Hard X-ray Imaging Research Articles

Development of the ZnO:Ga microrods - epoxy composite as a scintillation screen for ultrafast X-ray detection

In order to satisfy the requirements of ultrafast and hard X-ray detection and imaging in the existing and upcoming experimental facilities for high energy physics, the ZnO:Ga microrods - epoxy (ZnO:Ga-EP) composite were successfully synthesized by the hydrothermal and polymerization method. Under X-ray excitation, the ZnO:Ga-EP composite exhibits a narrow and intense near-band-edge emission located at 390 nm. More importantly, the decay time of the near-band-edge emission can reach up to subnanosecond (<1 ns), which is extremely significant for ultrafast X-ray detection and imaging. In addition, there exist an energy transfer from the epoxy host to the ZnO:Ga microrods in the ZnO:Ga-EP composite. In conclusion, this work indicates the ZnO:Ga-EP composite can be used as a potential ultrafast X-ray scintillation screen for applications in ultrafast and hard X-ray detectors.

Spatial Resolution of an Inorganic Crystal-Based Hard X-Ray Imager

Gigahertz hard X-ray imaging presents an unprecedented challenge to both timing and spatial resolutions for inorganic scintillator-based front imagers. A beam test with 30-keV X-rays from the Advanced Photon Source (APS) showed that 5-mm BaF2 plates resolve well 30-keV X-ray septuplets of 27-ps width and 2.83-ns spacing. Pixelated crystal screens with a pitch down to $400~\mu \text{m}$ were fabricated by mechanic slicing for BaF2, BaF2:Y, and LYSO crystals. Their spatial resolution and detection efficiency for hard X-rays are defined by the pitch and thickness, respectively. Thicker monolithic crystal screens show poorer spatial resolution, which may be improved using a small optical aperture with a loss in both efficiency and dynamic range for hard X-rays. Future plans include pursuing smaller crystal pitches by laser slicing and research and development on novel ultrafast inorganic scintillators.

Morphology and Photoluminescence Properties of Lu2O3:Eu Films Prepared by LCVD Method

Efficient and dense scintillator Lu2O3:Eu is one of the most promising candidates used for high resolution hard X-ray imaging detector. In this paper, Lu2O3:Eu films were prepared through laser chemical vapor deposition on single crystal yttrium stabilized zirconia substrates. The structure and morphology of the films were investigated by X-ray diffraction and scanning electron microscopy. Lu2O3:Eu films, with micro-columnar and single crystal morphologies, were obtained through adjusting growth parameters. The growth mechanisms were also discussed based on related phenomena. The photoluminescence properties of the films were measured and discussed, including photoluminescence excitation, photoluminescence spectra and photoluminescence decay curves.

Optimizing contrast and spatial resolution in hard x-ray tomography of medically relevant tissues

Hard x-ray tomography with Paganin's widespread single-distance phase retrieval filter improves the contrast-to-noise ratio (CNR) while reducing spatial resolution (SR). We demonstrate that a Gaussian filter provided larger CNR at high SR with interpretable density measurements for two medically relevant soft tissue samples. Paganin's filter produced larger CNR at low SR, though a priori assumptions were generally false and image quality gains diminish for CNR &amp;gt; 1. Therefore, simple absorption measurements of low-Z specimens combined with Gaussian filtering can provide improved image quality and model-independent density measurements compared to single-distance phase retrieval.

Preferential Stripping of a Lithium Protrusion Resulting in Recovery of a Planar Electrode

Lithium metal is a high-energy-density battery electrode material, but the largely irreversible growth of lithium protrusions on an initially planar electrode during cycling makes it unsuitable for incorporation into a commercial battery. In this study, a lithium electrode with globular protrusions was stripped electrochemically, and the local morphology of the electrode as a function of time was determined by hard X-ray tomography. We demonstrate that globules are preferentially stripped compared to a planar electrode in our system, which incorporates a nanostructured block copolymer electrolyte. We report current density at the electrode as a function of micron-scale position and time. The local current density during the electrode healing process calculated from a reference frame at the electrode/electrolyte interface provides insight into the driving forces responsible for selective stripping of the globule. These results imply the possibility of discharging protocols that may return a lithium electrode to its initial planar state.

