Detection Of Ionizing Radiation Research Articles

Orientation and mobility control of 4HCB organic film for flexible X-ray detectors with high performance

• The space-confined melt process is used to produce highly orientated organic semiconducting crystalline films with a large area. • Confined molecular packing significantly improves the hole mobility. • The 4HCB based X-ray detectors can achieve a high sensitivity with low dark current, result in outstanding direct imaging capabilities. • The device shows steady flexibility, with no degradation in detecting function after 100 cycles of bending. In comparison to inorganic counterparts, organic semiconducting (OSC) crystalline films are promising for building large-area and flexible ionizing radiation detectors for X-ray imaging or dosimetry due to their tissue equivalence, simple processing and large-scale production accessibility. Fabrication processes, however, hinder the ability to generate aligned and large-area films with high carrier mobility. In this work, the space-confined melt process is used to produce highly orientated 4HCB (4-hydroxycyanobenzene) OSC films with a large area of 15 × 18 mm 2 . The out-of-plane direction of the 4HCB film is <001>, and the benzene rings are found to be extensively overlapped inside the in-plane direction, according to the XRD patterns. The film exhibits a high resistivity up to 10 12 Ω cm, and high hole mobility of 10.62 cm 2 V −1 s −1 . Furthermore, the 4HCB (80-μm-thick film) based X-ray detectors can achieve a sensitivity of 93 μC Gyair −1 cm −2 and on/off ratio of 157. The device also shows steady flexibility, with no degradation in detecting function after 100 cycles of bending. Finally, the proposed 4HCB film detectors demonstrated a high-resolution X-ray imaging capability. The imaging of several materials with sharp edges (copper and polytetrafluoroethylene) has been obtained. This work has developed a fast but efficient approach for producing large-area, highly oriented OSC films for high-performance X-ray detectors.

Additive-Enhanced Crystallization of Inorganic Perovskite Single Crystals for High-Sensitivity X-Ray Detection.

Inorganic cesium lead halide perovskite single crystals are particularly intriguing to ionizing radiation detection by virtue of their material stability and high attenuation coefficients. However, the growth of high-quality inorganic perovskite single crystals remains challenging, mainly due to the limited solubility. In this work, an additive-enhanced crystallization method is proposed for cesium lead perovskites. The additive can remarkably increase the solubility of cesium bromide in dimethyl sulfoxide (DMSO) forming a balanced stoichiometric precursor solution, which prevents the formation of impurity phases. In addition, the additives would react with DMSO generating glyoxylic acid (GLA) via nucleophilic substitution and Kornblum oxidation reactions. The GLA can form stable PbBr2 -DMSO-GLA complexes, which enables better crystallinity, uniformity and much longer carrier lifetimes for the grown single crystals. The X-ray detectors using the additive-enhanced crystals exhibit an ultra-high sensitivity of 3.0 × 104 µC Gyair -1 cm-2 which is more than two orders of magnitude higher than that for the control devices.

CsPbBr3@PbBrOH 3D/1D molecular matrix for a high-performance scintillator

All-inorganic cesium lead halide perovskite nanocrystals (NCs) have become highly sought-after materials for X-ray detection and imaging because of their outstanding intrinsic electronic and optical properties. However, because of their highly ionic crystal structure, perovskite materials suffer severe moisture, thermal, and photo instability problems, which hinder their commercialization. To resolve this annoying problem, three-dimensional (3D)/1D CsPbBr3@PbBrOH composite structures in terms of molecular structure are designed by incorporating highly luminescent 3D CsPbBr3 NCs into a 1D PbBrOH matrix to form an “emitter-in-matrix”. The prepared CsPbBr3@PbBrOH exhibits excellent stability without sacrificing photoluminescence quantum yield. Meanwhile, 1D PbBrOH can be considered a perfect host, and the presence of heavy atom Pb in its matrix enhances X-ray absorption. The luminescent CsPbBr3 NCs embedded in an inert PbBrOH host are subjected to X-ray detection and imaging. The CsPbBr3@PbBrOH scintillator shows bright radiation luminescence and sensitive response to X-ray signals. In addition, the scintillator is made into a thin film screen for imaging, obtaining a clear image of the transmission electron microscopy grid hidden inside the capsule, and the resolution of CsPbBr3@PbBrOH film is calculated to be as high as 50 lp mm−1. This property of CsPbBr3@PbBrOH scintillators demonstrates their promising application prospects for ionizing radiation detection, particularly for X-ray imaging.

