Phosphor Screen Research Articles

Neutron imager with micro channel plates (MCP) in electrostatic mirror configuration: Neutron beam test

A recent advancement in a new high transparency monitor device based on Micro Channel Plate (MCP) has been proposed for monitoring flux and beam spatial profiles of neutrons. It consisted of the assembly of a very thin aluminum (Al) foil with a 6Li deposit placed along the beam and a MCP equipped with a phosphor screen readout viewed by a CCD camera outside the beam line. The peculiar feature of this device is that it uses an electrostatic mirror to minimize the perturbation of the neutron beam, i.e. absorption and scattering. It can be used at existing time-of-flight facilities, in particular at the neutron Time-of-Flight (n_TOF) facility at CERN, for monitoring the flux and the spatial profile of neutron beams in the thermal and epithermal region. In this contribution, the device experimental test carried out on the n_TOF neutron beam at CERN will be presented and discussed.

ADVANCED TECHNOLOGY OF LUMINOPHOR SCREENS FOR SOLID RADIOLUMINESCENT LIGHT SOURCES

The article observes different methods of coating the phosphor screens on the tritiated titanium matrices for creating the solid-state radioluminescent light sources (SRLS). Technology of SRLS is alternative to the existing technology of the gas-filled radioluminescent light sources. The main idea of SRLS is in bonding the working isotope (tritium) in the solid matrix and combining it with the phosphor. The key problem of SRLS is to provide the closest contact between the tritiated carrier matrix and phosphor screen. The basic requirements for the phosphor screens for SRLS would be the strength of fixation on the plate, uniformity and radiological and thermal stability. There have been made a comparison of various techniques of coating and fixing the phosphor screens by their effect on spectral and brightness characteristics of SRLS. The improved sol-gel technique of suspended sedimentation of phosphor screen from the potassium water glass binder solution was developed. The composition of the solution was established experimentally and we get the strong and uniform experimental prototypes of the glass coated phosphor screens of various thickness. The developed technology allows to deposit the strong and uniform phosphor coatings without using any additional dispersing agents. Screen thickness regulates by the amount of phosphor in the suspension. Also the optimal thickness of the phosphor screen, giving the maximum luminescence intensity was determined. The two laboratory prototypes of solid-state radioluminescent light sources were manufactured by coating the phosphor directly on the tritium β-source.

Measuring the Gain of a Microchannel Plate/Phosphor Assembly Using a Convolutional Neural Network

This paper presents a technique to measure the gain of a single-plate micro-channel plate (MCP)/phosphor assembly by using a convolutional neural network to analyse images of the phosphor screen, recorded by a charge coupled device. The neural network reduces the background noise in the images sufficiently that individual electron events can be identified. From the denoised images, an algorithm determines the average intensity recorded on the phosphor associated with a single electron hitting the MCP. From this average single-particle-intensity, along with measurements of the charge of bunches after amplification by the MCP, we were able to deduce the gain curve of the MCP.

18F]-AV-1451 binding profile in chronic traumatic encephalopathy: a postmortem case series

