Powder Scintillator Research Articles

Benefits of front coating crystalline scintillator screens for phase-contrast synchrotron micro-tomography

Transparent crystalline scintillators such as cerium-doped YAG or LuAG are widely used in X-ray imaging for the indirect detection of X-rays. The application of reflective coatings on the front side to improve the optical gain is common practice for flat panel detectors with CsI or Gd2O2S powder scintillators but still largely unknown for crystalline scintillators such as LuAG. This work shows experimentally and quantitatively how a black and reflective coating on the X-ray side of a 2 mm LuAG:Ce scintillator improves the image quality compared to a 2 mm LuAG:Ce scintillator without a coating. The measurements have been done for two different distances, with 2 m and 29.7 m on the BM18 beamline of the European Synchrotron. The Modulation Transfer Function (MTF) and the Signal-to-Noise-Ratio (SNR2) power spectrum as well as contrast-to-noise ratio are used for comparing image quality. Propagation-based phase contrast strongly enhances the SNR2 amplitudes (gain ≈10 from 2 m to 29.7 m object-detector distance) of the raw images’ spectrum independent of the scintillator coating. For both detector positions, the reflective coating is able to raise SNR2 by up to 80% through the improved optical gain, while black coating does the opposite (decrease SNR2 by 20%) with respect to no coating. With the tested optical setups, changes in MTF /sharpness between the coatings are minor. Comparing CNR2 in CT scans of a multi-material sample, in this case an electric motor, we observe the reflective coating yielding better material contrast for plastic and air. Application and effect of Wiener-deconvolution, along with Paganin-type phase retrieval, are also discussed in the context of CT image quality.

Light yield measurement of the Ce3+ activated LuAG nano-powder garnet scintillating detector

This paper focuses on the characterization of nano-powder (NP) scintillator, specifically presenting preliminary results of the measurement of the light yield (LY) of a newly synthesized Lutetium Aluminum (LuAG) garnet phosphor NP scintillator, doped with 0.1% cerium. The scintillation light yield was measured using the comparative method. Considering the light-scattering and self-absorbing properties of powder scintillators, alpha particles from 241Am source were used for excitation instead of Gamma/X rays, while a Ce3+ activated LuAG single crystal (SC) was employed as the reference detector due to its well-established light yield. A photomultiplier tube (PMT) served as the photodetector, and signals were read out by a nuclear instrumentation chain. The results demonstrate that the newly prepared LuAG:Ce NP exhibits a light output that is approximately 90% of that of the single crystal reference. These findings highlight the promising potential of NP scintillators as a viable alternative to single crystals, especially in applications where the preference for powder scintillators is evident.

Photoluminescence and X-ray induced scintillation in Gd3+-Tb3+ co-doped fluoride-phosphate glasses, and derived glass-ceramics containing NaGdF4 nanocrystals

The glass system (50NaPO3–20BaF2–10CaF2–20GdF3)-xTbCl3 with x = 0.3, 1, 3, 5, and 10 wt % was investigated. We successfully produced transparent glass ceramic (GC) scintillators with x = 1 through a melt-quenching process followed by thermal treatment. The luminescence and crystallization characteristics of these materials were thoroughly examined using various analytical methods. The nanocrystallization of Tb3+-doped Na5Gd9F32 within the doped fluoride-phosphate glasses resulted in enhanced photoluminescence (PL) and radioluminescence (RL) of the Tb3+ ions. The GC exhibited an internal PL quantum yield of 33 % and the integrated RL intensity across the UV-visible range was 36 % of that reported for the commercial BGO powder scintillator. This research showcases that Tb-doped fluoride-phosphate GCs containing nanocrystalline Na5Gd9F32 have the potential to serve as efficient scintillators while having lower melting temperature compared to traditional silicate and germanate glasses.

Alpha-ray imaging with alkali copper halide scintillator

Internal exposure for decommissioning workers at the Fukushima Daiichi Nuclear Power Plant must be prevented, and we have developed a monitoring system for alpha-ray emitting dust (alpha dust). When the dust size is less than several tens of micrometers, a dust protection maskdoes not work effectively to prevent internal exposure. Since no devices have been operated to observe alpha-dust images in real-time up to now, we have developed an alpha-ray imaging detector consisting of a scintillation material and imaging detector. Scintillators are required to have high light output and chemical stability. Cs3Cu2I5 (CCI) scintillator was found to be one of the candidates, and an imaging test was operated with this material. The CCI crystal was grown by the Bridgman-Stockberger method, and a scintillation sheet for alpha-ray imaging was prepared by CCI microcrystals with a thickness of approximately 70 μm on a 200-μm thickness transparent polyethylene terephthalate film as a first imaging test. The sheet was irradiated with 5.5-MeV alpha rays from an 241Am source, and scintillation photons were detected with a CMOS camera through an optical lens. We succeeded in visualizing alpha rays, and a position resolution of our system achieved approximately 16.2 ± 2.6 μm (10–90 %). This resolution was similar value to other imaging devices with Ag:ZnS powder scintillator, and a CCI single crystal sheet was expected to reach better resolution.