Novel Ultraviolet and Ionizing Radiation Detectors Made From TiO Wide-Bandgap Semiconductor

We describe the fabrication and characterization of a novel ultraviolet (UV) and ionizing radiation detector using a polycrystalline TiO2 wide-bandgap semiconductor as the active material. The detector geometry we have developed and tested is a polycrystalline TiO2 thin film with planar electrode contacts for signal pickup. Several prototypes were fabricated using two single-step techniques. We present the dc characterization of these devices and the signal response to the UV light and low-energy proton beam irradiation. The detector prototypes show excellent dc characteristics and fast ac signal response at bias voltage as low as 50 V.

Application and development of liquid argon detector in rare event detection

Rare event detection is a frontier subject in particle physics and nuclear physics. In particular, dark matter detection, neutrino-free double beta decay and neutrino-nucleon coherent elastic scattering are being planned and implemented gradually. Rare event detection requires not only the detectors to possess excellent performances but also extremely low environmental background, so the selection of detectors and related materials is an important issue in rare event detection. Liquid argon has become an important scintillator material for scintillator detectors because of its low cost, good scintillation performance and large volume. Liquid argon was first studied in the 1940s as a sensitive material for ionizing radiation detectors. The first measurements of high-energy beta particles were obtained by using a liquid argon ionization chamber in 1953. The ICARUS group put forward the idea of constructing liquid argon temporal projection chamber, and made attempt to construct liquid argon temporal projection chamber in 1977. The scintillation light signals were collected for the first time in a liquid argon temporal projection chamber in 1999. Thus, the drift time of the particle can be obtained to determine the particle track. After development, single-phase liquid argon scintillator detector and two-phase argon time projection chamber have become two common types of liquid argon detectors, and have been extensively used in rare event detection experiments in recent years. For dark matter detection, the DEAP group and DarkSide group have achieved good results with single-phase liquid argon scintillation detector and two-phase argon time projection chamber, respectively. For neutrino-free double beta decay experiments, the GERDA group has done a lot of researches of liquid argon anti-coincidence system and applied the said system to experiments. The LEGEND group, which is the combination of GERDA and MAJORANA experimental group, upgraded the liquid argon anti-coincidence system which was applied to the following LEGEND-200 project. For neutrino-nucleon elastic scattering experiments, COHERENT obtained the latest results by using the liquid argon detectors. The Taishan neutrino-nucleon coherent elastic scattering project of the High Energy Institute of Chinese Academy of Sciences has also begun to study the feasibility of liquid argon anti-coincidence system. Finally, this paper discusses the direction of optimizing the liquid argon detector, such as exposure, background level and optical readout scheme, and gives a good prospect of liquid argon detector applied to rare event detection in the future.

Chromium Luminescence in Plasma Electrolytic Oxidation Coatings on Aluminum Surface

With plasma electrolytic oxidation (PEO), one can easily obtain thick (tens of microns), mechanically resilient and chemically stable oxide coating on aluminum and other valve metal alloys. The study of luminescent PEO coatings is a relatively new subfield of the already well-established coating preparation methods. In recent years, many new luminescence-based approaches have been developed, one of which is the detection of ionizing radiation of carbon-doped PEO alumina coating. This study presents an improved approach by doping the alumina coating with chromium using citric acid as an additive in the electrolyte. Trivalent chromium ions replacing aluminum in the crystalline lattice of the coating exhibit characteristic sharp lines in the luminescence spectrum. The effectiveness of different DC voltages, process times and citric acid concentrations in electrolyte were examined. The use of citric acid in the electrolyte also provides the conditions required for the formation of an energy trap in the bandgap of the material, thus opening up the possibility for the coating to be used as an ionizing radiation detector by measuring its thermoluminescence. Chromium atoms are incorporated in the coating from the Al6082 aluminum alloy itself and are not added in the electrolyte, therefore making the process much more reliable, repeatable, and environmentally friendly.