IntroductionChronic traumatic encephalopathy (CTE) is a tauopathy associated to repetitive head trauma. There are no validated in vivo biomarkers of CTE and a definite diagnosis can only be made at autopsy. Recent studies have shown that positron emission tomography (PET) tracer AV-1451 (Flortaucipir) exhibits high binding affinity for paired helical filament (PHF)-tau aggregates in Alzheimer (AD) brains but relatively low affinity for tau lesions in other tauopathies like temporal lobal degeneration (FTLD)-tau, progressive supranuclear palsy (PSP) or corticobasal degeneration (CBD). Little is known, however, about the binding profile of this ligand to the tau-containing lesions of CTE.ObjectiveTo study the binding properties of [18F]-AV-1451 on pathologically confirmed CTE postmortem brain tissue samples.MethodsWe performed [18F]-AV-1451 phosphor screen and high resolution autoradiography, quantitative tau measurements by immunohistochemistry and Western blot and tau seeding activity assays in brain blocks containing hippocampus, superior temporal cortex, superior frontal cortex, inferior parietal cortex and occipital cortex from 5 cases of CTE, across the stages of disease: stage II-III (n = 1), stage III (n = 3), and stage IV (n = 1). Importantly, low or no concomitant classic AD pathology was present in these brains.ResultsDespite the presence of abundant tau aggregates in multiple regions in all CTE brains, only faint or no [18F]-AV-1451 binding signal could be detected by autoradiography. The only exception was the presence of a strong signal confined to the region of the choroid plexus and the meninges in two of the five cases. Tau immunostaining and Thioflavin-S staining ruled out the presence of tau aggregates in those regions. High resolution nuclear emulsion autoradiography revealed the presence of leptomeningeal melanocytes as the histologic source of this off-target binding. Levels of abnormally hyperphosphorylated tau species, as detected by Western Blotting, and tau seeding activity were both found to be lower in extracts from cases CTE when compared to AD.ConclusionAV-1451 may have limited utility for in vivo selective and reliable detection of tau aggregates in CTE. The existence of disease-specific tau conformations may likely explain the differential binding affinity of this tracer for tau lesions in different tauopathies.

Novel timing application using microchannel plate with phosphor screen

A signal tapping circuit has been designed to derive the fast timing signal from the Chevron type, 2 stage MCP having phosphor screen as a readout device. Using this, the timing property of the MCP-BaF2 system has been studied using the digital storage oscilloscope in which a timing resolution of ~ 500 ps has been obtained. The applicability of MCP with phosphor screen configuration for timing measurements has been demonstrated.

Charge calibration of DRZ scintillation phosphor screens

As a basic diagnostic tool, scintillation screens are employed in particle accelerators to detect charged particles. In extension to the recent revision on the calibration of scintillation screens commonly applied in the context of plasma acceleration [T. Kurz et al., Rev. Sci. Instrum. 89 (2018) 093303], here we present the charge calibration of three DRZ screens (Std, Plus, High), which promise to offer similar spatial resolution to other screen types whilst reaching higher conversion efficiencies. The calibration was performed at the Electron Linac for beams with high Brilliance and low Emittance (ELBE) at the Helmholtz-Zentrum Dresden-Rossendorf, which delivers picosecond-long beams of up to 40 MeV energy. Compared to the most sensitive screen, Kodak BioMAX MS, of the aforementioned recent investigation by Kurz et al., the sample with highest yield in this campaign, DRZ High, revealed a 30% increase in light yield. The detection threshold with these screens was found to be below 10 pC/mm2. For higher charge-densities (several nC/mm2) saturation effects were observed. In contrast to the recent reported work, the DRZ screens were more robust, demonstrating higher durability under the same high level of charge deposition.

Engineering of K3YSi2O7To Tune Photoluminescence with Selected Activators and Site Occupancy

The luminescence of rare earth ions (Eu2+, Ce3+, and Eu3+)-doped inorganic solids is attractive for the screening of phosphors applied in solid-state lighting and displays and significant to probe ...

MCP-based detectors: calibration and first photon radiation measurements.

Detectors based on microchannel plates (MCPs) are used to detect radiation from free-electron lasers. Three MCP detectors have been developed by JINR for the European XFEL (SASE1, SASE2 and SASE3 lines). These detectors are designed to operate in a wide dynamic range from the level of spontaneous emission to the SASE saturation level (between a few nJ up to 25 mJ), in a wide wavelength range from 0.05 nm to 0.4 nm for SASE1 and SASE2, and from 0.4 nm to 4.43 nm for SASE3. The detectors measure photon pulse energies with an anode and a photodiode. The photon beam image is observed with an MCP imager with a phosphor screen. At present, the SASE1 and SASE3 MCP detectors are commissioned with XFEL beams. Calibration and first measurements of photon radiation in multibunch mode are performed with the SASE1 and SASE3 MCPs. The MCP detector for SASE2 and its electronics are installed in the XFEL tunnel, technically commissioned, and are now ready for acceptance tests with the X-ray beam.

