Composite Scintillators Research Articles

A Monte Carlo Model of the Neutron Detector Based on Lithium-Glass Scintillator

A Monte Carlo model of the thermal-neutron scintillation detector based on NE 912 lithium glass has been created and verified. The simulation was validated by comparing its result to experimental data from a prototype detector exposed to thermal-neutron and γ-ray beams. The light yield in the scintillator for a captured thermal neutron, the quenching factor, and the decay times of the scintillator were determined. The accuracy in reproducing the pulse shapes obtained in the experiment is sufficient to allow analysis of experimental data and estimation of the efficiency of n/γ discrimination techniques. Based on the simulation, it is possible to develop detector models with a low γ-ray sensitivity using heterogeneous composite scintillators with various geometries.

Zinc oxide/polystyrene composite based scintillator for alpha particle monitoring

The preparation of Zinc oxide/polystyrene (ZnO/PS) composite scintillator was carried out with different percentages of ZnO varying from 5 to 50% (w/w) on the quartz substrate. The enhanced absorbance is observed at ~ 385 nm for low % (w/w) of ZnO, which is red-shifted to 390 nm for higher ZnO % (w/w) composite samples. The pristine polystyrene sample showed excitation at ~271 nm, equivalent to the measured bandgap of polystyrene. A photoluminescence emission of 385 nm in ZnO/PS composite is observed, which is equivalent to the measured ZnO bandgap ~3.22 eV. Alpha excited radioluminescence, obtained using 5.2 MeV alpha particles from 239Pu, showed emission at ~387 nm together with polystyrene emission at ~ 430 nm. The scintillation characteristics for the composite samples are investigated using the pulse height spectrum after coupling the composite films with a photomultiplier tube (PMT) and multichannel analyzer (MCA). The significant increase in pulse height is observed for 5% (w/w) or more ZnO in PS. This is clearly discernible in contrast to polystyrene without ZnO. The integrated counts increase linearly up to 20% (w/w) ZnO and showed reduction for 50% (w/w) ZnO/PS sample. The reduction in the counts is attributed to the reduced transmittance for higher % (w/w) ZnO in PS matrix. The maximum detection efficiency and minimum detectable activity (MDA) are ~23% and ~0.4 Bq, respectively, for 50% (w/w) ZnO/PS. Further, a linear response is observed with activity for all scintillating samples. These findings suggest that ZnO/PS composite materials may be a good candidate for efficient monitoring of alpha radioactivity with high sensitivity and very low MDA.

New types of composite scintillators based on the single crystalline films and crystals of Gd3(Al,Ga)5O12:Ce mixed garnets

This work presents the results of creation of novel composite scintillators based on the Gd3Al5-x GaxO12:Ce (x = 1.16–2.67) single crystalline films (SCF), grown by the LPE method onto Gd3Al2.5 Ga2.5O12:Ce single crystal (SC) substrates. The scintillation properties of film/crystal epitaxial structures were investigated under α–particle and γ–quantum excitations. Under α–particle excitation, the light yield of mentioned SCF scintillators is significantly less than that in their substrates due to the influence of Pb2+flux contamination and formation of Pb2+-Ce4+centers. Meanwhile, these SCF scintillators under α–excitation possess significantly faster decay kinetics than that of their substrates under γ–excitation. Therefore, the Gd3Al5-xGaxO12:Ce SCFs (x = 1.16–2.67) /Gd3Al2.5Ga2.5O12:Ce SC epitaxial structures can be usedas composite scintillators for simultaneous registration of the components of mixed ionizing fluxes,specifically for detection of α–particles (SCF) and γ–quanta (substrate). The separation of the response from the SCF and substrate parts of composite scintillators under α–particle (241Am) andγ–quantum (137Cs) excitations occurs at large tγ/tα = 1.7–4.2 ratio.

