To date, more than 200 scintillation materials have been developed, however only a few of them are widely used for detectors design and construction. A general trend is to use for detectors the ...elements produced from the selected top-quality grade scintillation materials instead of expensive novel chemically not stable halides. Another trend, which came in the last few years, is to apply new achievements from the theory of scintillation materials to engineer the properties of the materials for a particular application. From that point of view, the complex oxides with garnet structure is a family of materials, for which properties can be tuned for the best performance for a particular application at the ionizing radiation detection.
Ce-doped tetracationic garnets (Gd, M)
3
Al
2
Ga
3
O
12
(M = Y, Lu) form a family of new multipurpose promising scintillation materials. The aim of this work was to evaluate the scintillation yield ...in the materials of quaternary garnets activated by cerium ions with partial isovalent substitution of the matrix-forming gadolinium ions by yttrium or lutetium ions.Materials were obtained in the form of polycrystalline ceramic samples, and the best results were shown by samples obtained from the raw materials produced by the coprecipitation method. It was found that ceramics obtained from coprecipitated raw materials ensure a uniform distribution of activator ions in the multi-cationic matrices, which enables the high light yield and fast scintillation kinetics of the scintillation. It was demonstrated that the superstoichiometric content of lutetium/gadolinium in the material is an effective method to suppress phosphorescence accompanied scintillation. For ceramics with the composition (Gd, Lu)
3
Al
2
Ga
3
O
12
, a scintillation yield of more than 50.000 ph/MeV was achieved. The scintillation kinetics was measured to be close to the kinetics with a decay constant of 50 ns.In terms of the set of the parameters, the developed scintillation materials are close to the recently developed alkali halide materials LaBr
3:
Ce, GdBr
3
:Ce. Moreover, they have high mechanical hardness, are characterized by the absence of hygroscopicity, and are better adapted to the manufacture of pixel detectors used in modern devices for medical diagnostics.
Cerium-doped mixed garnet-type single crystals (GdxY1-x)3Al2Ga3O12 with different yttrium content have been fabricated and studied as a prospective scintillating material enabling improvement of ...scintillation properties by tuning the composition of the matrix-building crystal. The influence of the matrix composition on the emitting Ce ion is studied using linear and time-resolved nonlinear optical absorption and time-resolved photoluminescence spectroscopy. The study of photoluminescence at resonant excitation revealed a composite origin of Ce3+ emission band. This behavior is interpreted by the contribution of Ce3+ ions located in inequivalent positions expected due to the disorder caused in the garnet-type lattice of a mixed crystal by compositional fluctuations. The substitution of gadolinium by yttrium in the lattice results not only in an emission blue shift and in decreased splitting of the lowest doublet 5d state of Ce3+ but also in an increased separation between the lowest doublet level 5d1 and the lowest triplet 5d3 level, as well as in changing the rates of intracenter and extracenter energy relaxation.
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•Photoluminescence spectrum is composite due to inequivalent positions of Ce3+ ions.•Decay time of Ce3+ emission decreases from 55 ns at 1.9 eV to 40 ns at 2.5 eV.•Substitution of Gd by Y decreases 5d1-5d2 splitting of Ce3+ and increases 5d1-5d3 separation.•Introduction of Y in GAGG lattice increases Ce3+ intracenter relaxation time.•Capture of trapped electrons to nonradiative recombination centers is enhanced in GYAGG.
Coincidence time resolution (CTR) of scintillation detectors based on Ce- and Mg-codoped Gd 3 Al 2 Ga 3 O 12 (GAGG) scintillation crystals and high-density silicon photomultipliers (SiPMs) is shown ...to be 165 ps (full width at half maximum) for 511-keV <inline-formula> <tex-math notation="LaTeX">\gamma </tex-math></inline-formula>-quanta, approaching that achieved by using LSO scintillators. To study the prospective for further improvement of the time resolution, the population of the emitting Ce centers was investigated by optical pump and probe technique using selective photoexcitation and probing by a white light continuum with subpicosecond time resolution. The importance of free electron trapping for excitation transfer to emitting Ce ions was revealed. The influence of transfer delay on the scintillation response time is described, and the dynamics of electron relaxation to the lowest excited level of Ce ion is studied experimentally and analyzed by taking into account intracenter relaxation and relaxation via conduction band. The influence of electron diffusivity on the rise time of the population of the emitting level is described. It is shown that codoping of GAGG:Ce by magnesium even at the level as low as 10 ppm efficiently decreases the scintillator response time by enhancing the electron diffusivity.
The effect of sintering additives of B, Mg, Zr and Si compounds on the morphology and luminescent properties of Gd
1.5
Y
1.5
Al
2
Ga
3
O
12
:Ce (GYAGG:Ce) ceramic quaternary garnets produced by free ...sintering has been studied. The microstructure of the ceramics, their optical absorption, steady-state luminescence spectroscopy and kinetics, as well as scintillation parameters upon excitation by α-particles (
E
= 5.5 MeV) were studied. Analysis of the results allows to conclude that additives based on Zr improve the optical and spectral properties of the ceramic material of the given composition.
