMS detector are mounted on a PCB that makes contact with the sensor through spring-loaded pins. It is used to perform noise and charge collection efficiency measurements with irradiated sensors without the need for module assembly. We present the design of the ARRAY and Hexaboard systems as well as measurements performed on different CMS prototype silicon sensors. We also compare the results with alternative multi-needle setups.

Modeling radiation damage in the pixel sensors of the ATLAS detector

As the integrated luminosity delivered by the Large Hadron Collider increases, radiation damage effects are increasingly apparent in the response of the vertex detectors of the experiments. In this contribution, measurements of these effects are discussed for the Pixel Detector of the ATLAS experiment, which by the end of LHC Run 2 has received a fluence of up to 1015neqcm−2. Measurements of leakage current, Lorentz angle, and charge collection efficiency are discussed and compared to predictions from the Hamburg radiation damage model, TCAD based calculations, and a detailed simulation of the pixel sensor response which accounts also for the modifications to the electric field and charge collection efficiency induced by the radiation damage.

Photoelectron Collection Efficiency Measurement of Vp81 Photocathode

We present experimental measurement of photoelectron collection efficiency of a new organic semiconductor photocathode Vp81in pure methane and argon methane mixtures in different ratios as a function of applied reduced electric field at a gas pressure of 200 torr. It is confirmed that collection efficiency increases in charge collection mode and reaches near the vacuum value at high gas gain. The general universal behavior was also confirmed as predicted by some authors.

Performance of four CVD diamond radiation sensors at high temperature

Ionising radiation detectors based on wide band-gap materials have the potential to operate at temperatures higher than 200°C. Such detectors are important in applications such as monitoring near nuclear reactors and in deep oil and gas well borehole logging. We discuss the development of alpha particle detectors, based on CVD diamond, which operate with high charge collection efficiency and energy resolution at temperatures up to 225°C. Four nominally identical commercial, electronic grade, CVD diamonds have been coated with a thin metal conductive layer in our laboratory and then attached to ceramic PCB. We present the I–V characteristics, the charge collection efficiency and the energy resolution for alpha particles from a mixed 239Pu,241Am,244Cm source, for the four sensors operating at temperatures from 20 to 250°C. Monte Carlo simulations of the energy spectra and charge collection efficiency and experimental measurements of these are presented. Energy resolutions between 1.6% and 4.0% at elevated temperatures with charge collection efficiency exceeding 96% were measured. The potential for thermal neutron detection is discussed.

Determination of radiation hardness of silicon diodes

In this paper, we describe an experiment aimed to measure the physical observables, which can be used for the assessment of the radiation hardness of commercially available silicon photo diodes commonly used as nuclear detectors in particle accelerator laboratories. The experiment adopted the methodology developed during the International Atomic Energy Agency (IAEA) Coordinated Research Project (CRP No. F11016) “Utilization of Ion Accelerators for Studying and Modelling Ion Induced Radiation Defects in Semiconductors and Insulators”.This methodology is based on the selective irradiation of micrometer-sized regions with different fluences of MeV ions using an ion microbeam and on the measurement of the charge collection efficiency (CCE) degradation by Ion Beam Induced Charge (IBIC) microscopy performed in full depletion condition, using different probing ions.The IBIC results are analyzed through a theoretical approach based on the Shockley-Read-Hall model for the free carrier recombination in the presence of ion-induced deep traps. This interpretative model allows the evaluation of the material radiation hardness in terms of recombination parameters for both electrons and holes.The device under study in this experiment was a commercial p-i-n photodiode, which was initially characterized by i) standard electronic characterization techniques to determine its doping and ii) the Angle-Resolved IBIC to evaluate its effective entrance window. Nine regions of (100 × 100) µm2 were irradiated with 11.25 MeV He ions up to a maximum fluence of 3·1012 ions/cm2. The CCE degradation was measured by the IBIC technique using 11.25 MeV He and 1.4 MeV He as probing ions.The model presented here proved to be effective for fitting the experimental data. The fitting parameters correspond to the recombination coefficients, which are the key parameters for the characterization of the effects of radiation damage in semiconductors.

Dion-Jacobson Two-Dimensional Perovskite Solar Cells Based on Benzene Dimethanammonium Cation.

Organic-inorganic perovskite structured compounds have recently emerged as attractive materials in the fields of photovoltaic due to their exciting optical properties and easy syntheses, as well as exceptional structural and optical tunability. This work presents a Dion-Jacobson two-dimensional (2D) perovskite using diammonium as the barrier molecule. We show that the diammonium barrier molecule is responsible for the perovskite layers' orientation supported by Hall Effect measurements, which results in a high efficiency solar cell for 2D perovskite without the need for additives or any additional treatment. The 2D perovskite cells achieved an efficiency of 15.6%, which was one of the highest reported for low-dimensional perovskite. Charge extraction, voltage decay, and charge collection efficiency measurements show the beneficial alignment of the 2D perovskites related to the selective contacts. Stability characterization shows that the stability for the 2D perovskite was enhanced compared with their 3D counterparts.

