Strong X-ray Absorption Research Articles

Efficient metal free organic radical scintillators

The development of high-performance metal-free organic X-ray scintillators (OXSTs), characterized by a synergistic combination of robust X-ray absorption, efficient exciton utilization, and short luminescence lifetimes, poses a considerable challenge. Here we present an effective strategy for achieving augmented X-ray scintillation through the utilization of halogenated open-shell organic radical scintillators. Our experimental results demonstrate that the synthesized scintillators exhibit strong X-ray absorption derived from halogen atoms, display efficacious X-ray stability, and theoretically achieve 100% exciton utilization efficiency with a short lifetime (∼18 ns) due to spin-allowed doublet transitions. The superior X-ray scintillation performance exhibited by these organic radicals is not only exploitable in X-ray radiography for contrast imaging of various objects but also applicable in a medical high-resolution micro-computer-tomography system for the clear visualization of fibrous veins within a bamboo stick. Our study substantiates the promise of organic radicals as prospective candidates for OXSTs, offering valuable insights and a roadmap for the development of advanced organic radical scintillators geared towards achieving high-quality X-ray radiography.

Achieving High Operating-Temperature Self-powered X-Ray Detection in Multilayered Hybrid Perovskites through Arylamine Intercalation.

Polar metal halide hybrid perovskites (PHPs) that exhibit outstanding bulk photovoltaic effect (BPVE), excellent semiconductor features, and strong radiation absorption ability, have shown prominent advantages in highly sensitive direct X-ray detection. However, it is still a challenge to explore PHPs with high BPVE temperature ranges, answering the demand of developing thermally stable passive X-ray detection. Herein, by intercalating arylamine into lead tribromide and inducing order-disorder phase transition, a 2D multilayered PHPs (BZA)2(MA)Pb2Br7 (BZPB, BZA = benzylamine, MA = methylamine) is synthesized. BZPB crystallizes in a polar space group Aea2 at a low-temperature phase and demonstrates a significant open-circuit of 0.3V deriving from BPVE under X-ray irradiation. Meanwhile, the strong X-ray absorption coefficient and outstanding carrier transport capability of the bilayered lead halide framework associated with the polar BPVE give BZPB excellent X-ray detection abilities. At 0V bias, the impressive sensitivity of BZPB is 98 µC Gy-1 cm-2. Importantly, the introduction of the rigid BZA ring increases the energy barrier of phase transition and thus dramatically enhances the X-ray detection operating temperature of BZPB up to 409 K without significant performance degradation. This work strongly reveals the great potential of rational design of metal halide hybrid perovskites for X-ray detection applications.

High-confidence placement of low-occupancy fragments into electron density using the anomalous signal of sulfur and halogen atoms.

Fragment-based drug design using X-ray crystallography is a powerful technique to enable the development of new lead compounds, or probe molecules, against biological targets. This study addresses the need to determine fragment binding orientations for low-occupancy fragments with incomplete electron density, an essential step before further development of the molecule. Halogen atoms play multiple roles in drug discovery due to their unique combination of electronegativity, steric effects and hydrophobic properties. Fragments incorporating halogen atoms serve as promising starting points in hit-to-lead development as they often establish halogen bonds with target proteins, potentially enhancing binding affinity and selectivity, as well as counteracting drug resistance. Here, the aim was to unambiguously identify the binding orientations of fragment hits for SARS-CoV-2 nonstructural protein 1 (nsp1) which contain a combination of sulfur and/or chlorine, bromine and iodine substituents. The binding orientations of carefully selected nsp1 analogue hits were focused on by employing their anomalous scattering combined with Pan-Dataset Density Analysis (PanDDA). Anomalous difference Fourier maps derived from the diffraction data collected at both standard and long-wavelength X-rays were compared. The discrepancies observed in the maps of iodine-containing fragments collected at different energies were attributed to site-specific radiation-damage stemming from the strong X-ray absorption of I atoms, which is likely to cause cleavage of the C-I bond. A reliable and effective data-collection strategy to unambiguously determine the binding orientations of low-occupancy fragments containing sulfur and/or halogen atoms while mitigating radiation damage is presented.