A modified sol–gel technique of phosphor screens preparation for tritium solid-state radioluminescent light sources (SRLS)

Method of coating the phosphor screens on the tritiated titanium substrates is considered for creating the solid-state radioluminescent light sources (SRLS). The key problem of SRLS is found to be providing the closest contact between the tritiated carrier substrate and phosphor screen. The improved sol–gel technique of suspended sedimentation of phosphor screen from the potassium water glass binder solution was developed. The composition of the solution was established experimentally and the strong and uniform experimental prototypes of the glass coated phosphor screens were prepared with various thickness. The screen thickness was controlled by the amount of phosphor in the suspension. The optimal thickness of the phosphor screen, giving the maximum luminescence intensity was also determined. The two laboratory prototypes of solid-state radioluminescent light sources were fabricated by coating the phosphor directly on the tritium β-source.

Nonlinear response of phosphor screen used in velocity map imaging spectrometry

We present an approach to experimentally investigate the nonlinear response of phosphor screen (PS) module applied in velocity-map-imaging spectrometry under the condition of microchannel plate (MCP) module working in an appropriate amplifier voltage to ensure a constant unsaturation gain. Our approach, taking the Photek's VID240 detector system as an example, is based on the measurements of the position spectra of 87Rb+ photoion pulses with well-determined numbers of ions and duration times at various voltage differences (Uf) between MCP and PS modules. The measured spectra allow us to obtain the relationship between the two-dimensional distribution of luminescence (the luminescence intensity in the kth pixel) and the total number of ions in one pulse at a given Uf value. The obtained relationship leads to the luminescence efficiency and the acceptable limit of input ion flux density (the maximal number of ions arriving at MCP per unit time per unit area to avoid the nonlinear response) for a particular PS to be determined.

Compact Thomson parabola spectrometer for fast diagnostics of different intensity laser-generated plasmas

A compact Thomson parabola spectrometer for diagnostics of laser-generated plasma, projected in Messina University, has been employed in different experiments concerning diagnostics of laser-generated plasmas. It allows to detect charged particles emitted from hot laser plasma and fast analyzing of their charge state, kinetic energy and mass-to-charge ratio. Moreover, it is possible to detect electrons emitted from laser-generated plasma. The spectrometer consists of a double pinhole input for alignment direction, a permanent magnet (0.004-4 kG) and an electric field ($0.05--5\text{ }\text{ }\mathrm{kV}/\mathrm{cm}$) both orthogonal to the direction of the incident particles, and different type of planar detectors (multichannel plates, phosphorous screen, gafchromic, CR39 and PM 355 track detectors). Measurements have been acquired at MIFT in Messina observing electrons up to 10 keV kinetic energy, at INFN-LNS of Catania using ions emitted from plasma submitted to a postacceleration up to 30 kV per charge state and at PALS Laboratory in Prague detecting energetic ions above 1 MeV per charge state. The particles recognition using the Thomson spectrometer has been obtained comparing the experimental parabola curves with the theoretical simulations obtained using COMSOL software. Results will be presented and discussed.

Preparation and characterization of multilayer Gd2O2S:Tb phosphor screen for X‐ray detection application

AbstractGd2O2S:Tb (GOS) phosphor screen, generally with a multilayer structure, has been widely used in digital X‐ray imaging. GOS phosphor screen is fabricated via a slip casting route, which is an effective method to obtain multilayer composites with good strength. The GOS slurry was prepared using the menhaden oil, polyvinyl butyral and PEG‐400 as dispersant, binder and plasticizer, respectively, and slip casted on a support layer. After the GOS scintillation layer is formed, a transparent polyethylene terephthalate film is covered on it as a protective layer. The X‐ray excited emission spectra of the obtained GOS phosphor screen is well match to the spectral response of a‐Si:H photodiode, and the spatial resolution was close to 3.7 LP/mm, which could meet the request of the commercial application.