The effect of large doses of radiation on of composite radiation-resistant scintillators cracking

In our previous works in this series, we investigated composite scintillators, i.e. scintillators based on a transparent gel composition containing single crystal grains of inorganic crystals (GSO:Ce, GPS:Ce, Al2O3:Ti, YSO:Ce and YAG:Ce). The gel composition was not only a binding material for scintillation grains. It was both a light-collecting medium in which a total scintillation signal from various grains was forming as well as a coating that protected scintillation grains from the effects of chemically active components of the atmosphere. At large cumulative doses of D, we observed a previously undescribed effect of scintillator cracking.In this work, as in previous works in this series, we irradiated composite scintillators on a linear electron accelerator. The electron energy was 10 MeV. We irradiated for a low (0.2 Mrad/h) and a high dose rate (1500 Mrad/h). At the low dose rate, cracking occurs at lower D values (about 100–200 Mrad) than under irradiation with the high dose rate (up to 500 Mrad). The luminescent characteristics of the scintillator changed insignificantly until the gel composition fixing single-crystal grains cracked. After the destruction of the gel composition, an abrupt deterioration in the properties of the sample was occurring. Additional studies have allowed us to show that nitrogen compounds, including nitric acid, can appear in the irradiation zone under the influence of radiation. The scintillator in the irradiation zone can either begin to expand under the influence of heating or (and) to crack when exposed to aggressive atmospheric components. There are two main hypotheses for describing the cracking of composite scintillators, requiring an analysis of the irradiation conditions, which this work is devoted. In this article, we conducted additional studies when the irradiated scintillators were in the atmosphere, or in a vacuum to compare and analyse the “temperature” and “radiation-chemical” hypothesis of composite scintillators cracking, as well as to confirm the conclusions of our analysis.The analysis we carried out in work proves that, at the low dose rate, nitrogen-containing compounds forming in the irradiation zone have a decisive influence on the effect of scintillator cracking. At the high dose rates, the main effect that leads to the cracking of scintillators is their heating, occurring under the influence of radiation.

Composite scintillators based on polymers and inorganic nanoparticles

Development of organic–inorganic nanocomposite scintillators as a new class of scintillators is reviewed. Advantages and shortcomings of polymer-based organic scintillators, i.e. plastic scintillators, are described among the desired properties of scintillators. Development of scintillators by addition of organometallic compounds in the plastic scintillators as an approach to overcome the shortcomings is introduced. In comparison to this approach, nanocomposite scintillators comprising plastic scintillators added with inorganic nanoparticles are introduced. The synthesis methods achieved their properties and their applications are reviewed. Finally, possible strategies for further improvement of the properties of the nanocomposite scintillators are presented.

Compound pulse characteristics of a heterogeneous composite scintillator in a gamma-ray field

An important aspect of radiation detection in scintillators is the time dependence of emitted fluorescence, which results in characteristic measured pulse shape. In some materials, a relatively strong dependence of the scintillation pulse shape on stopping power exists, which can provide reliable identification of the incident particle. An alternative method to realize particle identification is by combining materials with different fluorescence lifetimes into heterogeneous structures. Such composite scintillators derive their properties from both the constituent material characteristics and the geometry of the composite structure. In composite scintillators with a high degree of heterogeneous loading, a superposition of fluorescence contributions originating in multiple materials, which is observed as single waveform with an intermediate pulse shape, may affect its ability to reject γ rays. We measure the time dependence of light output from a scintillator composed of 6Li-containing glass shards and scintillating polyvinyl toluene and identify events that exhibit such compound behavior when exposed to γ rays and fast neutrons. We develop a modeling and simulation framework that reproduces the pulse shapes in heterogeneous scintillators and use it study the effect that the weight percentage of 6Li glass has on γ rejection. The modeling framework is applied to the experimentally studied scintillator, finding a good agreement. The developed modeling and simulation approach will help optimize the design of heterogeneous scintillators to meet the desired trade-off between neutron capture efficiency and γ-ray rejection.