High-Performance Flat-Panel Perovskite X-ray Detectors Enabled by Defect Passivation in Ruddlesden-Popper Perovskites.

Halide perovskites have emerged as promising candidates in X-ray detection due to their strong X-ray absorption and excellent optoelectronic properties. The development of sensitive and stable flat-panel X-ray detectors with high resolution is crucial for practical applications. In this paper, we introduce a novel flat-panel X-ray detector that integrates quasi-two-dimensional (2D) Ruddlesden-Popper (RP) perovskite with a pixeled thin film transistor (TFT) backplane. We incorporate 2,5-dibromopyrimidine (DBPM) as an additive to passivate the Lewis acid defects in the quasi-2D RP perovskite. This modification results in suppressed ion migration, improved optoelectronic performance, and enhanced operational stability of the device. Impressively, the activation energy of the RP perovskite increases from 0.96 to 1.35 eV with the DBPM additive. As a result, X-ray detectors exhibit a high sensitivity of ∼13,600 μC Gyair-1 cm-2, a low detection limit of 6.56 nGyair s-1, and excellent operational stability. Moreover, the flat-panel detectors demonstrate a high spatial resolution of 3.7 line pairs per millimeter and excellent X-ray imaging properties under a remarkably low X-ray dose of ∼50 μGyair, which is just half of the X-ray dose typically used in commercial equipment. This study opens new avenues for the development of flat-panel perovskite X-ray detectors with significant potential for various applications.

Polycrystalline Lead-Free Perovskite Direct X-Ray Detectors with High Durability and Low Limit of Detection via Low-Temperature Coating.

Direct X-ray detectors represent a transformative technology in the realm of radiography and imaging. The double halide-based perovskite cesium silver bismuth bromide (Cs2AgBiBr6) has emerged as a promising material for use in direct X-ray imaging, owing to its nontoxic composition, strong X-ray absorption, decent charge mobility lifetime product (μτ), and low-cost preparation. However, formidable issues related to scalability and ion migration, stemming from intrinsic factors such as halogen vacancies and grain boundaries, have presented significant impediments. These issues have been associated with substantial noise, baseline instability, and a curtailment of detection performance. In response to these multifaceted challenges, we propose a slurry-based in situ treatment technique for fabricating robust Cs2AgBiBr6 thick films. This novel approach adeptly mitigates halogen vacancies, actively passivates grain boundaries, and concurrently elevates the ion migration activation energy, thus effectively suppressing ion migration. Consequently, the obtained X-ray detector exhibits excellent operating stability with minimal signal drift of 8.5 × 10-9 nA cm-1 s-1 V-1 and achieves a remarkable 385% increase in sensitivity with a limit of detection as low as 7.8 nGyair s-1. These results mark a significant step toward the development of high-performance and long-lasting lead-free perovskite direct X-ray detectors.

Thermally Activated Delayed Fluorescence (TADF)-active Coinage-metal Sulfide Clusters for High-resolution X-ray Imaging.

The study of facile-synthesis and low-cost X-ray scintillators with high light yield, low detection limit and high X-ray imaging resolution plays a vital role in medical and industrial imaging fields. However, the optimal balance between X-ray absorption, decay lifetime and excitonic utilization efficiency of scintillators to achieve high-resolution imaging is extremely difficult due to the inherent contradiction. Here two thermally activated delayed fluorescence (TADF)-actived coinage-metal clusters M6 S6 L6 (M=Ag or Cu) were synthesized by simple solvothermal reaction, where the cooperation of heavy atom-rich character and TADF mechanism supports strong X-ray absorption and rapid luminescent collection of excitons. Excitingly, Ag6 S6 L6 (SC-Ag) displays a high photoluminescence quantum yield of 91.6 % and scintillating light yield of 17420 photons MeV-1 , as well as a low detection limit of 208.65 nGy s-1 that is 26 times lower than the medical standard (5.5 μGy s-1 ). More importantly, a high X-ray imaging resolution of 16 lp/mm based on SC-Ag screen is demonstrated. Besides, rigid core skeleton reinforced by metallophilicity endows clusters M6 S6 L6 strong resistance to humidity and radiation. This work provides a new view for the design of efficient scintillators and opens the research door for silver clusters in scintillation application.