Performance of semi-insulating metal-semiconductor-metal GaN prototype devices as ionizing radiation detector

We describe the fabrication and characterization of semi-insulating GaN devices for the detection of ionizing radiation with applications in high radiation environment. We present the DC characterization and the signal response of such devices from Am-241 α-source. The detector prototypes show up to 80% charge collection efficiency with bias voltages as low as -40V. Wide band gap semiconductors like synthetic diamond, GaN, SiC have gained immense importance in the field of charged particle detection due to their low intrinsic noise and high radiation tolerance. The ability of suppressing the thermal noise generated by intrinsic carriers, makes the fabrication of these devices simpler when compared to the multi-step lithography required for doping of traditional silicon-based solid-state detectors. We have made interdigitated metal-semiconductor-metal(MSM) device on a 3μm in thick GaN epitaxial layer grown on sapphire substrate by MOCVD technique. We employed Ni/Pt/Au metal stack for Schottky contact with finger width of 4μm, spacing of 8μm and finger length of 120μm. Details of the experimental set-up for fabrication and characterization will be presented.

Trap States Ruling Photoconductive Gain in Tissue‐Equivalent, Printed Organic X‐Ray Detectors

AbstractOrganic semiconductors are excellent candidates for X‐ray detectors that can adapt to new applications, with unique properties including mechanical flexibility and the ability to cover large surfaces. Their chemical composition, primarily carbon and hydrogen, makes them human tissue equivalent in terms of radiation absorption. This is a highly desirable property for a radiation dosimeter to be employed in medical diagnostics and therapy, however a low‐Z composition limits the absorption of ionizing radiation. The detection efficiency can be enhanced by considering the photoconductive gain (PG) effect, a significant contributor to the ionizing radiation detection mechanism in this class of materials. In this work, a process of controlled solution deposition by nozzle printing and crystallization of an organic semiconductor thin film is demonstrated whereby a flexible, arrayed thin‐film X‐ray detector with record X‐ray sensitivities among flexible radiation detectors (S = (9.0 ± 0.4) × 107 µC Gy−1 cm−3) is developed. The excitonic peaks responsible for the activation of the PG effect are investigated and identified using a novel technique called photocurrent spectroscopy optical quenching, and the analysis of the changes in trap states is further demonstrated.

Single-Crystal Perovskite Solar Cells Exhibit Close to Half A Millimeter Electron-Diffusion Length.

Single-crystal halide perovskites exhibit photogenerated-carriers of high mobility and long lifetime, making them excellent candidates for applications demanding thick semiconductors, such as ionizing radiation detectors, nuclear batteries, and concentrated photovoltaics. However, charge collection depreciates with increasing thickness; therefore, tens to hundreds of volts of external bias is required to extract charges from a thick perovskite layer, leading to a considerable amount of dark current and fast degradation of perovskite absorbers. However, extending the carrier-diffusion length can mitigate many of the anticipated issues preventing the practical utilization of perovskites in the abovementioned applications. Here, single-crystal perovskite solar cells that are up to 400 times thicker than state-of-the-art perovskite polycrystalline films are fabricated, yet retain high charge-collection efficiency in the absence of an external bias. Cells with thicknesses of 110, 214, and 290µm display power conversion efficiencies (PCEs) of 20.0, 18.4, and 14.7%, respectively. The remarkable persistence of high PCEs, despite the increase in thickness, is a result of a long electron-diffusion length in those cells, which wasestimated, from the thickness-dependent short-circuit current, to be ≈0.45mm under 1 sun illumination. These results pave the way for adapting perovskite devices to optoelectronic applications in which a thick active layer is essential.