Novel flexible and conformable composite neutron scintillator based on fully enriched lithium tetraborate

Thermal neutron detection is a key subject for nuclear physics research and also in a wide variety of applications from homeland security to nuclear medicine. In this work, it is proposed a novel flexible and conformable composite thermal neutron scintillator based on a fully enriched Lithium Tetraborate preparation (^{6}Li_2^{10}B_4O_7) combined with a phosphorescent inorganic scintillator powder (ZnS:Ag), and is then distributed into a polydimethylsiloxane matrix. The proposed scintillator shows a good neutron detection efficiency (max. sim 57% with respect to the commercial EJ-420), an average light output of sim 9000 ph/neutron-capture, a remarkable insensitivity to gamma-rays (Gamma Rejection Ratio <10^{-11}), and an extraordinary flexibility, so as to reach extremely small curvature radii, down to 1.5 mm, with no signs of cracking or tearing. Its characteristics make it suitable to be employed in scenarios where non-standard geometries are needed, for example, to optimize the detector performance and/or maximize the detection efficiency. Finally, the response of a hybrid detector made of a plastic scintillator, wrapped with the proposed scintillator, coupled to a silicon photomultiplier array is described, and the excellent discrimination between gamma-rays, fast and thermal neutrons resulting from data processing is demonstrated.

Development of a real-time in vivo dosimetry tool for electron beam therapy using a flexible thin film solar cell coated with scintillator powder.

A real-time solar cell based in vivo dosimetry system (SC-IVD) was developed using a flexible thin film solar cell and scintillating powder. The present study evaluated the clinical feasibility of the SC-IVD in electron beam therapy. A thin film solar cell was coated with 100 mg of scintillating powder using an optical adhesive to enhance the sensitivity of the SC-IVD. Calibration factors were obtained by dividing the dose, measured at a reference depth for 6-20 MeV electron beam energy, by the signal obtained using the SC-IVD. Dosimetric characteristics of SC-IVDs containing variable quantities of scintillating powder (0-500 mg) were evaluated, including energy, dose rate, and beam angle dependencies, as well as dose linearity. To determine the extent to which the SC-IVD affected the dose to the medium, doses at R90 were compared depending on whether the SC-IVD was on the surface. Finally, the accuracy of surface doses measured using the SC-IVD was evaluated by comparison with surface doses measured using a Markus chamber. Charge measured using the SC-IVD increased linearly with dose and was within 1% of the average signal according to the dose rate. The signal generated by the SC-IVD increased as the beam angle increased. The presence of the SC-IVD on the surface of a phantom resulted in a 0.5%-2.2% reduction in dose at R90 for 6-20 MeV electron beams compared with the bare phantom. Surface doses measured using the SC-IVD system and Markus chamber differed by less than 5%. The dosimetric characteristics of the SC-IVD were evaluated in this study. The results showed that it accurately measured the surface dose without a significant difference of dose in the medium when compared with the Markus chamber. The flexibility of the SC-IVD allows it to be attached to a patient's skin, enabling real-time and cost-effective measurement.