Autoradiography validation of novel tau PET tracer [F-18]-MK-6240 on human postmortem brain tissue

[F-18]-MK-6240, a novel tau positron emission tomography (PET) tracer recently discovered for the in vivo detection of neurofibrillary tangles, has the potential to improve diagnostic accuracy in the detection of Alzheimer disease. We have examined regional and substrate-specific binding patterns as well as possible off-target binding of this tracer on human brain tissue to advance towards its validation. We applied [F-18]-MK-6240 phosphor screen and high resolution autoradiography to postmortem samples from patients with a definite pathological diagnosis of Alzheimer disease, frontotemporal lobar degeneration-tau (Pick’s disease, progressive supranuclear palsy and corticobasal degeneration), chronic traumatic encephalopathy, frontotemporal lobar degeneration-Tar DNA-binding protein 43 (TDP-43), dementia with Lewy bodies, cerebral amyloid angiopathy and elderly controls free of pathologic changes of neurodegenerative disease. We also directly compared the binding properties of [F-18]-MK-6240 and [F-18]-AV-1451 in human tissue, and examined potential nonspecific binding of both tau tracers to monoamine oxidases (MAO) by using autoradiography in the presence of selective monoamine oxidase A (MAO-A) and monoamine oxidase B (MAO-B) inhibitors. Our data indicate that MK-6240 strongly binds to neurofibrillary tangles in Alzheimer disease but does not seem to bind to a significant extent to tau aggregates in non-Alzheimer tauopathies, suggesting that it may have a limited utility for the in vivo detection of these pathologies. There is no evidence of binding to lesions containing β-amyloid, α-synuclein or TDP-43. In addition, we identified MK-6240 strong off-target binding to neuromelanin and melanin-containing cells, and some weaker binding to areas of hemorrhage. These binding patterns are nearly identical to those previously reported by our group and others for [F-18]-AV-1451. Of note, [F-18]-MK-6240 and [F-18]-AV-1451 autoradiographic binding signals were only weakly displaced by competing concentrations of selective MAO-B inhibitor deprenyl but not by MAO-A inhibitor clorgyline, suggesting that MAO enzymes do not appear to be a significant binding target of any of these two tracers. Together these novel findings provide relevant insights for the correct interpretation of in vivo [F-18]-MK-6240 PET imaging.

Focusing of x-rays emitted by a pyroelectric x-ray generator for micro x-ray fluorescence

Micro x-ray fluorescence spectroscopy (μXRF) is a technique for local chemical analyses of materials. There are several advantages in comparison to other similar methods like energy dispersive x-ray spectroscopy in a scanning electron microscope (SEM). The main advantage is the possible abdication of an evacuated sample chamber, which offers the possibility to analyze wet and oil contaminated specimens as well as specimens with intrinsic pores in addition to conventional samples used in SEM analyses. The subject of this report is the investigation of the pyroelectric effect with regard to its application for the generation of focused x-rays and first steps to a successive usage of the generated radiation for μXRF applications. In order to answer questions concerning the energy and intensity of primary radiation and geometric parameters for a successful focusing, this paper describes several experiments and results against the background of the described aims. Different setups and measurements have been used, optimizing the experimental setups to find the basic parameters to potentially generate focal spots of the primary x-rays. Emission behavior of electrons has been visualized and characterized by using a phosphor screen positioned in front of a pyroelectric crystal. Radiation has been measured and characterized by using an energy dispersive silicon drift x-ray detector. All x-ray experiments were executed in a vacuum test rig. This allowed the optimization of the working pressure of the residual gas surrounding the crystal in an evacuated atmosphere (rarefied air). It has been shown that emitted x-ray energies are strongly influenced by the vacuum pressure. Lithiumniobate and lithiumtantalate of different geometries were used as the pyroelectric material. Different target materials and target angles have been compared to optimize the combination of the constructed x-rays source with an aperture as well as with an x-ray optic to focus the primary x-rays. A glass fiber capillary lens was used as the focusing optic. A first step to a μXRF application is shown.