CsPbBr3 deposited by laser ablation: effects of post-growth aging, oxygen adsorption and annealing on film properties

All-inorganic perovskites are widely investigated as a new generation of materials thanks to their superior optoelectronic properties and better stability than hybrid organic–inorganic perovskites. In particular, cesium lead bromide (CsPbBr3) exhibits advantageous properties for numerous applicative fields (photovoltaics, light-emitting diodes, photodetectors, lasing, field effect transistors, and ionizing radiation detectors). The performance of CsPbBr3 being critically dependent on the deposition technique, proper understanding and optimization of the fabrication process are demanding. Despite the well-known potentiality of the Pulsed Laser Deposition (PLD) technique in depositing films with complex stoichiometry, a very limited number of literature studies report on the successful deposition of CsPbBr3 films by PLD. Recently, the authors disclosed the impact of the uneven masses of Cs, Pb, and Br on the film stoichiometry and guidelines to recover the desired composition. Herein, we exploit stoichiometric mechano-chemically synthesized targets to deposit, by nanosecond-PLD (λ = 248 nm, τ = 20 ns, room temperature, fluence of 1 J/cm2), CsPbBr3 films to be studied following time aging, thermal heating and exposure to high relative humidity. Even in the presence of the characteristic absorption peak at ~ 520 nm, the freshly deposited film shows no photoluminescence. Photoluminescence is switched on by thermal annealing (at 250 and 350 °C) or after a few days (at least 15) of exposure to air and it persists over time. Films present interesting morphology evolution and oxygen adsorption following heating.

Investigation of the Solution Chemistry of Hybrid Organic-Inorganic Indium Halides for New Material Discovery.

Recently, metal halide perovskites (MHPs) have emerged as a new class of materials for optical and electronic applications such as solar cells and ionizing radiation detectors. Although the solution-processability of MHPs is among their greatest advantages, the solution chemistries of most metal halide systems and their relationship with the observed structural and chemical diversity are poorly understood. In this work, we study the solution chemistry of a model indium halide system, methylammonium (MA)-In-Br, using a combination of the UV-vis spectroscopy, electrospray ionization mass spectrometry (ESI-MS) measurements, small-angle X-ray scattering (SAXS), and density functional theory (DFT) calculations. Our results show that indium could form either octahedral [InBr63-] or tetrahedral [InBr4-] anions in solution or a combination of both, depending on the loading ratios of MABr and InBr3 reactants. Understanding the solution chemistry of this system and recognizing the optical fingerprints of these polyanions allow for targeted crystallization of two novel compounds: MAInBr4 featuring tetrahedral [InBr4-] anions and MA2InBr5 containing both octahedral [InBr63-] and tetrahedral [InBr4-] anions. Further increase of the MABr content leads to the formation of previously reported MA4InBr7, containing only octahedral [InBr63-] anions separated by Br- anions. Our results suggest that understanding the solution chemistry of multinary metal halide systems could be a valuable tool for discovering functional materials for practical applications.

Spray-coating of AgI incorporated metal halide perovskites for high-performance X-ray detection

Metal halide perovskites have emerged as a promising candidate for ionizing radiation detection, thanks to the facile fabrication, excellent optoelectronic properties and high attenuation coefficient. In order to fully absorb the incident X-ray photons, X-ray detectors require relatively thick active layers. However, it is challenging to obtain thick perovskite films based on conventional solution-based techniques, due to the limited solubility and viscosity of the perovskite precursors. In this work, we introduced spray-coating to deposit perovskite films on various substrates, and achieved tunable and thick films. On the other hand, the charge transport is another issue limiting the device performance of perovskite X-ray detectors. Compared with conventional inorganic semiconductors, hybrid perovskites possess relatively poor charge carrier mobility and lifetime. To address this issue, we incorporate AgI within the perovskite precursor, and systematically investigated their optoelectronic properties. It was found that the optimized AgI incorporated perovskite films exhibited the highest mobility-lifetime product, resulted X-ray sensitivity up to 3433 μGyair−1 cm−2 and ultra-low detection limit of 3.5 nGyair s−1, suggesting great potential for X-ray detection.

