Fast X-ray Detector Research Articles

Solution processed high aspect ratio ultra-long vertically well-aligned ZnO nano scintillators for potential X-ray imaging applications

We report the photon (PL), electron (CL) and X-ray (XEL) induced luminescence characteristics of high aspect ratio ultra-long (~ 50 µm) ZnO nanorods (NRs) and discuss the potential for fast X-ray detection based on the consistent and efficient visible emission (~ 580 nm) from ZnO NRs. Nanostructured ZnO scintillators were rearranged to form a vertically well-aligned NR design in order to help light absorption and coupling resulting in luminescent and fast scintillation properties. The design of the nanorod array combines the key advantages of a low-cost growth technique together with environmentally friendly and widely available materials. A low temperature hydrothermal method was adopted to grow ZnO NRs in one cycle growth and their structural, optical and X-ray scintillation properties were investigated. The relatively short (~ 10 µm) ZnO NRs emitting in the near-band-edge region were found to be almost insensitive to X-rays. On the other hand, the higher XEL response of long ZnO NRs, which is a key parameter for evaluation of materials to be used as scintillators for high quality X-ray detection and imaging, along with a decay time response in the order of ns confirmed promising scintillation properties for fast and high-resolution X-ray detector applications.

A new method to characterize low stopping power and ultra-fast scintillators using pulsed X-rays

The demand for detectors with a time resolution below 100 ps is at the center of research in different fields, from high energy physics to medical imaging. In recent years, interest has grown in nanomaterials that, benefiting from quantum confinement effects, can feature ultra-fast scintillation kinetics and tunable emission. However, standard characterization methods for scintillation properties–relying on radiation sources with an energy range of several hundreds of keV–are not suitable for these materials due to their low stopping power, leading to a slowdown of this R&D line. We present a new method to characterize the time resolution and light output of scintillating materials, using a soft (0–40 keV energy) pulsed X-ray source and optimized high-frequency readout electronics. First, we validated the proposed method using standard scintillators. Then, we also demonstrated the feasibility to measure the time resolution and get an insight into the light output of nanomaterials (InGaN/GaN multi-quantum well and CsPbBr3 perovskite). This technique is, therefore, proposed as a fundamental tool for characterization of nanomaterials and, more in general, of materials with low stopping power to better guide their development. Moreover, it opens the way to new applications where fast X-ray detectors are requested, such as time-of-flight X-ray imaging.

Characterization of 128 × 128 MM-PAD-2.1 ASIC: a fast framing hard x-ray detector with high dynamic range

We characterize a new x-ray Mixed-Mode Pixel Array Detector (MM-PAD-2.1) Application Specific Integrated Circuit (ASIC). Using an integrating pixel front-end with dynamic charge removal architecture, the MM-PAD-2.1 ASIC extends the maximum measurable x-ray signal (in 20 keV photon units) to > 107 x-rays/pixel/frame while maintaining a low read noise across the full dynamic range, all while imaging continuously at a frame rate of up to 10 kHz. The in-pixel dynamic charge removal mechanism prevents saturation of the input amplifier and proceeds in parallel with signal integration to achieve deadtime-less measurements with incident x-ray rates of > 1010 x-rays/pixel/s. The ASIC format consists of 128 × 128 square pixels each 150 μm on a side and is designed to be 3-side buttable so large arrays can be effectively tiled. Here we use both laboratory x-ray sources and the Cornell High Energy Synchrotron Source (CHESS) to characterize two single ASIC prototype detectors for both low (single x-ray) and high incident flux detection. In the first detector the ASIC was solder bump-bonded to a 500 μm thick Si sensor for efficient detection of x-rays below 20 keV, whereas the second detector used a 750 μm thick CdTe sensor for x-rays above ∼ 20 keV.

Fully volumetric tracking of melting fronts in phase change materials with computed tomography

Recent advances in laboratory X-ray computed tomography (XCT) enabled short acquisition times on the order of a few minutes, which enable the investigation of dynamic processes in-situ by time-lapse measurements. These advances open new opportunities for revealing information on the solid-liquid phase transformation occurring in phase changes materials (PCMs), which are a promising solution for designing compact latent thermal energy storage systems (LTES). In this contribution we report results obtained from the XCT System, “LuCi”, recently installed at Lucerne university of Applied Sciences and Arts, where the evolution of the melting process in an ice cube confined within a cylindrical, X-ray transparent sample holder is tracked. Our results indicate that even tiny differences of a few percent in the density of the two different phases can be differentiated in XCT measurements. The high-power X-ray source and a fast X-ray detector of LuCi enable the acquisition of a XCT measurement in a short period (< 1 – 6 minutes). By using proper image processing methods, estimates for the volumetric melting rate, the local melting front velocity, and the tree dimensional (3D) shape of the melting front were obtained from the four-dimensional (4D) imaging data. These results will help to build more efficient thermal energy storage systems in the future, which will support the energy turnaround.