Heterointerface Design of Perovskite Single Crystals for High-Performance X-Ray Imaging.

Metal halide perovskite single crystals (MHP-SCs) are known for their facile fabrication into large sizes using inexpensive solution methods. Owing to their combination of large mobility-lifetime products and strong X-ray absorption, they are considered promising materials for efficient X-ray detection. However, they suffer from large dark currents and severe ion migration, which limit their sensitivity and stability in critical X-ray detection applications. Herein, a heterointerface design is proposed to reduce both the dark current and ion migration by forming a heterojunction. In addition, the carrier transport performance is significantly improved using heterointerface engineering by designing a gradient band structure in the SCs. The SC heterojunction detectors exhibit a high sensitivity of 3.98 × 105 µC Gyair -1 cm-2 with a low detection limit of 12.2 nGyair s-1 and a high spatial resolution of 10.2 lp mm-1 during imaging. These values are among the highest reported for state-of-the-art MHP X-ray detectors. Moreover, the detectors show excellent stability under continuous X-ray irradiation and maintainclear X-ray imaging after 240 d. This study provides novel insights into the design and fabrication of X-ray detectors with high detection efficiency and stability, which are beneficial for developing inexpensive, high-resolution X-ray imaging equipment.

High-Efficiency Narrow-Band Green-Emitting Manganese(II) Halide for Multifunctional Applications.

Zero-dimensional (0D) Mn2+-based metal halides used as luminescent materials and scintillators have become a research hotspot in the field of photoelectric materials and devices due to their unique composition, structure, and fluorescence properties. It is of great value to explore new Mn2+-based metal halides to achieve multifunctional applications. Herein, the novel 0D Mn2+-based metal halide single crystal (BPTP)2MnBr4 is synthesized by a simple solvent-antisolvent recrystallization method. Under excitation at 468 nm, the (BPTP)2MnBr4 single crystal shows a pronounced narrow-band green luminescence centered at 515 nm derived from the d-d transition of the Mn2+ ion. This emission has a relatively narrow full width at half maximum of 43 nm and a high photoluminescence quantum yield (PLQY) of 82%. In addition, (BPTP)2MnBr4 exhibits good thermal stability at 393 K with a retention of 79% of the initial photoluminescence intensity at 298 K. Benefiting from its strong blue light excitation, high PLQY, and good thermal stability, we manufacture an ideal white light-emitting diode (LED) device using a 460 nm blue LED chip, green-emitting (BPTP)2MnBr4, and commercial K2SiF6:Mn4+ red phosphor. Under 20 mA drive current, the LED shows a high luminous efficiency of 112 lm/W and a wide color gamut of 110.8%, according to the National Television System Committee standard. In addition, (BPTP)2MnBr4 crystals show a strong X-ray absorption. Based on the commercial Lu3Al5O12:Ce3+ scintillator, the calculated light yield of (BPTP)2MnBr4 reaches up to about 136,000 photons/MeV and the detection limit reaches 0.282 μGyair s-1. Additionally, a melt quenching approach is used to construct a (BPTP)2MnBr4 clear glass scintillation screen, realizing a spatial resolution of 10.1 lp/mm. The proper performances of (BPTP)2MnBr4 as phosphor-converted LED materials and the X-ray scintillator with the addition of eco-friendly, low-cost solution processability make 0D Mn2+-based metal halides potential luminescent materials for multifunctional applications.