Pepperpot emittance measurements of ion beams from an electron beam ion source

A pepperpot emittance meter was used to measure the transverse emittance of multiply charged beams from REXEBIS, an Electron Beam Ion Source (EBIS) used for charge breeding of radioactive ion beams. The emittance meter is equipped with a Micro Channel Plate (MCP), a phosphor screen and a CCD camera for detection of the ion signal. The pulsed beam structure of low duty cycle imposes challenging constraints on the detector settings. In this article we give a careful analysis of the optimal operating parameters of the pepperpot emittance meter for ion beams of varying intensities. Emittance values for mass-separated and non-separated beams for different operating modes of the EBIS are presented. Furthermore we report on aberrations created in our injection∕extraction system.

Photon Counting Based on Solar-Blind Ultraviolet Intensified Complementary Metal-Oxide-Semiconductor (ICMOS) for Corona Detection

For the detection of weak signals, photon counting technology has attracted much attention. In this paper, a method based on photon counting is experimentally demonstrated to realize corona discharge detection at solar-blind ultraviolet (UV) wavelength. In our setup, a solar-blind UV optical filter and a Te-Cs cathode are used to eliminate the effects of light with undesired wavelengths, i.e., outside of the solar-blind band. A two-stage microchannel plate with a high voltage can achieve a gain of up to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> . A phosphor screen coupled with a CMOS can capture complete images without image distortion. By using an ICMOS, the setup can detect single-photon events. Then, applying photon counting statistics, a theoretical probability model of the photon numbers is obtained. Meanwhile, through analyzing the structure of the photon events considering both pixel and temporal resolution, two photon counting algorithms are proposed. Through experiments with an UV light source, the algorithm based on temporal resolution is proved to be more accurate. Finally, through an experiment with a corona discharge device, a solar-blind photon counting image is captured, and the photon number is calculated through the proposed counting algorithm. The probability curve of the practical photon numbers is acquired via several experiments carried out at the same conditions, which proves the accuracy of the setup and algorithm when compared with the theoretical probability model. Therefore, the proposed method can provide a scientific evaluation for corona detection.

Understanding Detrimental and Beneficial Grain Boundary Effects in Halide Perovskites.

Grain boundaries play a key role in the performance of thin-film optoelectronic devices and yet their effect in halide perovskite materials is still not understood. The biggest factor limiting progress is the inability to identify grain boundaries. Noncrystallographic techniques can misidentify grain boundaries, leading to conflicting literature reports about their influence; however, the gold standard - electron backscatter diffraction (EBSD) - destroys halide perovskite thin films. Here, this problem is solved by using a solid-state EBSD detector with 6000 times higher sensitivity than the traditional phosphor screen and camera. Correlating true grain size with photoluminescence lifetime, carrier diffusion length, and mobility shows that grain boundaries are not benign but have a recombination velocity of 1670 cm s-1 , comparable to that of crystalline silicon. Amorphous grain boundaries are also observed that give rise to locally brighter photoluminescence intensity and longer lifetimes. This anomalous grain boundary character offers a possible explanation for the mysteriously long lifetime and record efficiency achieved in small grain halide perovskite thin films. It also suggests a new approach for passivating grain boundaries, independent of surface passivation, to lead to even better performance in optoelectronic devices.

Feasibility Study of Phosphor Screen Containing Nano-Scale Anti-Reflection Layer for Improved Optical Properties in Indirect X-ray Detector.