Development of a capillary plate based fiber-structured ZnS(Ag) scintillator

Silver-doped zinc sulfide (ZnS(Ag)) is an opaque powder scintillator that is mainly used for detection or imaging of charged particles such as alpha particles. Since ZnS(Ag) is not transparent, the thickness of ZnS(Ag) was limited to ∼10 μm. If a thicker ZnS(Ag) scintillator could be developed, it would be useful for studies such as high-energy particle ion detection as well as beta particle or gamma photon detection. We developed a ZnS(Ag) fiber-structured scintillator using a capillary plate in which ZnS(Ag) powder was encapsulated in the capillaries. The thickness of the capillary plate was 400 μm, and the light produced in ZnS(Ag) escaped from the capillaries, spread through the transparent lead glass area, and reached the opposite side of the plate; consequently, the opaque character and absorption of light could be avoided. The amount of light emitted from the capillary plate based fiber-structured ZnS(Ag) was almost the same as that of a commercially available ZnS (Ag) film, but the detection efficiency was about 1/5 (∼ 20%). The amount of light emitted from beta particles and gamma photons per MeV was less than 1% of that from alpha particles. The spatial resolution of the developed capillary plate based fiber-structured ZnS(Ag) scintillator for 5.5 MeV alpha particles was ∼200 μm FWHM. Imaging of the slits and light spots from alpha particles could be achieved with the developed scintillator combined with an electron-multiplied charge-coupled device (EM-CCD) camera. The developed capillary plate based fiber-structured ZnS(Ag) will be useful for detecting high-energy particle ions.

Flexible, High Scintillation Yield Cu3Cu2I5 Film Made of Ball‐Milled Powder for High Spatial Resolution X‐Ray Imaging

AbstractCu halide materials with low electronic dimension show great scintillation properties with high photoluminescence quantum yield (PLQY) and large Stokes shift, which can result in reabsorption‐free scintillators. However, there is still a need for a large‐scalable method to fabricate large amount of scintillation powder and large‐size scintillation films. In this regard, a high scintillation yield Cu3Cu2I5−PDMS flexible film utilizing ball‐milled Cu3Cu2I5 powder is developed. The ball‐milled Cu3Cu2I5 powder shows a high PLQY of 74.5%, narrow emission peak of 80 nm and good ambient stability, demonstrating the potential of ball‐milling method for large‐scale scintillator production. Furthermore, the Cu3Cu2I5−PDMS film shows even high PLQY exceeding 90%, which may be ascribed to the passivation effect of PDMS resulting in a little longer carrier lifetime. The flexible Cu3Cu2I5−PDMS film can further deliver high spatial resolution of 6.8 lp mm−1@0.2 MTF in X‐ray imaging and good stability under steady X‐ray illumination. This work demonstrates that the ball‐milling method could be an effective approach for large‐scale fabrication of low electronic dimensional scintillation materials.

Utilization of YAP:Ce powder scintillator for 57Fe Mössbauer spectroscopy

Using a powder scintillator for a detection of gamma and X-rays allows to create detectors of various shapes, moreover the handling and fabrication of such scintillators is much easier than in the case of large or thin monocrystals. We report on the application of YAlO3:Ce powder to Mössbauer spectroscopy. The detection efficiency and the energy resolution of the scintillators made of powders of two different granularities (grain size ≤30μm and 50–70μm) were investigated. The powder scintillators exhibited a comparable energy resolution and detection efficiency as YAlO3:Ce monocrystal with thickness of 400μm. Burying the YAlO3:Ce grains into the epoxy resin increased the energy resolution of powder scintillators. The studied scintillators were found to be suitable for experiments in Mössbauer spectroscopy. The performance of YAP is also compared to the NaI:Tl scintillator.

The ways of characteristics improvement for alpha–beta detectors on ZnSe based composite scintillators

The design and technological scheme of alpha particle detectors based on crystal granules of ZnSe–Al were developed. We have found that the ZnSe–Al semiconductor scintillator has a number of advantages compared to the ZnS–Ag namely the terms of sensitivity and the ability to obtain scintillation powder of the desired dispersion. The results of tests of sensitivity, homogeneity and ability to registration simultaneously both alpha and beta particles are presented. The measured sensitivity of detectors towards alpha particles (239Pu source) was more than 0.3 pulse per sec/Bq (pps/Bq) and towards beta particles (90Sr-90Y source) was more than 0.25 pps/Bq. The light output inhomogeneity of scintillators within the area did not exceed 2%. This makes it possible to produce the large area detectors.An algorithm for separating the scintillation signal from alpha and beta particles during their simultaneous registration is proposed. Potentially, statistical algorithms will allow 100% separation of alpha and beta particle pulses.

Simple measurement of actinides in urine using solid-state scintillation

Rapid methods for determination of internal contamination play a key role during emergency situations in particular for incident response teams and affected populations. For this reason, these methods and their particular techniques must be fast, reliable, robust, simple and cost-efficient, as well as providing high-quality throughput. On the other hand, they are characterized by lower precision and they are often biased. The presented method is based on direct measurement of urine using powder scintillator YAP:Ce together with an alkaline medium as a replacement for traditional liquid scintillation cocktail. The overall efficiencies for trivalent actinides (Am-241 and Cm-244) were greater than 85% and 94%.