Bottom-Up Photosynthesis of an Air-Stable Radical Semiconductor Showing Photoconductivity to Full Solar Spectrum and X-Ray.

Single-component semiconductors with photoresponse to full solar spectrum are highly desirable to simplify the device structure of commercial photodetectors and to improve solar conversion or photocatalytic efficiency but remain scarce. This work reports bottom-up photosynthesis of an air-stable radical semiconductor using BiI3 and a photochromism-active benzidine derivative as a photosensitive functional motif. This semiconductor shows photoconductivity to full solar spectrum contributed by radical and non-radical forms of the benzidine derivative. It has also the potential to detect X-rays because of strong X-ray absorption coefficient. This finding opens up a new synthetic method for radical semiconductors and may find applications on extending photoresponsive ranges of perovskites, transition metal sulfides, and other materials.

Interlayer-Spacing Engineering of Lead-Free Perovskite Single Crystal for High-Performance X-Ray Imaging.

Lead-free A3 Bi2 I9 -type perovskites are demonstrated as a class of promising semiconductors for high-performance X-ray detection due to their high bulk resistivity and strong X-ray absorption, as well as reduced ion migration. However, due to their long interlamellar distance along their c-axis, their limited carrier transport along the vertical direction is a bottleneck for their detection sensitivity. Herein, a new A-site cation of aminoguanidinium (AG) with all-NH2 terminals is designed to shorten the interlayer spacing by forming more and stronger NH···I hydrogen bonds. The prepared large AG3 Bi2 I9 single crystals (SCs) render shorter interlamellar distance for a larger mobility-lifetime product of 7.94×10-3 cm2 V-1 , which is three times higher than the value measured on the best MA3 Bi2 I9 SC (2.87 ×10-3 cm2 V-1 ). Therefore, the X-ray detectors fabricated on the AG3 Bi2 I9 SC exhibit high sensitivity of 5791 uCGy-1 cm-2 , a low detection limit of 2.6nGy s-1, and a short response time of 690µs, all of which are far better than those of the state-of-the-art MA3 Bi2 I9 SC detectors. The combination of high sensitivity and high stability enables astonishingly high spatial resolution (8.7 lpmm-1 ) X-ray imaging. This work will facilitate the development of low-cost and high-performance lead-free X-ray detectors.

Recent Advances in Metal-Based NanoEnhancers for Particle Therapy.

Radiotherapy is one of the most common therapeutic regimens for cancer treatment. Over the past decade, proton therapy (PT) has emerged as an advanced type of radiotherapy (RT) that uses proton beams instead of conventional photon RT. Both PT and carbon-ion beam therapy (CIBT) exhibit excellent therapeutic results because of the physical characteristics of the resulting Bragg peaks, which has been exploited for cancer treatment in medical centers worldwide. Although particle therapies show significant advantages to photon RT by minimizing the radiation damage to normal tissue after the tumors, they still cause damage to normal tissue before the tumor. Since the physical mechanisms are different from particle therapy and photon RT, efforts have been made to ameliorate these effects by combining nanomaterials and particle therapies to improve tumor targeting by concentrating the radiation effects. Metallic nanoparticles (MNPs) exhibit many unique properties, such as strong X-ray absorption cross-sections and catalytic activity, and they are considered nano-radioenhancers (NREs) for RT. In this review, we systematically summarize the putative mechanisms involved in NRE-induced radioenhancement in particle therapy and the experimental results in in vitro and in vivo models. We also discuss the potential of translating preclinical metal-based NP-enhanced particle therapy studies into clinical practice using examples of several metal-based NREs, such as SPION, Abraxane, AGuIX, and NBTXR3. Furthermore, the future challenges and development of NREs for PT are presented for clinical translation. Finally, we propose a roadmap to pursue future studies to strengthen the interplay of particle therapy and nanomedicine.