Increase of the photoconductivity quantum yield in silicon irradiated by neutrons to extremely high fluences

An enhanced quantum yield observed in silicon ionizing radiation detectors, neutron-irradiated to extremely high fluences, could be attributed to impact ionization via deep levels. The quantum yield was investigated by the intrinsic photoconductivity optical spectroscopy in silicon irradiated by neutrons to a wide range of fluences up to 1 × 1017 neutron cm−2. An increase of quantum yield was observed in highly irradiated samples. We have demonstrated that the quantum yield enhancement could be attributed to the impact ionization via deep levels, this process being presumably related to disordered defect clusters regions in Si. The proposed mechanism explains the observed decrease of the impact ionization energy by at least an order of magnitude at low temperature. The impact ionization energy values of up to 0.30–0.36 eV and less, and 0.38–0.40 eV were determined at T ∼ 21–33 K and at T = 195 K, respectively.

Perovskite semiconductors for ionizing radiation detection

AbstractThe detection of ionizing radiation such as X‐ray, γ‐ray, α‐particle, and neutrons has been widely required in medical and industrial areas. Perovskite semiconductor detectors are arousing widespread interest and achieving significant progresses in this area. Unique material strengths, such as large attenuation coefficient, defect tolerant nature, balanced carrier mobilities, and feasible preparation techniques, make perovskite semiconductor detector a strong competitor to existing commercial products. Inspired by the booming development of this area, we review the current achievements of ionizing radiation detection with perovskite semiconductors. Firstly, a comprehensive summary of the device preparation techniques is provided, followed by a profound discussion of the detector physics. Then, the broad applications of perovskite semiconductor detectors are illustrated. Finally, we give an outlook of the current challenges pending to be tackled for commercialized applications. We believe the perovskite semiconductor detectors will be new blood to the current ionizing radiation detection market.image

Efficient Eco-Friendly Flexible X-ray Detectors Based on Molecular Perovskite.

Next-generation wearable electronics requires mechanical robustness. In addition to the previously reported eco-friendliness, low cost, and light weight of molecular perovskites, flexibility is also a desired merit for their practical use. Here we design a flexible X-ray detector based on a novel molecular perovskite, DABCO-CsBr3 (DABCO = N-N'-diazabicyclo[2.2.2]octonium), which is the missing link between metal-free molecular perovskites A(NH4)X3 (A = divalent organic ammoniums) and conventional metal halide based ABX3 (B = divalent metal cations) perovskites. DABCO-CsBr3 inherits its band nature from A(NH4)X3, while it exhibits a stronger stopping power. DABCO-CsBr3 shows potential for high-performance ionizing radiation detectors due to low dark current, low ion migration, and an efficient mobility-lifetime (μτ) product. Finally, a molecular-perovskite-based flexible X-ray detector is demonstrated on the basis of the DABCO-CsBr3/poly(vinylidene fluoride) composite, with a sensitivity of 106.7 μC Gyair-1 cm-2. This work enriches the molecular perovskite family and highlights the promise of molecular perovskites for the next-generation eco-friendly and wearable optoelectronic devices.

Ultrafast (600\xa0ps) \u03b1-ray scintillators

Large-size scintillators with high efficiency and ultrafast radiation fluorescence have shown more potential in the applications to ionizing radiation detection of medical diagnosis, nuclear control and high-energy physics. Currently, although traditional scintillators have made tremendous progress in scintillation efficiency, there are still challenges left in fluorescence lifetime. Faced with that problem, we adopted 2-inch ZnO as the substrate and doped gallium as activator to realize an ultrafast fluorescence excited by α-ray, of which the decay time is only 600 ps that is the shortest scintillation decay time reported so far. The results show that the shallow donor related with gallium not only effectively suppresses band-edge self-absorption, but makes ultrafast radiation possible, which gets gallium-doped ZnO as a potential scintillator for high-quality ultrafast dynamic imaging proved.