A Diamond-Based Dose-per-Pulse X-ray Detector for Radiation Therapy

One of the goals of modern dynamic radiotherapy treatments is to deliver high-dose values in the shortest irradiation time possible. In such a context, fast X-ray detectors and reliable front-end readout electronics for beam diagnostics are crucial to meet the necessary quality assurance requirements of care plans. This work describes a diamond-based detection system able to acquire and process the dose delivered by every single pulse sourced by a linear accelerator (LINAC) generating 6-MV X-ray beams. The proposed system is able to measure the intensity of X-ray pulses in a limited integration period around each pulse, thus reducing the inaccuracy induced by unnecessarily long acquisition times. Detector sensitivity under 6-MV X-photons in the 0.1–10 Gy dose range was measured to be 302.2 nC/Gy at a bias voltage of 10 V. Pulse-by-pulse measurements returned a charge-per-pulse value of 84.68 pC, in excellent agreement with the value estimated (but not directly measured) with a commercial electrometer operating in a continuous integration mode. Significantly, by intrinsically holding the acquired signal, the proposed system enables signal processing even in the millisecond period between two consecutive pulses, thus allowing for effective real-time dose-per-pulse monitoring.

Converting existing optical detectors into fast x-ray detectors.

The very short burn time and small size of burning plasmas created at advanced laser-fusion facilities will require high-spatial-resolution imaging diagnostics with fast time resolution. These instruments will need to function in an environment of extremely large neutron fluxes that will cause conventional diagnostics to fail because of radiation damage and induced background levels. One solution to this challenge is to perform an ultrafast conversion of the x-ray signals into the optical regime before the neutrons are able to reach the detector and then to relay image the signal out of the chamber and into a shielded bunker, protected from the effects of these neutrons. With this goal in mind, the OMEGA laser was used to demonstrate high-temporal-resolution x-ray imaging by using an x-ray snout to image an imploding backlighter capsule onto a semiconductor. The semiconductor was simultaneously probed with the existing velocity interferometry system for any surface reflector (VISAR) diagnostic, which uses an optical streak camera and provided a one-dimensional image of the phase in the semiconductor as a function of time. The phase induced in the semiconductor was linearly proportional to the x-ray emission from the backlighter capsule. This approach would then allow a sacrificial semiconductor to be attached at the end of an optical train with the VISAR and optical streak camera placed in a shielded bunker to operate in a high neutron environment and obtain time-dependent one-dimensional x-ray images or time-dependent x-ray spectra from a burning plasma.

Diamond composite with embedded YAG:Ce nanoparticles as a source of fast X-ray luminescence in the visible and near-IR range

The diamond composite materials with embedded yttrium-aluminum garnet doped with cerium (YAG:Ce) nanoparticles have been produced by microwave plasma-assisted chemical vapor deposition (CVD). Nanoparticles were synthesized by co-precipitation from an aqueous solution while CVD diamond served as the transparent matrix with high thermal conductivity, hardness, and resistivity to radiation damage. The composite films show high-intensity X-ray luminescence (XRL) with a broad band peaking around the wavelength of 550 nm (5d → 4f transition in Ce3+ ion), and a narrow peak of silicon-vacancy (Si–V) centers at 738 nm. The characteristic decay time was measured at τCe < 50 ns for cerium emission and at τSiV∼1 ns for Si–V centers. Excitation spectra of both luminescence types measured near yttrium K-edge (17.1 keV) show a strong correlation, attributed to the excitation of Si–V luminescence by photoelectrons ejected from YAG:Ce nanoparticles. The discovered phenomenon suggests a new way to control X-ray visualization by luminescent diamond composites for fast X-ray detectors and screens.

