Littérature scientifique sur le sujet « Opaque scintillation »

Abstract In 2021, the Institute of High Energy Physics proposed a design of glass scintillator coupled with SiPM as a new solution for the next generation calorimeter, to explore the application of glass scintillators in high energy physics and nuclear radiation detection. The Large Area Glass Scintillator Collaboration Group was established to research and develop a glass scintillator with high density, high light yields and fast decay time. Through continuous optimization, the glasses have excellent scintillation performance with a light yield of 1000 ph/MeV and a density of 6 g/cm3. Moreover, the neutron response of the glasses was investigated, and different high-energy particles can be distinguished by signal amplitude. In addition, the radiation resistance of different glasses was tested under proton beam. All the glasses appeared opaque and produced a high radioactive background, because Gd element interacts with proton to produce radionuclides with high activity and long half-life.

Scintillators are one of the luminescent materials, and have a function to convert a quantum of ionizing radiation to thousands of low energy photons immediately via interactions between the material and ionizing radiation [1,2]. Generally, scintillators are combined with photodetectors, and when the scintillation photons are emitted from the scintillator, photodetectors convert them to electrical signals. When the target ionizing radiation is high energy photons such as X- and gamma-rays, heavy materials are preferable for scintillators since the detection efficiency against high energy photons depends on density and effective atomic number. Up to now, many types of materials have been examined for scintillators, such as single crystals, glasses, and opaque and transparent ceramics [2]. Among them, bulk single crystalline scintillators have been applied for scintillation detectors owing to a superior optical quality including high transmittance and luminescence efficiency. In the conference, some recent results of development of heavy scintillators mainly containing Lu, Hf, Ta and Tl are introduced. These materials were synthesized by some single crystal growth techniques such as the floating zone and bridgman method. After the synthesis, they were examined on optical (photoluminescence excitation and emission spectra and decay curve) and scintillation (scintillation emission spectrum, decay curve, afterglow and pulse height) properties. In Lu-based crystals, rare earth doped Lu2O3 crystals are introduced, and especially, Tb- and Eu-doped ones show a high scintillation light yield. In Hf-based ones, some results of rare earth doped AEHfO3 (AE = alkali earth) crystals are presented, and Ce-doped (Mg,Ca)HfO3 shows a high scintillation light yield [3]. Among Ta-based crystals, Mg4(Nb,Ta)2O9 crystals have a high light yield due to charge transfer luminescence of Ta/Nb and O [4]. In Tl-based crystalline compounds, TlMgCl3 shows a high light yield and energy resolution [5]. In the conference, these results will be introduced. References [1] T. Yanagida, Proc. Jpn. Acad., Ser. B, Phys. Biol. Sci., 94(2) 75 (2018). [2] T. Yanagida, T. Kato, D. Nakauchi, N. Kawaguchi, Jpn. J. Appl. Phys., 62 010508 (2023). [3] H. Fukushima, D. Nakauchi, T. Kato, N. Kawaguchi, T. Yanagida, Jpn. J. Appl. Phys., 62 010506 (2023). [4] T. Hayashi , K. Ichiba, D. Nakauchi, K. Watanabe, T. Kato, N. Kawaguchi, T. Yanagida, J. Lumin., 255 119614 (2023). [5] Y. Fujimoto, M. Koshimizu, T. Yanagida, G. Okada, K. Saeki, K. Asai, Jpn. J. Appl. Phys., 55 090301 (2016).

A scintillator is one of the phosphors for radiation detection. Typical application fields of scintillators are medical, security, and environmental dosimetry. In nuclear facilities, there are high doses of α-ray, and monitoring of α-ray is necessary. Up to now, Ag-doped ZnS is used for α-ray detection. Although Ag-doped ZnS has high light yield, the detection efficiency is limited because the material form is opaque polycrystal. Therefore, a novel scintillator with high transparency is required for α-ray detection. Spinel materials are one of the candidates for radiation detection because of their high radiation resistant. According to the previous study, scintillation properties of MgGa2O4 and ZnGa2O4 have been studied under γ-ray irradiation. On the other hand, these materials seem to be suitable for α-ray detection rather than γ-ray detection because of the low effective atomic number. In addition, other spinel materials also worth studying. In this study, we synthesized MgAl2O4, MgGa2O4, ZnAl2O4, and ZnGa2O4 single crystals and evaluated the optical and scintillation properties. The starting powders were MgO, ZnO, Al2O3, Ga2O3. The powders were mixed into homogeneously and shaped into cylindrical rods by packing into balloon and applying hydrostatic pressure. Then, the rods were sintered 1400°C for 8 h in air to obtain ceramics precursor. Single crystalline samples were synthesized by the floating zone method using the ceramics precursor. For measurements, the synthesized crystals were processed to approximately 5 mm in diameter and 1 mm in thickness by cut and polishing. The transparent and single-phase of the MgAl2O4, MgGa2O4, ZnAl2O4, and ZnGa2O4 single crystals were successfully obtained by the floating zone method. According to the total transmission spectra, the total transmittances of the crystals were 70−80% in visible region. In the X-ray-induced scintillation spectra, MgAl2O4, MgGa2O4, ZnAl2O4, and ZnGa2O4 single crystals showed a luminescence peak around 380, 400, 300, and 350 nm, respectively. The luminescence origin of each crystal was considered to be due to oxygen vacancies of the host materials. Figure 1 shows the pulse height spectra of the spinel crystals under 241Am α-ray irradiation. The spectra of a commercial Bi4Ge3O12 (BGO, 8000 ph/MeV) single crystal under 137Cs γ-ray irradiation is also shown as a reference. As shown in Figure 1, all the crystals showed a clear full energy peak. From the comparison with the peak position of BGO, the light yields of the MgAl2O4, MgGa2O4, ZnAl2O4, and ZnGa2O4 single crystals were 200, 4300, 700, 5700 ph/5.5MeV-α, respectively. The details will be discussed in the conference. Figure 1