Standardized Method for Measuring Collection Efficiency from Wipe-sampling of Trace Explosives

One of the limiting steps to detecting traces of explosives at screening venues is effective collection of the sample. Wipe-sampling is the most common procedure for collecting traces of explosives, and standardized measurements of collection efficiency are needed to evaluate and optimize sampling protocols. The approach described here is designed to provide this measurement infrastructure, and controls most of the factors known to be relevant to wipe-sampling. Three critical factors (the applied force, travel distance, and travel speed) are controlled using an automated device. Test surfaces are chosen based on similarity to the screening environment, and the wipes can be made from any material considered for use in wipe-sampling. Particle samples of the explosive 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) are applied in a fixed location on the surface using a dry-transfer technique. The particle samples, recently developed to simulate residues made after handling explosives, are produced by inkjet printing of RDX solutions onto polytetrafluoroethylene (PTFE) substrates. Collection efficiency is measured by extracting collected explosive from the wipe, and then related to critical sampling factors and the selection of wipe material and test surface. These measurements are meant to guide the development of sampling protocols at screening venues, where speed and throughput are primary considerations.

Standardized Method for Measuring Collection Efficiency from Wipe-sampling of Trace Explosives.

One of the limiting steps to detecting traces of explosives at screening venues is effective collection of the sample. Wipe-sampling is the most common procedure for collecting traces of explosives, and standardized measurements of collection efficiency are needed to evaluate and optimize sampling protocols. The approach described here is designed to provide this measurement infrastructure, and controls most of the factors known to be relevant to wipe-sampling. Three critical factors (the applied force, travel distance, and travel speed) are controlled using an automated device. Test surfaces are chosen based on similarity to the screening environment, and the wipes can be made from any material considered for use in wipe-sampling. Particle samples of the explosive 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) are applied in a fixed location on the surface using a dry-transfer technique. The particle samples, recently developed to simulate residues made after handling explosives, are produced by inkjet printing of RDX solutions onto polytetrafluoroethylene (PTFE) substrates. Collection efficiency is measured by extracting collected explosive from the wipe, and then related to critical sampling factors and the selection of wipe material and test surface. These measurements are meant to guide the development of sampling protocols at screening venues, where speed and throughput are primary considerations.

Airflow and particle transport simulations for predicting permeability and aerosol filtration efficiency in fibrous media

In this work, synchrotron X-ray microtomography was used to produce high spatial resolution images of two kinds of binderless and monodisperse fibrous filter media, made of fiberglass and sintered stainless steel respectively. Representative computational domains were created based on these images. Both flow and collection efficiency simulations were then carried out using the flow and particle transport modules of the GeoDict® code. An image analysis program based on Matlab® was used to determine the structural properties of the computational domain, namely the thickness, the solid volume fraction and the fiber size distribution. In parallel, permeability and collection efficiency measurements were performed on the same media, to provide an experimental comparison. Very good agreement was found between the experimental and the simulated permeability values. We showed that, in order to compare collection efficiency from experiments with those simulated with GeoDict®, it was necessary to take into account the difference between the thickness of the fibrous structures that were used to create the calculation domain, and the averaged experimental thickness characterized by SEM. Using this way of comparison, we obtained the first experimental validation of the GeoDict® code on both permeability and efficiency aspects for aerosols filtration.

Measurement of the photoelectron collection efficiency in MCP PMT

A method of direct measurement of the photoelectron collection efficiency in microchannel plate photomultiplier tubes (MCP PMT) has been developed. The method was verified by testing a PMT with conventional dynode system. The measurement accuracy of 5% was achieved. Large number of MCP PMTs produced in Novosibirsk (Russia) was tested.

Electron mobility-lifetime and resistivity mapping of GaAs:Cr wafers

Previous works onchromium compensated gallium arsenide (GaAs:Cr) have shown high efficiency, good spatial and energy resolution, which is obviously connected with the high quality of material itself. The purpose of this research was to aggravate the diffusion process by increasing the annealing temperature and to observe whether there will be any degradation of material characteristics. The investigation of three 3-inch GaAs:Cr wafers with different annealing temperature of chromium was carried out. Resistivity and mobility-lifetime measurements were made using pad sensors made of these wafers. The I-V curves were built to estimate the resistivity across the wafer. Furthermore charge collection efficiency (CCE) measurements were carried out in order to estimate the μeτ e product of GaAs:Cr. The resistivity mapping has showed a variation of resistivity across the wafer in the range from 1.25 × 109 to 5.5 × 108 Ohm cm. Although the third wafer showed quite good uniformity, the resistance didn't reached values higher than 3.5 × 108 Ohm cm. In spite of harsh diffusion conditions all the materials showed quite good CCE (about 90%) and μ eτe more than 5 × 10−5 cm2/V. Also a strong dependency between the resistivity and mobility-lifetime product was found only for one wafer. So the uniformity of μeτ e product across the wafer can be stated independently of resistivity. More detailed information and discussion of experimental results is presented in the article.