Composite Scintillators Based on the Films and Crystals of (Lu,Gd,La)2Si2O7 Pyrosilicates

This article is directed on the creation of composite scintillators which are based on the films and crystals of R2Si2O7:Ce (R = Lu, Gd, La) pyrosilicates using the liquid phase epitaxy (LPE) growth method for application in the radiation monitoring of different components of mixed ionization fluxes. Such types of composite scintillators are epitaxial structures containing film scintillators grown by the LPE method onto the substrates of crystal scintillators. In this article, the film and crystal parts of the composite scintillators were fabricated from effective scintillation materials on the base of Ce3+ doped Gd2- x Lu x Si2O7 and Gd2- x La x Si2O7, and $x = {0}$ and 0.25 mixed pyrosilicates with various scintillation decay kinetics due to the different Lu/Gd/La cation content. We briefly report on the results of the LPE growth of the composite scintillators based on the Ce3+ doped (Lu,Gd)2Si2O7 films and (Gd,La)2Si2O7:Ce crystal substrates, as well as the results of investigation of their luminescent and scintillation properties.

Radioactivity induced in radiation-resistant composite scintillators by irradiation with bremsstrahlung photons

Radioactivity induced in radiation-resistant composite scintillators by irradiation with bremsstrahlung photons

Monte Carlo Calculations of the Detection Efficiency of Composite Scintillator Arrays for Fast and Moderated Neutrons, and for Gamma-Ray Spectroscopy

Fissionable materials can be distinguished from normal materials by their emission of fast neutrons and neutrons moderated by surrounding materials. Radioisotopes can often be identified by their gamma-ray spectra. In this work, we use the nuclear physics Monte Carlo package MCNP6.2 to compare the detection efficiencies of different detector designs for the triple-mode detection of fast and moderated neutrons, and gamma-ray spectroscopy. For each design, we tabulate the detection efficiencies for neutrons from 0.1 eV to 5 MeV and for the full absorption of gamma rays from 0.1 to 5 MeV. All designs use 100 scintillators 1 cm $\times $ 1 cm $\times $ 5 cm. Of these, 36 are Cs2 LiLaBr6:Ce (90% 6Li) (CLLB) and 64 are polyvinyl toluene (PVT). The first design uses separate arrays of $6\times 6$ CLLB and $8\times 8$ PVT scintillators. Three other designs are $10\times 10$ composite arrays using all 100 scintillators combined in different ways. PVT is a fast scintillator that can be used to detect fast neutrons by time-separated multiple proton recoils and discriminate against gammas. PVT in the three composite designs serves to moderate neutrons of all energies for capture by the 6Li in the CLLB. Gamma rays interact in the PVT and CLLB by Compton scattering and pair production; full energy absorption requires photoelectric absorption in the CLLB. The energy deposited by each gamma ray can be determined from a weighted sum of the CLLB and PVT signals from separate photodetectors. We find that for a fixed number of neutrons/cm2, one of the composite arrays has much higher 6Li detection efficiencies than the design that uses separate CLLB and PVT arrays, and has similar detection efficiencies for fast neutrons and gammas. We also find that in all cases, the average energy of the neutrons at capture by 6Li is well above the 25-meV thermal energy.

Luminescence and scintillation properties of Eu2+ doped CaF2 glass ceramics for radiation spectroscopy

A new scintillation material including CaF2: Eu nanocrystals contained in SiO2–Al2O3–CaO–CaF2–LiF system was successfully prepared via melting method with additional heat treatment. Structural and luminescence properties were investigated by characterization techniques including XRD, SEM, photoluminescence (PL) excitation and emission spectra and absorption profile. The emission intensity of the glass ceramics containing CaF2: Eu nanocrystals under illumination at 356 nm were significantly more than the as-made glass and enhanced with increasing the temperature and duration of the heat treatment. Spectral analysis of gamma rays showed a full-energy peak in comparison with the similar chemical compositions that do not show such a response. Also an energy continuum with specific reaction-product peak was detected for thermal neutrons. The scintillation efficiency was enhanced with increasing crystallization. The fabricated Eu-doped transparent CaF2 glass ceramics has the potential to be a desired composite scintillator for detection of low energy gamma rays and thermal neutrons.

Liquid phase epitaxy growth of high-performance composite scintillators based on single crystalline films and crystals of LuAG

Top – Scheme of the composite scintillator for registration of α-particles and γ-quanta. Bottom – Samples of the LuAG:Ce SCF/LuAG:Sc SC (a) and LuAG:Pr SCF/LuAG:Sc SC (b) composite scintillators prepared using the liquid phase epitaxy growth method.