AGILE search for gamma-ray counterparts of gravitational wave events

AGILE is a space mission of the Italian Space Agency dedicated to X-ray and gamma-ray astrophysics operating since 2007. Since the discovery of gravitational wave (GW) events by the LIGO-Virgo Collaboration (LVC) announced in February 2016, AGILE is playing a very important role in the search for possible X-ray and gamma-ray counterparts. The large fields of view of the gamma-ray and hard X-ray imagers (2.5 sr and 1 sr, respectively) and the current spinning mode allow AGILE to cover at any moment a very large fraction of the sky. We present here an overview of AGILE observations of GW events during the LVC observing periods O1 and O2 which span the time interval September 2015–August 2017. In particular, we focus on the main characteristics of AGILE observations of the events GW150914, GW170104, and GW170817. The latter event is of great relevance being associated with a “kilonova” counterpart: we establish important physical constraints on the possible $$\gamma$$-ray emission from a magnetar-like remnant in the first $$\sim 1000$$ s following the GW event time. We also present further developments and preliminary results obtained in preparation of the O3 observing run (start in April 2019). AGILE is fully operative in the search for GW event counterparts, and continues to observe the sky in a unique way because of its combination of large field-of-view hard X-ray and gamma-ray detectors.

Joint hard X-ray observations with ASO-S/HXI and SO/STIX

This paper discusses the potential of future joint hard X-ray solar flare observations between the Hard X-ray Imager (HXI) onboard the Advanced Space-based Solar Observatory (ASO-S) mission and the Spectrometer/Telescope for Imaging X-rays (STIX) on Solar Orbiter. The different viewing perspectives of the two telescopes relative to the Sun will allow us for the first time to systematically study non-thermal hard X-ray emissions stereoscopically. During the 4-years of the nominal mission of ASO-S, we expect to jointly observe about 160 flares above GOES M1 class to systematically study hard X-ray directivity. For about 16 partially limb-occulted STIX flares, we will have observations of the entire flare by HXI. Such observations will enable us to simultaneously study the all-important coronal hard X-ray sources, which are generally lost in the instrument’s individual imaging dynamic range, in combination with the chromospheric footpoint emissions. The two different detector systems used in the two telescopes make the relative calibration between the two instruments a key task that needs to be addressed before creditable science results can be published. If an accurate inter-calibration can be achieved using jointly observed flares on the disk, observations with HXI and STIX will provide new and essential key diagnostics for solar flare physics.

Simulations and software development for the Hard X-ray Imager onboard ASO-S

China’s first solar mission, the Advanced Space-based Solar Observatory (ASO-S), is now changing from Phase B to Phase C. Its main scientific objectives are summarized as ‘1M2B’, namely magnetic field and two types of bursts (solar flares and coronal mass ejections). Among the three scientific payloads, Hard X-ray Imager (HXI) observes images and spectra of X-ray bursts in solar flares. In this paper, we briefly report on the progresses made by the HXI science team (data and software team) during the design phase (till May 2019). These include simulations of HXI imaging, optimization of HXI grids, development of imaging algorithms, estimation of orbital background, as well as in-orbit calibration plan. These efforts provided guidance for the engineering, improved HXI’s imaging capability and reduced the cost of the instrument.

Hard X-ray Imager (HXI) onboard the ASO-S mission

Hard X-ray Imager (HXI) is one of the three scientific instruments onboard the Advanced Spacebased Solar Observatory (ASO-S) mission, which is proposed for the 25th solar maximum by the Chinese solar community. HXI is designed to investigate the non-thermal high-energy electrons accelerated in solar flares by providing images of solar flaring regions in the energy range from 30 keV to 200 keV. The imaging principle of HXI is based on spatially modulated Fourier synthesis and utilizes about 91 sets of bi-grid sub-collimators and corresponding LaBr3 detectors to obtain Fourier components with a spatial resolution of about 3 arcsec and a time resolution better than 0.5 s. An engineering prototype has been developed and tested to verify the feasibility of design. In this paper, we present background, instrument design and the development and test status of the prototype.

Advanced Space-based Solar Observatory (ASO-S): an overview

The Advanced Space-based Solar Observatory (ASO-S) is a mission proposed for the 25th solar maximum by the Chinese solar community. The scientific objectives are to study the relationships between the solar magnetic field, solar flares and coronal mass ejections (CMEs). Three payloads are deployed: the Full-disk vector MagnetoGraph (FMG), the Lyman-α Solar Telescope (LST) and the Hard X-ray Imager (HXI). ASO-S will perform the first simultaneous observations of the photospheric vector magnetic field, non-thermal imaging of solar flares, and the initiation and early propagation of CMEs on a single platform. ASO-S is scheduled to be launched into a 720 km Sun-synchronous orbit in 2022. This paper presents an overview of the mission till the end of Phase-B and the beginning of Phase-C.

Investigation of (micro-)meteoritic materials at the new hard X-ray imaging PUMA beamline for heritage sciences.