Fast X-ray detectors based on bulk β-Ga2O3 (Fe)

(010) EFG-grown Fe-doped β-Ga2O3 was tested as a low-noise X-ray detector with Ti/Au electrodes vertical structure. Its performance at low, high and no applied voltages was examined. The fabricated detector showed high X-ray detection performance manifested in its signal’s short fall and rise time ( 103). Moreover, the X-ray-induced current signal exhibits high stability. Sub-band UV photocurrent signal showed a significantly slower response compared to X-ray-induced conductivity signal. Possible charge transport mechanisms involving ion migration are suggested and discussed. In this study, Fe doping is shown to significantly improve X-ray detection performance of Ga2O3, consolidating the applicability of Ga2O3 as a next-generation X-ray detector functioning with low power, high SNR and linearity, and significantly improved transient characteristics.

Studies of kaonic atoms at the DAΦNE collider: from SIDDHARTA to SIDDHARTA-2

The DAΦNE electron-positron collider of the Laboratori Nazionali di Frascati of INFN is a worldwide unique low-energy kaon source and for this reason is suitable for low-energy kaon physics like kaonic atoms and kaon-nucleons/nuclei interaction studies. Kaonic atoms are atomic systems where an electron is replaced by a negatively charged kaon, containing the strange quark, which interacts in the lowest orbits with the nucleus also by the strong interaction. As a result, their study offers the unique opportunity to perform experiments equivalent to scattering at vanishing relative energy. This allows to study the strong interaction between the antikaon and the nucleon or the nucleus “at threshold”, without the need of ad hoc extrapolation to zero energy, as in scattering experiments. The most precise kaonic hydrogen measurement to date, together with an exploratory measurement of kaonic deuterium, were carried out by the SIDDHARTA collaboration at the DAΦNE electron-positron collider of LNF-INFN, by combining the excellent quality kaon beam delivered by the collider with new experimental techniques, as fast and precise Silicon-Drift X-ray Detectors. The measurement of kaonic deuterium will be realized in the near future by SIDDHARTA-2, a major upgrade of SIDDHARTA.

Synchrotron characterization of high-Z, current-mode x-ray detectors.

Fast x-ray detectors are critical tools in pulsed power and fusion applications, where detector impulse response of a nanosecond or better is often required. Semiconductor detectors can create fast, sensitive devices with extensive operational flexibility. There is typically a trade-off between detector sensitivity and speed, but higher atomic number absorbers can increase hard x-ray absorption without increasing the charge collection time, provided carriers achieve high velocity. This paper presents x-ray pulse characterization conducted at the Advanced Photon Source of x-ray absorption efficiency and temporal impulse response of current-mode semiconductor x-ray detectors composed of Si, GaAs, and CdTe.

Kaonic Deuterium Measurement with SIDDHARTA-2 on DA$\Phi $NE

The interaction of antikaons with nucleons and nuclei in the low-energy regime represents an active research field in hadron physics with still many important open questions. The investigation of light kaonic atoms is, in this context, a unique tool to obtain precise information on this interaction. The most precise kaonic hydrogen measurement to date, together with an exploratory measurement of kaonic deuterium, were carried out by the SIDDHARTA Collaboration at the DAΦNE electron–positron collider of LNF-INFN, by combining the excellent quality kaon beam delivered by the collider with new experimental techniques, as fast and precise Silicon-Drift X-ray detectors. The measurement of kaonic deuterium will be realized in the near future by SIDDHARTA-2, a major upgrade of SIDDHARTA.

Ice formation and solvent nanoconfinement in protein crystals.

Ice formation within protein crystals is a major obstacle to the cryocrystallographic study of protein structure, and has limited studies of how the structural ensemble of a protein evolves with temperature in the biophysically interesting range from ∼260 K to the protein-solvent glass transition near 200 K. Using protein crystals with solvent cavities as large as ∼70 Å, time-resolved X-ray diffraction was used to study the response of protein and internal solvent during rapid cooling. Solvent nanoconfinement suppresses freezing temperatures and ice-nucleation rates so that ice-free, low-mosaicity diffraction data can be reliably collected down to 200 K without the use of cryoprotectants. Hexagonal ice (Ih) forms in external solvent, but internal crystal solvent forms stacking-disordered ice (Isd) with a near-random stacking of cubic and hexagonal planes. Analysis of powder diffraction from internal ice and single-crystal diffraction from the host protein structure shows that the maximum crystallizable solvent fraction decreases with decreasing crystal solvent-cavity size, and that an ∼6 Å thick layer of solvent adjacent to the protein surface cannot crystallize. These results establish protein crystals as excellent model systems for the study of nanoconfined solvent. By combining fast cooling, intense X-ray beams and fast X-ray detectors, complete structural data sets for high-value targets, including membrane proteins and large complexes, may be collected at ∼220-240 K that have much lower mosaicities and comparable B factors, and that may allow more confident identification of ligand binding than in current cryocrystallographic practice.