Multiwavelength study of NGC 1365: The obscured active nucleus and off-nuclear compact X-ray sources

ABSTRACTWe present a multiwavelength study of the active nucleus and the off-nuclear X-ray sources in the nearby spiral galaxy, NGC 1365 using three simultaneous UV/X-ray observations by AstroSat over a two months period and archival IR observations performed with Spitzer and Herschel. Utilizing the data from the Soft X-ray Telescope (SXT) onboard AstroSat, we find spectral variability mainly caused by the variation in the X-ray column density, (NH ∼ 1022–1023 cm−2). With the accurate spatial resolution of the UVIT onboard AstroSat, we separate the intrinsic AGN flux from the host galaxy emission and then correct for the Galactic and the internal reddening. We detect no significant variation in the NUV emission over the observation period. The AGN in FUV band is undetectable due to heavy intrinsic extinction. Further, the multiwavelength IR/UV/X-ray AGN SED reveals that the AGN is in a low-luminosity phase with accretion rate ∼0.01 LEdd. The steady UV emission and strong X-ray absorption variability suggest that the obscuring clouds are likely compact and affect the compact X-ray source only and do not possibly cover the extended UV emitting region. In addition, the UVIT is able to resolve two bright spots at a radius of 7 arcsec (∼6.3 Kpc) from the central nucleus in the South-West (SW) direction. In the UVIT image of the entire galaxy, we identify UV counterparts to four Chandra identified bright X-ray sources. One well-known ultra-luminous X-ray source (ULX) NGC 1365 X2 is identified with its UV counterpart at 86 arcsec from the nucleus in the North-East (NE) direction from the active nucleus.

Tween-20-Modified BiVO4 Nanorods for CT Imaging-Guided Radiotherapy of Tumor.

Oral cancer is the most common malignant tumor in the oral and maxillofacial region, which seriously threatens the health of patients. At present, radiotherapy is one of the commonly used methods for oral cancer treatment. However, the resistance of cancerous tissues to ionizing radiation, as well as the side effects of X-rays on healthy tissues, still limit the application of radiotherapy. Therefore, how to effectively solve the above problems is still a challenge at present. Generally speaking, elements with high atomic numbers, such as bismuth, tungsten, and iodine, have a high X-ray attenuation capacity. Using nanomaterials containing these elements as radiosensitizers can greatly improve the radiotherapy effect. At the same time, the modification of nanomaterials based on the above elements with the biocompatible polymer can effectively reduce the side effects of radiosensitizers, providing a new method for the realization of efficient and safe radiotherapy for oral cancer. In this work, we prepared Tween-20-modified BiVO4 nanorods (Tw20-BiVO4 NRs) and further used them in the radiotherapy of human tongue squamous cell carcinoma. Tw20-BiVO4 NRs are promising radiosensitizers, which can generate a large number of free radicals under X-rays, leading to the damage of cancer cells and thus playing a role in tumor therapy. In cell experiments, radiotherapy sensitization of Tw20-BiVO4 NRs significantly enhanced the production of free radicals in oral cancer cells, aggravated the destruction of chromosomes, and improved the therapeutic effect of radiotherapy. In animal experiments, the strong X-ray absorption ability of Tw20-BiVO4 NRs makes them effective contrast agents in computed tomography (CT) imaging. After the tumors are located by CT imaging, it helps to apply precise radiotherapy; the growth of subcutaneous tumors in nude mice was significantly inhibited, confirming the remarkable effect of CT imaging-guided radiotherapy.

GSH-activatable camptothecin prodrug-loaded gold nanostars coated with hyaluronic acid for targeted breast cancer therapy via multiple radiosensitization strategies.