At the French synchrotron facility SOLEIL, a new X-ray imaging facility PUMA (Photons Utilisés pour les Matériaux Anciens) has been made available to scientific communities studying materials from cultural heritage. This new instrument aims to achieve 2D and 3D imaging with microscopic resolution, applying different analytical techniques including X-ray fluorescence spectroscopy (XRF), X-ray absorption spectroscopy (XAS), X-ray diffraction and phase-contrast imaging. In order to discover its capabilities a detailed analytical characterization of this beamline as an analytical and imaging tool is deemed necessary. In this work, (confocal) XRF and XAS analyses are demonstrated using the Seymchan pallasite meteorite and an Antarctic unmelted micrometeorite as case studies. The obtained spatial resolution (2 µm × 3 µm) and sensitivity (detection limits <10 p.p.m. for 1 s acquisition at 18 keV) show that PUMA is a competitive state-of-the-art beamline, providing several high-profile and high-in-demand analytical methods while maintaining applicability towards a wide range of heritage-oriented sciences.

Ex vivo evaluation of an atherosclerotic human coronary artery via histology and high-resolution hard X-ray tomography

Atherosclerotic arteries exhibit characteristic constrictions and substantial deviations from cylindrical shape. Therefore, determining the artery’s cross-section along the centerline is challenging, although high-resolution isotropic three-dimensional data are available. Herein, we apply high-resolution computed tomography in absorption and phase to a plaque-containing human artery post-mortem, through the course of the preparation stages for histology. We identify the impact of paraffin embedding and decalcification on the artery lumen. For automatic extraction of lumen’s cross-section along centerline we present a dedicated pipeline. Comparing fixated tissue before and after paraffin embedding gives rise to shape changes with lumen reduction to 50–80%. The histological slicing induces further deformations with respect to tomography. Data acquired after decalcification show debris unintentionally distributed within the vessel preventing the reliable automatic lumen segmentation. Comparing tomography of laboratory- and synchrotron-radiation-based X rays by means of joint histogram analysis leads us to conclude that advanced desktop tomography is capable of quantifying the artery’s lumen as an essential input for blood flow simulations. The results indicate that the most reliable lumen quantification is achieved by imaging the non-decalcified specimen fixed in formalin, using phase contrast modality and a dedicated processing pipeline. This study focusses on a methodology to quantitatively evaluate diseased artery segments post-mortem and provides unique structural parameters on the treatment-induced local shrinkage, which will be the basis of future studies on the flow in vessels affected by constrictions.

BaF2:Y and ZnO:Ga crystal scintillators for GHz hard X-ray imaging

Abstract Gigahertz (GHz) hard X-ray imaging for the proposed MaRIE project presents an unprecedented challenge for the front imager in both speed and radiation hardness. We proposed two ultrafast inorganic-scintillator-based front imager concepts: a total absorption one and a multilayer one, and investigated optical and scintillation properties for a set of inorganic scintillators at the Caltech HEP crystal laboratory. The results show that yttrium doped barium fluoride crystals and gallium doped ZnO nano-particle-based films are promising for these two concepts, respectively. In this paper, we report their optical and scintillation property as well recent progresses on slow component suppressing in barium fluoride crystals by yttrium doping, and its radiation hardness.

Design and Analysis of Hard X-Ray Microscope Employing Toroidal Mirrors Working at Grazing-Incidence

A high resolution microscope is designed for plasma hard X-ray (10–20[Formula: see text]keV) imaging diagnosis. This system consists of two toroidal mirrors, which are nearly parallel, with an angle twice that of the grazing incidence angle and a plane mirror for spectral selection and correction of optical axis offset. The imaging characteristics of single toroidal mirror and double mirrors are analyzed in detail by the optical path function. The optical design, parameter optimization, image quality simulation and analysis of the microscope are carried out. The optimized hard X-ray microscope has a resolution better than 5[Formula: see text][Formula: see text]m at 1[Formula: see text]mm object field of view. The experimental data shows that the variation of the resolution is smaller in the direction of incident angle decrease than that in the increasing direction.

Initial assessment of multilayer silicon detectors for hard X-ray imaging

Silicon detectors with lower material budget, ultrafast readout and radiation hardness are under developments. These unique features make pixelized silicon sensors a good option for hard X-ray imaging. To verify the performance of spatial resolution and energy sensitivity of silicon sensors to hard X-rays, a two layer setup of Pixelink PL-D725MU sensors has been tested at the Argonne National Laboratory Advanced Photon Source (APS) ID-10 sector with 29.2 keV high photon flux (4.5×10^8 to 4.5×10^(10) photons per second) X-rays. Better than 3 μm spatial resolution and clear energy characterization have been achieved by both layers. Commercial CMOS sensors with superior spatial resolution could be used for phase contrast imaging in current synchrotrons. These studies pave the path for future multilayer ultrafast silicon sensor development with ns to sub-ns readout speeds in hard X-ray imaging at synchrotrons and XFEL beamlines.