High radiative efficiency in moderately doped n- InP results in the transport of holes dominated by photon-assisted hopping, when radiative hole recombination at one spot produces a photon, whose interband absorption generates another hole, possibly far away. Due to "heavy tails" in the hop probability, this is a random walk with divergent diffusivity (process known as the Lévy flight). Our key evidence is derived from the ratio of transmitted and reflected luminescence spectra, measured in samples of different thicknesses. These experiments prove the non-exponential decay of the hole concentration from the initial photo-excitation spot. The power-law decay, characteristic of Lévy flights, is steep enough at short distances (steeper than an exponent) to fit the data for thin samples and slow enough at large distances to account for thick samples. The high radiative efficiency makes possible a semiconductor scintillator with efficient photon collection. It is rather unusual that the material is "opaque" at wavelengths of its own scintillation. Nevertheless, after repeated recycling most photons find their way to one of two photodiodes integrated on both sides of the semiconductor slab. We present an analytical model of photon collection in two-sided slab, which shows that the heavy tails of Lévy-flight transport lead to a high charge collection efficiency and hence high energy resolution. Finally, we discuss a possibility to increase the slab thickness while still quantifying the deposited energy and the interaction position within the slab. The idea is to use a layered semiconductor with photon-assisted collection of holes in narrow-bandgap layers spaced by distances far exceeding diffusion length. Holes collected in these radiative layers emit longwave radiation, to which the entire structure is transparent. Nearly-ideal calculated characteristics of a mm-thick layered scintillator can be scaled up to several centimeters.

In solid-state ionizing radiation detectors, there are two main types of approaches: direct conversion and indirect conversion. The former generally uses semiconductor detectors (e.g., Si photodiodes) that convert radiation directly into electronic signals. The latter, on the other hand, uses phosphors and converts radiation into low-energy photons, which are then detected with a photodetector. Such phosphors are divided into scintillators and storage phosphors. Scintillators emit photons when electrons and holes generated by ionizing radiation recombine at emission centers. These are widely used in security, medical imaging, and basic physics. In storage phosphors, electrons and holes generated by ionizing radiation are temporarily captured in the trapping levels. When the storage phosphors are externally stimulated, these captured electrons and holes are re-excited and recombine at emission centers. Storage phosphors are used as personal dosimeters and imaging plates. In general, the requirements for scintillators are high light yield (LY), short decay time constants, large effective atomic number (Z eff), low afterglow levels, and chemical stability. The search for scintillators has a long history, but no material has been developed that fulfills all the required properties. Therefore, various scintillators with different chemical compositions have been developed, and scintillators have been selected and used for different measurement applications. Single crystals have been the most commonly used scintillator material form because of their high light transfer efficiency at emission wavelengths. However, these are problematic because of the long time and high cost required for their preparation. To solve the problems that single crystals have, translucent ceramics have attracted attention in recent years. Ceramics are synthesized by solid-phase reactions, which generally take a shorter time and cost less than single crystals grown by melt growth techniques. In this context, our group has successfully developed translucent ceramic scintillators with high luminescence efficiency. We reported that Y3Al5O12:Ce [1] and Lu3Al5O12:Ce [2] translucent ceramics showed higher LYs than single crystals of the same composition. Since translucent ceramics have only recently begun to be developed, only a few materials have been fabricated. In this study, we developed BaFCl:Eu in translucent ceramic form. Ba-based complex anions have been actively studied as scintillators and dosimetric materials because of their high luminescence intensity and high Z eff (~50). In particular, BaFCl:Eu is known to have an emission wavelength suitable for general photodetectors (~380 nm), a relatively fast decay time constant (~5 μs), and chemical stability [3]. These properties are suitable for scintillators to detect X- and γ-rays. BaFCl:Eu has been fabricated in opaque ceramics and studied in detail with dosimetric properties, but there are still no reports of BaFCl:Eu translucent ceramics. In this study, BaFCl translucent ceramics doped with 0.01, 0.1, 0.5, and 1.0% Eu were synthesized by the spark plasma sintering method. The optical and scintillation properties of the fabricated samples were investigated, and their potential as scintillators was examined. Photoluminescence (PL) emission spectra and X-ray-induced scintillation spectra of the BaFCl:Eu translucent ceramics were measured, both of which were dominated by an emission peak at 390 nm. According to the report [3], this emission peak was suggested to originate from the 5d–4f transition of Eu2+. Pulse height spectra were measured to determine a scintillation light yield, which was 15,000 ph/MeV at a maximum. This value is about twice that of commercially used Gd2SiO5:Ce (8,000 ph/MeV, [4]). We will present a detailed attribution of the luminescence in BaFCl:Eu translucent ceramics and the concentration dependence of the samples. <reference> [1] T. Yanagida et al., IEEE Trans. Nucl. Sci., 52, 1836 (2005). [2] T. Yanagida et al., Radiat. Meas., 46, 1503 (2011). [3] M. Ignatovych et al., Radiat. Prot. Dosimetry, 84, 185 (1999). [4] I. G. Valais et al., IEEE Trans. Nucl. Sci., 54, 11 (2007).