Breast cancer has overtaken lung cancer to rank as the top malignant tumor in terms of incidence. Herein, a gold nanostar (denoted as AuNS) is used for loading disulfide-coupled camptothecin-fluorophore prodrugs (denoted as CPT-SS-FL) to form a nanocomposite of AuNS@CPT-SS-FL (denoted as AS), which, in turn, is further encapsulated with hyaluronic acid (HA) to give the final nanoplatform of AuNS@CPT-SS-FL@HA (denoted as ASH). ASH effectively carries the prodrug and targets the CD44 receptor on the surface of tumor cells. The endogenously overexpressed glutathione (GSH) in tumor cells breaks the disulfide bond to activate the prodrug and release the radiosensitizer drug camptothecin (CPT) and the fluorescence imaging reagent rhodamine derivative as a fluorophore (FL). The released FL can track the precise release position of the radiosensitizer camptothecin in tumor cells in real time. The AuNS has strong X-ray absorption and deposition ability due to the high atomic coefficient of elemental Au (Z = 79). At the same time, the AuNS can alleviate the tumor microenvironment (TME) hypoxia through its mild photothermal therapy (PTT). Therefore, through the multiple radiosensitizing effects of GSH depletion, the high atomic coefficient of Au, and hypoxia alleviation, accompanied by the radiosensitizer camptothecin, the designed ASH nanoplatform can effectively induce strong immunogenic cell death (ICD) at the tumor site via radiosensitizing therapy combined with PTT. This work provides a new way of constructing a structurally compact and highly functionalized hierarchical system toward efficient breast cancer treatment through ameliorating the TME with multiple modalities.

Biotin-decorated hollow gold nanoshells for dual-modal imaging-guided NIR-II photothermal and radiosensitizing therapy toward breast cancer.

Radiotherapy (RT) is dominantly used in breast cancer therapy but is facing fierce side effects because of the limited difference between tumor and normal tissues in response to ionizing radiation. Herein, we construct a core-shell nanoparticle of UiO-66-NH2@AuNS. Then the solid gold shell was etched into hollow AuNS (HAuNS) and further modified with biotin-PEG-SH (PEG-bio) to obtain HAuNS@PEG-bio. HAuNS@PEG-bio demonstrates effective near infrared II (NIR-II) region photothermal therapy (PTT) performance, and the increase of temperature at the tumor site promotes the blood circulation to alleviate the hypoxia in the tumor microenvironment (TME). Meanwhile, HAuNS exhibits strong X-ray absorption and deposition ability due to the high atomic coefficient of elemental Au (Z = 79) and hollowed-out structure. Through the dual radiosensitization of the high atomic coefficient of Au and the hypoxia alleviation from PTT of HAuNS, the breast cancer cells could undergo immunogenic cell death (ICD) to activate the immune response. At the in vivo level, HAuNS@PEG-bio performs NIR-II photothermal, radiosensitization, and ICD therapies through cellular targeting, guided by infrared heat and CT imaging. This work highlights that the constructed biotin-decorated hollow gold nanoshell has a promising potential as a diagnostic and treatment integration reagents for the breast cancer.

Halide Perovskite: A Promising Candidate for Next-Generation X-Ray Detectors.

In the past decade, metal halide perovskite (HP) has become a superstar semiconductor material due to its great application potential in the photovoltaic and photoelectric fields. In fact, HP initially attracted worldwide attention because of its excellent photovoltaic efficiency. However, HP and its derivatives also show great promise in X-ray detection due to their strong X-ray absorption, high bulk resistivity, suitable optical bandgap, and compatibility with integrated circuits. In this review, the basic working principles and modes of both the direct-type and the indirect-type X-ray detectors are first summarized before discussing the applicability of HP for these two types of detection based on the pros and cons of different perovskites. Furthermore, the authors expand their view to different preparation methods developed for HP including single crystals and polycrystalline materials. Upon systematically analyzing their potential for X-ray detection and photoelectronic characteristics on the basis of different structures and dimensions (0D, 2D, and 3D), recent progress of HPs (mainly polycrystalline) applied to flexible X-ray detection are reviewed, and their practicability and feasibility are discussed. Finally, by reviewing the current research on HP-based X-ray detection, the challenges in this field are identified, and the main directions and prospects of future research are suggested.

Flexible perovskite scintillators and detectors for X-ray detection.