Cracking of composite scintillators after significant doses of irradiation

Cracking of composite scintillators after significant doses of irradiation

Features of pulse shape discrimination capability of organic heterogeneous scintillators

Abstract This work studies the PSD (pulse shape discrimination) capability of organic heterogeneous (polycrystalline and composite) scintillation materials, i.e. their ability to separate ionizing radiations by the difference in the form of scintillation pulses generated by the radiations with different specific energy losses (dE/dx). It analyses the parameters describing the formation of a scintillation pulse, the knowledge of which is useful for the design and creation of electronic units optimally solving the PSD problem for a given scintillator. The comparative analysis of the results shows that the PSD capability of organic heterogeneous scintillators is close to the corresponding values for reference single crystals. Stilbene-based materials have the best PSD capability to a separate detection of the ionizing radiations with different values of dE/dx. Organic heterogeneous scintillators based on stilbene and p-terphenyl are promising candidates for development of effective detectors for the ionizing radiations with high dE/dx-values (e.g., fast neutrons and alpha particles) in a presence of gamma background.

Alpha and gamma spectroscopy of composite scintillators based on the LuAG:Pr crystals and single crystalline films of LuAG:Ce and (Lu,Gd,Tb)AG:Ce garnets

Alpha and gamma spectroscopy (pulse height spectra and scintillation decay time profiles) were used to study scintillating properties of composite scintillators systems consisting of single crystalline films (SCF) and single crystal (SC) substrate plates. α-particles of 241Am of energy 5.4857 MeV and γ-quanta of 137Cs of energy 661.66 keV are used as excitation sources of SCFs or SC substrates, respectively. As SC substrates mainly LuAG:Pr single crystal plates are used and these plates are characterized by light yield (LY) between 10-21 × 103 ph/MeV, Energy Resolution (ER) ~5% at 661.66 keV and good proportionality. LuAG:Ce, Lu2-xGdTbxAG:Ce and Lu3-xTbxAG:Ce SCFs at x = 0.15–2.285 were prepared by LPE method onto LuAG:Pr substrates and investigated. LY of LuAG:Ce SCF under α-particles excitation is about of 60% than that of LuAG:Pr SC substrate. The LY of Lu3-x TbxAG:Ce SCFs depend nonlinearly on Tb3+ concentration in the 0.15–2.285 range and changed from 60-62% to 106–109%, respectively, in comparison with LY of LuAG:Pr SC substrate. Detailed scintillation decay time profiles have shown that there are differences between the decay curves of composite scintillators under α-particles and γ-quanta excitations. Such differences are characterized using the tα/tγ ratio between the time of scintillation decay to 1/e, 0.1, 0,05 and 0.02 levels under α-particles excitation (tα) and γ-quanta excitation (tγ). From all studied types of composite scintillators, based on the LuAG:Pr substrates, the highest value of tα/tγ ratio can be reached for Lu3-xTbxAG:Ce SCF/LuAG:Pr SC substrate composite scintillators at Tb content x = 2.15–2.275, where this ratio is equal to 4.2–6.2 at scintillation decay level of 0.1.

Dynamical forming and applications of nanocomposites from organic and inorganic components for new trends in material research and technologies

The composite scintillators from inorganic scintillators and organic phosphors provide unique combination of high light yield and nanosecond temporal resolution. Preparation of microfibers of these composites by means of centrifugation resulted in forming of axial nanosplitting and transverse micromodulation of their structure and optical properties, These modulations result in essential improvement of scintillation parameters of the composite providing the development of relatively simple and cheap X-Ray microscope. Ball rolling of inorganic solids provides superfast introduction of organic and inorganic components into subsurface layers for the special modifications of their properties. The superfast introduction is explained by propagation of nanocracks involving necessary dopants into the solid.