Spectrometer of hard X-ray imager payload onboard the ASO-S mission

A spaceborne hard X-ray spectrometer, composed of an array of 99 scintillation detectors and associated readout electronics, has been developed for the hard X-ray imager (HXI). The HXI is one of the three payloads onboard the advanced space-based solar observatory (ASO-S), which is scheduled to be launched in early 2022 as the first Chinese solar satellite. $$\hbox {LaBr}_3$$ scintillators and photomultiplier tubes with a super bialkali cathode are used to achieve an energy resolution better than 20% at 30 keV. Further, a new multi-channel charge-sensitive readout application-specific integrated circuit guarantees high-frequency data acquisition with low power consumption. This paper presents a detailed design of the spectrometer for the engineering model of the HXI and discusses its noise and linearity performance.

Ultrafast inorganic scintillator-based front imager for Gigahertz Hard X-ray imaging

State-of-the art X-ray imaging cameras using silicon sensors for X-ray detection have demonstrated a frame-rate of 10 MHz and excellent performance for X-ray energies below 20 keV. We proposed a pixelated ultrafast inorganic scintillator-based front imager for GHz hard X-ray imaging. The proposed imager is featured with a total absorption for hard X-ray photons, and provides sub-ns scintillation pulse width crucial for X-ray bunches of a few ns spacing foreseen at the proposed MaRIE facility. We measured temporal response of a dozen ultrafast and fast inorganic scintillators at the 10-ID-B site of the Advanced Photon Source (APS) of ANL. Crystal’s response to hybrid X-ray beam of 30 keV, consisting of singlet bunches of 50 ps width and septuplet bunches of 27 ps width with 2.83 ns bunch spacing, was measured. Ultrafast inorganic scintillators, such as BaF2:Y and ZnO:Ga, show clearly resolved X-ray bunches for septuplets, as well as no degradation of amplitude for continuous eight septuplets, providing a proof of principle for the ultrafast inorganic scintillator-based total absorption front imager for the proposed MaRIE project.

In-situ radiography of a split-Hopkinson bar dynamically loaded materials

This paper presents a description and the demonstration results of a custom-designed bespoke Split-Hopkinson Pressure Bar (SHBP) which has been installed at the ID-19 beamline at the European Synchrotron Radiation Facility (ESRF). Building upon recent advances in real-time x-ray imaging, this system enables the study of dynamic mechanical phenomena through ultra-high-speed x-ray phase-contrast radiographs captured every 528 ns with high spatial-temporal resolution. By adding synchronized strain gauges measurements in the same experiment, bulk stress-strain behaviour can be correlated to the local processes underlying deformation, damage and failure. This article briefly outlines the newly installed hardware and its design. Demonstration experiments showing damage development in dynamically loaded Ti-6Al-4V and concrete are presented to underline the potential of an SHBP to be used in combination with synchrotron-based high-speed hard x-ray imaging.

NuSTAR Observations of the Supernova Remnant RX J1713.7–3946

Abstract The shock waves of supernova remnants (SNRs) are prominent candidates for the acceleration of the Galactic cosmic rays. SNR RX J1713.7−3946 is one well-studied particle accelerator in our Galaxy because of its strong nonthermal X-ray and gamma-ray radiation. We have performed Nuclear Spectroscopic Telescope Array (3–79 keV) observations of the northwest rim of RX J1713.7−3946, which is the brightest part in X-ray and has a shock speed of about 4000 km s−1. The spatially resolved X-ray emission from RX J1713.7−3946 is detected up to 20 keV for the first time. The hard X-ray image in 10–20 keV is broadly similar to the soft-band image in 3–10 keV. The typical spectrum is described by power-law model with exponential cutoff with the photon index Γ = 2.15 and the cutoff energy ε c = 18.8 keV. Using a synchrotron radiation model from accelerated electrons in the loss-limited case, the cutoff energy parameter ranges from 0.6–1.9 keV, varying from region to region. Combined with the previous measurement of the shock speed, the acceleration of electrons is close to the Bohm-limit regime in the outer edge, while the standard picture of accelerated particles limited by synchrotron radiation in SNR shock is not applicable in the inner edge and the filamentary structure.

Laser chemical vapor deposition of Lu2O3:Eu scintillation film

Lu2O3:Eu scintillation film is one of the most attractive candidate for the hard x-ray imaging, especially above 20 keV. A micro-columnar film with 10 μm thickness of Lu2O3:Eu was firstly obtained by laser chemical vapor deposition on not-oriented Lu2O3 single crystal substrate. The morphology of obtained film was investigated by the scanning electron microscopy. The photoluminescence and scintillation properties were measured and discussed, including photoluminescence excitation and photoluminescence curves, photoluminescence decay curves, and x-ray excited luminescence curve.