Ceramics of quaternary garnets (Gd,Y)3Al2Ga3O12 doped with Ce, Tb have been fabricated and evaluated as prospective materials for indirect energy converters of α-and β-voltaic. Samples were ...characterized at excitation with an X-ray source and an intense 150 keV electron beam and showed good temperature stability of their emission and tolerance to irradiation. The role of X-rays accompanied the α-particle emitting in the increase of the conversion efficiency is clarified. The garnet-type structure of the matrix in the developed materials allows the production of quality crystalline mass with a light yield exceeding that of the commonly used YAG: Ce scintillator by a factor of two times.
Lead tungstate scintillation material Annenkov, A.A; Korzhik, M.V; Lecoq, P
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2002, Letnik:
490, Številka:
1
Journal Article
Recenzirano
In this paper we summarize the results of a research programme on lead-tungstate (PWO) crystals performed by the CMS Collaboration at CERN, as well as by other groups who promoted the progress of the ...PWO scintillation crystal technology. Crystal properties, mass production technology, scintillation mechanism, origin of colouring, defects in crystal and radiation induced phenomena, light yield improvement and results of beam tests are described.
The aim of this work has been to improve the time resolution of radiation detectors for future high-energy physics experiments and medical imaging applications. Ce-doped oxyorthosilicate Lu2SiO5:Ce ...(LSO) and mixed oxyorthosilicate Lu1.6Y0.4SiO5:Ce (LYSO) have been investigated as prospective scintillators for such high-time-resolution applications. A differential optical absorption technique with sub-picosecond time resolution upon selective excitation of Ce3+ ions to different excited states has been adopted to study carrier dynamics in these scintillators, and coincidence time resolution measured using 511 keV γ-quanta has been exploited to test their timing properties. A delay in population of the emitting level of Ce3+ has been observed, and is interpreted in terms of electron trapping, which is more pronounced in mixed yttrium-containing LYSO crystals due to composition fluctuations. It is shown that the delay, which affects the luminescence response time, can be eliminated by co-doping of LYSO:Ce with calcium at concentrations as low as 5 ppm. The faster kinetics of electron transfer correlates with a better coincidence time resolution. Thermalization and spatial distribution of non-equilibrium carriers has been studied theoretically to link the results obtained by the time-resolved differential optical absorption technique with the behavior of the non-equilibrium carriers generated by irradiation.
•The time resolution of LYSO is more affected by carrier trapping than that of LSO.•Carrier trapping in LYSO is enhanced by fluctuations in the compound composition.•Ca-co-doping, even at a concentration of 5 ppm, improves the response time of LYSO:Ce.•Femtosecond pump-probe spectroscopy is a useful tool for improving Ce-doped scintillators.
Abstract In the process of irradiation of materials by fluxes of heavy particles (protons, neutrons, alpha particles), damage to material structure is often observed. As a result of the accumulation ...of such damages, there is a subsequent change in the properties of materials, in particular, its embrittlement and hardening. Monitoring of the embrittlement process is important for nuclear reactor vessels exposed to high neutron fluxes. In this work, to observe the effect of heavy irradiation particles on the mechanical properties of metals, we propose to use vibrating wire resonators, in which the natural frequency of oscillations of the wire strongly depends on its tension. The change in the elastic characteristics of the wire alters the value of the natural frequency of wire oscillations. The natural oscillations are generated by a special circuit. Preliminary experiments to study the embrittlement effect of a stretched wire are performed by heating the wire with an electric current. In the case of short pulses, a significant increase in frequency is achieved, which is explained by the process of hardening of the material as a result of the thermal impact on the wire (rapid heating and cooling).
We investigated the influence of the silica-based glass composition and its synthesis conditions on the oxidation states of luminescent rare earths like Ce, Tb, and Eu dopant ions. It was found that ...the repeated melting of the glass led to the stabilization of rare-earth ions in higher oxidation states; in the case of Ce doping, this caused a significant decrease in the scintillation yield, whereas for Tb doping no significant modifications were noticed. Furthermore, it was concluded that the glass matrix influences the rare-earth oxidation state depending on the ions modifying the glass structure. This effect was clearly observed for the Eu-doped series of Ca, Sr and Ba di-silicate glasses, where the conversion of Eu3+ to Eu2+ was found to be dependent on the distortion of the silica network. The influence of glass crystallization on the rare-earth oxidation state stabilization is also discussed.
•The synthesis effect on Ce, Tb, Eu ions valence state in glasses was studied.•The valence state of Ce, Tb, Eu ions was found to be dependent on glass composition.•The possibility of Eu and Ce ions valence control by glass crystallization was shown.
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