The kaonic atoms research program at DAΦNE: overview and perspectives

The interaction of antikaons with nucleons and nuclei in the low-energy regime represents an active research field in hadron physics with still many important open questions. The investigation of light kaonic atoms is, in this context, a unique tool to obtain precise information on this interaction. The energy shift and broadening of the lowest-lying states of such atoms, induced by the kaon-nucleus strong interaction, can be determined with high precision from atomic X-ray spectroscopy. This experimental method provides unique information to understand the low energy kaon-nucleus interaction at threshold. The lightest atomic systems, kaonic hydrogen and kaonic deuterium, deliver the isospin-dependent kaon-nucleon scattering lengths. The most precise kaonic hydrogen measurement to date, together with an exploratory measurement of kaonic deuterium, were carried out by the SIDDHARTA collaboration at the DAΦNE electron-positron collider of LNF-INFN, by combining the excellent quality kaon beam delivered by the collider with new experimental techniques, as fast and precise X-ray detectors: Silicon Drift Detectors. The measurement of kaonic deuterium will be realized in the near future by SIDDHARTA-2, a major upgrade of SIDDHARTA. In this paper an overview of the main results obtained by SIDDHARTA together with the future plans, are given.

MIXI: Mobile Intelligent X-Ray Inspection System

A novel, low-dose Mobile Intelligent X-ray Inspection (MIXI) concept is being developed at RadiaBeam Technologies. The MIXI concept relies on a linac-based, adaptive, ramped energy source of short X-ray packets of pulses, a new type of fast X-ray detector, rapid processing of detector signals for intelligent control of the linac, and advanced radiography image processing. The key parameters for this system include: better than 3 mm line pair resolution; penetration greater than 320 mm of steel equivalent; scan speed with 100% image sampling rate of up to 15 km/h; and material discrimination over a range of thicknesses up to 200 mm of steel equivalent. Its minimal radiation dose, size and weight allow MIXI to be placed on a lightweight truck chassis.

Fast x-ray detector system with simultaneous measurement of timing and energy for a single photon

We developed a fast X-ray detector system for nuclear resonant scattering (NRS) experiments. Our system employs silicon avalanche photo-diode (Si-APD) as a fast X-ray sensor. The system is able to acquire both timing and energy of a single X-ray photon simultaneously in a high rate condition, 106 counts per second for one Si-APD. The performance of the system was investigated in SPring-8, a synchrotron radiation facility in Japan. Good time resolution of 120 ps (FWHM) was achieved with a slight tail distribution in the time spectrum by a level of 10-9 at 1 ns apart from the peak. Using this system, we successfully observed the NRS from the 26.27-keV level of mercury-201, which has a half-life of 630(50) ps. We also demonstrated the reduction of background events caused by radioactive decays in a radioactive sample by discriminating photon energy.

A high time resolution x-ray diagnostic on the Madison Symmetric Torus.

A new high time resolution x-ray detector has been installed on the Madison Symmetric Torus (MST) to make measurements around sawtooth events. The detector system is comprised of a silicon avalanche photodiode, a 20 ns Gaussian shaping amplifier, and a 500 MHz digitizer with 14-bit sampling resolution. The fast shaping time diminishes the need to restrict the amount of x-ray flux reaching the detector, limiting the system dead-time. With a much higher time resolution than systems currently in use in high temperature plasma physics experiments, this new detector has the versatility to be used in a variety of discharges with varying flux and the ability to study dynamics on both slow and fast time scales. This paper discusses the new fast x-ray detector recently installed on MST and the improved time resolution capabilities compared to the existing soft and hard x-ray diagnostics. In addition to the detector hardware, improvements to the detector calibration and x-ray pulse identification software, such as additional fitting parameters and a more sophisticated fitting routine are discussed. Finally, initial data taken in both high confinement and standard reversed-field pinch plasma discharges are compared.