With increasingly strict regulations regarding patient exposure, research on digital radiography technology has recently focused on indirect methods that can produce high-quality images for a low radiation dose. In particular, medical imaging systems based on indirect methods universally use rare-earth metal phosphors, because of their high atomic number and excellent luminescence efficiency. Thus, various studies aiming to improve the luminescence efficiency of phosphors have been conducted. Despite this research, however, the current luminescence efficiencies are insufficient. Here, we report a basic study aiming to develop a phosphor screen containing a three-quarter-wave optical-thickness layer to improve the light transmission efficiency. Specifically, the fabrication and measurement of a Gd2O2S:Tb phosphor screen containing a single three-quarter-wave optical-thickness layer is presented. The screen is fabricated via a screen-printing and spin-coating method. Based on histograms of the degree of luminescence and the pixel values, we demonstrate that the light transmission efficiency is improved by the three-quarter-wave optical-thickness layer. Note that analysis of the full width at half maximum of the pixel value distribution reveals the possibility of resolution loss when obtaining medical images. Overall, the results of this study confirm that the light transmission efficiency can be improved through use of a single-layer anti-reflection coating. However, because the emission spectrum of the Gd2O2S:Tb screen is in the 480-600-nm band, it is necessary to expand the areas exhibiting the lowest reflectance to the wavelengths at the edge of this band. Thus, further study should be conducted to optimize the optical thickness.

Muon Profile Measurement After Acceleration With a Radio-Frequency Quadrupole linac

We have measured the muon beam profile after acceleration using a radio frequency quadrupole linac (RFQ). Positive muons are injected to an aluminum degrader and negative muoniums (Mu−) are generated. The generated Mu−’s are extracted by an electrostatic lens and accelerated to 89 keV by the RFQ. The accelerated Mu−’s are transported to a beam profile monitor (BPM) through a quadrupole magnet pair and a bending magnet. The BPM consists of a micro-channel plate, a phosphor screen, and a CCD camera. The measured profile in the vertical direction is consistent with the simulation. This profile measurement is one of the milestones for realizing a muon linac for measurement of the muon anomalous magnetic moment at the Japan Proton Accelerator Research Complex.

Fast High-Energy X-Ray Imaging for Severe Accidents Experiments on the Future PLINIUS-2 Platform

The future PLINIUS-2 platform of the Commissariat a l’Energie Atomique (CEA) of Cadarache will be dedicated to the study of corium interactions in severe nuclear accidents, and will host innovative large-scale experiments. The nuclear measurement laboratory of CEA Cadarache is in charge of real-time high-energy X-ray imaging setups, for the study of the corium–water and corium–sodium interaction, and of the corium stratification process. Imaging such large and high-density objects requires a 15 MeV linear electron accelerator coupled to a tungsten target creating a high-energy bremsstrahlung X-ray flux, with corresponding dose rate about 100 Gy/min at 1 m. The signal is detected by phosphor screens coupled to high-framerate scientific CMOS cameras. The imaging setup is established using an experimentally validated home-made simulation software High-Energy MODeling for RAdiography and TOmography (MODHERATO). The code computes quantitative radiographic signals from the description of the source, object geometry and composition, detector, and geometrical configuration (magnification factor, etc.). It accounts for several noise sources (photonic and electronic noises, and swank and readout noise), and for image blur due to the source spot-size and to the detector unsharpness. In a view to PLINIUS-2, the simulation has been improved to account for the scattered flux, which is expected to be significant. This paper presents the scattered flux calculation using the Monte-Carlo N-particle transport code, and its integration into the MODHERATO simulation. Then, the validation of the improved simulation is presented, through confrontation to real measurement images taken on a small-scale equivalent setup on the PLINIUS platform. Excellent agreement is achieved. This improved simulation is therefore being used to design the PLINIUS-2 imaging setups (source, detectors, and cameras). Simulation will be presented for different configurations, as well as preliminary tests of alternative detectors considered for PLINIUS-2.