Energy Transfer Assisted Fast X-ray Detection in Direct/Indirect Hybrid Perovskite Wafer.

Metal halide perovskite scintillators encounter unprecedented opportunities in indirect ionizing radiation detection due to their high quantum yields. However, the long scintillation lifetime of microseconds upon irradiation, known as the afterglow phenomenon, obviously limits their fast development. Here, a new type of hybrid X‐ray detector wafer combining direct methylamine lead iodide (MAPbI3) semiconductor and indirect zero‐dimensional cesium copper iodide (Cs3Cu2I5) scintillator through low‐cost fast tableting processes is reported. Due to the fast energy transfer from Cs3Cu2I5 to MAPbI3, the device response time to X‐rays is dramatically reduced by nearly 30 times to 36.6 ns, which enables fast X‐ray detection capability by a large area detector arrays within 1 s. Moreover, Cs3Cu2I5 exists at the grain boundaries of MAPbI3 crystals, and blocks the paths of mobile ions of perovskite, leading to the lowest detectable dose rate of hybrid X‐ray detector is thus reduced by 1.5 times compared with control MAPbI3 direct‐type semiconductor, and 10 times compared with the Cs3Cu2I5 indirect‐type scintillator. The direct/indirect hybrid wafer also exhibits improved operation stability at ambient conditions without any encapsulation. This new kind of hybrid X‐ray detectors provides strong competitiveness by combining the advantages of both direct perovskite semiconductors and indirect perovskite scintillators for next‐generation products.

Surface tension of Cd0.9Zn0.1Te melt

Cd0.9Zn0.1Te is widely used as a material for X-ray and γ-ray ionizing radiation detectors. In this work surface tension of the melt is studied experimentally and compared with the Shishkovsky equation.

Application of gold nanomaterials for ionizing radiation detection

Au nanomaterials are known to change their properties significantly depending on their particle size. The prepared chloride glasses exhibited yellow emission (520 nm) upon UV rays (250 nm) irradiation, and the intensity of emission was found to decrease with X-ray dose. We concluded that this is because luminescent Au nanoclusters (AuNCs) of a few nanometers in size grow into Au nanoparticles (AuNPs) of a few tens of nanometers in size due to the photoreduction effect induced by irradiating X-ray, and the absorption (550 nm) attributed to the surface plasmon effect of AuNPs make decrease the AuNCs emissions. From the results of the changes of photoluminescence (PL) intensity concerning the irradiation X-ray dose, it was found that the PL intensity monotonically decreased 3000 mGy or more. This suggests that the Au-doped CsCl–BaCl2–ZnCl2 glass can act as an X-ray detection material in a specific dose region.

Combined Purification and Crystal Growth of CsPbBr3 by Modified Zone Refining

The all-inorganic semiconducting perovskite Cesium Lead Bromide, CsPbBr3, exhibits promising properties for ionizing radiation detection applications. In this work, polycrystalline CsPbBr3 was synthesized from the melt of binary compounds CsBr and PbBr2. Moisture and oxides in the synthesized CsPbBr3 compounds were removed by a reduction process under hydrogen. The CsPbBr3 materials were purified and grown into high-quality single crystals via a modified zone refining process. The single-crystal samples obtained from the combined zone-refining/crystal growth process exhibited total trace impurity levels below 1 ppm (w.t.). Obtained single crystals exhibited an electrical resistivity within a range of 10^8~10^9 Ω·cm. Stoichiometry imbalance was observed in the CsPbBr3 crystal growth. Around 1% Cs deficiency was observed in all the samples, despite different ratios between the starting materials of PbBr2 and CsBr. The positive impact of excess PbBr2 in starting materials was also revealed. With a slight excess Pb (2%), CsPbBr3 single crystals displayed significantly higher photosensitivity compared to the stoichiometric or excess Cs samples.