Lead Tungstate and Silicon Photomultipliers for Transmission Z-spectroscopy in Cargo Inspection Systems

The bremsstrahlung X-ray spectrum in high-energy, high-intensity X-ray cargo inspection systems is attenuated and modified by cargo materials depending on the cargo atomic number (Z). Spectroscopy of transmitted x rays is thus useful to measure the approximate Z of the cargo. Due to the broad features of the energy spectrum, excellent energy resolution is not required. Such “Z-Spectroscopy” (Z-SPEC) is possible at low enough count rates. A statistical approach, Z-SCAN (Z-determination by Statistical Count-rate ANalysis), can also be used, complementing Z-SPEC at high count rates. Both approaches require fast X-ray detectors and fast digitizers. Z-SPEC, in particular, benefits from very fast scintillators, in order to avoid signal pile-up.Preferentially, Z-SPEC, Z-SCAN and cargo imaging are implemented in a single detector array to reduce system cost, weight, and complexity. To preserve good spatial resolution of the imaging subsystem, dense scintillators are required.Previously, we studied ZnO, BaF2 and PbWO4, as well as suitable photo-detectors, read-out electronics and digitizers. ZnO is not suitable because it self-absorbs its scintillation light. BaF2 emits in the UV, either requiring fast wavelength shifters or UV-sensitive solid state read-out devices, and it also has a long decay time component. PbWO4 is currently the most attractive choice because it does not have these problems, but it is significantly slower and has low light output. There is thus a need for alternative fast high-density scintillators that emit visible light. Alternatively, there is a need for a fast solid-state read-out device that is sensitive to UV light for use with BaF2, or other UV-emitting scintillators. Here, we present results of tests performed with PbWO4 crystals, reflector materials and silicon photomultipliers.

Fast and Wide Dynamic Range X-ray Detectors Enable Novel Science

New and improved synchrotron radiation sources enable experiments that demand the ability to acquire successive hard (e.g., 10 keV) x-ray images at sub-microsecond rates or to quickly acquire x-ray patterns encompassing intensities that vary by 10^6 or more across single images. We describe two novel integrating Pixel Array Detectors (PADs) developed at Cornell University that accomplish these objectives. The Mixed-Mode PAD (MM-PAD) frames at &gt; 1 KHz and can readily detect signals within a single image ranging from single x-rays to over 107 x-rays/pixel/frame. The Keck-PAD can acquire 8-12 successive images at frame rates approaching 10 MHz with a range of single x-rays up to about 10^4 x-rays/pixel/frame. The operating principles of the MM-PAD and Keck-PAD, respectively, are described. We also describe examples of experiments that have been performed at various synchrotron radiation sources.

Scaling-induced enhancement of X-ray luminescence in CsI(Na) crystals

We report on the diameter dependence luminescence property of CsI(Na) crystals under X-ray excitation. When CsI(Na) crystal diameter decreases to nano-scale, the X-ray excited luminescence decay time is speeding up from ∼600 ns to ∼10 ns and 420 nm Na-related cathodeluminescence is affected drastically. The reason is confirmed that diameter reduction leads surface effect to accelerate the excitons' quenching. These measurement results identify a critical distinguished boundary ∼20 μm) of crystal diameter, which provide a new way to potential application of CsI(Na) crystals in the development of fast X-ray and gamma scintillator film detectors with large area.

In Vivo Imaging of Neurovascular Remodeling After Stroke

Stroke is one of the leading causes of adult disability throughout the world and, even though neural mechanisms of loss of function have been extensively studied, many aspects of poststroke cerebral responses remain poorly understood. Of particular interest is the mounting evidence of the capacity of the adult brain to reorganize after injury, which is believed to contribute to limitation of the extent of neural dysfunction and to restoration of affected neural functions. Processes such as neuronal plasticity, glial proliferation, and neovascularization may be essential for preservation or recovery of function after stroke and may conceivably go hand-in-hand at nearby and remote sites of active tissue reorganization.1,2 Specifically, the acute initiation of neurovascular remodeling, stimulating the proliferation and growth of existing arteries/arterioles (ie, arteriogenesis) or new capillaries (ie, angiogenesis), may be critical to facilitate the survival and restructuring of neural tissue, which ultimately may contribute to functional recovery at later stages.3 A variety of vascular imaging strategies is available for in vivo detection, characterization, and quantification of these processes, which can significantly aid in elucidation of the role of neurovascular remodeling after stroke, as discussed in this review. Because most of the described imaging modalities are present in experimental and clinical settings, this raises significant opportunities for translational studies. Growth and remodeling of existing and nascent vascular networks in health and disease involve a number of critical steps that have been comprehensively described by Risau4 and Carmeliet.5 Arteriogenesis involves adaptive growth and proliferation of preexisting (collateral) arteries and arterioles in response to increase in intravascular shear forces. The increased shear stress leads to upregulation of cell adhesion molecules, followed by accumulation of monocytes and other leukocytes that release cytokines and growth factors around the proliferating and maturating arteries.6 Although arteriogenic growth of collateral …