Structural and optical properties of LSO scintillator-polymer composite films

Composite films containing homogeneously dispersed scintillation nano-particles of Lu2SiO5:Ce3+, in optically transparent polymer matrix, have been prepared and characterized through X-ray diffraction, Thermogravimetric analysis TGA, electron scanning microscopy morphology SEM and PL photoluminescence. Lu2SiO5:Ce3+ scintillator powder was successfully synthesized via Sol-Gel method. This study is realized with different mass ratios of nano-particles embedded in polystyrene and polylactic acid polymer matrix (5, 10, 15, 20%) to see the influence of nano-particles on the mechanical, structural and optical properties of films. The composites have been prepared with 200 μm thickness. It’s found that the structural proprieties change with mass ratio on each sample. PL photoluminescence show the characteristic Lu2SiO5:Ce3+ emission in the blue region and intensity varied for each film.

Multi-point gamma-ray monitoring at radioprotection levels with image devices

A multi-point system for the simultaneous interrogation of several extrinsic polymer optical fiber-based gamma-ray sensors is demonstrated. As a proof of concept, four different sensing heads have been measured, all of them based on a chemically etched fiber tip plus an inorganic scintillator powder. Two inorganic scintillators have been tested, namely Terbium doped Gadolinium Oxysulfide (Tb:GADOX) and Cerium doped Yttrium-Aluminum garnet (YAG:Ce). These sensing heads are interrogated with a commercial image device (CMOS camera). Such device does not need any cooling stage, optical filters or image intensifier elements. The response for each individual transducer is inside a 2D grid-shape array image, which provides a multiplexing method scalable with the number of the desired interrogation points. The interrogation procedure takes advantage of well-stablished digital image processing techniques, which include the selection of the regions of interest (ROIs) associated to the response of each individual sensing-head, plus the suitable RGB channel selection to improve the signal to noise ratio in the final measurement. Thus, only the Green channel has been found to render useful signal for gamma ray monitoring. Furthermore, the selection of the exposure time in the CMOS camera also permits to adjust the radiation levels to be detected.All tests were run under gamma irradiation from a calibrated 137Cs source, the reference isotope for environmental protection. The obtained results show the feasibility of simultaneously interrogating several gamma ray sensors, which can provide reliable measurements to quickly detect the presence of hazardous radioactive materials in large accidental leakage scenarios.

Determination of the gross activity of uranium, plutonium, americium and strontium in environmental samples using solid-state scintillation

Rapid determination of selected gross alpha and beta emitters in environmental matrices by solid-state scintillation technique is discussed. This method is based on sample treatment using microwave reactor and direct measurement of digested products using powder scintillator and alkaline solution as a substitute for traditional liquid scintillation cocktail. The selected group of radionuclides was chosen with respect to their use in nuclear industry, high radiotoxicity, and the possibility of potential misuse. The work aimed at verifying the connection of microwave decomposition using alkaline solution with solid-state scintillation using a powder scintillator YAP:Ce together with an alkaline medium.

Hydrothermal synthesis of CdWO4 for scintillator-polymer composite films development

Composite films of CdWO4 embedded in polystyrene have been prepared and characterized through microtomography, photoluminescence and X-ray excited optical luminescence. CdWO4 scintillator powder was successfully produced via microwave-assisted hydrothermal method using oxide precursors. With the control of synthesis pH, CdWO4 wolframite structure was obtained at temperatures as low as 100 °C for reaction time of 1 h. Surface modification of CdWO4 particles by stearic acid promoted good dispersion of scintillator nanoparticles within the polymeric matrix. The composites have been prepared with 220 µm or 440 µm thickness and CdWO4/PS mass ratios of 10% and 20%. Optical measurements show the characteristic CdWO4 emission in the blue region as well as PS luminescence due to PPO, POPOP and PTO organic impurities. Under X-ray excitation, the light output was proportional to the increase of scintillator content and sample thickness. The emission intensity varied for each film face irradiated, being the most homogeneous condition achieved for the composite of 440 µm and CdWO4/PS = 10%.