X-ray detection and imaging technology has been rapidly developed for various fields since 1895, offering great opportunities to scientific and industrial communities. Particularly, flexible X-ray detectors have drawn numerous attention in medical-related applications, solving the uniform issues of traditional rigid X-ray detectors. Out of all the potential materials, metal halide perovskites (MHPs) have been emerged as excellent candidates as flexible X-ray scintillators and detectors owing to the advantages including low temperature solution processable, strong X-ray absorption coefficient, large mobility lifetime product and tunable bandgap. In this review, the recent advances of MHP-based flexible X-ray detectors are comprehensively summarized, focusing on the scalable synthesis technologies of materials and diverse device architectures, and covering both direct and indirect X-ray detection. A brief outlook that highlights the current challenges impeding the commercialization of flexible MHP-based X-ray detectors is also included with possible solutions to those problem being provided.

X-ray absorption and reprocessing in the z ∼ 2.5 lensed quasar 2MASS J1042+1641

ABSTRACT We present new broad-band X-ray observations of the z ∼ 2.5 lensed quasar 2MASS J1042+1641, combining XMM–Newton, Chandra, and NuSTAR to provide coverage of the X-ray spectrum over the 0.3–40 keV bandpass in the observed frame, corresponding to the ∼1–140 keV band in the rest frame of 2MASS J1042+1641. The X-ray data show clear evidence for strong (but still Compton-thin) X-ray absorption, NH ∼ 3–4 × 1023 $\rm \, cm^{-2}$, in addition to significant reprocessing by Compton-thick material that must lie away from our line of sight to the central X-ray source. We test two different interpretations for the latter: first that the reprocessing occurs in a classic active galactic nucleus torus, as invoked in unification models, and second that the reprocessing occurs in the accretion disc. Both models can successfully reproduce the observed spectra, and both imply that the source is viewed at moderately low inclinations (i < 50°) despite the heavy line-of-sight absorption. Combining the X-ray data with infrared (IR) data from WISE, the results seen from 2MASS J1042+1641 further support the recent suggestion that large X-ray and IR surveys may together be able to identify good lensed quasar candidates in advance of detailed imaging studies.

Terbium-doped LiYbF4nanomaterial-based scintillator responding to X-rays with high-resolution imaging applications

As a new scintillation material, LiYbF4nanocrystals exhibit high stability and strong absorption of X-rays, and appear competitive in high-resolution X-ray imaging with a spatial resolution of 20 LP mm−1(MTF = 0.35).

Nucleation bursts of primary intermetallic crystals in a liquid Al alloy studied using in situ synchrotron X-ray radiography

The nucleation of primary Pt-rich intermetallic compound (IMC) crystals was studied in a model Al-Pt-Er alloy as an analogue to Al13Fe4 that forms in commercial Al alloys. The Pt-rich IMCs provided strong X-ray absorption contrast that allowed earlier detection of formation events and the resolution of solute diffusion fields. Crystal formation behaviour was investigated during directional and isothermal solidification when the alloy was inoculated with TiB2 particles at cooling rates of 0.1 Ks−1 to 8 Ks−1 using in situ synchrotron X-ray radiography. Different from previous studies that concerned disordered, solid solution phases such as α-Al dendrites, for the first time nucleation bursts of ordered compound crystals were observed, where the nucleation of the IMC crystals proceeded in distinct cascades (in the time domain) or waves (in the spatial domain), the magnitude of which increased with increasing cooling rate and particularly with decreasing thermal gradient in the melt. Comparing the crystal number density with the estimated number density of TiB2 particles suggested that the IMC crystals nucleated only on the most potent TiB2 particles, accounting for ∼0.5% of the total TiB2 number density in the melt. The effect of the thermal gradient and cooling rate on the magnitude of the nucleation waves and the IMC number density was revealed in terms of the available undercooling in the liquid in front of an individual IMC and the solute depleted liquid fraction that arose from the interaction of an ensemble of IMC crystals.