Scintillators are vital components for nuclear instrumentation and its applications, including plasma diagnostics and imaging. As yields in controlled fusion experiments increase, the radiation tolerance of scintillator candidates for use in instrumentation is of particular importance. High radiation exposure can damage scintillating materials and alter the optical properties. The effects of radiation damage in Ce-doped mixed garnet ceramics over the compositional range (Y,Gd,Lu)3(Al,Ga)5O12 are investigated using optical techniques. The samples were exposed to 200 keV protons to an accumulated fluence of 1016 protons per square centimeter, then characterized using diffuse reflectance spectroscopy (DRS). DRS with visible light can assess the radiation tolerance of opaque poly-crystalline samples, which can be easily sintered from powders and thus offer distinct advantages in characterization compared to single crystals. Qualitative trends in induced absorption are presented as a function of composition, and the ideal cerium dopant concentration for Y2LuAl5O12 is determined to be 0.60–0.75 mol. %.

Abstract 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.

Abstract A survey meter was developed to reliably detect and visualize surface contamination of suits and objects by α-nuclides in high γ/n-rays background radiation environment. The survey meter features a semi-opaque ZnS:Ag scintillator mounted directly onto a multi-anode photomultiplier tube (MA-PMT) and amplification circuits, ensuring output gain equalization for all channels. α-ray events induce localized light emission in thin-film scintillators. By directly mounting the scintillator, diffusion of light before reaching the MA-PMT is suppressed, concentrating it in just a few channels, thereby facilitating discrimination from background radiation. This design also enables clear visualization of the shape of surface contamination. The prototyped survey meter is capable of responding up to 2.1 × 107 cpm, with no γ-ray response even in high-radiation environments exceeding 1 Sv/h. In actual environments with high background radiation, contamination of ~1/100th of the surface contamination density limit of 4 Bq/cm2 could be reliably detected.

L'étude des neutrinos a été un important moteur de découverte depuis la première proposition de l'existence de cette particule par Pauli en 1930. Les détecteurs a milieu transparent liquide sont au premier plan de ce relativement nouveau champ de la Physique. Ces détecteurs utilisent l'émission de lumière causée par les particules-filles des interactions de neutrinos pour caractériser cette particule furtive ainsi que ses nombreuses possibles sources. Le taux d'interaction extrêmement faible du neutrino a encouragé les Physiciens a développer des détecteurs de plus en plus volumineux pour augmenter les statistiques, ce qui a également révélé les principales limitations de ce type de détecteur. La technologie LiquidO propose une méthode innovante de détection des particules basée sur l'utilisation de liquides opaques et le confinement de la lumière. Dans cette thèse, nous discuterons des principales difficultés dans le développement de détecteur a milieu transparent et des solutions proposées par la technologie LiquidO. Le travail qui sera ensuite présenté concerne 3 principaux stages de développement de cette nouvelle technologie. Dans un premier temps, l'analyse des données d'un prototype LiquidO de 20 L et la caractérisation du confinement de la lumière en milieu opaque. Ensuite, l'instrumentation et le design d'un détecteur de 1000 L en construction. Enfin, nous explorerons les capacité des cette technologie par le biais de simulations phénoménologiques d'un détecteur de neutrino complet qui sera construit dans le futur
The study of neutrinos has been a major driver of discovery ever since the proposition of the existence of this particle by Pauli in 1930. At the forefront of this relatively new field of Physics are transparent liquid-based particle detectors, that use the emission of light caused by daughter particles of neutrino interactions to characterize both this elusive particle and its multiple possible sources. The extremely low interaction probability of neutrinos has prompted physicists to move towards bigger and bigger experiments to increase statistics. This, in turn, has revealed the current limitations of this type of detector. The LiquidO technology proposes an innovative new method to detect particles using opaque liquids and confinement of light. This thesis will discuss the current challenges of transparent medium detectors and how Liquido tackles these issues. The work that will then be presented focuses on 3 stages of development of this technology. First, the analysis of the data of a 20 L LiquidO prototype and the characterization of the confinement of light with an opaque medium. Followed by the instrumentation and design discussions of a 1000 L detector currently under construction, and its aim at identifying particles and exploring simple particle Physics. Finally, we will explore what this technology is truly capable of with phenomenological simulations of a fully-fledged neutrino detector to be built in the future