RADIATION RESISTANCE OF COMPOSITE SCINTILLATORS

Radiation resistance of composite scintillators containing grains of organic or inorganic single crystals has been analysed. The analysis is based on the study of composite scintillators containing grains Gd2SiO5:Ce (GSO:Ce), Gd2Si2O7:Ce (GPS:Ce), Al2O3:Ti, Y2SiO5:Ce (YSO:Ce) or Y3Al5O12:Ce (YAG:Ce). This paper presents the results of research and suggests possible mechanisms as well as processes of radiation changes that occur in scintillators due to irradiation. It also discusses how these effects can affect the scintillation characteristics of composite scintillators exposed to radiation.

Development features of radiation-resistant materials for composite scintillators and wavelength shifting light guides

Abstract The paper discusses the possible processes of radiation-induced changes that occur during irradiation of composite scintillators containing grains of inorganic crystals, and investigates the effect of these processes on radiation resistance of composite systems. All crystalline inorganic scintillation materials contain defects, which can play the role of quenching centres. An irradiation destroys and changes not only the main material of a scintillator but such the centres as well. As a result, the luminescence intensity can grow for a while due to weakening the effect of quenching. In this case, the luminescence spectrum of a scintillator does not change its shape under various accumulated doses D because no new luminescence centres appear. A modification of the properties of the luminescence centres arising under the action of irradiation has to lead to a change in the spectral characteristics of the luminescence. Therefore, the appearance or absence of such the changes is evidence of which centres are predominantly damaged because of irradiation with given dose D. The paper as well discusses the possibilities of obtaining radiation-resistant materials for the development of wavelength shifting light guides for composite scintillators. We investigated samples based on non-luminescent transparent silicone elastomer containing p-terphenyl or 1,4-di[2-(5-phenyloxazolyl)]benzene (POPOP) molecules.

The SoLid reactor anti-neutrino detector

The SoLid collaboration has developed a highly segmented, composite scintillator anti-neutrino detector which will be deployed between 6 and 9 m from the BR2 research reactor in the coming months. The detector is designed to perform anti-neutrino oscillation searches, anti-neutrino energy spectrum measurements and demonstrate the capability for reactor monitoring. Some results from a 288 kg prototype deployment in 2015 are presented, along with details of the upgrades being used in the full 2 t detector that is currently being constructed.

Fabrication of Ce-doped (Gd2Y)Al5O12/Y3Al5O12 composite-phase scintillation ceramic

In this paper, a novel Ce(Gd2Y)Al5O12/Ce:Y3Al5O12(Ce:GYAG/Ce:YAG) composite scintillation ceramic was designed and fabricated by a solid-state reaction method. The phase, luminescence and scintillation properties were investigated. The Ce:GYAG/Ce:YAG composite ceramic consisting of two-phase has a broad emission band ranging from 500 to 750 nm. The total mass attenuation coefficient of Ce:GYAG/Ce:YAG is 0.3864 cm−1, in between those of Ce:YAG and Ce:GYAG ceramics. In addition, the composite ceramic had a high light yield of 20430 ph/MeV. By controlling the ratio of GYAG and YAG, the composite ceramic can realize a spectrum design and total mass attenuation coefficient control to meet the requirements for wide-X-ray-energy-range detectors.

Evaluating the energy dependence of various polystyrene based plastic scintillators

Plastic scintillation detectors (PSDs) have been extensively tested as in-vivo dosimeters for brachytherapy dosimetry, but they are known to suffer from an energy dependence in low energy photon beams, an unwanted characteristic of any dosimeter. It has been demonstrated that the base material of the plastic scintillator can have a significant impact on the PSDs energy dependent behavior in x-ray beam voltages from 25 to 100kVP (Peralta and Rêgo, 2014). In this work, a comprehensive range of polystyrene based PSDs are studied to determine if the scintillator composition and geometry has any impact on their energy dependent behavior in superficial x-ray beams in the 30 to 150 kVP range. The relative response of each scintillator tested was found to vary by up to 77% across the 0.014–0.061 MeV effective energy range, with a maximum variation in relative response of 13.1% between the different scintillators. These results demonstrate the PSD diameter, formulation and cladding do not significantly impact the scintillator performance in the studied energy region.