Dynamic gamma-ray monitoring at radioprotection levels with extrinsic polymer optical fiber sensors

The dynamic performance of extrinsic gamma-ray sensors at radioprotection levels is studied. The sensors have been fabricated with chemically etched polymer optical fibers covered with an inorganic scintillator powder (Terbium doped Gadolinium Oxysulfide). This scintillator shows a maximum emission peak at 543 nm, therefore only the signal amplitude at this wavelength has been measured with a commercial grade CCD spectrometer. The transducers have been done at the end of both short (1 m) and large fiber patchcords (27 m). Short patchcords are further mechanically spliced to a fiber link 25 m length through an industrial grade connector-less mating sleeve, and therefore can be easily replaced if needed.All tests were run under gamma irradiation from a 137Cs source, the reference isotope for environmental protection. The measured response of the devices is very repeatable and stable, with a percentage standard deviation below 2% when the air kerma rate is above 1 Gy/h. This deviation increases for lower rates. A Limit of Detection of 0.2 Gy/h, with an integration time at the detection stage of 10 s, has been achieved for transducers done in the 1 m length patchcords spliced to the 25 m length fiber link. This integration time can be further reduced when no splice is included between transducer and detection unit. The behavior of the devices is linear with the delivered air kerma rate, and can provide reliable measurements under repeated radiation exposures. This behavior makes the sensors useful to quickly detect the presence of hazardous radioactive materials in accidental leakage scenarios.

An experimental approach to the determination of the gross activity of uranium, plutonium, americium and strontium in human biological samples using solid-state scintillation

Rapid bioassay methods have been mainly proposed for the sequential measurements of actinides in human blood, bone marrow and urine. The method involves sample treatment using microwave digestion techniques followed by direct measurement of digested products using powder scintillator and alkaline solution as a replacement for traditional liquid scintillation cocktail. The selected group of radionuclides was chosen due to their occurrence in the nuclear fuel cycle, nuclear accident, high radiotoxicity, and the possibility of potential misuses, such as dirty bombs. The work aimed at verifying the connection of microwave digestion using alkaline solution with solid-state scintillation using a powder scintillator YAP:Ce together with an alkaline medium.

The comparison of scintillation properties of YAP:Ce, YAG:Ce and ZnO:Ga powders as a potential substitution of LSC cocktail

The work investigates the possibility of substitution of a traditional liquid scintillation cocktail by a scintillation powder with grain size up to 30 μm. Based on previous research, YAP:Ce, YAG:Ce and ZnO:Ga powders were selected. The parameters, which often affect the measurement, were tested, such as pH and OH−, geometry, efficiency and activity linearity dependency, the amount of scintillator as well as secondary parameters such as afterglow, temperature dependency and repeatable usage. All parameters were simultaneously tested and compared with an AquaLight scintillation cocktail.

Image Quality Assessment of a CMOS/Gd2O2S:Pr,Ce,F X-ray Sensor

The aim of the present study was to examine the image quality performance of a CMOS digital imaging optical sensor coupled to custom made gadolinium oxysulfide powder scintillators, doped with praseodymium, cerium and fluorine (Gd2O2S:Pr,Ce,F) screens. The screens, with coating thicknesses 35.7 and 71.2 mg/cm2, were prepared in our laboratory from Gd2O2S:Pr,Ce,F powder (Phosphor Technology, Ltd) by sedimentation on silica substrates and were placed in direct contact with the optical sensor. Image quality was determined through a single index image quality parameter (information capacity). The CMOS sensor/Gd2O2S:Pr,Ce,F screens combinations were irradiated under the RQA-5 (IEC 62220-1) beam quality. The detector response function was linear for the exposure range under investigation. Under the general radiography conditions, both Gd2O2S:Pr,Ce,F screen/CMOS combinations exhibited comparable overall imaging properties, in terms of the information capacity, to previously published scintillators, such as Gd2O2S:Eu.

A new anti-neutrino detection technique based on positronium tagging with plastic scintillators

The main signature for anti-neutrino detection in reactor and geo-neutrino experiments based on scintillators is provided by the space–time coincidence of positron and neutron produced in the Inverse Beta Decay reaction. Such a signature strongly suppresses backgrounds and allows for measurements performed underground with a relatively high signal-to-background ratio. In an aboveground environment, however, the twofold coincidence technique is not sufficient to efficiently reject the high background rate induced by cosmogenic events. Enhancing the positron–neutron twofold coincidence efficiency may pave the way to future aboveground detectors for reactor monitoring. We propose a new detection scheme based on a threefold coincidence, among the positron ionization, the ortho-positronium (o-Ps) decay, and the neutron capture, in a sandwich detector with alternated layers of plastic scintillator and aerogel powder. We present the results of a set of dedicated measurements on the achievable light yield and on the o-Ps formation and lifetime. The efficiencies for signal detection and background rejection of a preliminary detector design are also discussed.